why do most thunderstorms have flat tops?
The cloud would be able to rise higher were it not for the fact that the troposphere ends at a certain height in the atmosphere (between 10 to 20 km altitude, at the equator it's 20 km near the poles it's 10 km).
What happens is that the temperature gradient in the atmosphere suddenly decreases, and then the temperature will start to rise as a function of height (temperature inversion).
Now, clouds cannot rise when there is a temperature inversion, so what happens is that the cloud will expand in the horizintal direction. This leads to the flat top.
Above this point the stratosphere starts (the region between thepoint where the temperature gradient decreases and the point where the stratosphere starts is the tropopause).
The temperature inversion in the stratosphere is caused by ultraviolet rays that are absorbed in the stratosphere (which also leads to the formation of ozone). The energy that is dumped in the stratosphere causes it to heat up, and more so at higher altitudes.
Most thunderstorms have flat tops due to a phenomenon called the anvil shape or overshooting top. This occurs when the updraft within a thunderstorm reaches a point where it can no longer continue to rise, usually due to the lack of atmospheric instability or the presence of a stable layer of air above.
To understand why most thunderstorms have flat tops, we can examine the basic structure of a thunderstorm. A thunderstorm consists of an updraft, a downdraft, and the surrounding environment. The updraft is the area where warm, moist air rises rapidly. As this warm air ascends, it cools and condenses, forming a dense cloud filled with moisture.
As the updraft continues to rise, it eventually encounters the tropopause, which is the boundary between the troposphere (lower atmosphere) and the stratosphere (upper atmosphere). The tropopause represents a stable layer of air that inhibits further upward movement of the storm. This stable layer acts as a "lid" on the thunderstorm, preventing it from growing vertically.
When the updraft reaches the tropopause, it begins to spread out horizontally, forming the characteristic flat top of a thunderstorm. This spreading is caused by the strong winds at the level of the tropopause, known as the tropopause jet stream. These winds blow horizontally and effectively shear off the top of the storm, creating the flat appearance.
Furthermore, as the updraft spreads out horizontally, it can generate an overshooting top. An overshooting top occurs when a portion of the updraft continues to rise above the level of the tropopause. This happens when the updraft is particularly strong or encounters less stable layers within the stratosphere. The overshooting top extends vertically beyond the flat anvil top and can be seen as a dome or bulge on the top of the thunderstorm.
In summary, most thunderstorms have flat tops because the updraft within the storm reaches a stable layer of air at the tropopause, causing it to spread out horizontally. This spreading is influenced by the strong winds at that level. Occasionally, a thunderstorm may exhibit an overshooting top, which is a result of a particularly strong updraft pushing beyond the tropopause.