Tropical Ice Cloud Microphysical Transition Downwind of Convection

The life cycle of cirrus clouds is heavily influenced by the microphysical and dynamical processes that affect the number concentration, shape, and size of the individual ice crystals. Improving our understanding of the competing effects of these processes will allow for improved modeling of cirrus evolution and quantification of cirrus radiative effects. Toward this end, the current study combines observations from ATTREX (Airborne Tropical Tropopause Experiment), POSIDON (Pacific Oxidants, Sulfur, Ice, Dehydration, and cONvection), and ACCLIP (Asian Summer Monsoon Chemical and Climate Impact Project) to investigate the transition in ice crystal properties such as size, number concentration, and habit downwind of deep convection. All three campaigns sampled cirrus clouds in the Tropical Pacific under varying environmental conditions, providing observations of local 3-D winds, water vapor provided by either DLH (Diode Laser Hygrometer) or VCSEL (Vertical Cavity Surface Emitting Laser), and ice particle concentration and size distributions provided by the CDP or FCDP (Fast- Cloud Droplet Probe) and 2D-S (2 Dimensional-Stereo Probe), and particle habit from the CPI (Cloud Particle Imager). We utilize back trajectories from the aircraft flight track to analyze these in situ observations in the context of time since the observations were last influenced by convection. Habit classification of CPI and 2D-S imagery allows for assessing the progression in ice particle habit as influenced by the microphysical and dynamical processes driving the cirrus lifecycle evolution downwind of convection. Analysis yields distinct differences in the microphysics near and far downwind of convection, as well as regions with evidence of in situ regrowth of the ice particles in particular habits, which are investigated in closer detail.