Linkage among Mesoscale Dynamics, Ice Crystal Orientation and Precipitation Structures Revealed by Collocated Microwave Radiometer and Multi-frequency Radar Observations

Ice clouds and floating snow are ubiquitous globally and play important roles in the Earth's radiation budget and precipitation processes. Ice particle microphysical properties (e.g., size, habit and orientation) are not only influenced by ambient environment's dynamic and thermodynamic conditions, but also intimately connect to the cloud radiative effects and particle fall speeds, which therefore impact the onset-time, location, type and strength of surface precipitation.

We previously identified frequent occurrence of horizontally-oriented ice particles inside anvil/stratiform precipitating clouds using the Global Precipitation Measurement Microwave Imager (GPM-GMI) high-frequency polarimetric difference (PD) observations. In this current work, we further investigate the dynamic/thermodynamic mechanisms and precipitation structures associated with ice crystal orientations. In order to do so, medium thick ice clouds are separated into high/low PD groups, and the collocated CloudSat (W-band) and GPM-DPR (Ku/Ka bands) radar observations as well as ECMWF atmosphere background profiles are grouped accordingly. We found that high-PD scenes with more horizontally-oriented ice crystals have more middle-level clouds and a well-defined melting layer. These features are often found when convection is mature and stratiform precipitation prevails. On the contrary, low-PD scenes with more randomly-oriented ice crystals have more upper-level cloud, more aloft precipitation-sized particles but no significant melting layer, all indicating that convection is still developing and not yet mature. High (low) PD scenes are associated with stronger (weaker) boundary layer and upper-troposphere shears and wetter (drier) ambient environment. Further analysis of an ensemble of squall line cases confirms that preference of horizontally (randomly) aligned ice crystals is closely associated with mature (developing) convections.

This pioneering work links observational evidence of ice microphysical orientation with convection life stage and precipitation structures, implying great potential that instantaneous polarimetric measurements could contribute to the understanding and modeling of mesoscale deep convective systems.