Dr. M. LeMone, NCAR/MMM
and
Dr. R. Grossman, Program in Atmospheric and Oceanic Science, University of Colorado
The Cooperative Atmosphere-Surface Exchange Study (CASES) is a grass-roots collaboration to study of the interaction between the atmosphere and surface over a watershed for periods of seconds to years. The Walnut River Watershed east of Wichita, Kansas, was selected for this purpose because of its size, its location within a dense meteorological observing network, its long stream-gauge record, and its location in a well-instrumented region.
We use data from a network of 8 NCAR surface flux/meteorological stations, the Wyoming King Air and NOAA Twin Otter aircraft, three radar wind profilers operated by Argonne National Laboratory as part of its Atmospheric Boundary Layer Experiments array, and serial NCAR/CLASS radiosondes from the profiler sites from the first episodic field program, CASES-97, which was held from 21 April -- 17 June, 1997, to illustrate several features of the diurnal changes of temperature and mixing ratio within the 60-km equilateral trangle that outlines the southern end of the watershed. We discuss the evolution of 2-m mixing ratio and temperature and its relationship to elevation and surface cover, and the evolution of PBL temperature and mixing ratio during the day, and then focus on the causes of temperature and mixing ratio evolution during the late morning (10-12 LST).
Major results are:
(a) a linear dependence of 2-m temperature with elevation, that is closely related to static stability during the night,
(b) a dependence of 2-m temperature on surface cover, once the elevation effect is removed,
(c) interesting inconsistencies involving the two aircraft and surface data, some of which may be related to surface cover,
(d) the influence of surface properties on PBL growth, and
(e) a strong suggestion of direct heating of the PBL by radiative flux divergence during the late morning, especially for the day with nonuniform soil moisture. Mesoscale (order 10 km) eddies may have also played a role in heating on this day.