NWC REU 2004
May 24 - July 31



Relationships between sounding-based parameters and precipitation field decorrelation

John Gensic, Michael Baldwin, and Matthew Wandishin



The understanding of precipitation field evolution is valuable to radar nowcasters and weather modelers. Precipitation field evolution can be evaluated with a decorrelation time that corresponds to how quickly the precipitation field changes from its initial state. Longer decorrelation times are associated with temporally consistent precipitation fields, while short decorrelation times are associated with rapidly changing precipitation fields. The decorrelation times for 246 cases from 1 March 2004 to 6 June 2004 were determined using both Eulerian and Lagrangian perspectives. Lagrangian decorrelation times were nearly 4 times longer than Eulerian times, on the average. No strong linear relationships were determined between the shear and instability parameters collected from nearby observed soundings and the decorrelation time. To further the analysis, Lagrangian decorrelation times were divided into long-lived (decorrelation time > 5 h) and short-lived (decorrelation time < 5) cases. This being done, specific short cases with high CAPE and low helicity could be separated from the long cases. Long cases typically had lower CAPE and higher helicity values, but there were as many short cases meeting these criteria, making discrimination between long-lived and short-lived events difficult in those cases.

Full Paper [PDF]