CaPE Experiment
A distributed land surface model (SHEELS - Simulator for Hydrology and Energy
Exchange at the Land Surface) has been derived from the BATS point model
by modifying several of its components. The focus of this project has been
on developing a measurement/modeling strategy with which to investigate
surface water and energy fluxes within a limited area. We have applied SHEELS
together with a statistical/dynamical method for representing subgrid surface
variability using high resolution satellite data from the Convection and
Precipitation/Electrification Experiment (CaPE) in Florida during the summer
of 1991 (Crosson et al., 1995). One finding from these simulations is that,
for our particular space/time domain, modeled surface energy fluxes are
insensitive to sub-grid scale variability of leaf area index and albedo,
so long as the basic landcover types are represented (Cooper et al., 1995).
This is significant because it indicates that the relationship between
key energy fluxes and certain surface properties is approximately scale-invariant.
Extensions of this work will: 1) apply similar methodologies to examine
surface energy fluxes at large scales over the TVA and GCIP domains; 2)
incorporate surface and sub-surface water routing algorithms appropriate
for local and regional scales; 3) utilize ASTER and MODIS to develop retrieval
algorithms for land surface properties, and perform scale sensitivity studies;
4) provide inputs to regional-scale hydrologic assessments by linking
the surface model to an atmospheric model; and 5) interface the MSFC precipitation
product derived from NWS radar data with the Penn State coupled soil hydrology
model in the SRBEX domain.
The ice sheet regions are planned as a future area for coupled model simulations
because of their significance in the global hydrologic cycle and because
of the prospects of long-term sea level change. The results of this research
(Alley 1995; Alley and Anandakrishnan, 1995; Alley et al., 1995; Kapsner,
1994; Kapsner et al., 1994; Shuman and Alley, 1994; Shuman et al., 1995a,b)
address five important topics: 1) Analysis of grain size and shape relationships
with SSM/I (microwave brightness) yielding a better understanding of ice
cores and interannual variability of snow accumulation. This research demonstrates
that snow thermometry can be conducted from space and the air temperature
gaps between surface stations can be filled. 2) Analysis of GISP2 cores
demonstrates that the temperature - increased precipitation relationships
utilized by IPCC is not valid. Apparently atmospheric dynamics dominates
the snow accumulation, not temperature changes. 3) Rapid change in ice
sheet mass balance have been noted in ice cores, documenting "switches"
over periods of one to a few years. 4) Seasonality in warm periods (i.e.
secondary warm peaks) evident from the observations can now be documented
in ice cores. 5) Alley and colleagues have refined the flow law used in
glacier modeling and demonstrated the importance of soft glacier beds in
governing ice sheet behavior.
We plan continued use of SSM/I data (with C. Shuman - now at NASA/Goddard)
and continued use of ice-core and ice-geophysical data. Slow progress on
laser altimetry has reduced the priority of this research, resulting in
greater emphasis on ice cores.
Rudy Slingerland and Greg Tucker (NASA Global Change Fellow) have constructed
a Geophysical Landscape Evolution Model (GOLEM), which has been calibrated
for use in the Mahantango Watershed of the SRBEX region. The behavior of
the model has been explored under various initial and boundary conditions
and we have discovered that the evolution of the landscape is critically
dependent upon the functional relationship between fluvial erosion rate
and slope discharge (Tucker and Slingerland, 1994; 1995).
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