While much progress has been made over the last decade in understanding the structural characteristics of severe weather systems, many questions remain unanswered on the critical factors that trigger deep convection. Recent work has shown that the dryline, a sharp horizontal gradient in moisture and often found over the south central United States in spring and early summer, creates a favorable environment for initiation of convection. This mesoscale phenomenon is significant because it is often linked to the occurrence of severe weather, which tends to develop along and to the east of the dryline. This is particularly true during a cold frontal approach, which furnishes a mechanism for the lifting of the moist air. To date however, there have been very few detailed studies of the moisture structure and evolution of the dryline.
The Principal Investigators will perform a three year study to quantify the detailed vertical and horizontal moisture stratification of the pre-thunderstorm environment and drylines as well as the potential role of humidity in the development and initiation of convective storms using the capability of Raman lidar systems. They will use the Raman lidar to verify theoretical as well as numerical predictions of dryline characteristics dryline-front interactions and associated convection. This project relies on acquiring and utilizing Raman lidar observations of water vapor mixing ratio and aerosol profile data observed between 1994 and 2000 during several field missions at different parts of the U.S.A. Data from the International H20 Project (IHOP), planned for May-June 2002 in the southern Great Plains of the United states, and the Water Vapor Intensive Operations (WVIOP) conducted by the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) program, also will be utilized. A combination of analyses of existing data from Raman lidars, rawinsonde, radars, microwave radiometers, wind profilers and other conventional data sets and a numerical model will be used to achieve the objectives of this research. Dynamic, thermodynamic and moisture structure of convergence zones, frontal surfaces, and drylines as well as the temporal development of the boundary layer will be analyzed.
Areas of focus include the effects of small-scale variations in the vertical structure of moisture during drylines and cold fronts on storm initiation and convection and the role of the structure of the mid-tropospheric layer in storm dynamics and initiation and/or inhibition. The calculation of convective available potential energy and convective inhibition as well as simple model simulations of selected case studies to better understand the role of wind shear in the initiation of convection are included.
The results of the research should provide a better understanding of the diurnal characteristics of the dryline, complement the theoretical predictions of convective initiation by proving or disproving the predicted quantities and eventually contribute towards improvements in the forecasting skills of severe weather conditions.
