Observations of the Horizontal and Vertical Variability of Cloud Hydrometeors in Stratiform Regions behind Bow Echoes: Implications for Mesoscale Models

Mesoscale modeling studies have shown that microphysical processes, such as sublimation, melting, evaporation, riming and aggregation can substantially influence the structure and dynamics of mesoscale convective systems (MCSs) through their impacts on the horizontal and vertical distributions of latent heating and cooling. To quantify the manner in which latent cooling affects the dynamics of the MCSs, information on the vertical and horizontal variability of the sizes, shapes and phases of hydrometeors in the stratiform regions behind MCSs is required.

In this paper, a unique set of data on the vertical variability of the size, shape and phase distributions of hydrometeors in stratiform regions behind bow echoes obtained during the recent Bow Echo and Mesoscale Vortex Experiment (BAMEX) is presented. During BAMEX, the NOAA P-3 executed 16 Lagrangian spiral descents in stratiform regions behind convective lines, giving the first set of data on the microphysical properties of clouds directly behind bow echoes. In this paper, the vertical variability of cloud size distributions and bulk mass contents is presented and explained in context of the microphysical processes thought to be occurring and in terms of differences in ambient humidity noted on different days; particularly unique characteristics were noted for a spiral made in sub-saturated conditions on June 29 directly in a descending rear-inflow jet. The observed distributions are fit to gamma distributions and the distribution parameters are compared against fit distributions and observations in other stratiform precipitating clouds and against distributions used to represent hydrometeor distributions in mesoscale models. It is also shown how the microphysical distributions can be used to calculate equivalent radar reflectivity for comparing against the radar observations collected during BAMEX.