Global Energy and Water Cycle Experiment (GEWEX) Continental-Scale International Project A Review of Progress and Opportunities (1998) / Chapter Skim
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1 WATER AND ENERGY CYCLES
1 WATER AND ENERGY CYCLES
Pages 13-29
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From page 13... ...
GCIP's conceptual framework for analysis of water and energy cycling is that of a coupled land-atmosphere system. Thus, the Mississippi River basin includes not only the land surface and the earth beneath it but also the atmosphere above it.
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From page 14... ...
Latent heating and radiative effects of the water substance provide strong coupling between the water and energy cycles. The picture of net atmospheric water vapor convergence, net transfer to the surface, and runoff to the ocean obscures several important features of water and related energy cycles in the Mississippi basin.
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From page 15... ...
Climate model studies have suggested that midlatitude anomalies in soil water could persist for periods of months (Rind, 1982; Yeh et al., 1984~. Such model studies also suggested that North American soil water anomalies of sufficient magnitude and geographical extent could induce large systematic responses in computed water and energy balances.
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From page 16... ...
16 , ~ ~ Cal , 'd o ~ .0 ._.
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From page 17... ...
Early empirical studies identified a tendency toward persistence of summer droughts that could be ascribed to soil moisture anomalies (Namias,1958~. Recent extreme hydroclimatic events in the Mississippi basin have provided a focal point for studies of landatmosphere interactions in the GCIP region, illustrating the complexity of the atmospheric response to surface anomalies.
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From page 18... ...
, (1.4) in which ha and hi are the vertically integrated enthalpy of atmosphere and land, respectively; Ch is a term including net atmospheric convergence of enthalpy and its production by vertical motions; R is the net absorption (absorption minus emission)
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From page 19... ...
However, the estimation and prediction of these terms often cannot be accomplished without more detailed information on the vertical distribution of atmospheric water content or energy fluxes, individual components of land water storage, or their spatial distributions. Consequently, GCIP cannot be limited to consideration of the lumped, large-scale quantities introduced above but must also analyze many processes at finer scales.
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From page 20... ...
between the land surface and the atmosphere are not readily estimated from routine observations. Specialized equipment and technical expertise are required to obtain accurate measurements, and such measurements are representative of a horizontal length scale of no more than 100 m.
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From page 21... ...
Such systems can be driven by observations or analyzed fields of precipitation and surface radiation, and may also make use of discharge observations to adjust predicted land surface wetness. Whenever possible, the validity of estimates derived by balances or data assimilation must be tested, if only partially, by comparison with point measurements and theoretical estimates.
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From page 22... ...
This storage term is of major importance at the diurnal time scale, when it is comparable to radiative and sensible and latent heat fluxes. Its magnitude is usually considered to be relatively small on monthly to seasonal time scales (e.g., in the computation of seasonal energy balances)
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From page 23... ...
Currently, hourly estimates of net shortwave radiation are available on a 40-km grid on a near real-time basis. It is expected that this product will be valuable in the immediate future for studies of land surface process variability.
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From page 24... ...
. CAGEX provides detailed in situ and satellite measurements of vertical profiles of radiative fluxes, atmospheric temperature and moisture, and cloud properties for testing radiative transfer models and satellite retrieval algorithms [particularly for use with the National Centers for Environmental Prediction (NCEP)
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From page 25... ...
Studies of soil water variability have been conducted with both observed and modeled fields, which have been found to account for much of the temporal and spatial variance of Russian soil moisture data measured under natural field conditions (Vinnikov et al., 1996~. Based on estimates of soil moisture distribution constructed from historical climate data and a soil water accounting model, spatial scaling properties of soil water in the GCIP have been explored (Guetter and Georgakakos, 1996~.
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From page 26... ...
Specific recommendations relevant to these and related issues are discussed below. Develop Improved Estimates of Precipitation, Longwave Radiation, and Land Water Storage Using Existing Observational Networks GCIP was planned with the expectation that NEXRAD would provide a high-resolution precipitation data set of high accuracy and consistency.
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From page 27... ...
These should be improved by processing in situ and remotely sensed data on profiles of atmospheric properties using radiative transfer models. The strong influence of clouds and water vapor on longwave fluxes presents a major challenge (Ellingston et al., 1994~.
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From page 28... ...
What are the relative roles of land surface processes and remote forcing, such as ocean surface temperatures, in generating and modulating atmospheric and surface anomalies (precipitation, temperature, river discharge) in the Mississippi basin?
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From page 29... ...
How do seasonal freezing and changes in soil structure affect infiltration and runoff? Finally, do the details of land surface topography play a significant role in the area-averaged water balance?
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