|
Description:
|
The dryline is a low -level atmospheric boundary that is characterized by a strong horizontal moisture gradient across a narrow zone . Numerous previous studies have already established the dryline’s role of producing lift and convergence necessary for the development of thunderstorms . One of the many forecasting challenges facing the operational meteorologist is determining the evolution of the high plains dryline .
This dissertation examines a type of dryline called the “quiescent” dryline . The quiescent dryline exists in a synoptic environment characterized by relatively weak environmental wind . This dryline is observed to advance eastward during the day and retreat westward at night , often repeating this cycle for several days . The exact nature of the motion and evolution of the quiescent dryline is dependent on many factors that occur at different scales in the atmosphere -land /soil system .
In order to perform the study , a field experiment was designed to investigate the mesoscale ( ~10 to 100 km ) structure and evolution of the quiescent drylines . The West Texas Mesonet , a network of instrumented towers centered on Lubbock , Texas was utilized along with several additional towers deployed for the experiment . Data was collected and analyzed for several drylines that occurred across the South Plains of West Texas during the spring of 2002 . A framework was created to identify and characterize advancing and retreating drylines through the objective analysis of several meteorological quantities . The results showed that the dryline could be identified through strong gradients of moisture , along with moisture advection and convergence , in agreement with previous studies . Relatively high values of moisture advection and convergence were observed in conjunction with retreating drylines . Mobile instrumented platforms were also utilized to examine a quasi -stationary dryline , obtaining detailed measurements of moisture gradients in the vicinity of the dryline at scales less than one kilometer . Additionally , the drylines were simulated by two common meteorological mesoscale models and their forecast skill was evaluated . The results show that simulations with higher horizontal resolutions are not necessarily more accurate in forecasting the dryline evolution . |