Wednesday, 17 January 2007
Causes of summertime Texas drought
Exhibit Hall C (Henry B. Gonzalez Convention Center)
Since Texas normally receives most of its precipitation in the warm season, precipitation deficits in summertime may bring serious agricultural and hydrological disasters. While underlying physical processes of summer precipitation deficit and drought are unclear, they can be understood in terms of convective instability. This research is designed to investigate how convective instability influences monthly mean precipitation in Texas in the summertime and to examine the modulation of convective instability and precipitation by moisture transport, soil moisture, vertical motion, and low-tropospheric warm air transport using NCEP/NCAR reanalysis data. Statistical approaches including correlation analysis, multiple linear regression analysis and back trajectory analysis were used to reveal the underlying dynamics of their linkage and causality. Initial results show that warming at 700 mb and surface dryness result in excessive convective inhibition (CIN), leading to precipitation deficit on monthly time-scale. Temperature at 700 mb (Tlt) and surface dewpoint have little correlation on monthly time-scale suggesting different processes contribute to warming at 700 mb and surface dryness, respectively. Back trajectory analysis reveals that a significant contributor to warming at 700 mb is the inversion caused by warm air transport from the Rocky Mountains and Mexican Plateau where the surface potential temperature is greater than 307.5K rather than by subsidence. While transport of diabatically heated warm air from the Rocky Mountains is associated with enhanced descent, more investigation is needed to verify which mechanisms are responsible for this feature for more clear linkage. On the other hand, strong coupling between soil moisture, latent heat, sensible heat, and surface dewpoint suggests that surface moisture content is more sensitive to soil moisture than to horizontal moisture transport. Back trajectory analysis will be used again to test whether volume of moist air from the Gulf of Mexico influences surface dewpoint or not.