Extended Abstract (1.4M)6.8
The effects of diabatic redistribution of potential vorticity on cold frontal rainbands and cold front propagation
Heather Dawn Reeves, North Carolina State University, Raleigh, NC; and G. M. Lackmann
The relationship between diabatic potential vorticity (PV) redistribution and the speed of cold frontal propagation is investigated. A case study of a cold front which underwent an acceleration from 6m/s to 14m/s during a six hour interval is presented. During the time of acceleration, the cold front possessed the ingredients for horizontal PV propagation to occur: shear, latent heating, and a positive PV anomaly in the frontal zone. A PV budget revealed that positive, diabatic PV tendencies existed in the prefrontal zone during the time of acceleration. The development of positive PV in the prefrontal zone indicates that front-like characteristics were introduced in the prefrontal zone. It is hypothesized that the existence of PV in the prefrontal zone can lead to frontal acceleration by shifting the location of front-like activity forward.
Correct placement and intensity of PV anomalies is dependent on correct placement and intensity of latent heating rates by numerical weather prediction (NWP) models. In particular, failure of a model to accurately represent precipitation in the prefrontal zone may lead to errors in forecasts of frontal movement. This poses a special problem in the arena of cold frontal weather prediction, since quantitative precipitation forecasting (and associated latent heating) is a known weakness of NWP models.
Session 6, Winter Weather and Climatological Studies
Wednesday, 14 August 2002, 8:00 AM-10:00 AM
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