HR: 17:15h
AN: A34B-06    [Abstracts]
TI: Radiative influences on the glaciation time-scales of mixed-phase stratus
AU: * Harrington, J Y
EM: harring@mail.meteo.psu.edu
AF: Department of Meteorology Pennsylvania State University, 503 Walker Building, University Park, PA 16802
AU: Lebo, Z
EM: zjl104@mail.com
AF: Department of Meteorology Pennsylvania State University, 503 Walker Building, University Park, PA 16802
AU: Johnson, N
EM: ncj107@psu.edu
AF: Department of Meteorology Pennsylvania State University, 503 Walker Building, University Park, PA 16802
AB: 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 with some studies using ice spheres. 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 possibly 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 as large as 5 - 10 minutes. Thus, we expect mixed-phase arctic stratus to glaciate faster when radiation is considered. Furthermore, we find a larger decrease in the glaciation time during the winter months when solar radiation is essentially negligible.
DE: 0320 Cloud physics and chemistry
DE: 0321 Cloud/radiation interaction
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005