Characterization of plumes on top of a deep convective storm using AVHRR imagery and radiative transfer simulations

Cirrus clouds often form on top of intense convective storms and influence the radiation exchange at the top of the atmosphere. From time to time these cirrus assume a typical plume form, whose origin is yet to be clearly explained. Investigation on plume’s structure and composition is necessary using satellite observations and radiative transfer modeling, since in situ measurements are generally not available for the storm’s extreme scenarios. Plumes of ice crystals produce a significant increase of cloud top reflectivity in channel 3 (3.55 - 3.93 ¼m) of NOAA AVHRR, due to the small size of the crystals (of the order of the channel wavelength). AVHRR measurements over a severe storm are compared with radiative transfer simulations through a 1-D, plane-parallel radiative transfer model. The hydrometeor vertical distribution of a cumulonimbus tower is assumed, composed of a water droplet layer underlying an ice crystal layer. The presence of the plume on top of the cumulonimbus is simulated by an ice crystal layer whose optical depth and ice crystal size and habit are varied. The results of the comparisons show that channel 3 conveys relevant information on the ice crystal size and habit.