Friday, 8 August 2003: 2:50 PM
Microphysical influences on frontal structure during 2-3 Feb event
During the 1997-1998 El Nino event, the CALifornia Land-falling JETs (CALJET) Experiment was conducted off the western coast. One of the strongest events during the field project occurred from 2-3 Feb 1998 in association with a strong upper-level low off the northern California coast and an intense front making landfall in advance of the system. Two periods of significant rainfall were observed throughout much of southern California. One period was in conjunction with a low-level jet preceding the frontal region; the other was associated with the frontal region itself and more convective in nature. The structure of the front became quite complex as it approached the coast. The event has been simulated with the Navy's Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPSTM) developed at the Naval Research Laboratory. A new microphysics package has recently been introduced into the model which allows for the presence of graupel and the interaction of liquid and solid hydrometeors. Many of the complex features of the storm system were simulated well by the model although the timing of the frontal passage was not as well simulated. We investigate the sensitivity of the convection to the hydrometeor interactions present in the model, and show how the action of the convection leads to a modification of the frontal zone itself. Observational data from CALJET as well as radar imagery will be used to assess the validity of the model microphysics processes, and possible reasons for the discrepancy between observed and simulated frontal positions will be discussed.