Wessel Wessels

Author Archives: Wessel Wessels

Lifelong weather enthusiast and researcher. Interested in all things weather-related, and how global climate and local weather interact. Owner of multiple home weather stations for almost two decades, but still learning and expanding his knowledge base every day. He is dedicated to sharing his expertise and knowledge to get more people involved and interested in both their local and global weather and how it interacts with climate on a worldwide scale. Love sharing my knowledge on home weather stations, how they work, and the many ways you can use them to your advantage. All in all, he is just a bit of weather nerd.

Ephemeral Stream: What It Is And How It Occurs

Ephemeral-Stream - What It Is And How It Occurs

From the largest rivers to the smallest creeks, all play a crucial role in supplying the land, animal, and human population with vital resources. It even applies to the most modest temporary stream.

Not all rivers and streams continuously flow throughout the year. Some of them are seasonal, and some only flow during specific events. No matter what their size or frequency, they all form part of the Water Cycle that distributes and cycle water around the planet.

One such temporary stream is called an ephemeral stream. It does not flow often and only for a short duration during specific occurrences. Yet, it is still just as an important source of water than any extensive permanent river system. 

This post examines what an ephemeral stream is, how it forms, and how it differs from other types of streams and rivers.

Ephemeral Stream Definition

Most major river systems and larger streams flow throughout the year, meaning they are perennial. (Like the Rhine in Europe, the Amazon in South America, and the Nile in Africa.) An ephemeral stream, though, is not only transitory but is not even a seasonal occurrence.

To be able to describe how and why this type of stream form, one needs to gain a clear understanding first of what precisely an ephemeral stream is:

What Is An Ephemeral Stream?

What Is An Ephemeral Stream

An ephemeral stream is a temporary stream that only flows for a brief period as a direct result of precipitation.

It occurs mainly in arid and semi-arid regions where rainfall occurs infrequently.

The word, ephemeral, is derived from the 16th Century Greek word "ephēmeros," which aptly means "lasting for a very short time." And it is the brief occurrence of an ephemeral stream that is its most defining characteristic.

Since these streams occur for such a brief period, it does not have the time to carve out a deep and wide channel, as is the case with a perennial river. It also occurs in predominantly dry regions, where the groundwater table forms much deeper below the surface.

As a result of these two factors, ephemeral streams occur above the groundwater table, compared to more permanent streams and rivers, which riverbeds lie below the water table. The significance of the groundwater table height will become clear in a later section.

How Ephemeral Streams Formed

In arid or semi-arid regions, precipitation occurs very infrequently. As a result, when a large enough amount of rainfall does occur, it often forms a temporary stream on the surface.

The stream can create a new path, or follow an existing channel (also called a dry wash) established by previous occurrences of ephemeral streams.

The paths these streams follow can link up with larger networks of intermittent or perennial streams and rivers. 

Dry Stream Bed

They can also continue to flow for a short distance, before evaporating completely without reaching any significant point or being absorbed into the soil to form groundwater.

Ephemeral streams flow for a limited time and dry up quickly, only leaving a dry stream bed behind. These dried-up channels are sometimes more accurately described as arroyos, which are synonymous with the arid and semi-arid areas where ephemeral streams occur. 

It is important to note that the ephemeral stream and the channel (arroyo) if flows in are not the same thing. The stream itself is the actual flow of water that is transitory, while the channel it flows in remains a permanent fixture of the landscape.

Importance Of Ephemeral Streams

It is only natural to conclude that ephemeral streams play an insignificant role in contributing to the Water Cycle and have any other beneficial influences on the environment. Such a conclusion can not be further from the truth.

These streams play an essential role in supplying fresh and maintaining existing resources in at least three different ways:

1) Fresh Water Supply To Perennial Water Networks

Even though ephemeral streams only flow during or after a spell of rain, the combination and frequency of these streams have a huge impact. In fact, they contribute the vast majority of freshwater to the entire river network in arid and semi-arid regions.

For example, 95% of all streams in the Arizona Dessert are seasonal, of which a substantial amount are ephemeral. Even in wetter regions with frequent rainfall, it is estimated that more than 50% of the total stream network comprises of temporary streams.

2) Supply Of Fresh Sediment To  Downstream Regions

Fresh Sediment Supply

During extended dry spells, dried-up stream beds (arroyos) builds up a layer of soil, which nutrient content hasn't been depleted by vegetation growth. 

The organic matter created by dead animals and insects, as well as the remains of dead plants, also accumulate in arroyos, further enriching the nutrient content of the soil.

When a spell of rain causes an ephemeral stream to flow, it carries this nutrient-rich soil downstream, where it gets deposited on riverbanks and the surrounding areas, replenishing the land with much needed fresh sediment.

3) Maintenance And Replenishment Of Groundwater Tables

As the arid and semi-arid regions, where ephemeral stream occurs, don't contain much moisture, the groundwater tables are situated much further below the surface than in wetter areas with an abundance of rain.

When a substantial amount of rain falls, it allows ephemeral streams to contain a large enough volume of water to have some of it absorbed by the ground to replenish its deep water tables.

It can also flow far enough to connect with more permanent (perennial) river networks downstream. It not only supplies these systems with additional water but also assists in maintaining and replenishing their groundwater tables as well.

The Difference Between Ephemeral And Intermittent Streams

Some confusion exists among observers about the difference between ephemeral streams and intermittent streams since they are both regarded as temporary streams.

Ephemeral streams have already been clearly defined as temporary streams that only flow as a direct result of precipitation. The depth of their groundwater tables also means that they can't access this water source to sustain their flow in any way.

Difference Between Ephemeral And Intermittent Streams

Intermittent streams, however, differ in more than one way. They are often seasonal, meaning that although they don't flow throughout the year, they receive a steady supply of water during the rainy season, which allows them to flow for sustained periods.

They also have deeper and more prominently defined river beds, combined with shallower groundwater tables as a result of the availability of more water. It allows the river beds to lie below the water table, allowing them to access groundwater to sustain their flow.

Conclusion

What became clear through this article, is how a seemingly insignificant occurrence can play a significant role in a much more extensive network.

An ephemeral stream is not only temporary but only flows for a brief period during or after a spell of rain. Yet, in many regions, they account for the vast majority of water supply to major river networks, enabling them to flow throughout the year.

This article explained what an ephemeral stream is, how it forms, and its importance to larger, more perennial water networks. It also addressed and clarified the difference between an ephemeral and intermittent stream.

Feel free to leave any comments, questions, or suggestions you may have. Your opinion is valued and will be attended to as soon as possible.

Never miss out again when another interesting and helpful article is released and stay updated, while also receiving helpful tips & information by simply  clicking on this link .

Until next time, keep your eye on the weather!

Wessel


Cap Cloud – What It Is And How It Differs From Lenticular Clouds

Cap Cloud - What It Is And How It Differs From Lenticular Clouds

Clouds literally come in all shapes and sizes. The majority we know is a result of different weather elements, like heat, wind, and moisture. Some, though, occur as a result of variations on the Earth's surface.

Variations on the planet's surface influence a variety of meteorological occurrences like wind, temperature, and yes, cloud formation. Especially elevations and dips on the surface play a significant role in the development of certain clouds. 

One type of cloud that is a direct result of the physical elevation in terrain is called a cap cloud. In this post, we look at what cap clouds are, how they form, and how they differ from the more familiar lenticular clouds.

Cap Cloud

As mentioned in the introduction, a cap cloud is the result of a change in physical terrain, but this is not the only factor at play in the formation of this cloud system.

What Is A Cap Cloud?

Before looking into how a cap cloud is formed, one must first define what precisely it is, and describe its characteristics in more detail: 

What Is A Cap Cloud?

What Is A Cap Cloud

A cap cloud is a stationary orographic cloud that forms over the peak of a mountain, where moist air is forced up the windward slopes and condensates as it flows over the top.

This cloud is characterized by its unique mushroom or upside-down saucer shape, and can always be found on top or above a mountain peak.

It is not that uncommon to see two cap clouds on top of each other, hovering over the same mountain top. It occurs typically when a layer of dryer air separates two layers of moist air.

How Cap Clouds Form

Cap clouds form as a result of orographic cooling (which is part of the Orographic Effect). As prevailing winds push moist air against a raised terrain like a mountain, it forces the layer of air to rise against the slopes.

As the air rises, it starts to cool down. It continues to cool down until it reaches dew point and condensation takes place near the top of the mountain. As a result, the air flowing over the mountain top creates the flat, dome-shaped cloud that is the trademark of a cap cloud.

The raised terrain does not only cause the air to rise on the windward side of the mountain, but as it starts to descend down the leeward slopes, it also creates a wave in the airflow. And it is here where lenticular clouds come into play.

Lenticular Clouds

The wave formed in the wake of the air lifted over an elevated terrain forms the foundation for the occurrence of lenticular clouds.

What Is A Lenticular Cloud?

As with cap clouds, one first needs to get a clear understanding of the definition of a lenticular cloud before looking into how these clouds develop:

What Is A Lenticular Cloud?

What Is A Lenticular Cloud

A lenticular cloud is a stationary cloud that occurs high in the troposphere on the leeward side of a mountain. It is characterized by its saucer or lens-like shape.

It forms on the crest of a wave that is the result of air forced to lift due to a rise in physical terrain. Its alignment is usually perpendicular to the direction of air movement.

As mentioned in the description, lenticular clouds form at a high altitude in the troposphere. This is mainly due to the elevated terrain, specifically mountains, that is responsible for creating the conditions favoring the formation of these clouds. 

A few elements need to be in place to form the ideal conditions for lenticular clouds to occur. The creation of wave movement on the leeward side of a raised terrain is the crucial element in the formation of these clouds.

The saucer or lens-like shape is another unique characteristic of lenticular clouds. Since it does not appear close to the surface, it is not often visible from the ground. As a result, it is often mistaken for a UFO (Unidentified Flying Object) or another artificial object.

The layered (pancake) shape of the cloud is the result of multiple layers of cold air reaching dew point at the crest of downwind waves. The crucial role these downward waves play in the formation of lenticular clouds will become evident in the next section.

How Lenticular Clouds Form

For a lenticular cloud to form, three elements need to be present and in place:

  • Adequate Moisture In The Air
  • Prevailing Wind
  • Formation Of A Wave In The Air Movement On The Leeward Side Of A Mountain

As mentioned earlier, it is this wave of air that is primarily responsible for the formation of a lenticular cloud.

After the formation of a cap cloud, the air which lifted on the windward side of a raised terrain dips on the leeward side. More importantly, it creates a continuous wave in the air moving downwind.

How Lenticular Clouds Form

The wave consists of a series of crests and troughs continuing downwind. When moist air reaches the crest of a wave, and the temperature drops below dew point, condensation takes place, which allows for the development of a lenticular cloud.

When the prevailing wind persists, the crests and troughs in the wave of air continue to form downwind, which can result in a series of lenticular clouds to form. These formations are better known as a wave cloud.

The clouds seem to remain stationary, but there is a constant flow of air through them. The reason they "stay in place" is that the air dips below dew point at the crest of the wave, allowing the cloud to form. When the wave dips down, it evaporates as the air warms up.

Difference Between Cap Clouds & Lenticular Clouds

What will have become evident during the description of cap and lenticular clouds is that their formation is almost identical. The only difference is that a lenticular cloud forms on the wave of air created due to forced elevation on the leeward side of a mountain.

Several articles and papers clearly state that cap clouds are actually lenticular clouds, due to the almost identical formation process and similar cloud shape. Technically, this statement is correct, and a cap cloud can be classified as a lenticular cloud.

However, from a practical standpoint, and when described in layman's terms, there are subtle but significant differences between the two that can be summarized as follows: 

  • While cap clouds occur directly over a mountain peak, lenticular clouds usually form on the leeward side of the mountain.
  • Cap clouds have a flat, dome-shaped form while lenticular clouds have a layered or stacked shape in the form of a lens or saucer.

As already stated, these are subtle but significant differences.

Conclusion

It is clear that there can be some confusion when discussing cap clouds and lenticular clouds and why they are often seen as the same type of formation. This post managed to highlight the small but notable differences between the two.

And that was the aim of this article: To explain what cap clouds are and how they form, and how they differ from lenticular clouds in formation and shape.

Feel free to leave any comments, questions, or suggestions you may have. Your opinion is valued and will be attended to as soon as possible.

Never miss out again when another interesting and helpful article is released and stay updated, while also receiving helpful tips & information by simply  clicking on this link .

Until next time, keep your eye on the weather!

Wessel


Adiabatic Process: What It Is And How It Occurs

Adiabatic Process-What It Is And How It Occurs

Air pressure plays a vital role in meteorology and can be found in a wide variety, if not almost every possible weather event. In a confined space, air pressure plays a unique role, and not only in meteorology.

Think of the internal combustion engine (ICE) used in traditional motor vehicles. Without the air pressure created in the combustion chamber to drive the piston inside a cylinder, the ICE will not be able to operate.

Similarly, the steam engine, which was widely used during the early stage of the Industrial Revolution, operates on the same principle. Heat is applied to a confined chamber, causing moist air inside to expand, which in turn forces cylinders to move up and down.

The three factors that play an essential role in both these processes are heat, air pressure, and a confined body of air. And it is these three factors that also create a similar process in meteorology. It is called the adiabatic process.

As already shown, the adiabatic process is used in a variety of different disciplines. However, this post will focus exclusively on the adiabatic process as it applies to meteorology.

Adiabatic Process

During the introduction, you already received plenty of clues as to what the adiabatic process entail and was probably able to form a vague idea of its definition.

It is essential, however, to get a clear and concise definition of what precisely the adiabatic process is, before examining how this phenomenon takes place.

What Is The Adiabatic Process?

Adiabatic Process

The adiabatic process describes the heating or cooling of a body of air without any form of energy exchanged between this system and the surrounding environment.

Temperature change within a pocket of air mainly takes place due to its compression or expansion as a result of a change in air pressure in the surrounding atmosphere.

One of the most vital characteristics of the adiabatic process to highlight is the fact that the process takes place in relative isolation. It simply means that no mixing of air takes place between the body of air and the surrounding atmosphere.

There is a second important characteristic of the adiabatic process in meteorology. And this is that it occurs as a result of the surrounding atmosphere's pressure on the air pocket, specifically in adiabatic cooling and heating.

Now that it has been established that the heating and cooling of a body of air is one of the primary impacts of the adiabatic process, the focus should now be on how these cooling and heating processes take place.

Adiabatic Cooling

Adiabatic cooling is a natural occurrence that takes place in the lower atmosphere and is primarily due to a change in altitude. Usually, the altitude change occurs through one of two processes. These two processes are:

  1. The Heating Of A Layer Of Air At The Surface
  2. Forced Elevation Due To A Rise In Geographical Terrain

1) The Heating Of A Layer Of Air At The Surface

Adiabatic Heating

When solar radiation heats the Earth's surface, it also warms the air above it. The warm body of air is less dense (and lighter) than the surrounding air and starts to rise. As it gains altitude, it continues to move into areas with less density, causing it to expand even further.

Any body of air contains a large number of molecules that vibrate and bounce off each other. The closer these molecules are to each, the quicker they vibrate and collide with each other. We observe this as a rise in temperature. 

In this case, however, the body of air expands as it gains altitude where the atmosphere has less air pressure. It means the molecules move further away from each other, becoming less energetic with fewer collisions occurring, resulting in a drop in temperature. 

2) Forced Elevation Due To A Rise In Geographical Terrain

Sometimes adiabatic cooling is not the result of the heating of a surface. When prevailing winds (like a sea breeze blowing inland) are present, a layer of air is moved horizontally but sometimes encounters a raised terrain like a mountain or large hillside.

As a result, the layer of air is forced to rise against the mountainslopes. As the altitude increases, the atmospheric pressure becomes less, allowing the air pocket to expand and cool down in the same way a body of warm air rising from the surface would. 

This form of adiabatic cooling is also known as orographic cooling, which forms part of the Orographic Effect. To find out more about this phenomenon and how it occurs, you can read the in-depth article here.


The rate at which temperature drops as altitude increases is called the adiabatic lapse rate. The amount of moisture in the air plays a role at the rate at which temperature decreases, and can be divided into the:

Dry Adiabatic Lapse Rate: When there is little or no moisture present in the air parcel, it will cool at an average rate of 10° Celsius per 1 000 meters (5.6° Fahrenheit / 1 000 Feet).

Wet (Moist) Adiabatic Lapse Rate: When a substantial amount of moisture is present in a body of air that is rising,  it will cool at an average rate of 5° Celsius per 1 000 meters (3.2° Fahrenheit / 1 000 Feet).

Please note that these figures are just average lapse rates and will vary according to more specific atmospheric conditions.

Adiabatic Heating

The adiabatic process takes place in reverse during an occurrence of adiabatic heating.

When a body of air at higher altitudes starts sinking to the ground, it gets subjected to increased atmospheric pressure as it moves closer to the planet's surface. The increased pressure causes the air parcel to compress and shrink in size.

Orographic Heating

As already discussed, when a body of air contracts, the molecules inside get energized as it starts to vibrate more quickly and collide with each other at an accelerated pace. This process manifests as a rise in temperature.

One example of adiabatic heating occurs during a heat burst when a layer of cold, dry air drops to the ground from a high altitude in the wake of a dissipating thundercloud.

Another example is part of the Orographic Effect as cold, dry air drops down the slopes on the leeward side of a mountain.

Conclusion

The adiabatic process plays a vital role in many fields and disciplines. It also has a significant role to play in several meteorological occurrences.

In this post, we focused on adiabatic heating and cooling and illustrated how they could impact the weather without any energy exchange with external elements like solar radiation, wind, and moisture.

The main goal of this article was to explain the adiabatic process, how it occurs, and highlighted some examples of this phenomenon.

Feel free to leave any comments, questions, or suggestions you may have. Your opinion is valued and will be attended to as soon as possible.

Never miss out again when another interesting and helpful article is released and stay updated, while also receiving helpful tips & information by simply  clicking on this link .

Until next time, keep your eye on the weather!

Wessel

The Hottest And Coldest Time Of The Day – When They Occur And Why

Hottest Time Of The Day - When Is It And Why

The warmest time of the day is when the Earth receives the most solar radiation from the sun, and it is closest above your location, correct? Actually, no. Though it sounds obvious, you will be off by a few hours.

The same applies to the coldest part of the day. Both the hottest and coolest part of the day occur much later than you may think.

It does not seem to make sense since the Earth receives the most amount of solar radiation from the sun around noon (depending on your location and the time of year.) 

Similarly, the surface will keep on cooling down during the night until sunrise when it starts to receive sunlight and begins warming up. It is natural to reason, therefore, that the coldest time of the day will be just before sunrise. But this is not the case.

This article examines when the warmest and coldest part of the day is, and why they occur at these different times. It also looks at the various factors involved in these occurrences.

Hottest Time Of The Day

As already mentioned, the Earth's surface receives the most amount of solar radiation around noon, yet this is not the part of the day that is the warmest.

Before we look into why this occurs, it is important to define a clear definition first of when precisely the hottest part of the day is:

What Is The Hottest Time Of The Day?

Hottest Time Of The Day

The hottest time of the day occurs between 3 pm and 4:30 pm, around 3-5 hours after noon (when the sun is at its highest point in the sky, and the Earth receives the most amount of solar radiation.)

This delay is due to the Earth's surface receiving and absorbing heat at a higher rate than it is able to radiate until mid to late afternoon when the process reverses.

Although this summary is an accurate average to use to judge when a day will be at its warmest, a couple of factors can cause the actual peak temperature to occur earlier or later in the afternoon.

Weather elements such as cloud cover and wind can have a significant impact on peak daily temperatures. Geographical location also has an effect, where inland regions can reach its highest temperatures of the day much later in the afternoon than coastal areas.

Why The Hottest Time Of Day Occur In The Afternoon

Although the sun is at its highest point in the sky and the Earth receives the most amount of solar radiation around noon, we now know that the day's highest temperature does not occur until around 3 pm. This delay is also known as thermal response

Surface Radiation

Thermal response occurs as follows: After noon, even though the sun's radiation starts to drop, the Earth retains much of its heat while still receiving solar radiation. It means the heat building at the surface is higher than that which the planet can radiate away. 

As a result, the temperature continues to rise until the solar radiation is weak enough for the Earth's ability to radiate heat back into the atmosphere, becomes greater than the radiation it receives. And this occurs between 3 pm and 4:30.

Coldest Time of the Day

Like the hottest time of the day, the coldest time of the day occurs much later than one might expect. What makes it even more confusing, is the fact that weather forecasters often refer to daily lows that will be experienced "during the evening."

It is statements like these that backs up the common belief that the coolest time of day should occur during the night. As much as this type of thinking seems to make sense, it is not accurate at all.

As is the case with the warmest time, it is important to define when precisely the coldest time of day is first before we delve into explaining why and how this takes place:

The Coldest Time of the Day

Coldest Time Of The Day

The coldest time of the day occurs some time after sunrise.

It occurs when the sun's radiation is still too weak to warm the planet's surface at a greater rate than the Earth is radiating heat away from the surface into the atmosphere.

This may not seem to make sense at first since solar radiation is the primary source of heat and light to the Earth every day.

Take into consideration, though, that when we perceive the sun to rise on the horizon, it is still 6 degrees below the horizon (aka twilight). The atmosphere can bend light like a lens, making it appear that we receive sunlight when no actual solar radiation is yet present.

Depending on your location and time of the year, after sunrise, it will also still take the sun between 3 and 8 hours to reach its highest point in the sky and the Earth to receive maximum solar radiation after sunset.

Although these are all contributing factors, the main reason for the coldest time of the day involves the same factors responsible for the warmest part of the day, which we will address in the next section.

Why The Coldest Time Of Day Occur After Sunrise

After the hottest time of the day, which occurs around 3 pm, the Earth continues to radiate heat out into the atmosphere at an accelerated pace. At the same time, solar radiation decreases until completely disappearing around sunset.

The planet's surface continues to cool down as it radiates heat throughout the night. After sunrise, the ground starts to receive solar radiation, but it is still too weak to counteract the rate at which the surface continues to cool down as it radiates heat into the atmosphere.

Solar Radiation

The coldest time of the day occurs once the speed at which the Earth radiates heat is no longer stronger than the incoming solar radiation, and the ground starts to warm up. As already stated, this occurs some time after sunrise. 

The exact time the coldest stage of the day takes place depends on atmospheric conditions, as well as the location and the time of the year.

Conclusion

Although it may not have made sense in the beginning, it should now be clear why the hottest and coldest times of the day occur when they do. It also explained why the delay between the period of maximum solar radiation and the hottest time of the day takes place.

This delay occurs on a seasonal basis as well. The warmest and coldest days of the year (and the hottest and coldest months) are based on the same principle. To find out more about these occurrences, you can find the in-depth article here.  

This article aimed to examine when the warmest and coldest part of the day is and why they occur at these times. It also looked at the various factors involved in these occurrences.

Feel free to leave any comments, questions, or suggestions you may have. Your opinion is valued and will be attended to as soon as possible.

Never miss out again when another interesting and helpful article is released and stay updated, while also receiving helpful tips & information by simply  clicking on this link .

Until next time, keep your eye on the weather!

Wessel


Huayco: What It Is And How It Is Caused

Huayco - What It Is And How It Is Caused

Most of you are familiar with an avalanche that causes millions of tons of snow to rush down a mountainside and bury everything in its path. In the tropics, a different but similar event occurs with potentially deadly consequences.

Regions in and around the Tropics get subjected to large amounts of rainfalls throughout the year. These include areas like the Caribbean, Southeast Asia, Central & South America, as well as the mountainous terrain of Asia. It can have deadly and devastating occurrences.

Due to the heavy torrential rain, flash flooding and mudslides occur quite frequently in these areas, especially in the high mountainous terrain of Peru. These events that are so synonymous with this part of the world are more commonly referred to as huaycos.

This post explores what a huayco is, how it gets formed, and its potentially devastating effect on its surroundings.

What Is A Huayco?

As you might have already concluded, a huayco is a mudslide, accompanied by flash flooding, which is the result of heavy rains in the mountains of Peru. It sounds simple enough, but there are, in fact, many more factors at work to create this event.

Before looking at the different mechanisms at work in the formation of this event, though, one first needs a concise formal definition of what precisely a huayco is:

What Is A Huayco?

What Is A Huayco

The term, Huayco, refers to the flash flooding and accompanying mudslides that occur in the Peruvian region of South America as a result of heavy torrential rains.

It originates high in the mountainous regions of the country, and the event is closely related to the weather produced by the El Niño phenomenon.

The weather may be the impetus that sets the process in motion but cannot act on its own. The moist, soft soil covering the ground surface, combined by the gravitational force of the steep mountain slopes, largely contributes to the development of a huayco.

In the next section, we will briefly look at the meaning of the term "huayco" and its origins before continuing to explore the formation of this occurrence.

Meaning And Origin Of The Term, Huayco

A huayco is also known as a huaico. When you look at the origin and translation of both these terms, it will become clear how accurately they describe the characteristics of this specific phenomenon.

The word, huayco, is derived from the Quechuan word, wayqu. The Quechuan language is spoken by the Quechua people living in the Andes region of Peru. The term, huayco translates to either "valley" or "depth."

The word, huaico, has a Spanish origin (the most widely spoken language in Peru.) It translates to "avalanche," a phenomenon that shares many characteristics with a huaico.

What Causes A Huayco

The Tropics, where Peru is situated, already receives a large amount of rainfall throughout the year. Occasionally, though, a weather phenomenon called El Niño causes the region to receive an abnormally high percentage of precipitation.

In short, an El Niño occurs when the warm waters of the Pacific Ocean that would normally travel west and accumulate at the coast of Southeast Asia, are forced to flow in an easterly direction and build up against the northwestern coastline of South America.

(You can learn more about the formation and characteristics of El Niño in this article.)

The moisture-rich water that builds up against the South American coast results in the largescale formation of rainclouds, which leads to a significant increase in precipitation in regions like Peru.

Torrential Rain

The increased rainfall causes riverbanks to overflow and runoff areas to exceed their boundaries. This leads to flash flooding over parts of the mountainous terrain in the land.

The dry mountain slopes of the Andes in southern Peru have little or no vegetation cover. Combined with heavy deposits of soil, they are left vulnerable and exposed to extreme weather elements. 

During an El Niño event, water from burst river banks and dried-up runoff areas, rush down the mountain slopes while picking up the loose dry soil on the ground. It continues to race down the mountain, gathering even more soil until it starts turning into a dense mudslide.

The sheer momentum and size of the mudslide allow it to pick up objects like rocks and tree trunks, creating a potentially devastating and deadly force capable of wiping out almost anything in its path. 

It is this deadly combination of mud, rock, trees, (and other objects mixed in) that can completely overwhelm and cover vegetation and small villages at the bottom of the mountain slopes. (More on the impact and effects of a huayco in the next section.)

Contributing Factors To Huayco Formation

Although they have already been mentioned in passing, three main contributing factors help to create very favorable conditions for a huayco to occur in the Peruvian region of South America:

  1. Location of Peru
  2. Climate of Peru
  3. Geography of Peru

Although none of these factors cause a huayco by themselves, each one contributes and combined, they create a very favorable environment for the occurrence of this event.

1) Location of Peru

Peru is situated in the Tropics, just south of the Equator. The western part of the country borders the west coast of South America, which makes it highly susceptible to the weather that occurs over the Pacific Ocean (including the El Niño Effect.)

To the east, the Andes Mountains raise the terrain where higher rainfall creates lush vegetation that forms part of the Amazon Rain Forest.

2) Climate of Peru

Since Peru experience a tropical climate, it is subjected to large amounts of rainfall throughout the year, especially in the mountainous region to the east.

However, the influence of the Pacific Ocean to the east creates a dryer climate, while the Andes Mountains raise the terrain, creating wet & rainy weather conditions to the east of the country.

It is the contrast between the dry low-lying west and elevated east with its higher rainfall that creates a favorable environment for a huayco to develop.

3) Geography of Peru

Essentially, Peru can be broken up in three geological regions:

  • The Amazon Rain Forest
  • The Highlands
  • The Coast

The Amazon Rain Forest forms the northeastern border of Peru. Although it forms the largest region in Peru (59%), only 12% of the population lives in this region. The relatively flat landscape is covered with dense bush and trees that are so synonymous with the Amazon.

The Highlands mainly consists of the Andes Mountains with its peaks and valleys, reaching a maximum height of 6 768 meters (22 204 feet). It occupies 36% of the land, and 30% of the country's population lives in this area.

The Coast occupies the smallest part of the country (11%), yet the largest part of the population (52%) lives on this relatively small strip of coastal land. The dry, yet fertile piece of land extends from the ocean to the foothills of the Andes Mountains.

From the geographical layout of the country, it is clear to see how heavy rainfalls originating in the Andes mountains can trigger a huayco as water rush down the slopes and picks up the dry fertile ground and turn into devastating mudslides.

Effects Of A Huayco

The impact of a huayco can and usually is devastating. The widespread damage and injury (and in most cases loss of life) of largescale mudslides have already been well documented and covered in the mainstream media.

To give you an indication of the sheer size and power a mudslide, the following list of characteristics will provide some perspective:

  • Flash flooding can trigger one or multiple mudslides at a time. 
  • They vary in size, but a typical big mudslide can be 300 meters (984 feet) wide, 50 meters (164 feet) thick, and 1 600 meters (1 000 feet) long.
  • Mudslides travel downhill at around 80 km/h (50 mph) but can reach speeds of up to 322 km/h (200 mph) on steep slopes.
  • One of the most dangerous aspects of a mudslide is its unpredictability. It can occur suddenly and without warning, leaving little chance to get out of its way. 

From these characteristics, it is clear to see just how devastating a mudslide can be. The following are only a summary of the most significant types of impact a huayco can have:

1) Infrastructure Damage And Destruction

Infrastructure Damage

The sheer speed and size with which a huayco can strike any area will cause either damage or create complete destruction on a broad scale, depending on the size of the mudslide.

It can bury entire villages under meters of mud and completely destroy roads and bridges. Power lines, railroads, and other forms of information can also get washed away in a matter of minutes.

2) Injuries And Fatalities

Many villages in Peru are situated at the bottom mountain slopes. It makes them especially exposed and vulnerable to a huayco. When a mudslide does occur, it can bury an entire village, as already mentioned.

It usually leads to dozens of fatalities, with hundreds of people left injured and displaced. This is just the scenario for a single small village. When a more extensive region and more communities get effected, this number can easily more than double.

3) Loss Of Crops And Livestock

At the bottom of a slope, a mudslide can quickly spread over large areas. These include large fields of crops that are easily destroyed and can also lead to entire herds of livestock being killed off in minutes.

Since many villages live off the land and rely on their crops and livestock for survival, this can have a severe impact and leave people without food for undetermined periods.

4) Disruption Of Water Supply

Water supply and treatment facilities are also adversely affected by mudslides. Reservoirs can get damaged or destroyed. Even if they do not get demolished, the water of dams and water treatment facilities are polluted with contaminants they carry with them.

Water is the lifeblood of any community, and without it, villages and towns in affected areas will suffer and not be able to endure indefinitely.

5) Economic Cost

It should already be evident from the damage and destruction just described, but the economic impact of strong mudslides on the country is severe. It can quickly run into billions of dollars of damage.

One can easily see how a series of these events in quick succession can put a region and the entire country under extreme financial pressure.

Conclusion

Although mudslides occur all over the world, the conditions that create a huayco in the Peruvian region are quite unique, as was illustrated throughout this post.

This article clearly illustrated what a huayco is and how it develops. It also looked at its defining characteristics and impact on the areas it affects as well as human life.

Feel free to leave any comments, questions, or suggestions you may have. Your opinion is valued and will be attended to as soon as possible.

Never miss out again when another interesting and helpful article is released and stay updated, while also receiving helpful tips & information by simply  clicking on this link .

Until next time, keep your eye on the weather!

Wessel


Heat Burst: What It Is And How It Forms

Heat Burst-What It Is And How It Forms

If you are one of the few people who ever experienced a sudden gust of warm, dry wind that came out of nowhere on a hot summer's night, you may just have encountered a rare weather phenomenon. 

Readers who closely follow the articles on this platform would have noticed that more recent posts focused on meteorological phenomena surrounding severe weather events, specifically those involving thunderstorms.

The majority of articles focused on events taking place within thunderclouds, as well as those occurring when these storm systems interact or work with each other in unison.

The subject of this post is yet another example of the "byproduct" of a thunderstorm. Unlike most other weather events involving these storms, though, it is not characterized by cold or wet weather. A heat burst is a rare occurrence with unique characteristics.    

This article examines what a heat burst is, how it gets formed, and also takes a look at it its specific features.

What Is A Heat Burst?

The introduction already gave away some hints of the makeup of this weather event and its formation. What precisely it is and how it develops will shortly be discussed in detail. 

Before delving in, though, it is imperative to provide a more formal and concise definition of a heat burst to provide a solid foundation to work from:  

What Is A Heat Burst?

What Is A Heat Burst

A heat burst is a sporadic meteorological event that is defined by strong gusts of dry winds accompanied by a sudden and significant rise in temperature.

This phenomenon typically occurs during the evening in the wake of a dissipating thunderstorm on warm days during the summer months.

In simple terms, a heat burst is a warm and dry gust of wind that occurs on a hot day during the summer months and usually takes place in the evening. It follows in the wake of a dissipating thunderstorm and causes a significant rise in the surrounding air temperature.  

Its formation is similar to that of a microburst, but as you will soon learn, a few subtle differences create a very different outcome.

How A Heat Burst Develops

When a storm cloud starts to dissipate, lifts, and clears up, it leaves a layer of cold air behind. At this stage, most moisture has been removed from the air during rain showers or other forms of precipitation.

Due to gravity and disappearing updrafts, the dense air starts to sink to the ground. As it accelerates down, it gets subjected to increasing air pressure and friction.

The increased atmospheric pressure causes the air to warm adiabatically (similar to chinook of föhn winds down the slopes of a mountain). The friction between falling and stationary particles creates additional heat that contributes to the thermal buildup of the falling air.

Development Of A Heat Burst

The red arrows indicate the dispersing warm & dry winds of a heat burst below remnants of a dissipating storm cloud. Click on the image for a larger view.

The heated air also forces the remaining moisture to evaporate while momentum allows the layer of air to continue to speed to the ground. The result is a heated, dry pocket of air that hits the surface, forcing warm gusty wind to disperse away from this point of impact. 

To those readers familiar with a microburst, this process may sound similar to the formation of a microburst. There are some similarities, but also a few different characteristics that allow for the creation of a very different phenomenon.

These are among some of the defining characteristics of a heat burst that will be discussed in the next section.  

Characteristics Of A Heat Burst

For a heat burst to take place, a few conditions need to be in place. Some of them are not only characteristic of the phenomenon but also are what differentiate them from other weather events like microbursts. We look at them first.

1) High Elevation

A heat burst typically originates high in an anvil cloud (that is so synonymous with thunderstorms). It is due to the fact that the phenomenon occurs in the wake of dying thunderstorms, when clouds start to lift and dissipate, leaving a layer of cold air behind.

Anvil Cloud

It is this high altitude at which a heat burst forms, which allow it to travel further when it sinks to the ground. The greater distance enables it to be subjected to increased pressure and friction for an extended period, causing more heat to build up in the layer of falling air.

The lower altitude (combined with a higher moisture content) at which a microburst occurs, is part of the reason that the air reaching the ground remains cold and sometimes mixed with different types of precipitation.

2) Little Or No Moisture 

Another characteristic that is unique to a heat burst compared to similar events is the extremely dry air associated with this phenomenon.

By the time a heat burst starts forming, the storm system already dissipated, and most of the moisture lost due to heavy rainfall that occurred during the peak of the thunderstorm.

The little moisture that is left in the pocket of air evaporates in the warm air as it plummets to the ground. It is not uncommon to observe the phenomenon called virga (visible rain that evaporates before reaching the ground) beneath the cloud base where a heat burst occurs.

The opposite is true for a microburst. The high moisture content within a thundercloud allows this phenomenon to stay cold or even be cooled further as it descends to the surface.

3) Strong Winds

One of two main characteristics of a heat burst is the strong gusts of winds that it produces as the pocket of warm air hits the ground gets dispersed in multiple directions over the surface of the surface.

The height from which the layer of air falls, allows it to accelerate and reach high velocities before hitting the ground. Wind gusts can easily exceed 121 km/h (75 mph). For example, in May 1996, Oklahoma experienced a heat burst with wind gusts of up to 153 km/h (95 mph).

4) Sharp And Significant Temperature Rise

Temperature Rise

The second and most defining main characteristic of a heat burst is the sudden and significant rise in temperature at the surface. This sudden rise in temperature can last anything from a few minutes to a couple of hours.

In most cases, the rise in temperature occurs in a short amount of time. The temperature increase is also significant. It is capable of increasing the current atmospheric warm air by as much as 10° Celsius (50° Fahrenheit) or more.

Extreme examples include Almeria (Spain) in July 2019. Temperatures jumped from 28° Celsius (82° Fahrenheit) to an incredible 41° Celsius (106° Fahrenheit) in just 30 minutes. 

In July 2016, Oklahoma also experienced a similar heat burst when the temperature rose from 27° Celsius (80° Fahrenheit) to 41° Celsius (106° Fahrenheit).

Conclusion

What became clear throughout this post, is that a heat burst may not be such a well-known weather event, but one that will definitely be noticed if ever experienced. It has a dramatic effect over a short period, as the few examples in the last section illustrated. 

It should not be confused with a heatwave, though, which can last for days or months and also have a significant impact on weather and climate of any region it impacts.

This post aimed to illustrate what a heat burst is, how it develops, as well as highlighting the characteristics that define it. If the phenomenon were unknown or unclear to you, you would now be able to understand it, as well as the mechanisms that underlie it, entirely.

Feel free to leave any comments, questions, or suggestions you may have. Your opinion is valued and will be attended to as soon as possible.

Never miss out again when another interesting and helpful article is released and stay updated, while also receiving helpful tips & information by simply  clicking on this link .

Until next time, keep your eye on the weather!

Wessel


What Are The Doldrums? The Intertropical Convergence Zone Explained

What Are The Doldrums-The Intertropical Convergence Zone Explained

Many of you might have heard the saying, "down in the doldrums," usually meaning someone is depressed or lacking energy. But this term actually has its roots in meteorology and dates quite far back.

In truth, it dates back as far as the mid 19th century when this nautical term originated with sailors of the time when they used it to describe their predicament when their ships came to a stop and were unable to make any progress for days or even weeks on end.

This article explores what precisely the doldrums are, how it occurs, and look at some of its main characteristics.

What Are The Doldrums?

During the introduction, you already got a glimpse of what the doldrums are, but the description is vague and needs a more thorough and precise explanation. Before delving into the details, though, it is important to define the term first to lay the foundation:

What Are The Doldrums?

Sailing Boat

The doldrums is a term that refers to the Intertropical Convergence Zone, a calm and windless region close to the Equator where the northeastern and southeastern trade winds come together and clash.

It is an old nautical term used by sailors during the 19th century to refer to this part of the ocean when their sailing ships got stuck and were unable to make much progress due to the lack of wind.

It is clear from the definition that the doldrums is a location (the Intertropical Convergence Zone), and not a situation as the introduction implied. It may sound a bit confusing, but as you will soon learn, this is simply a result of miscommunication during the 19th Century.

As you can imagine, there were no radio or any other modern form of direct communication during this period. As a result, communication between ships and their headquarters thousands of miles away had to be relayed via written word or simple "word of mouth."

As a result, when reports reached officials on the mainland, describing the conditions they experienced as being "in the doldrums", it were misinterpreted as the sailors describing an actual location called the doldrums.

Without the misunderstanding corrected, a president was set, and the rest, as they say, is history. Today, the Intertropical Convergence Zone (ITCZ) still commonly gets referred to as the doldrums.   

How The Intertropical Convergence Zone Is Formed

As mentioned in the description, the Intertropical Convergence Zone (ITCZ), develops where the northeastern and southeastern trade winds meet at the thermal equator. (The thermal equator is not a fixed position on the planet's surface, but more on that in the next section.)

The ITCZ moves with the thermal equator as it shifts around 5 degrees north and south of the physical equator throughout the year. (For easier reading, the Intertropical Convergence Zone will be referred to as the ITCZ or doldrums for the remainder of this article.)

Formation Of The Intertropical Convergence Zone

The formation of a high-pressure system in the ITCZ. Click on the image for a larger view. 

The sun heats the surface of the land and sea at the thermal equator, causing it to warm the air directly above the surface. As the air warms and expands, it starts to rise, creating an area of low pressure at the surface. (Learn more about low-pressure systems in this article.)

The southern and northeastern trade winds approach each other and converge at the thermal equator. As they encounter the low-pressure system and rising air in the region, these stop moving in a horizontal direction and starts to move vertically with the rising air.  

As a result, there is almost no horizontal air movement remaining at the surface, and the little wind present is highly erratic. It is these windless conditions that form the ITCZ, more commonly described as the doldrums by the mariners of the 19th century.  

This band of low-pressure and relatively windless conditions, called the ITCZ or doldrums, encircle the entire planet and follow the thermal equator as it meanders to the north and south throughout the year.

Features Of The Intertropical Convergence Zone

With a clear understanding of how the ITCZ or doldrums develops, it is also beneficial to be aware of the different characteristics that this weather phenomenon display. The most notable of these have already been touched on but needs to be explained in more detail:

  1. Shifting Position
  2. Low-Pressure System
  3. Large Amounts Of Humidity And Rainfall
  4. Very Little And Erratic Air Movement

By looking at each characteristic individually, it will be easier to understand and see how it fits into the larger mechanism that drives the ITCZ.

1) Shifting Position

Throughout the year, the ITCZ moves with the thermal equator as it shifts around 5 degrees north and south of the geographical equator. This movement is closely related to the seasonal movement of the sun.

ITCZ Seasonal Shift

As a result, the ITCZ moves north during the summer months in the Northern Hemisphere and reaches its furthest point during July/August. It then returns south and crosses into the Southern Hemisphere, reaching its most southern position around January/February.

This is a very general description of the movement of the ITCZ. Its actual motion is more complex, and its position can shift unexpectedly over some regions. It can also remain over an area or stay away from it for extended periods with potentially devastating results.

Another variable that influences the movement of the ITCZ is the fact that the ground surface warms up more quickly than the ocean's water when exposed to solar radiation. It results in the ITCZ extending further over land than the sea at the same latitude.

Countries within the Tropics rely on the rainfall that occurs with the arrival of the ITCZ, which means that they can be severely affected by an unnaturally long stay or absence.

During a prolonged absence, a region may experience severe drought, depending on the length of time the ITCZ stays away. When this occurrence remains over an area for an abnormally long period, however, the large amount of rain can lead to widespread flooding.

2) Low-Pressure System

Although this post already briefly mentioned the development of a low-pressure system, it needs a more elaborate explanation to understand its importance.

The planet's surface at the Tropics receives more direct and intense solar radiation from the sun than any other part of the world. As a result, both the ocean and land surface gets extensively warmed up.  

In turn, the surface heats the air directly above it. As the air gets warmer, it expands and becomes less dense than the surrounding cold air. This leads to the lighter layer of air to start to rise, which leaves an area of intense low pressure near the ground. 

The importance of this powerful low-pressure system can not be emphasized enough. It is this weather condition that forces the air from the approaching trade winds to be sucked up in the strong vertical lift, which disrupts its horizontal movement.

3) Large Amounts Of Humidity And Rainfall

If you look at a satellite image of the Earth, the ITCZ can easily be identified by the band of clouds encircling the planet near the Equator. It represents the high humidity that forms the numerous rainclouds and thunderstorms occurring in this part of the world.

Heavy Rainfall

The high temperatures at the surface in the Tropics, combined with an abundance of water sources, leads the air to be saturated with moisture. As the moist air starts to rise and gain altitude until it reaches dew point, and condensation takes place.

The resulting stormclouds that form contain a large volume of water droplets. When it can no longer carry them, a burst of intensive and heavy rainfall follows. Although the rain does not last long, a large amount of water gets released in a very short period of time.

It is these short, intense rain showers that are so typical of the weather produced in the Intertropical Convergence Zone.

4) Very Little And Erratic Air Movement

It has been mentioned numerous times throughout this article, but as it is the primary reason for this article and the reason the term doldrums exist, it is worth noting again.

The most well-known characteristic of ITCZ is the absence of wind or very little and erratic air movement. The reason for this phenomenon has already been thoroughly explained.

It is also important to note that even modern sailing boats, no matter how technologically advanced, still battle to make progress and attempt to avoid getting caught in the clutches of this windless region at any cost. 

Conclusion

Even though the saying, "in the doldrums" may become a bit outdated, it is still used across the world without knowing the real origin of the term.

By now, there should be no confusion or doubt as to where the term, the doldrums, originated. Whether you want to refer to it as the doldrums or the Intertropical Convergence Zone, the dangerous windless conditions that define them, remain ever-present.

Feel free to leave any comments, questions, or suggestions you may have. Your opinion is valued and will be attended to as soon as possible.

Never miss out again when another interesting and helpful article is released and stay updated, while also receiving helpful tips & information by simply  clicking on this link .

Until next time, keep your eye on the weather!

Wessel



What Is A Derecho And How Does It Develop?

What Is A Derecho

We are so used to the characteristics of well-known storm systems like hurricanes, tornadoes, and heavy thunderstorms, that it's easy to mistake a lesser-known destructive storm as a more familiar one.

Occasionally though, the extreme weather you are experiencing may be part of something much bigger and more destructive. Since it exhibits the same characteristics as a weather event you are familiar with, it is easy to dismiss it as just that.

But what if the weather phenomenon you are experiencing, has a bow-shaped line of winds at least 400 kilometers (250 miles) wide, accompanied by strong gusts that can reach 121 km/h (75 mph) or more. Also, this long-lived system can easily travel more than 600 miles.

The weather phenomenon that is the focus of this article is precisely one such storm. It is called a derecho. From the figures you saw in the previous paragraph, it should be clear that this is an enormous event with potentially widespread and devastating consequences. 

This article examines what a derecho is and how it develops. It also looks at the widespread effect on humans and the environment.

What Is A Derecho?

From the introduction alone, it will become self-evident that a derecho is a very large weather event that affects a vast area. Before examining how this phenomenon develops, it is essential to have a clear definition of what precisely a derecho is:

What Is A Derecho?

What Is A Derecho

A derecho is a large-scale weather event that is characterized by a powerful bow-shaped line of wind storms that is driven forward by a series of severe thunderstorm systems.

These widespread and fast-moving winds extend over several hundred miles and last for an extended duration. They often result in the formation of tornadoes, hail, & flooding, and can cause widespread damage and destruction.

The name, Derecho, is derived from Spanish, which literally means "straight in English. It is highly appropriate since the winds that characterize this storm system travels in a long straight (with a slight bow-like curve).

For a weather event to be classified as a derecho, winds must reach sustained speeds of at least 93 km/h (58 mph), and the area affected by wind damage is at least 400 kilometers (250 miles) wide. Occasional wind gusts of at least 121 km/h (75 mph) must also occur.

Visually, an approaching derecho is often characterized by a bank of heavy shelf clouds (also known as an arcus clouds), which are synonymous with this extreme weather event. These clouds have a distinct shape that is as awe-inspiring as it is ominous.

How A Derecho Develops

One of the most critical components and main driving forces of a derecho is an extensive grouping of a series of thunderstorms traveling in the same direction. 

However, there are specific factors, both inside and outside these thunderstorms, that trigger and causes a derecho to form and grow into the widespread and devastating weather event we know:

Downbursts

The strong winds that are so characteristic of a derecho are produced through multiple occurrences of a process called a downburst within thunderclouds.

How A Derecho Is Formed

Early stages in the development of a derecho. Click on image for a larger view.

A downburst is a column of cold air that develops in the upper regions of a thundercloud. It starts to sink and accelerate to the ground. When the air hits the ground, strong winds get dispersed in multiple directions.

(Downbursts can further be divided into microbursts and macrobursts. You can find out more about microbursts in this article.)

Under the right conditions, a thunderstorm can generate multiple downbursts repeatedly within a specific region with a size of up to 100 kilometers (62 miles). The downburst clusters that occur as a result favor the creation of a derecho.

Prevailing Winds

Probably the most critical element responsible for a group of thunderstorms to start moving in a specific direction is the presence of prevailing winds. Without a consistent driving force to move storm systems unidirectionally, a derecho will not be able to form.

The influence of these winds can be observed from the moment a downburst of cold air hits the ground. The air diverges typically in all directions away from the point of contact. An overarching directional wind, however, causes a momentum shift in a specific direction.

When prevailing winds are present, the air diverging away from a downburst accelerates faster in the direction the surrounding wind is blowing. As a result, the momentum and forward movement of the storm system follow the direction of the prevailing wind.

Creation Of New Thunderstorms And Bow Echos

Usually, downbursts signals then end of the thunderstorms in which they are occurring. Due to prevailing winds, though, the pool of cold air that spreads faster in the general direction of the surrounding air cuts underneath the lighter warm in front of it, forcing it to rise.

New Thunderstorm And Pool Of Cold Air

New thunderstorm and pool of cold air reinforce Derecho. Click on image for a larger view.

The warm humid air that has been lifted by the cold winds ahead of the storm front, starts to cool down, and condensation takes place, which can result in the formation of an entirely new thunderstorm.

As the newly formed storm matures, another column of cold air develops and eventually drops to the ground. As a result, the pool of cold behind it already present from previous storms get reinforced by fresh downbursts from the new thunderstorm.

It becomes clear how this process can keep on repeating itself under the right conditions, gain momentum, and grow in size and strength. Under these conditions, the bow-shaped storm front that is so synonymous with Derechos, called a bow echo, develops.

This repetitive process is what makes it possible for Derechos to travel for hundreds of miles and cause so much destruction over such a widespread area.

At the leading edge of the storm front, distinctive-looking clouds called shelf clouds (also known as arcus clouds) form, which is as spectacular as they are ominous looking. They are as synonymous with Derechos as the bow echos these storm systems produce.

Characteristics And Effects Of Derechos

The effect a derecho has on any region it impacts is comparable to a large percentage of other extreme weather events like tornadoes and hurricanes. It is therefore not surprising that this storm system often gets confused with another weather event.

There are two characteristics of a derecho, though, that sets it apart from other storms and makes it so unpredictable and dangerous...

Surprise Element Of A Derecho

With most extreme weather events, there are some identifiable buildup or accompanying weather conditions that give meteorologists a fair amount of time to provide potentially affected regions with weather alerts of an approaching storm system.

Hurricanes can be tracked from their origins over the warm waters of the Subtropics and their path calculated with forecasting models. The buildup of supercells that have a high probability of tornadoes occurring can also be identified with Doppler radar systems.

Radar Image Of Derecho

Radar image showing the development and scope of bow echos that are so synonymous with a derecho. 

Although Derechos are widely recognized today and weather conditions conducive to their formation identified, they remain unpredictable and can seem to strike out of nowhere.

Hurricane strength winds, sometimes followed by a downpour of rain, can catch an entire region completely off-guard and hit without any visible warning. Although it moves through an area fairly rapidly, it can cause widespread damage and injuries in a short period.

It is this "surprise element" that is so characteristic of a derecho, that makes it so dangerous and potentially deadly.  

(Even experienced meteorologists can identify the conditions favorable for a derecho to form and signal a weather alert, but won't know for sure until it actually happens. It is part of what makes predicting this type of storm so tricky.)

Sheer Size And Scope Of Affected Regions

The second characteristic that sets a derecho apart from other storms is the sheer size of the area affected. As prevailing winds move a grouping of a thunderstorm in the same direction and form a singular weather event, it has a widespread effect.

The fact that a weather event needs to be at least 400 kilometers (250 miles) wide to be classified as a derecho, already points to the scale of the storm. In many cases, Derechos far exceed this minimum requirement.

Under favorable conditions, this storm system can also build momentum and travel for hundreds of miles. The damage on this scale, can not only be measured in injuries or loss of life but overall costs as well, which can run into hundreds of millions of dollars.

(The derecho that occurred during June 2012 in the Mid-Atlantic and Midwest of the United States, resulted in damage estimated to be in excess of 2.9 billion dollars.)

Wind Damage And Flash Flooding

The majority of destruction and injury caused by Derechos is the result of powerful winds and flash flooding that occur during the storm.

Widespread Destruction Of Trees By Derecho

Widespread destruction of trees by a Derecho weather event.

The sudden arrival of strong winds without any (or little) warning can cause severe damage to any region. Trees, power lines, and lamp posts, etc. can be completely flattened and structures severely damaged with winds reaching speeds of up to 160 km/h (100 mph.)

When enough moisture is present in a group of thunderstorms, and it moves slow enough over an area, flash flooding can occur. A region's topography with steep slopes and valleys can also result in the quick buildup of water, which can also trigger flash floods.  

Apart from the damage to structures and the environment, people caught outside or in nature carry the highest risk of getting injured or worse. The majority of fatalities caused by Derechos is as a result of people being struck by fallen trees/objects or drowning.

The widespread downing of power lines can also result in the loss of power to millions of homes and have a substantial impact on the region's economy. (The derecho of June 2012, mentioned earlier, caused a power outage to 4.2 million users over multiple states.)

Conclusion

What is clear from this article is that even though most people are not aware of its existence, a derecho is a powerful and widespread storm system. (Even though there is still a debate among meteorologists around the specifics of this phenomenon.)

The argument can be made that a derecho is just the sum of thunderstorms working in unison under the right conditions. But the same can be said about a thunderstorm or tornado that is also the result of individual mechanisms operating in the right environment.

This article explained what a derecho is and how it forms. It also looked at its characteristics and some of the most significant impacts it has on human life and the environment.

Feel free to leave any comments, questions, or suggestions you may have. Your opinion is valued and will be attended to as soon as possible.

Never miss out again when another interesting and helpful article is released and stay updated, while also receiving helpful tips & information by simply  clicking on this link .

Until next time, keep your eye on the weather!

Wessel


What Is A Microburst, And How Is It Caused?

What Is A Microburst - And How It Is Caused

At any point, while being outside, you might have experienced a sudden and unexpected downpour of rain, accompanied by extreme gusts of winds. You may just have encountered a microburst.  

A microburst usually occurs during a thunderstorm or heavy rain shower and often is relatively short-lived. It also dissipates as quickly as it arrived.

Wind speeds can reach up to 160 km/h (100 mph) as the air hits the ground and disperse. As a result, this phenomenon often gets confused for a tornado or hurricane.

This post examines what a microburst is, how it develops, and also looks at the different types of microbursts.

What Is A Microburst?

Meteorologist Ted Fujita was responsible for labeling the term microburst. He defined it as a downburst that occurs over a small area that affects a region with a diameter of no more than 4 kilometers (2.5 miles.) in size.

(He was also responsible for the term, macroburst, to identify downbursts larger than 4 kilometers (2.5 miles.))

Although a microburst displays many of the characteristics of a tornado (and sometimes a hurricane), it is a completely different type of meteorological event. Before examining how it develops in more detail, one needs to define what precisely a microburst is:

What Is A Microburst?

What Is A Microburst

A microburst is a localized and powerful downdraft created by a column of sinking air through the base of a storm or rain cloud.

The phenomenon can be divided into dry and wet microbursts, both of which can cause severe damage to the surface and objects in their path.

A cumulonimbus cloud, in which a thunderstorm usually occurs, can reach heights of up to 16 000 meters (52 000 feet). It is at these high altitudes where the cold air develops that form the basis for a microburst.

One more characteristic that makes it so difficult for meteorologists to forecast is the speed at which a microburst develops and also dissipates. This is also what makes it so unpredictable and dangerous.

How A Microburst Develops

With a clear understanding of what a microburst is, it is important to know how it develops. It will not only help to create a clear understanding of how and why it occurs but also why it displays the characteristics that are so unique to this phenomenon.

Development Of A Microburst

Development and execution of a typical microburst. Click on the image for a larger view. 

A microburst initially starts to form in the top part of a storm cloud, where pockets of cold and moist air accumulate and continue to build up. Two main factors trigger and contribute to a column of cold air to start dropping and accelerates to the ground:

  1. Precipitation Loading
  2. Evaporation Cooling

Sometimes, precipitation loading on its own can initiate a microburst, but it usually is a combination of both, working together to create a downburst with potentially devastating effects. A closer examination of each will show how they contribute to the occurrence.

1) Precipitation Loading

Precipitation loading is the raindrops, hail, ice crystal, graupel, and other forms of water that accumulate in the upper regions of a storm cloud. It gets carried up and kept airborne by the strong updrafts that occur within a large storm system.

Water carries a lot of weight, and when updrafts are no longer able to keep it in the air, it starts to drop to the ground. Sometimes it is the sheer weight of the moisture, combined with a dissipating storm system and weakening updrafts that trigger the event.

2) Evaporation Cooling

In the upper troposphere, external cold, dry air also comes in contact with the moist air in the cloud. It causes the moisture to start evaporating. Since evaporation is a cooling process, the air in the cloud begins to cool down.

The resulting pocket of cold air is much denser and heavier than the surrounding warmer air. As a result, this column of cold heavy air will start to sink to the ground.

When the sinking air exists the cloud base, it comes in contact with more dry air. Here, evaporation continues to take place, which cools the air down even further. As a result, the cold air drops even faster and accelerates towards the ground.


The actual occurrence of a microburst can be broken down into three primary stages:

  1. Contact Stage
  2. Outburst Stage
  3. Cushion Stage

By looking at each of these three stages individually, it will be easier to understand the complete process through which a microburst develops:

1) Contact Stage

Downburst Stage of a microburst

Microburst existing the cloud base before making contact with the ground.

During the initial stage of a microburst, cold air (often accompanied by raindrops) exists the cloud base and continues to accelerate to the ground.

The downdraft rushes towards and hits the ground at what is called the contact point (also called the splashdown point), from where strong winds diverge outwards. 

(For clarity, you can use the image of a water-filled balloon, dropped from a height and bursting open when it hits the ground with water being dispersed in all directions. The contact stage of a microburst closely resembles this image.)

2) Outburst Stage

The name of this stage itself is quite self-explanatory. During this stage, powerful winds get dispersed away from the splashdown point after contact with the ground.

These winds travel along the surface and can reach speeds of up to 160 km/h (100 mph) or more, powerful enough to cause severe damage to the environment and structures. Winds of this speed can flatten large trees and seriously damage large structures.

Depending on the type of microburst, the winds can be accompanied by heavy rain, which can add to the damage caused and pose additional dangers as well.

3) Cushioning Stage

In the final stages of the event, a layer of cold air forms at the surface where the downdraft first made contact with the ground. This cold air accumulated from the start of the microburst and build up as it progressed.

While the air, already at the surface and outer limits of the affected area, continues to blow strongly, the "cushion" provided by the layer of cold air below the downdraft prohibits any more air from reaching the ground.  

This final stage marks the start of the end of a microburst, which will blow itself out shortly after no more wind from the downdraft can reach the ground. The duration of a microburst can last anything from a few seconds to a couple of minutes.

Types Of Microbursts

As I briefly touched on in the summary of what a microburst is, there are mainly two forms of this event:

1) Dry Microburst

A dry microburst occurs when no rain is present in the column of air reaching the ground. It happens when there is very little moisture present in the cloud, and the cloud base is situated at a relatively high altitude.

The little rain that emerges from the cloud base with the downdraft quickly evaporates in the dry air below the cloud before it can reach the ground (also known as virga). As a result, it is only the dry air that reaches the round and gets dispersed in multiple directions.

2) Wet Microburst

A wet microburst occurs when a combination of heavy rain and wind reaches and gets dispersed over the ground. This happens where there is a high percentage of moisture present in a cloud.

Wet Microburst

A wet microburst occurring over Phoenix.

When the combined weight of the different sources of moisture in the top part of the cloud becomes too heavy, it starts to sink. As it drops through the cloud, it drags the surrounding air down with it, which accelerates the speed of the sinking column of air.

Subsequently, a combination of rain and wind is caught in the column of air that crashes into the ground, and both get propelled outwards with potentially devastating results.

Conclusion

They may not be as well-known as tornadoes and hurricanes as extreme weather events, but microbursts are just as severe and destructive. It should be very clear to you after reading this post.

This article also illustrated that, even though many of the characteristics are the same as a tornado, a microburst is an entirely separate weather phenomenon that is formed and develops through very different mechanisms.

After reading this article, you will know exactly what a microburst is, how it is formed, and what mechanisms are at work in the process.

Feel free to leave me any comments, questions, or suggestions, and I will get back to you as soon as possible.

Never miss out again when another interesting and helpful article is released and stay updated, while also receiving helpful tips & information by simply  clicking on this link .

Until next time, keep your eye on the weather!

Wessel


What Is A Mirage, And How Does It Occur?

What Is A Mirage And How Does It Occur

We have all seen a movie or cartoon where a thirsty wanderer in the desert spots an "oasis with water and trees at a distance," only to find nothing but sand when they reach its location.

This phenomenon can also be seen when you travel on a long stretch of road on a hot day, and you spot a large puddle of water at a distance. As you approach it, it continues to move further away.

Your eyes are not playing tricks on you, and you are not hallucinating. What you experience is nothing more than an optical distortion called a mirage.

In this article we explore what precisely a mirage is, how it is formed, and also look at the different types of mirages.

What Is A Mirage?

A mirage needs a combination of different variables to be in place for this phenomenon to take shape. Before we delve into a thorough explanation, it is important to have a short description to summarize what a mirage is:

What Is A Mirage?

What Is A Mirage

A mirage is an optical distortion that occurs naturally due to the refraction of light rays that creates a deceptive appearance of a distant object.

It usually occurs on a hot day where the temperature of the surface and air directly above it is much warmer than the air higher up in the atmosphere.

It is a simplified and concise summary of an event that needs a more detailed explanation to understand how it occurs and what mechanisms are at play during the process.

How Is A Mirage Formed?

The word mirage was directly borrowed from the french verb, mirer, which originated from the Latin word, mirari, which translates to "mirror" or "to look at." As you will shortly learn, this is quite an accurate description of the phenomenon.

Mirages can be divided into two types of optical distortions:

  1. Inferior Mirage
  2. Superior Mirage

By looking at them individually, it will soon become clear how each phenomenon is formed and why we see (or perceive) the resulting image in the way we do.

Inferior Mirage

The most familiar and commonly occurring form of this optical distortion is the inferior mirage. It can be seen on a hot day while traveling on a long stretch of road, or in the desert where the phenomenon first gained wide recognition.

A mirage is capable of producing a misplaced image of an object due to the capability of light to refract (bend) in a medium with non-uniform uniform attributes.

It is widely assumed that light travels in a straight path, especially at a speed of 299 792 kilometers per second (186 282 miles per second). In the vacuum of space, it does indeed travel in a straight line.

When traveling through a medium like the atmosphere, the difference in air density at different altitudes allows light to bend. This is because light always follows the quickest path, not the shortest path.

The illustration below will clarify how and why light behaves in this fashion, and how it contributes to the creation of a mirage:

How A Mirage Is Formed

This illustration shows how an Inferior Mirage is formed. Click on the image for a larger view

By making use of the illustration above, it will be much easier to explain and understand how an inferior mirage gets formed.

On a hot day, the Sun rapidly warms up the Earth's surface, which in turn, heats the air directly above the ground. It creates a substantial difference in air temperature between the warm air near the surface, and the colder air above it.

A medium with non-uniform properties has now been created with cold air, which is optically more dense, situated above warm air, which is optically less dense. 

Since light always follows the quickest past, and warm air with less resistance is much faster to travel through, the light will bend towards the hot air close to the ground.

As the red line in the illustration illustration shows, light travels from objects higher up in the colder air to the warm air close the ground, before bending back towards the eyesight of the observer.

The position where the light is not refracted anymore but reflects up towards the observer is called the point of total internal reflection. It is at this location where you will perceive the phenomenon to be located, when the actual object may, in fact, be hundreds of miles away.

Inferior Mirage

To simplify and make the description of a mirage easy to understand, an identical inverted image of the palm trees and water was used in the illustration. Although this is possible, more often than not, the objects in a mirage may appear to look like something it is not.

For example, the "water" you see may be nothing more than the blue sky reflected on the ground, and the palm trees may be a completely different object that got distorted as the light traveled through layers of hot and cold air. There may not even be a real object at all.

In summary:

  • An inferior mirage appears as a result of light bending towards warm air close to the ground, as the red line indicates.
  • It is possible since light follows the quickest (not shortest) path, which, in this case, is the warmer air near the ground, which provides less optical resistance.
  • The observer sees the distorted image much closer than it really is since the image is viewed via a direct line of sight by the observer, as indicated by the blue line.

The mirage is an optical distortion, meaning the image you see may be a distorted view of an actual object much further away. It can also show distortions that are not even part of the real object (e.g., the sky). It may even display items that don't even exist.

Superior Mirage

A superior mirage operates on precisely the same principles as an inferior mirage but has the exact opposite effect. Instead of showing an object much closer than it is, it displays an image of a distant object (that may be entirely out of view) on or above the horizon.

This type of mirage is a result of cold air that is trapped underneath a layer of warm air. This phenomenon is called temperature inversion (which you can read more about in this article.) As a result, light bends up, instead of down, towards the warmer air.

The illustration below will help to describe how a superior mirage gets formed:

How A Superior Mirage Is Formed

By making use of the illustration above, it will be easier to explain and understand how an superior mirage gets formed.

A superior mirage mostly occurs over the colder waters of the ocean or at the Arctic. The cold surface of the water or ice cools down the air directly above it, with a layer of warmer air lying on top of it.

In the case of this phenomenon, the light gets refracted up towards the warmer air, where it can travel faster before getting reflected back down towards the sight of the observer, as indicated by the red line in the illustration.

As a result, the observer perceives the object to hover above his/her eyesight and the horizon, as indicated by the blue line in the illustration. This occurrence is called looming.

Superior Mirage

Sometimes, you can observe this phenomenon while standing on the shoreline and watch a boat on the horizon, which seems to float in the air some distance above the water.

Superior mirages also occur when objects too far away to see due to their distance and curvature of the planet, "appears" above the horizon. This is possible due to the bending of light up towards the warmer air, and back down to the observer far away.

In summary:

  • A superior mirage appears as a result of light bending up towards warmer air situated above colder air near the surface, as the red line indicates.
  • It is possible since light follows the quickest (not shortest) path, which, in this case, is the warmer air higher in the atmosphere, which provides less optical resistance.
  • The observer sees the distorted image "floating" above the horizon since the image is viewed via a direct line of sight, as indicated by the blue line.

Conclusion

As you just learned, a mirage is not your eyes playing tricks on you. It is a real distorted image you see as a result of the refraction (bending) and reflecting of light. It is your brain that is programmed to interpret that what you see is something completely different. 

Often, it is the image of an actual object at a distant location, sometimes it is a distorted image that appears as something completely different, and sometimes there is no real object at all. 

Through this post, you learned what a mirage is, what the different types of mirages are, and how each one develops.

Feel free to leave me any comments, questions, or suggestions, and I will get back to you as soon as possible.

Never miss out again when another interesting and helpful article is released and stay updated, while also receiving helpful tips & information by simply  clicking on this link .

Until next time, keep your eye on the weather!

Wessel


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