Analysis of Pecan 2015 MCSs Utilizing Airborne In-Situ Microphysical Data Together with Airborne- and Ground-Based Doppler Observations

Data from the NOAA Tail Doppler Radar (TDR) installed on the NOAA P-3 aircraft acquired in 2 mesoscale convective systems (MCSs) sampled on 20 June and 6 July 2015 during the Plains Elevated Convection at Night (PECAN) experiment were synthesized with data from several ground-based Doppler radars using the Spline Analysis at Mesoscale Utilizing Radar and Airborne Instrumentation (SAMURAI) technique to provide the kinematic and radar reflectivity context of vertical profiles of cloud microphysical properties derived from Optical Array Probes (OAPs) on the same aircraft. The 20 June MCS exhibited a well-defined descending rear inflow jet (RIJ) behind a formative bowing segment of the convective line, with an average relative humidity (RH) of 41% below the melting layer in the stratiform region (SR). Ice was present at temperatures as warm as 7°C with low concentrations of 0.227 L^-1. Between the melting layer and -6°C, the average RH with respect to ice (RH_i) was 84% with an average ice concentration of 2.06 L^-1, while at temperatures below -6°C the average RH_i rose to 110% with an average ice concentration of 42.72 L^-1. The 6 July MCS was sampled in a more mature state and had relatively quiescent flow behind the convective line, much higher average RH of 85% below the melting layer in the SR, ice concentrations of 0.572 L^-1 at 4°C and liquid precipitation extending to the surface. Between the melting layer and -4°C, the average RH_i was 91% with an average ice concentration of 5.79 L^-1, while at temperatures below -4°C the average RH_i rose to 107% with an average ice concentration of 38.37 L^-1.

Thus, the two MCSs had similar characteristics in the supersaturation region well above the melting layer. Differences emerged in the region subsaturated with respect to ice above the melting layer, with the 20 June MCS exhibiting lower RH_i and ice concentrations suggesting sublimation was playing a stronger role here than on 6 July. In the bottom of the melting layer, the average RH and ice concentration dropped to less than half those in the same region on 6 July, supporting higher rates of evaporation. This analysis is consistent with the influence of microphysical processes on the observed descent of the RIJ on 20 June and relative absence of a RIJ on 6 July.