Certain meteorological events, specifically cloud formations, often have unique but also puzzling characteristics. Fallstreak holes are one such occurrence, but what are they, and how do they form?

Fallstreak holes are large circular or oval-shaped openings that form in cirrocumulus or altocumulus clouds when supercooled water is turned into ice crystals, causing the surrounding water droplets to evaporate. This occurrence is predominantly the result of aircraft passing through a cloud.

If you found yourself at the right time and place, you may have been in the unique position of observing what looked like a large appearing what seems to be spontaneously in a cloud formation.

These appearances may look very unnatural and are often confused with Unidentified Flying Objects (UFOs) or other artificial objects. Although they may seem artificially created objects, it is the result of a natural process, which was initiated by a manmade object.

In the following sections, we take a closer look at what fallstreak holes (also known as punch hole clouds) are and how they develop.

What Are Fallstreak Holes?

Before taking a more detailed look at how fallstreak holes develop, one needs to establish a more elaborate and detailed look at the definition and characteristics of this phenomenon. 

Also known as punch hole clouds, cavum, skypunch, or canal clouds, these meteorological phenomena predominantly occur in mid to high-level clouds such as altocumulus or cirrocumulus clouds at heights of 3 -12 kilometers (2 - 7 miles). 

At these high altitudes, clouds primarily consist of supercooled water, which creates the perfect environment for the development of fallstreak holes. 

As already mentioned, the development of these phenomena is primarily caused by aircraft as they pass through high-level clouds. Exactly how this occurs will be discussed in detail in the upcoming section.

Although fallstreak holes normally take the shape of a circle or oval, they can also develop in other forms, specifically cigar-shaped forms. This can be attributed to the angle at which an aircraft passes through a cloud.

A circular or oval-shaped hole is typically the result of an airplane passing through the cloud at an acute angle. When the approach through the cloud is more shallow, though, the aircraft spends more time in the cloud, which results in the cigar-shaped hole.

How Fallstreak Holes Develop

The following list details the development of fallstreak holes, starting with the conditions that need to be in place to make their formation possible:

Conclusion

Although fallstreak holes may appear very unnatural, there is a perfectly logical explanation for their development, as this article clearly illustrated. 

Actually, they are a combination of a natural process combined with an artificial object. The natural mechanisms involved in the formation of ice crystals and the evaporation of water droplets are initiated by an artificial object in the form of an aircraft passing through clouds.

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Certain cloud formations always manage to put on a striking display, but Mammatus (Bubble) clouds look almost ominous and threatening. But what are these cloud types, and what are their characteristics?

It is very hard not to notice this unique cloud formation with its pouch-like protrusions extending from the base of a storm cloud. Their unique appearance also makes it easy to distinguish them from other cloud types.

But what exactly are these meteorological phenomena, what causes their very recognizable shape and features, and are they really as dangerous as they appear?

We examine exactly what mammatus clouds are, how they form, as well as the characteristics and features that define them.

What Are Mammatus Clouds?

Before one can start taking a closer, more in-depth look at the characteristics of mammatus clouds and the potential ways in which they develop, a more detailed definition of this phenomenon is required:

The word "mammatus" is derived from the Latin word "mamma," which translates to "breast" or "udder." This is a very apt description, especially when looking at the physical appearance of this cloud formation.

As the title alluded to, mammatus clouds are informally or more commonly known as bubble clouds due to their appearance. It is officially known as mammatocumulus.

Technically, mammatus clouds are not individual types of cloud species. Rather, it is an extended feature of the cloud at which base it develops.

Although they are predominantly associated with storm clouds like cumulonimbus, they can also form at the base of other types of clouds like altostratus and stratocumulus. They are also known to form at the base of volcanic ash clouds.  

Mammatus clouds can spread out over hundreds of miles during a single event. Although the multiple clusters of lobes that constitute this formation can last anything from 15 minutes to a couple of hours, a single lobe typically lasts for an average of 10 minutes.

What makes mammatus clouds especially unique is not their appearance but rather their development, which is the inverse of normal cloud development. Clouds typically form when rising moist air reaches dew point, condensation occurs, which leads to cloud development.

On the contrary, mammatus clouds form as a result of sinking cold air that has enough momentum to continue descending until it passes through the cloud base of a cumulonimbus cloud and develops below it in the familiar "pouch-shaped" structures.

Mammatus Clouds Formation

A few common facts are known about mammatus cloud formation. We know that they form underneath the base of cloud formations, predominantly cumulonimbus clouds.

They also typically form in the presence of unstable air conditions where cold sinking air is directly responsible for their development. (Due to these unstable air conditions associated with these clouds, pilots keep their aircraft well clear of any mammatus cloud development.)

Apart from these well-established facts, very little is actually known about how these unique clouds form. There is much debate about their origin, and although many theories are in circulation attempting to describe their formation, most are principally flawed.

The predominant theory that is most widely accepted is proposing that saturated cold air in a cumulonimbus starts to spread out once it reaches the tropopause, where temperature inversion prohibits it from rising any further.

As a result, it starts to spread out horizontally in the anvil part of the cloud. The saturated air is heavier than the surrounding dry air and starts to descend. If enough momentum is present for the air to continue its descent, it emerges as mammatus below the cloud base.

The bottom line is that there is no clear explanation for mammatus cloud development, and their origins remain a mystery.

Mammatus Clouds Facts

Some of the information in this section already appear elsewhere in this article and are explained in more detail, but the following list highlights the key facts and characteristics that define mammatus clouds:

Although by no means an exhaustive list of all aspects involving this meteorological phenomenon, this list captures the most important defining characteristics of mammatus cloud structures.

Conclusion

It is clear that mammatus clouds are some of the most unique and fascinating cloud structures. Their large pouch-like protrusions make them look ominous and threatening, but as this article illustrated, they are completely harmless themselves.

And although their origins remain a mystery and a source of much debate, it has been established that these upside-down formations are the result of cold sinking air and typically form underneath the base of cumulonimbus clouds.

This article defined what exactly mammatus (bubble clouds) formations are, highlighted their key characteristics, and also had a look at their development.

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Certain cloud formations can result in some of the most awe-inspiring and spectacular events nature occasionally puts on display. We look at one such meteorological phenomenon known as Noctilucent clouds.

These cloud formations are not nearly as common as more familiar cloud types and can mostly be viewed at high latitudes during the summer months (during May-August in the Northern Hemisphere and during November-February in the Southern Hemisphere).

They are, however, of no less importance or any less spectacular. In fact, noctilucent clouds are often used by meteorologists to study wind movement in the upper atmosphere.

In this article, we take a closer look at the definition of noctilucent clouds, how they form, as well as the characteristics that define them.

What Are Noctilucent Clouds?

In order to understand how and why noctilucent clouds form and why they exhibit the characteristics that define them, one needs a more expansive and detailed definition of what precisely this cloud formation is:

The name "noctilucent" is derived from Latin words "nocto" and "lucent," which translates to "night shining" (A direct reference to the radiant characteristics of this cloud formation.)

Noctilucent clouds are also more commonly known as night shining clouds or polar mesospheric clouds. Their structure closely resembles the streaky or flaky characteristics of Cirrus clouds (another high-level cloud type).

They occur at an altitude of 76 - 85 km (47 - 53 miles) in the mesosphere, where it is too cold for water to remain in its liquid state, and ice crystals form on small dust particles, which are believed to be remains of meteors. (Meteors burn up in the mesosphere.)

The clouds are too faint to be visible during the day and only become visible after sunset when the sky is mostly covered in darkness. This allows ice crystals in the high-level noctilucent clouds that are still exposed to the sunlight to be illuminated.

Noctilucent clouds are typically observed at high latitudes (approximately 50 to 70 degrees north or south) since this is where temperatures in the mesosphere drop to below -120° Celsius (-184° Fahrenheit), which is a necessary condition for the clouds to form. 

An observer located at a high latitude on the planet's surface can view the illuminated phenomenon as cirrus-like cloud formations with a blue or silver hue.

(The blue color is a result of the absorption of ozone in the atmosphere.)

As the definition already eluded to, this cloud type is a fairly rare meteorological occurrence. The reason for this is the restrictive conditions that need to be in place for them to form and also be observed in the first place. We discuss them in the next section.

How Noctilucent Clouds Form

Noctilucent clouds are rare meteorological phenomena for a reason. The strict conditions necessary for their development only occur at certain latitudes & during specific times of the year. Noctilucent cloud formation occurs as follows, starting with the necessary conditions:

There are also other processes involved in the formation of noctilucent clouds, but this section highlighted the key steps involved in the development of this rare meteorological phenomenon. 

Facts About Noctilucent Clouds

Much of the information provided in this section has already been covered elsewhere in this article. However, the following list highlights the key facts that define and characterize noctilucent clouds:

This list does not cover every possible fact there is know about noctilucent clouds but highlights the most important ones.

Conclusion

Noctilucent clouds are not just some of the rarest meteorological phenomena on the planet, but their location in the mesosphere also makes them hard to study by meteorologists. (The location of the mesosphere makes it the hardest atmospheric layer to explore.)

This does not make them any less spectacular or stop scientists from studying them. After all, they have their own dedicated satellite observing them. NASA's AIM (Aeronomy Of Ice In The Mesosphere) satellite observes noctilucent cloud characteristics and behavior.

This article highlighted and defined what exactly noctilucent clouds are, how they develop, and the characteristics that define them.

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Rainbows are, without doubt, the most photographed and well-known meteorological phenomena on Earth. But what exactly are these events, how do they develop, and what causes their unique characteristics?

Almost every human on the planet is familiar with the multicolored arc of a rainbow formation spanning across the sky. Even the few readers who never observed one have probably seen several images and illustrations of this meteorological phenomenon.

Although it usually occurs on a rainy day when the sun breaks through the clouds, it can also happen under similar conditions when water droplets in the air come into contact and transform sunlight.

This post examines what a rainbow is, how it is formed and looks at the different types of rainbows. It also highlights the key facts that define this meteorological phenomenon.

What Is A Rainbow?

Before one can start looking at the formation of a rainbow and the key facts that define it, one needs a more elaborate definition of the phenomenon. The introduction already provided a brief description, but a more comprehensive description of a rainbow:

The word "rainbow" originated from the Latin word "arcus pluvius", which literally translates to "rainy arch."

A rainbow is a meteorological phenomenon that is, in fact, nothing more than an optical illusion. It is not an actual physical object and also has no physical location. It is simply light being reflected and dispersed that, under the right conditions, reach an observer's location.

It typically appears when raindrops are present in the air and are exposed to (usually) direct sunlight low on the horizon on the opposite side of the sky. This explains why rainbows normally appear in the west in the morning and the east in the late afternoon.

The multicolored arc one observes is a result of sunlight refracted and reflecting off the back of a water droplet, which also disperses the white sunlight and breaks it up into its seven spectral colors (red, orange, yellow, green, blue, indigo, and violet.)

Red (the color with the longest wavelength) bends at an angle of 42 degrees and appears on the outer edge of the bow, while violet (the color with the shortest wavelength) bends at an angle of 40 degrees and appears on the inner edge of the arc.

All rainbows are technically in the shape of a full circle, but since they occur so close to the ground, one only observes the arc visible above the horizon. The antisolar point, the theoretical center of a rainbow, is almost always positioned at a point below the horizon.

A rainbow and sun always appear on the opposite sides of the sky. As a result, when viewing a rainbow, an observer will always be standing with his/her back to the sun. (Sunlight travels past the onlooker, which gets reflected and dispersed by water droplets back to the viewer.) 

Rainbow Formation: How A Rainbow Develops

With a better understanding of what a rainbow is and the characteristics that define it, one needs to look at how a rainbow is formed to clarify why and how it occurs. The following steps detail the progression in the development of a rainbow:

There are other processes involved in the formation of a rainbow and also more factors influencing its appearance, but these are the key steps involved in the development of this meteorological phenomenon.

Types Of Rainbows

Although the principles defining a rainbow and its formation remain the shape, small variations and additional factors can result in different types of rainbows. The following are some of the most common types of rainbows besides primary rainbows:

There are even more variations on the primary type of rainbow, but these are some of the most commonly observed variations.

Rainbow Facts

Previous sections of this article already addressed the definition and formation of a rainbow. The following list provides the reader with some of the key facts and characteristics that define a rainbow:

Although this list does not contain all the data available about rainbows, it highlights the key facts and characteristics of this optical phenomenon.

Conclusion

As this article illustrated, although a rainbow can sometimes appear almost magical and supernatural, it is a simple optical, meteorological phenomenon that results from the refraction, reflection, and dispersion of sunlight by water droplets in the atmosphere.

This article described what exactly a rainbow is and how it develops. It also looked at the different types of rainbows, as well as the key facts defining this optical phenomenon.

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Earth's atmosphere consists of five different layers, each with its own unique features. We examine what precisely the outermost layer, the exosphere, is and what its defining characteristics are.

When viewed from the surface or low Earth orbit, our atmosphere seems to be one continuous layer of air. However, it consists of five different layers: The troposphere, stratosphere, mesosphere, thermosphere, and exosphere.

This article focus on the exosphere, the outermost layer of the atmosphere. It not only examines what the exosphere is but also looks at the characteristics or facts that define it.

Exosphere Definition

It was already briefly described during the introduction, but in order to examine the exosphere in more detail, a more comprehensive definition is required.

The name "exosphere" is derived from Ancient Greek, with "ἔξω éxō" meaning "outside," and "σφαῖρα sphaĩra" meaning "sphere." Directly translated "outside sphere" perfectly describes the exosphere since it is the Earth's outermost layer in a spherical shape.

The exosphere is situated just above the thermosphere, with a thin layer of air called the thermopause separating the two layers. It reaches up for thousands of miles and seamlessly merges with the vacuum of space, where all Earth's atmospheric characteristics disappear. 

It does not have a fixed lower boundary but starts at an altitude of approximately 500 - 1 000 km(311 - 620 miles), extending up to a height of roughly 10 000 km (6 200 miles). It also has no clear upper boundary.

The lower boundary is also called the exobase. The exobase is also known as the "critical altitude." Above this height, temperatures remain relatively stable, and barometric conditions are no longer relevant.

Compared to the four layers below it, the exosphere contains little to almost no traces of the characteristics that define the Earth's atmosphere. In fact, the "air" so thin that it resembles interplanetary space more than it does the rest of Earth's atmosphere.

(Gas molecules can travel for hundreds of miles without ever coming into contact or colliding with another particle.)

What sets the exosphere really apart, though, is the fact that small particles in the layer do not react the same as in other atmospheric layers where gas molecules mix and collide with each other. 

The few molecules present in the layer basically never collide. Instead, they enter the exosphere and typically follow a ballistic trajectory, which after reaching their apex (maximum altitude), curve back down and reenter the lower atmosphere.

(Some small particles travel too fast, though, and manage to break free from the Earth's gravitational pull and escape into space. As a result, smaller particles are continuously escaping the planet's atmosphere.)  

The small number of gas molecules present in the exosphere is mostly light gases such as hydrogen and helium. Heavier gas molecules like carbon dioxide and oxygen can be found closer to the exobase.

Temperatures can easily exceed 2 000° Celsius (3 632° Fahrenheit) in the exosphere, but there are no particles to transfer the heat, so one will never experience it. In fact, if exposed, one will experience the typically freezing cold temperatures of outer space in the exosphere.

As a result of its vastly different characteristics compared to the other atmospheric layers, it should come as no surprise that some scientists don't regard the exosphere as part of the atmosphere at all and see the thermosphere as Earth's uppermost layer.

Due to its altitude and composition, the exosphere is home to a large number of navigational, communication, and weather satellites. Its most famous inhabitant, though, is the Hubble Space Telescope.

Earth is not the only planet in our solar system that has an exosphere. Jupiter, Mars, and Saturn are just two examples of other planets also having exospheres.

(Even smaller satellites that do not have atmospheres containing a mix of gases, like the moon and three of Jupiter's moons, have what is called a "surface boundary exosphere.")

Facts About The Exosphere

The following list highlights the characteristics and facts of the exosphere in more detail.

This is by no means a comprehensive and exhaustive list that contains all the data available about the exosphere but highlights the key facts and characteristics that define this layer.

Conclusion

As this article highlighted, the exosphere still contains small of the gases present in the other four atmospheric layers, but these quickly disappear as altitude increase and the last traces of the atmosphere transition into the vacuum of space.

It is not surprising, then, that many scientists argue that the exosphere cannot be considered part of Earth's atmosphere and that the thermosphere constitutes the atmosphere's upper boundary.

It is technically still part of the atmosphere, though, and contains a small percentage of the gases found closer to the planet's surface. And, yes, it still has an important role to play, as just illustrated. 

If you are interested in the complete structure and make-up of the atmosphere, this article covers all five atmospheric layers and their relation to each other in more detail.

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On some rare occasions, while looking at the horizon during sunset or sunrise, one can observe what looks like "multiple suns." We take a closer look at this meteorological phenomenon known as a sundog.

A sundog or parhelion is defined as a bright optical phenomenon occurring near the horizon on the left, right, or both sides of the sun at a 22-degree radius. It is a result of sunlight refracted by hexagon-shaped ice crystals in Cirrus clouds with their primary axis vertically orientated.

A sundog (or sun dog) is part of a family of optical meteorological phenomena that occurs as a result of sunlight or moonlight being refracted (bent) by ice crystals in high-altitude Cirrus clouds that observers view as different shapes and displays.

The spectacular and more familiar solar halo (or ring around the sun) is the same phenomenon, as well as sun pillars, which also occur close to the horizon. They appear differently, though, partly due to the orientation of the ice crystals and the sun's position.

In this article, we examine what a sundog is and how it is created. We also look at its characteristics and highlight the important facts about this phenomenon.

Sundog Definition

During the introduction, a brief description of what a sundog is was already provided. In order to best understand its characteristics and formation, though, one first needs to establish a more detailed definition:

A sundog (sun dog) is officially known as a parhelion but is also referred to as a mock sun.

The word "parhelion" is derived from the Greek "para-" (meaning beside) and "-hēlios" (referring to the sun). Literally translated, it means "beside the sun," which is exactly where sundogs are situated.

The name "sun dog" also originated in Greek Mythology, where it was believed that Zeus walked his dogs across the sky. Consequently, sundogs represent the dogs of Zeus.

As already mentioned, a sundog is the result of light being refracted through hexagonal ice crystals in Cirrus clouds. But it is not only the hexagonal shape of the crystals that allows for the formation of this phenomenon.

The crystals also have a flat, plate-shaped form, which allows them to float horizontally in the air and create the appearance of a sundog on one or both sides of the sun. (As opposed to a solar halo where the ice crystals are more randomly orientated.)

Consequently, these horizontally orientated crystals cause the sunlight to bend through a 22° angle towards the observer and also break it up into its primary colors.

As a result, the inside edge of a sundog has a red-colored tint, while the rest of the colors blend together to reform the bright white color of the sun. Sometimes, though, a faint blue color forms on its outer edge, and at times the phenomenon displays the full array of rainbow colors.

A sundog is not visible to everyone where the sun shines through Cirrus clouds. It depends on your physical location in relation to the position of the sun. Depending on your position, the ice crystals refract the light from the sun at just the right angle to see the occurrence. 

What Causes Sundog

As mentioned in the previous section, the rings you see around the sun result from the ice crystals in cirrus clouds refracting and reflecting the light in such a way that you can see a ring appearing from your location on the planet's surface. 

A few things need to be in place in order, though, to observe sundogs beside the sun clearly.

As mentioned, a sundog is not always visible to anyone viewing the sun through a layer of cirrus clouds near the horizon. One has to be in the right location on the planet in relation to the sun's location, with plate-shaped ice crystals in the clouds also orientated correctly.

Facts And Characteristics Defining A Sundog

The following list summarizes and highlights some of the key facts and characteristics regarding a sundog, some of which have already been explained in more detail elsewhere in this article:

This is by no means an exhaustive and complete list but focused on the key aspects that define a sundog (or parhelion).

Conclusion

As this article clearly highlighted, the "mock sun" appearing on one or both sides of the sun is not an abnormal or inexplicable event.

It has a logical and scientific explanation for its occurrence, which has everything to do with what is going on in our own atmosphere, and nothing with what is happening in space around the sun itself.

It is also worth mentioning again that the ring one sometimes observes around the sun (solar halo) is also exactly the same type of phenomenon as a sundog.

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Meteorologists and weather enthusiasts are very well aware of the critical role humidity plays in the creation of different meteorological events. But what is humidity, and what are its characteristics?

Humidity primarily refers to the amount of water vapor or water in its gaseous state present in the air at a given time. It is typically represented in relative humidity. Although invisible to the naked eye, high humidity levels can be felt and are often associated with growing levels of discomfort.

At any given time, no matter where we find ourselves (indoors or outdoors), we are constantly surrounded by air containing a certain percentage of humidity.

There is no dispute about the vital role water play in meteorological activities. After all, it is the primary driving force of almost any weather occurrence.

But humidity plays an even more essential role in the transport of water between different regions. This clearly illustrated when one looks at The Water Cycle.

It is also crucial for air to contain just the right amount of moisture to maintain a "balanced" air ratio to benefit the environment and all living organisms. (Too little or too much humidity can negatively impact the environment and even human health.)

In the following sections, we take a closer look at how humidity is caused, how it is measured, and its impact on weather events.

What Causes Humidity?

With humidity clearly defined, one needs to take a close look at how it is caused in the first place and examine its formation: 

Humidity is caused when water turns from its liquid or solid state into its gaseous form (water vapor). This occurs due to evaporation and transpiration (known as evapotranspiration), typically resulting from heating due to solar radiation or friction as precipitation travels through air particles.

As radiation from the sun heats the planet's surface, water evaporates from bodies of water (oceans, lakes, dams, puddles) and also from surfaces that are rich in water content like soil. The evaporation process turns water into its gaseous state.

Vegetation in the form of trees and plants also releases water into the atmosphere through their leaves in a process called transpiration. (The combined processes of evaporation and transpiration are called evapotranspiration.)

The evaporation of water is not only the result of solar radiation, though. When precipitation takes place, waterdrops, hail, or snow starts falling towards the ground and accelerate. 

As it gains speed, the water starts experiencing drag due to friction with particles and molecules in the air. The friction creates heat, resulting in a significant amount of evaporation to take place, turning some of the precipitation into water vapor, 

All these processes are responsible for increasing the humidity in the air.

Facts About Humidity

In earlier sections, the definition and cause of humidity were already established. The following list, though, highlights the key facts and characteristics surrounding this element of weather:

This is a concise and cryptic list of the most important characteristics and facts that define humidity, but the details about specific aspects are highlighted in other sections throughout this report.

Relative Humidity Vs Absolute Humidity

Before explaining how humidity is measured, we need to address the difference between relative humidity and absolute humidity, as there is some confusion about the difference between the two.

Absolute humidity is the measurement of the amount of water vapor in the air. It is a very rigid form as measurement, as it does not take variables like temperature into consideration. It is normally indicated as grams of moisture per cubic meter of air (g/m3).

Relative humidity is also the measurement of the amount of water vapor in the air. Unlike absolute humidity though, it is measured relative to the temperature of the air.

In other words, relative humidity measures the percentage of water vapor present in the air relative to the maximum amount of vapor that can be held at a given temperature.

This is important, as warm air can hold much more water vapor than cold air.

If absolute humidity is used to measure the water vapor in both warm and cold air, and it measures identical water vapor percentages in both, it is misleading and not representative of the actual atmospheric conditions.

(In this case, the relative humidity in the cold air is much higher than that of the warm air since warm air holds more moisture than cold air. To get an equal absolute humidity reading, more water vapor must be present in cold air to match the warm air's moisture.)

For this reason, relative humidity is the best and most widely used way of measuring moisture levels as it most accurately reflects the actual atmospheric conditions.  

How Humidity Is Measured

The instrument used to measure the humidity in the air is called a hygrometer. There are a variety of these instruments that have been used throughout the years.

The psychrometer is probably the most well-known early example of a humidity measuring device. It basically consists of two thermometers (one being covered with a wet cloth) used to measure the humidity.

The bulb of the thermometer covered by the wet cloth measures a lower temperature as a result of the evaporation of the moisture in the cloth. By using the difference between the two different temperature readings, the humidity is measured.

Obviously, this is not a very accurate and reliable way of measuring humidity.

A capacitive or resistance hygrometer uses a much more reliable way to measure humidity. A material able to absorb moisture is used. The amount of moisture influences the material's ability to carry an electrical current. 

An electrical current is then sent through the material and measured. Based on the strength of the current (influenced by the amount of moisture absorbed by the material), the amount of humidity in the air can be measured.

The process clearly more complex than just explained. To get a better understanding of hygrometers and how they measure humidity, you can read more about them in this article.

The Effect Of Humidity On The Weather

Humidity is one of the main driving forces of almost all weather systems around the world. Actually, the combination of humidity and temperature is the impetus of many weather systems and occurrences.

The moist air in a warm front gently moves over a cold front and cools down as it rises. It results in condensation and cloud formation, which leads to the gentle precipitation that is welcoming to the agricultural sector. (Similar to the weather produced by a stationary front.)

On the other side of the scale, the warm moist air over the oceans of the tropics rises and forms powerful low-pressure systems. As the air keeps rising and rotating winds are pulled in and building up around the low-pressure center, the warm, humid air keeps feeding the growing system.

What was a tropical depression can now quickly build into a tropical storm. If enough humid air builds up in this system and stays over the warm ocean waters long enough, hurricanes of varying strength can be very destructive when it makes landfall.

And this whole process got started by some humid air rising up from the ocean's surface. That is why these warm tropical waters are called the engine rooms of big storm systems and the fuel that drives these massive systems.

Similarly, the torrential rains falling during the Monsoon Season over India and Southeast Asia are all part of the circulation pattern that brings huge amounts of humid air from the warm Indian and Western Pacific Oceans during the warm summer season.

As is the case with hurricanes and tropical storms, moisture-filled air is once again one of the main driving forces of a major weather system. This is also another example of how humidity and temperature work together in the creation of a major storm system.

There are obviously many more processes involved in the formation of all these weather systems. If you want to read in detail how hurricanes and monsoons are formed, as well as the role humidity plays in all this, you can read the in-depth article here. 

Conclusion

Although it cannot be seen, humidity plays a crucial role in the creation of almost all weather occurrences, as this article clearly illustrated. It highlighted what humidity is, how it forms and also described the different processes involved.

The powerful effect humidity has on the weather on a global scale should also be evident, and we just touched the surface. There is so much more to humidity than covered in this article, but the focus of this post was to capture its definition and illustrate its formation.

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On some odd occasions, while looking up at the sky, one may notice a hazy rainbow-colored ring around the sun. This phenomenon is called a solar halo or 22-degree halo, but what exactly is this occurrence?

Solar halos or 22-degree halos are hazy rainbow-colored rings that occur at a radius of approximately 22 degrees around the sun. It results from the sun's light being refracted by ice crystals in Cirrus clouds in the upper troposphere at altitudes of approximately 6000 meters or 20 000 feet.

These multi-colored optical phenomena can occur quite frequently and are not an unfamiliar sight, yet very few people really know what exactly these rings around the sun are or how they are formed. 

This article examines what these rings (or solar halos) are and how they are created. It also looks at its characteristics and the conditions surrounding it.

What Is A Solar Halo?

The introduction already provided a brief description of what this spectacular-looking meteorological phenomenon around the sun is. To better understand its formation, though, one first needs a more elaborate and detailed definition.

A solar halo goes by many different names. Sometimes it is simply referred to as "the ring around the sun." The scientific community refers to it as a 22° halo, but it is also known as a halo, sun halo, 46° halo, or rainbow halo.

The color of a solar halo varies from a faint rainbow color to a pale white tint. The rainbow colors are the result of the ice crystals breaking up the white light into its primary colors. Sometimes, though, the primary colors combine and blend together to form a white tint.

(The hue and intensity of the color largely depend on the strength of the sunlight, density of the clouds, and the angle of refraction.)

The halo is not visible to everyone where the sun shines through Cirrus clouds. It depends on your physical location in relation to the position of the sun. Depending on your position, the ice crystals refract the light from the sun at just the right angle to see the occurrence. 

A solar halo is exactly the same phenomenon that occurs during the daytime around another celestial body. The halo you see around the moon is the same meteorological phenomenon. Instead of sunlight, though, it is the moonlight that is refracted in this case.

What Causes The Ring Around The Sun

As mentioned in the previous section, the rings you see around the sun result from the ice crystals in cirrus clouds refracting and reflecting the light in such a way that you can see a ring appearing from your location on the planet's surface. 

A few things need to be in place in order, though, to observe these rings surrounding the sun clearly.

As already mentioned, an individual also has to be in the right geographical location on the planet's surface )in relation to the sun's location) to observe this phenomenon.

Characteristics Of The Rings Around The Sun

A notable feature of the halo surrounding the sun is the lack of a clear and well-defined border. The fuzzy border is the result of millions of ice crystals refracting the light in multiple directions that it makes it impossible to create a clear and well-defined border.

The ring around the sun has a mostly rainbow-colored hue but can also display a pale white color as a result of primary colors blending together and canceling each other out. This a direct result of the hexagon shape of the ice crystals.

Like the shape of raindrops causing the different colors in a rainbow to appear, the faceted (hexagon) shape of ice crystals refracts the light of the sun and breaks it up into its primary colors.

This is why you will occasionally notice some rings around the sun to have a red tint on the inside and a blue tint on the outside. 

As the sun is much brighter than the moon, the rings around the sun not only display a rainbow-colored hue but also appear much brighter and clearly defined due to the increased luminescence.

What is also very noticeable is the fact that the sky between the edge of the sun and the halo always appears darker than the rest of the sky.

On rare occasions, one may also catch a very rare glimpse of not one but a double halo surrounding the sun. 

Halo Around The Sun Superstition

Over centuries, many cultures worldwide believed a ring around the sun is a sign that rainy weather is on the way. This is neither a myth nor a superstition. The presence of high cirrus clouds is very often an indication of wet and stormy weather on the way.

Cirrus clouds normally precede low-pressure systems by a day or two, and as many of you may already know, low-pressure systems are normally at the heart of stormy wet weather. (You can read more about low-pressure systems and cold fronts in this article.)

During biblical times, the rainbow was used as a sign from God as evidence of His covenant with Noah to never flood the Earth again. The rainbow-colored halo around the sun has the name significance as the traditional rainbow.

In African mythology, a solar halo is seen as a sign of great change ahead. (They also believe that it signals the arrival of rain, which is more in line with scientific evidence.)

Conclusion

As this article clearly illustrated, the multicolored ring around the sun that sometimes occurs under ideal conditions is not nearly as mysterious or uncommon as one might think.

There is a very logical and scientific explanation for its occurrence, which has everything to do with what is going on in our atmosphere, and nothing to do with what is happening in space around the sun itself.

It is also worth mentioning again that the halo one sometimes observes around the moon is also exactly the phenomenon that occurs around the sun.

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Although most of us have never observed the Northern Lights in person, most readers would most definitely have seen images or heard of this meteorological phenomenon. But what exactly is the Aurora Borealis?

It is probably one of nature's most breathtaking displays, but due to its location, few of us ever get to see an Aurora Borealis occurrence. Situated over the Arctic and Antarctic regions, this phenomenon has also been the source of many awe-inspiring photographs.

This article examines what this multicolored light display is and also how it occurs. It also looks at the facts and characteristics that define it.

What Is The Aurora Borealis?

Several different factors are involved in the creation of the Aurora Borealis, which interactions with each other result in the occurrence of this optical phenomenon. Before examining it in more detail, one needs to obtain a more elaborate definition of this event.

The introduction already provided a brief description of what the Aurora Borealis is, but one needs a more detailed and concise explanation of this occurrence before continuing.    

The name, Aurora Borealis, is derived from the names of gods in Roman Mythology. "Aurora" was the Roman goddess of dawn, while "Borealis" is the god of the north wind. The term was coined by Galileo Galilei, an Italian astronomer, in 1619.

In Norse Mythology, the Aurora Borealis was believed to be a bridge made of fire that extended into the sky.

This meteorological phenomenon also goes by several names, including the Northern Lights, Polar Lights, Merry Dancers, and Aurora Polaris. It also has different names when it occurs in the Southern Hemisphere over Antarctica, but more on that later.

The primary colors that are displayed are luminous green, violet, and pink. It also produces hues of blue, yellow, and occasionally white and orange.

When particles collide with nitrogen, the result typically produces deep red and violet colors. When a collision between charged particles and oxygen occurs, though, it produces the colors green and yellow. 

The Aurora Borealis occurs in the magnetosphere, the magnetic field that surrounds and protects the Earth from incoming solar winds. It starts several hundred kilometers above the Earth's surface but extends further than 600,000 kilometers (370,000 miles) in altitude.

(It should not be confused with Earth's 5 atmospheric layers, though, which are categorized according to air density, temperature, meteorological activity, and gravitational force. Technically, the magnetosphere starts in the thermosphere and extends into outer space.)

Types Of Aurora Borealis

Auroras literally come in all shapes and sizes. According to astronomer Dr Stuart Clark, the Aurora Borealis can be divided into 5 categories. The following list names them in order from dimmest to brightest:

1. Diffused light appearing close to the horizon that may be hard to observe.
2. Bands of light that are similar to arcs but with more of a curvature.
3. Arcs appear that extend across the sky.
4. Rays are curtain-like light and dark stripes extending into the sky.
5. Coronas cover vast portions of the sky and extend from horizon to horizon.

There are, off-course, many other types and variations of this phenomenon, but at the core level, they can be broken down into these 5 types of Aurora Borealis.

How The Aurora Borealis Is Formed

The following steps will serve to illustrate how exactly the Aurora Borealis form and develop:

There are other and more detailed processes involved as well, but these steps captured the essence of how the Aurora Borealis forms.

Where Does The Aurora Borealis Occur?

Although we are very familiar with and the vast majority of attention is given to the Aurora Borealis (or Northern Lights), this meteorological phenomenon actually occurs over the polar regions of both the Northern and Southern Hemisphere.

If it occurs in the Southern Hemisphere over Antarctica and surrounding regions, it is known as Aurora Australis or Southern Lights.

In both hemispheres, Auroras are approximately 3 to 6 degrees in width. They are located between 10° and 20° from the geomagnetic poles.

In the Northern Hemisphere, they can be seen in the Arctic Circle and northern countries bordering it. In the Southern Hemisphere, it can be observed over Antarctica, the southernmost part of Argentina, Australia, and New Zealand. 

Facts About The Aurora Borealis

This is not a complete and exhaustive list but highlights the most important and relevant facts about the Aurora Borealis.

Conclusion

As this article clearly illustrated, the Aurora Borealis is a meteorological phenomenon that occurs on a gigantic scale (literally extending hundreds of miles into the edge of space), producing truly breathtaking lighting displays.

But as also explained, it is a natural phenomenon with a clear scientific explanation that has been widely researched throughout the last few centuries. And today, we understand even more about the Aurora Borealis than ever before.

It may not be the "fire bridge to the sky" as the North Germanic people believed, but that does not take anything away from the feelings of awe and magic this spectacular phenomenon evokes.

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Although it is one of the outermost layers of the Earth's atmosphere, the importance of the thermosphere cannot be underestimated. We take a closer look at this atmospheric layer and its characteristics.

Situated close to the boundary between the atmosphere and space, the thermosphere is only separated from outer space by the exosphere, Earth's fifth and outermost layer.

Although Earth's fourth atmospheric layer has very few characteristics in common with the three layers closer to the planet's surface, it still has a valuable role to play.

We examine not only what the defining characteristics of the thermosphere are but also the facts that separate it from the other four layers of the atmosphere.

Thermosphere Definition

The thermosphere is the last atmospheric layer which characteristics carry any resemblance to the rest of the atmosphere as we know it. Above its upper boundary, the exosphere blends seamlessly into the vacuum of space.

It was already briefly described during the introduction, but in order to examine the thermosphere in more detail, a more comprehensive definition is required.

The thermosphere is situated just above the mesosphere, with a thin layer of air called the mesopause separating the two layers. It reaches up to the exosphere, with another thin layer of air called the thermopause separating them.

The name of the thermosphere is derived from the Greek word, θερμός (thermos), meaning heat. (Referring to the high temperatures reached in the layer.)

At 513 km (319 miles), it is the thickest of the atmosphere's four inner layers and thicker than the troposphere, stratosphere, and mesosphere combined. (But not as thick as the exosphere that stretches for thousands of miles into space.)

By some definitions, space starts at 100 km (62 miles) above Earth, so it is not surprising that the thermosphere is seen as part of outer space in many circles. The air is extremely thin at this altitude, where the Earth's gravitational pull is also greatly reduced. 

Due to these characteristics, this is a highly utilized part of the atmosphere where over 800 active satellites orbit the planet, and it is also home to the International Space Station (ISS). 

(Not to mention the large number of space debris also orbiting in the thermosphere.)  

One of the most well-known characteristics of the thermosphere is the presence of the Aurora Borealis (Northern Lights), the spectacular meteorological phenomenon that occurs over regions in the Arctic Circle.

The Aurora Borealis is a result of charged particles from the sun colliding with gaseous particles in the thermosphere. This causes the colorful light display observers in the Northern Hemisphere are so familiar with. (Green is one of the common colors created.)

Another unique feature of the thermosphere is the extremely high temperatures that occur within this layer. With temperatures reaching up to 2 500° Celsius (4 530° Fahrenheit), the thermosphere is the hottest of all the atmosphere's layers by a huge margin.

The temperature is not constant, though. Between day and night, an average difference of 200° Celsius (360° Fahrenheit) can occur. The amount of solar radiation also has a direct influence on the temperature, causing as much as a 500° Celsius (900° Fahrenheit) variation.

You will also not be able to feel the extremely high temperatures this layer experiences. The air is so thin that it basically resembles a vacuum,  with no particles/atoms in the air to conduct the heat.

The stratosphere is well-known for containing the important ozone layer, which is essential for protecting life on Earth from the Sun's deadly UV radiation. The thermosphere, though, also plays a role in protecting the planet from solar radiation.  

It absorbs a large amount of incoming Ultraviolet and X-ray radiation, which emphasizes the importance of this layer. The incoming solar rays interact with gas molecules during the absorption process, which contributes to the high temperatures reached within this layer.

A large portion of the Ionosphere also falls within the thermosphere since ions are created when Ultraviolet Radiation causes the photoionization of molecules.

Facts About The Thermosphere

The following list highlights the characteristics and facts of the thermosphere in more detail.

Although this list does not contain all the data available about the thermosphere, it highlights the key facts and characteristics of this layer.

Conclusion

Like the three atmospheric layers below it, the thermosphere has a vital role to play in protecting the planet and all life in it, as this article illustrated.

Although it only has a fraction of the gas and other particles present in lower layers, the thermosphere is situated at the ideal height for low-obit space utilization and contains enough gas molecules to absorb a significant amount of dangerous solar radiation.

If you are interested in the complete structure and make-up of the atmosphere, this article covers all five atmospheric layers and their relation to each other in more detail.

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Until next time, keep your eye on the weather!

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