A Modeling Study of the Dryline in May 22 during IHOP 2002

This paper investigates a dryline event during 22-23 May 2002 (IHOP_2002). This event was simulated with a 4 km horizontal grid spacing using the Weather Research and Forecasting (WRF) model. The WRF simulation reproduced the basic features such as the timing and location of the dryline evolution. This dryline was forming in the vicinity of the OK panhandle. The near surface flow was dominated by a southwesterly jet with warm/dry air mass originally from the frontal system as well as a southerly cool/moist air mass from the Gulf of Mexico. A significant moisture gradient was simulated between the S-Pol and Homestead sites around 2100 UTC 22 May. The dryline lasted for about 12 hours in the vicinity of the OK panhandle. However, convective initiation was not found along the dryline. Sensitivity experiments have been conducted to investigate the effects of water vapor and horizontal resolution on the formation of dryline. The result from 1 km horizontal grid spacing simulation was very similar to the control experiment in terms of the dryline location. However, this fine-scale simulation provided a better result in terms of the structure of the dryline and a realistic upward motion. The results indicate the importance of low-level forcing associated with near surface horizontal velocity convergence-induced vertical motion, which increases rapidly as horizontal resolution increases. The experiments of 10% and 40% raising water vapor suggested that high water vapor would help convective initiation which provides the necessary destabilization and result in precipitation.