Mesoscale and diurnal variability of 2-m temperature and specific humitity in CASES-97

An array of flux/mesonet stations located to represent a range of elevations and vegetation reveals the relative role of topography and vegetation in determining the diurnal variation of temperature and mixing ratio 2 m above the surface. We use data from eight surface flux/mesonet stations located within a 60-km equilateral triangle, and serial radiosondes and radar wind profiler data at the vertices. The data are from CASES-97, which took place from 21 April--21 May 1997 over the Walnut River Watershed in SE Kansas. From late morning through much of the afternoon, vegetation and soil moisture account for the non-synoptic horizontal variability of moisture and potential temperature. Early-morning mixing ratios show strong peaks, whose amplitude and timing depend on station elevation, vegetation, and soil moisture. However, at night, the 2-m potential temperature has a close to linear dependence on station elevation. The slope of the line relating potential temperature to station elevation varies from large and positive to zero. The large positive slopes occur with large static stabilities (as measured by radiosondes) or light winds. When the dependence is dry-adiabatic, the thermal stratification is still stable but less so, and the winds are typically stronger. The dependence of the temperature-elevation relationship on environmental vertical stratification as measured by radiosondes and profilers will be examined, and the relationship between night-time 2 m temperature and surface properties will be investigated by analyzing deviations of individual station temperatures from the linear trends.