Tuesday, 8 August 2000: 8:45 AM
Robert L. Grossman, University of Colorado, Boulder, CO; and M. A. LeMone, K. N. Liou, and K. Ikeda
The Cooperative Atmosphere-Surface Exchange Study (CASES, see
http//:www.jos.ucar.edu/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
region with a strong east-west gradient in precipitation and land use.
The Atmospheric Boundary Layer Experiments array run by Argonne National
Laboratory provides long-term observations of the boundary layer and surface
carbon-dioxide exchange in the lower part of the watershed;
the Hydrologic Science Team of Oregon State University
has a dense raingauge network and soil-moisture measurements in the Whitewater
Subbasin. These long-term observations are supplemented by episodic intensive
field programs, two of which have now been held, in 1997 and 1999.
The first episodic field program, CASES-97 was held from 21 April -- 17 June,
1997, and included soil-moisture scaling and precipitation estimation as well
as fair-weather boundary-layer goals. Here, we present hourly budgets of
moisture and sensible heat over the watershed, from 1000 to 1300 LST,
under cloudless, fair-weather conditions for two of the five intensive
observing periods. One period had patchy surface moisture and vegetation
conditions and was two days after a moderate rain event; the second day had
more uniform vegetation conditions and a wet surface due to heavy rains the day
before. The budget computations use data
from 3 wind profilers, 90-minute serial radiosondes at the profiler sites,
surface meteorological and flux stations, and two aircraft with flux measuring
capability. We show how the
data from several different platforms are combined to estimate the budgets,
present the results including the apparent influence of surface processes, and
discuss some lessons learned from CASES-97.
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