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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 110, D06117, doi:10.1029/2004JD004542, 2005

Observed effects of horizontal radiative surface temperature variations on the atmosphere over a midwest watershed during CASES 97

Robert L. Grossman

Colorado Research Associates, Boulder, Colorado, USA


David Yates

National Center for Atmospheric Research, Boulder, Colorado, USA


Margaret A. LeMone

National Center for Atmospheric Research, Boulder, Colorado, USA


M. L. Wesely

Environmental Sciences Division, Argonne National Laboratories, Argonne, Illinois, USA


Jie Song

Environmental Sciences Division, Argonne National Laboratories, Argonne, Illinois, USA


Abstract

The association between ∼10-km scale horizontal variation of radiometric surface temperature (Ts) and aircraft-derived fluxes of sensible heat (H) and moisture (LE) is the focus of this work. We use aircraft, surface, and satellite data from a Cooperative Atmospheric-Surface Exchange Studies (CASES) field program, which took place in the southern part of the 60 × 100 km Walnut River (Kansas) watershed from 22 April to 22 May 1997, when winter wheat matured and prairie grass greened up. Aircraft Ts observed along repeated flight tracks above the surface layer showed a persistent pattern: maxima over ridges characterized by shallow soil and rocky outcroppings and minima over riparian zones. H and Ts reached maxima in the same longitude zone on two flight tracks 40 km apart. Satellite Ts data from March to June reveal similar persistent patterns with minima more persistent than maxima. Two mechanisms are suggested to explain the association of H and Ts maxima: (1) for winds between 6 and 8 ms−1, modulation of the surface energy budget by vegetation effects; or (2) for winds equal to or below 4 ms−1, a thermally driven circulation centered on Ts maxima. Both mechanisms were possibly enhanced by increased static instability over the Ts maxima. Owing to the small sample available, these results are suggestive rather than conclusive. Effects of rainfall and vegetation on watershed-scale Ts gradients are also explored.

Received 15 January 2004; accepted 16 July 2004; published 31 March 2005.

Keywords: biosphere-atmosphere interaction; mesoscale meteorology; boundary layer processes.

Index Terms: 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions (0426, 1610); 3307 Atmospheric Processes: Boundary layer processes; 3322 Atmospheric Processes: Land/atmosphere interactions (1218, 1631, 1843); 3329 Atmospheric Processes: Mesoscale meteorology.

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Citation: Grossman, R. L., D. Yates, M. A. LeMone, M. L. Wesely, and J. Song (2005), Observed effects of horizontal radiative surface temperature variations on the atmosphere over a midwest watershed during CASES 97, J. Geophys. Res., 110, D06117, doi:10.1029/2004JD004542.