4 km Effective Radius -

This product retrieves the effective radius of all clouds whose 10.7 µm brightness temperature is colder than -40 C. Pixels warmer than -40 C are replaced with the 10.7 micro;m brightness temperatures (grayscale), while the effective radii are assigned colors.

The retrieval is performed by first computing the 3.9 micro;m albedo, then using solar geometry and satellite position along with the 3.9 micro;m albedo to calculate the associated effective radius from a series of lookup tables. These lookup tables were created by using an observational operator to compute expected 3.9 micro;m albedos for a wide range of cloud ice crystal sizes and solar geometries. Droxtals are assumed as the ice crystal habit, so scattering phase functions associated with droxtals were used in the model to build the lookup tables.

Research has shown that lower values of ice cloud effective radius are generally associated with high-based thunderstorms with relatively strong updrafts, i.e., the types of thunderstorms common over the Rockies and High Plains during the summer. Additionally, optically thick mountain wave clouds tend to be composed of small ice crystals.