Strong convection redistributes heat and moisture in the tropical atmosphere. Distinctive anvil clouds form when hot, humid air (red) rises in a region called the convective core. As the air rises it cools, resulting in heavy precipitation. During the strong convection typical of the tropics the air can rise high into the troposphere (roughly 15 km altitude) where the column is truncated by high winds. This forms high-altitude cirrus clouds that stream out ahead of the storms. Cool air (still with a high relative humidity) drops out of the cap of cirrus clouds, which warms and dries as it falls. This process humidifies the air in the upper troposphere. Near the surface over the tropical oceans (beneath the boundary layer) the air is always humid and often filled with low-level clouds.
Robert Simmon from <a href="https://en.wikipedia.org/wiki/NASA_Earth_Observatory" class="extiw" title="en:NASA Earth Observatory">NASA Earth Observatory</a>
2002-06-12
Article <a rel="nofollow" class="external text" href="http://earthobservatory.nasa.gov/Study/Iris/">Does the Earth Have Iris Analog</a> by David Herring and Robert Simmon