Dependence of Ice Microphysical Properties on Environmental Parameters: Results from HAIC/HIWC Cayenne Field Campaign

High Ice Water Content (HIWC) regions composed mainly of small ice crystals above tropical mesoscale convective systems (MCSs) are characterized using data obtained during Phase 2 of the 2015 High-Altitude Ice Crystals (HAIC)/HIWC project based out of Cayenne, French Guiana. Observations from in-situ cloud probes on the French Falcon-20 and Canadian National Research Council (NRC) Convair-580 aircraft are used to determine the microphysical and thermodynamic properties of such regions. Data from a 2-D stereo probe and precipitation imaging probe show how statistical distributions of ice crystal mass median diameter (MMD), ice water content (IWC), total number concentration (Nt) for particles with maximum dimension (Dmax) > 55 µm, and ice crystal particle size distributions (PSDs) vary with environmental conditions such as temperature (T), and convective properties such as cloud type, MCS age, distance away from a convective peak (L), and surface characteristics. Results show that IWC is significantly correlated with vertical velocity (w), whereas MMD decreases and Nt increases with decreasing T, consistent with aggregation, sedimentation and vapor deposition processes at lower altitudes. High IWCs with small MMD, representing HIWC regions, are full of small columns and irregular ice crystals. MMD typically increases with IWC when IWC < 0.5 g m-3, but decreases with IWC when IWC > 0.5 g m-3 for -15 oC T -5 oC. Trends also depend on environmental conditions, such as presence of convective updrafts that are the ice crystal source, MMD being larger in older MCSs consistent with aggregation and less injection of small crystals into anvils, and IWCs decrease with increasing L at lower T. The strength of the relationship between IWC and MMD depends on environmental conditions, with the correlation decreasing with decreasing T. The strength of correlation between IWC and Nt increases as T decreases and varies with environmental conditions.