Organization and Structure of Clouds and Precipitation on the Mid-Atlantic Coast of the United States. Part IV: Retrieval of the Thermodynamic and Cloud Microphysical Structures of a Frontal Rainband from Doppler Radar Data

Abstract

The thermodynamic and cloud structure of a relatively weak wintertime frontal rainband are derived from dual-Doppler radar measurements, soundings and high resolution surface observations, and with a cloud model. These derivations are simplified by the high degree of two-dimensionality and steadiness of the rainband. Water vapor, cloud water, cloud ice, rain, and snow are parameterized in the cloud model, subject to a temperature distribution that is constrained to a dynamical balance. Air temperature is derived from buoyancy, which is retrieved from the airflow assuming momentum and heat balance. The results of the thermodynamic and cloud microphysical retrieval are compared with airborne measurements in the rainband. The analysis indicates that the rainband was driven by a weak cold front aloft (CFA), which made the prefrontal air conditionally symmetrically unstable. The CFA appeared as a midlevel intrusion of cold, dry air on the meso? scale. The CFA interacted dynamically with the planetary boundary layer, not only through cooling produced by evaporating hydrometeors but also by a shallow downdraft immediately to the rear of the rainshaft associated with the rainband. This study shows that the combined thermodynamic and cloud microphysical retrieval technique is a useful tool in analyzing force balances and assessing water and energy budgets, even in quite weak mesoscale precipitation systems.