Radiative Influences on Glaciation Time-Scales of Mixed-Phase Clouds

Harrington, Jerry The Pennsylvania State University

Category: Modeling

Mixed-phase stratus clouds are dominant in the Arctic during much of the year. These clouds typically have liquid tops that precipitate ice. Time scales for the complete glaciation of such clouds (the Bergeron process) are typically computed using the classical mass growth equations for crystals and liquid drops. However, mixed phase arctic stratus have significant infrared cooling and solar heating (during the warm season) rates that can affect the growth of water drops and ice crystals, and therefore the strength of the Bergeron process. To examine the influence of radiative heating and cooling on the Bergeron process, we incorporate a radiation model into the mass growth equations for liquid and ice. Regardless of crystal habit and temperature, our results show that infrared radiative cooling reduces the glaciation time scale at cloud top, with lesser reductions at cloud base. Radiative reductions in glaciation time are greatest for plate crystals at T = -10C, where the reduction can be between 5 - 10 min. Solar heating slows the Bergeron process throughout the middle and lower portion of the cloud leading to significantly longer glacation time-scales. Hence, our results suggest that the Bergeron process should be much faster at cloud top, and much slower in the middle and lower portions of a stratus deck, than computed without radiative effects.

This poster will be displayed at the ARM Science Team Meeting.