Mammatus Clouds: Everything You Need to Know

Have you ever looked up to the sky and felt astounded at the strange and distinctive cloud formations? If the clouds had sequences of bulges or pouches emerging from their bases, then most probably you were staring at Mammatus clouds. Mammatus are among the strangest and most unique cloud formations you’ll ever come across.

In this article, you’ll learn everything you wish to know about Mammatus clouds.

What Are Mammatus Clouds?

Clouds

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Also referred to as mamma or mammatocumulus, Mammatus clouds are cellular patterns of bags hanging beneath the base of a large cloud. Mammatus means mammary cloud. This is a typical cumulonimbus raincloud but it can be attached to other categories of parent clouds.

The name “Mammatus” comes from the Latin name “mamma”, which means “udder” or “breast”. The mamma cloud is a supplementary feature of a cloud, not a genus. It’s usually related to anvil clouds and severe thunderstorms. This cloud often extends from the bases of cumulonimbus clouds, but they can also occur underneath altostratus, volcanic ash, and cirrus clouds.

When this cloud occurs in cumulonimbus clouds, it indicates the presence of a strong storm. In the extremely shaved environment in which this cloud forms, aviators are often advised to avoid any cumulonimbus with a Mammatus because it indicates a convectively prompted turbulence. It’s also common to find contrails with lobes, but these ones aren’t genuine Mammatus clouds.

Mammatus clouds can be smooth, unkempt, or lumpy lobes that are either opaque or translucent. Since these clouds are groups of lobes, there can be a variation in the way they bond together. For instance, they can appear like an isolated cluster and a field of mammae spreading over hundreds of kilometers or gathered along a line. Sometimes they may be composed of unequal or equal lobes.

A standard Mammatus lobe measures 1-3 kilometers wide and half a kilometer long. Each lobe can remain visible for about 10 minutes, while a complete cluster of mamma lobes can last between 15 minutes and several hours. Mamma clouds are usually made of a mixture of ice and liquid water, but some are composed of liquid water.

As noted above, Mammatus clouds are usually indicative of an impending storm or other extreme weather conditions. Since these clouds consist of ice and liquid water, they are flexible enough to spread over hundreds of miles in different directions. Moreover, their individual formations can stay in one position for more than 15 minutes at a time.

The most important thing to note about Mammatus clouds is the fact that although they look ominous, they are just messengers of the larger Mother Nature – showing up before or even after extreme weather systems. Therefore, when you see these clouds in your area, prepare yourself accordingly for severe weather like a strong storm.

What Are the Formation Mechanisms of Mammatus Clouds?

Formation

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Mammatus clouds come in various formations, each with unique properties and appearing in unique environments. This variation has led to the formulation of multiple theories around the formation of Mammatus clouds.

One of the common hypotheses on the formation of Mammatus clouds that are shared across all domains is the concept of sharp inclines in temperature, moisture, and impetus (wind shear) through the anvil cloud or sub-cloud air frontier, which intensely influence relations therein.

Here are the most common mammatus cloud formation mechanisms being hypothesized. Each has its unique shortcomings that you should be aware of.

1. Cumulonimbus Cloud Subsides Gradually

It has been widely reported that the anvil of cumulonimbus clouds subsides gradually while spreading out from the source cloud. This theory further contends that as the air descends, it becomes warm. But cloudy air warms more slowly than dry air (sub-cloud air). Cloudy air warms at the moist adiabatic lapse rate, while sub-cloud dry air warms at the dry adiabatic lapse rate.

This theory has been rendered impractical by the presence of mammatus lobes without strong subsidence, making it hard to isolate the processes of hydrometeor fallout and cloud-based subsidence. Therefore, it’s unclear whether any of these processes occur.

2. Hydrometeor Fallout Causes Cooling

This mammatus cloud formation theory suggests that when hydrometeors fall into the sub-cloud air, the air with precipitation cools because of rerouting or evaporation.

Once the hydrometeors are cooler than the air around them and unstable, they drop into a static equilibrium, where a restoring force curves the edges of the hydrometeors effect back up, forming the lobes. One of the shortcomings of this theory is the fact that cloud base vaporization doesn’t always form mammatus.

Experts agree that while this formation mechanism may be responsible for the initial stages of the formation of mammatus clouds, other processes play a significant part in the formation and development of the lobes.

3. Melting Causes Destabilization at Cloud Base

Some experts argue that mammatus clouds occur when the cloud base is destabilized through melting. When there’s a cloud base near the freezing line, the cooling of the neighboring air due to melting leads to convective overturning. Unfortunately, this theory doesn’t hold much water because this strict temperature doesn’t always exist.

4. Dynamics of Hydrometeor Effect

Since the above-mentioned formation mechanisms rely on the disruption of the sub-cloud by adiabatic and latent heating mechanisms, some experts have come up with a different theory discounting the thermodynamical effect of the hydrometeor effect. This theory suggests that the dynamics of hydrometeor fallout alone can cause the formation of mammatus lobes.

They argue that the inhomogeneities existing in masses of hydrometeors along the cloud base can cause inhomogeneous descent along the cloud base. This descent involves frictional dragging of the related eddy-like structures that cause the formation of lobes. However, this theory is considered to be inconclusive because the vertical velocities in the mammatus lobes are usually superior to the speeds of the fall of hydrometeors in them.

5. Cloud-Base Detrainment Instability (CDI)

This theory was formulated by Kerry Emanuel, who suggested that cloudy air combines with dry sub-cloud air instead of precipitating into it. This theory works the same way as the convective cloud-top entrainment. According to Emanuel, mammatus clouds are formed when the cloudy air destabilizes because of evaporation, which leads to cooling.

6. Thermal Reorganization of Clouds

This theory suggests that mammatus clouds form through the thermal reorganization of clouds due to radiation during evolution. Radiation is believed to cause the formation of mammatus clouds when clouds are chilled radioactively at the top. Negatively floating clouds permeate down through the whole layer and appear as mammatus clouds at the cloud base.

This radiation can also occur when the cloud base warms up through radiative heating by the long wave emissions from the ground. This heating causes the cloud base to destabilize an overturn, forming mammatus clouds. But this process is only valid for visually thick mammatus clouds. The truth is that mammatus clouds are mainly made of liquid water and ice, which makes them relatively thin.

7. Gravity Waves

This theory proposes that gravity waves are responsible for the formation of linearly structured mammatus clouds. While wave patterns appear in mammatus clouds, they only occur due to gravity waves formed as a response to a convective updraft imposing on the tropopause and spreading out over the whole cloud in form of a wave. So, this theory doesn’t conclusively explain why mammatus clouds are prevalent in certain parts of the anvil.

Additionally, time and size balances for gravity waves and mammatus aren’t equal. Gravity wave sequences may cause the mammatus clouds instead of forming them.

8. Kelvin-Helmholtz (K-H) Instability

This theory suggests that the K-H instability occurs along cloud borderlines, causing the formation of wave-like overhangs commonly known as Kelvin-Helmholtz vapors. However, mammatus clouds aren’t the same as K-H vapors. Therefore, even though the suggested instability can cause the formation of the overhangs, another procedure has to occur to allow lobes to form.

However, the problem with this mechanism is that the K-H instability happens in a firmly stratified environment, while mammatus clouds normally occur in a somewhat turbulent environment.

9. Rayleigh-Taylor Instability Theory

This mammatus cloud formation theory suggests that the instability between two liquid substances of differing densities causes the formation of mammatus clouds. The denser substance moves over the less dense liquid, creating a pattern that forms mammatus clouds. Along the cloud base or sub-cloud interface, the air is laden with hydrometeors that make it denser than the neighboring air.

But the hydrometeors in the dense air cause it to mix with the less dense sub-cloud air, creating mammatus clouds. However, this theory is inconclusive because the instability along a static interface isn’t always applied to the border between two trimmed atmospheric flows.

10. Rayleigh-Benard Convection

This theory proposes that the differential heating (heating at the bottom and cooling at the top) of a layer of clouds results in convective overturning. In the case of mammatus clouds, the base is normally cooled thermodynamically. When the cloud base is descending, it forms mammatus lobes.

Next to the lobes is a compensating ascent. However, this theory is considered to be generally insubstantial.

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