[1] Flight-averaged CCN concentrations during the Rain in Cumulus over the Ocean (RICO) field project varied by a factor of four. This was sufficient to provide correlations with flight-averaged total cloud droplet concentrations (N c ) and mean diameters (MD) that showed greater influence of CCN than updraft velocity (w) on N c and especially MD. The product of CCN and w produced even stronger correlations with N c and MD. An earlier RICO study had shown an inverse relationship of N c and giant nuclei (GN) with large cloud droplet concentrations (N LD ). These two RICO studies now show that the aerosol with the most influence on N LD (MD) is CCN. The results of the present study are similar to earlier studies in more polluted clouds that also showed more influence of CCN than GN on MD/ N LD /drizzle. The present study indicates that variations in CCN concentrations even within maritime air masses modulate precipitation. Citation: Hudson, J. G., and S. Mishra

Polarimetric radar observations increasingly are used to understand cloud microphysical processes, which is critical for improving their representation in cloud and climate models. In particular, there has been recent focus on improving representations of ice collection processes (e.g., aggregation and riming), as these influence precipitation rate, heating profiles, and ultimately cloud life cycles. However, distinguishing these processes using conventional polarimetric radar observations is difficult, as they produce similar fingerprints. This necessitates improved analysis techniques and integration of complementary data sources. The Midlatitude Continental Convective Clouds Experiment (MC3E) provided such an opportunity. Quasi-vertical profiles of polarimetric radar variables in two MC3E stratiform precipitation events reveal episodic melting layer sagging. Integrated analyses using scanning and vertically pointing radar and aircraft measurements reveal that saggy bright band signatures are produced when denser, faster-falling, more isometric hydrometeors (relative to adjacent times) descend into the melting layer. In one case, strong circumstantial evidence for riming is found during bright band sagging times. A bin microphysical melting layer model successfully reproduces many aspects of the signature, supporting the observational analysis. If found to be a reliable indicator of riming, saggy bright bands could be a proxy for the presence of supercooled liquid water in stratiform precipitation, which may provide important information for mitigating aircraft icing risks and for constraining microphysical models.

[1] Ice fall velocity has a strong impact on climate feedback, influencing cirrus cloud coverage and radiative forcing as well as upper troposphere relative humidity. This study aims to provide the atmospheric modeling community with better parameterizations of the ice fall speed in cirrus clouds on the basis of aircraft measurements from recent field campaigns, especially the Tropical Composition, Cloud and Climate Coupling (TC4) campaign in 2007 and the Indirect and Semi-Direct Aerosol Campaign (ISDAC) in 2008. These campaigns provide improved measurements of the ice particle size distribution (PSD) where the concentrations of artifact small ice particles (due to shattering of ice particles on the probe inlet tube) are greatly reduced. In addition to the PSD, the mass-weighted fall velocity (V m ) depends on the ice particle projected area and mass. The calculation of V m was based on improved direct measurements of the PSD number and area concentration and improved estimates of ice particle mass. The effective diameter (D e ) was calculated in a similar way. The TC4 analysis has provided a diagnostic relationship that relates V m to both cloud temperature (T) and ice water content (IWC) with an r 2 of 0.78. A similar relationship for D e was also obtained with an r 2 of 0.82. The V m relationship and associated V m -IWC-T measurements were found to agree well with a V m scheme based on T and cloud radar retrievals of V m and IWC in tropical cirrus clouds. However, a critical climate-influencing parameter like the ice fall speed needs to be coupled with the cloud microphysics and radiation in climate models. This is made possible through strong correlations between D e and V m regarding TC4 and ISDAC cirrus. Finally, TC4 satellite retrievals of D e and V m are found to be consistent with corresponding observations.