MODIS view of tropical clouds and water vapor

The Moderate Resolution Imaging Spectrometer (MODIS), which is installed on both the Terra and Aqua satellites, provides an unprecedented view of global oceans, land, and atmosphere, including a number of fields useful for studying the tropical atmosphere. These fields include macroscale fields like cloud fraction, cloud top pressure, cloud optical depth, and column water vapor, and microscale fields like cloud effective radius. Most of the atmospheric fields resemble, in spatial pattern and temporal evolution, the cloud top temperature field; clear-sky water vapor, however, has a markedly different spatial pattern and temporal evolution, suggesting that large-scale controls on tropical water vapor are more complicated than a simple connection with large-scale convergence and convection would suggest.

Other studies have found a bimodality of cloud top height, which is confirmed by our analysis and which is even more pronounced when considering joint distributions with above-cloud water vapor. Cloud tops tend to be either very high or very low, but are rarely found at middle altitudes. For the tropics as a whole, column water vapor above low clouds has a normal (Gaussian) distribution, even though low clouds are most common in regions of subsidence and dry air.