Abstract
Drop-size distributions (DSDs) provide important microphysical information about rainfall and are used in rainfall estimates from radar. This study utilizes a four-year DSD dataset of 163 rain events obtained using a Joss–Waldvogel impact disdrometer located in southeast Texas. A seasonal comparison of the DSD data shows that small (~1 mm diameter) drops occur more frequently in winter and fall, whereas summer and spring months see an increase in the relative frequency of medium and large (~>2 mm diameter) drops, with notable interannual variability in all seasons. Each rain event is classified by dynamic forcing and radar precipitation structure to more directly link environmental and storm organization properties to storm microphysics. Cold fronts and upper-level disturbances account for 80% of the rain events, whereas warm fronts, weakly forced situations, and tropical cyclones comprise the other 20%. Warm frontal storms and upper-level disturbances have smaller drops compared to the climatological DSD for southeast Texas, whereas the more dynamically vigorous cold fronts and weakly forced environments have larger drops. Tropical cyclones generally produce smaller drops than the climatology, but their DSD anomalies are sensitive to what part of the storm is sampled. Regardless of dynamic forcing, storms with precipitation structures that are mostly deep convective or stratiform rain formed from deep convection have larger drops, whereas stratiform rain formed from non-deep convection has smaller drops. Reflectivity-rain rate (Z-R) relationships that account for dynamic forcing and precipitation structures improve rainfall estimates compared to climatological Z-R relationships despite a wide spread in Z-R relationships by storm.
Highlights
Southeast Texas experiences a range of tropical and extratropical synoptic conditions
A four-year climatology of drop-size distributions and storm types over southeast Texas has been assembled for December 2004 through September 2008 to determine how precipitation structure and dynamic forcing in the subtropics impacts storm microphysics
The shape of the four-year climatological Drop-size distributions (DSDs) observed by the disdrometer is partially explained by seasonal variations, but seasonal DSD anomalies vary from year to year, making further separation of the data necessary to better describe DSD variations associated with environmental factors and storm organization
Summary
Southeast Texas experiences a range of tropical and extratropical synoptic conditions. Previous studies have shown that DSDs vary between convective and stratiform rain around the globe including tropical oceanic sites in the Maldives [6], Papua New Guinea [6], and Micronesia [7]; tropical coastal sites in southern India [8] and northern Australia [6,9]; midlatitude continental sites in the southern Plains (Oklahoma) of the United States [6,10] and the southern slopes of the Alps in Switzerland [11]; and even a high-latitude continental site in Finland [6] In most of these studies, deep convective cells are assumed to be dominated by strong updrafts that lift precipitation particles formed at cloud base to upper levels within the convective core [12].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
