Wednesday, 9 August 2000: 2:45 PM
Fei Chen, NCAR, Boulder, CO; and D. Yates, H. Nagai, M. A. LeMone, R. L. Grossman, and K. Ikeda
To understand the effects of land-surface heterogeneity and the
interactions between the land-surface and the planetary boundary
layer at different scales, we developed a multi-scale data set based
on the Cooperative Atmosphere-Surface Exchange Study (CASES-97) field
observation conducted in the upper Walnut River watershed, Kansas. The
domain covered by this data set is 74x71 km, which approaches the grid
size used in many weather and climate models. The surface meteorological
conditions obtained from nine surface stations, high-resolution S-Pol
radar precipitation analysis, and 4-km hourly NCEP national precipitation
analysis are interpolated/mapped into half-hourly, continuous gridded
data with three resolutions of 1, 5, and 10 km. Also, the gridded
surface boundary conditions are comprised of a 1x1 km STATSGO soil
data, 1x1 USGS/EROS vegetation data, and 30 m Kansas land use map.
The 1x1 km AVHRR products which give the NDVI was also utilized to
specify the surface vegetation characterization.
We use this multi-scale surface forcing data set to drive three
land-surface models to generate one-month-long
gridded surface heat flux maps for
the CASES-97 area. To ensure the quality of the uniformly distributed surface
heat flux maps, the surface heat fluxes generated by the models are
validated against 1) continuous surface-heat-fluxes measured at eight
flux stations , and 2) heat fluxes obtained from two aircraft (the University
of Wyoming King Air and the NOAA Twin Otter) at low levels during 5 IOP days.
In general, the model results are favorably compared to these data.
Simulating the rapid greening process of grassland (a dominant land-use type
in the CASES-97 domain) is challenging and requires an accurate description of
underlying vegetation characteristics and its effect on canopy
evapotranspiration in models. Across the CASES-97 domain, the variability in
surface heat fluxes typically ranges from 50-150 W m-2, induced by the
differences in vegetation characteristics, soil moisture and surface radiation
forcing. This variability tends to decrease when the grassland reaches its
peak growing stage.
![](images/flag.png)
- Indicates paper has been withdrawn from meeting
![](images/blue_ribbon.png)
- Indicates an Award Winner