Understanding microphysical process links to surface drop-size distributions

 
Poster PDF

Authors

Brenda Dolan — Colorado State University
Steven A Rutledge — Colorado State University
Sue van den Heever — Colorado State University
Stephen Saleeby — Colorado State University

Category

Microphysics (cloud, aerosol and/or precipitation)

Description

Conceptual model linking parameters of the drop-size distribution (normalized intercept parameter Nw and the median drop diameter, D0) to microphysical processes as determined from statistical analysis of a large disdrometer dataset.
Disdrometer and radar observations are utilized in concert with cloud-resolving model simulations in order to better understand the link between observations of drop size distributions (DSDs) and microphysical processes. Understanding how observed modes of DSD variability relate to cloud processes shows promise for monitoring long-term trends of the relative frequency and spatial distribution of physical processes, as well as providing key insights into model representations thereof. A recent study using a large, global disdrometer dataset has shown there are at least six unique, repeatable modes of variability in surface DSDs. Limited radar observations have been used to infer microphysical processes underpinning these modes. For example, large numbers of small drops are found to be associated with shallow, weak convection while small number concentrations and large median drop diameters are indicative of deep, ice-based processes aloft. However, model data are required to fully link the physical processes (e.g. riming, aggregation, autoconversion, vapor deposition) to the surface DSDs. To this end, a large database of high resolution simulations from the Regional Atmospheric Modeling System (RAMS) will be probed to investigate how microphysical processes modify particle size distributions. Model microphysical conversion rates, precipitation rates, and updraft strength provide a framework for studying resultant DSD characteristics (median sizes, number concentrations, liquid water contents). Simulations from a variety of cloud systems (midlatitude mesoscale systems, supercells, isolated tropical convection) using a sophisticated 2-moment bulk microphysics scheme that predicts on number concentration and mixing ratio are considered. Resulting DSDs for different storm morphologies and dominant process rates will be compared with the disdrometer observations of DSD variability.