A METHOD FOR ESTIMATING REGIONAL SURFACE SENSIBLE HEATING USING SHELTER-LEVEL AIR-TEMPERATURE AND UPPER-AIR DATA

A diagnostic technique is developed to evaluate the 12-h time-integrat ed sensible heat flux at the land surface. The scheme relies on the se nsitivity of the planetary boundary layer (PBL) height to the time-int egral of surface sensible heating. In our prior work, it has only been possible to evaluate the PBL height and surface sensible heating at r adiosonde locations. In this study, we use shelter-level (2 m) measure ments of surface air temperature, available at relatively high horizon tal resolution, combined with analyses of radiosonde upper-air data, i n a technique for estimating both the height of the PBL and surface se nsible heating at a sub-synoptic scale. The method is relatively simpl e and can be applied over large geographical areas. A daytime maximum of shelter-level potential temperature (theta(max)) from surface measu rements, in combination with a 1200 UTC upper-air analysis constructed from synoptic upper-air reports, is used to diagnose a maximum daytim e height of the planetary boundary layer. Using this height and a simp le model describing the dependence of the time-change of the PBL heigh t on the time-integral of surface sensible heating, we are able to mak e an evaluation of the 12 h sensible heating total at the land surface . The technique is tested in stages, first using data from the First I SLSCP Field Experiment (FIFE) and lastly, in an application to a regio n covering the Midwest and Central Great Plains of the United States. Surface sensible heating totals and PBL heights estimated in this mann er compare well with observations made at the FIFE site for observatio n days in the Summer of 1987 and 1989 and the method was able to captu re a 'dry down' period (an increased amount of sensible versus latent heating) which occurred at the FIFE site in August of 1989. The region al application of the method is able to depict the general east-west g radient of increasing sensible heat flux across the Midwest and Great Plains, as well as the spatial variability in both sensible heating an d PBL heights caused by known variations in surface moisture. (C) 1997 Elsevier Science B.V.