A remote-sensing and modeling perspective of ice crystals in deep convective 
Clouds

Bastiaan van Diedenhoven

Tropical anvil clouds play an important role in the climate system. The delicate 
balance between short- and longwave radiative forcing by such clouds depends, 
among other factors, on ice water content, and sizes and shapes of the ice crystals. 
Also the temperature level at which glaciation occurs plays an important role in 
determining the net radiative forcing of such cloud systems, since it significantly 
affects the convective dynamics and, ultimately, cloud macrophysical properties. 
Insufficient knowledge on ice formation processes, which govern the glaciation 
temperature, ice water content, and crystal sizes and shapes, hampers the 
development of adequate parametrization of deep convective cloud systems in 
climate models. Here we show results of a study that aims to help better constrain 
glaciation temperatures, ice sizes and shapes using MODIS and POLDER satellite 
data in combination with detailed DHARMA cloud resolving model simulations 
based on the TWP-ICE campaign. Measurements indicate that glaciation starts at 
temperatures below -20 degrees C, but liquid cloud tops are observed down to -35 
degrees C. Ice crystal sizes and shapes are shown to depend on cloud top 
temperature. These observation are used to evaluate the ice formation in the 
DHARMA simulations.