5.1 Energy And Water Budgets
OBJECTIVE: Determine the time-space variability of the hydrological and energy budgets over the Mississippi basin.
There are four near-term objectives for the period covered by this major activities plan:
1. Sustain and enhance the program for the routine production of monthly- averaged energy and water budgets for the Continental-Scale Area (CSA) and four large-scale (LSA) sub-basins of the Mississippi River Basin.
2. Develop and implement, in support of the studies of cold season hydrological processes (ESOP-97), a capability to produce multi-scale energy and water budgets over the LSA-NC from basic and derived data sets and variable fields generated by four dimensional data assimilation (4DDA) procedures.
3. Produce and evaluate multi-scale water and energy budgets for the LSA-SW during the WY 1997 and for the LSA-NC during WY 1997 and WY 1998.
4. Implement the methodology developed for the LSA-SW to the evaluation of multi-scale budgets over the LSA-NC in support of the WY 97 study of cold season hydrological processes (ESOP-97) and adapt the methodology to the study of hydrological processes over the LSA-E in WY 98 and WY 99.
In order to meet these near-term objectives, diagnostic studies will be undertaken which (1) will obtain area-averaged variables from the available data and derived data products; (2) compare budget results obtained from model- generated 4DDA fields and MOLTS with results obtained from different sources of data and analyses in order to evaluate their relative quality and sources of error; and (3) critically compare budget residuals with limited measurements and empirically derived values of evaporation and soil water storage.
The emphasis of these "core" activities is on combined land-surface budgets. There will be additional ISA/SSA land-surface budget analyses based on the output of surface hydrological models to atmospheric forcing, e.g. observed precipitation and surface meteorological variables. These studies are viewed in the context of model output discussed in chapter 11.
The overall activities for budget studies include the following:
-
1) Water and energy budget studies over the GCIP area will be performed
using both operational analyses/forecast systems and free running
GCM's.
2) Intercomparisons will be performed among several regional models including the Eta, MAPS, LFE and NCEPs Regional Spectral Model.
3) Intercomparisons will be performed of model simulated precipitations and observational estimates.
4) The NCAR Climate Model CCM3 simulations will be compared to GCIP observations and model assimilated fields.
5.1.1 Budget Variables
The basic budget variables to be examined and the potential sources of estimates for these variables are summarized in Tables 5-1 and 5-2 with separate tables for the two different scales. Table 5-1a identifies the Atmospheric Profile variables and the potential data sources for the CSA and LSA scales. Table 5-1b provides the same information for the ARM/CART region.
MODEL
VARIABLE MEASURED REMARKS DERIVED REMARKS OUTPUT REMARKS
--------------------------------------------------------------------------------------------------------
Water Vapor (q) X RWS X Sec. 5.1
Dry Static Energy (CpT+qZ) X Investigator Derived X Sec. 5.1
Wind X RWS & Profilers X Sec. 5.1
Water Vapor Flux X Investigator Derived X Sec. 5.1
Dry Static Energy Flux X Investigator Derived X Sec. 5.1
Vapor Flux Divergence X Investigator Derived X Sec. 5.1
Energy Flux Divergence Investigator Derived X Sec. 5.1
Longwave Flux X NESDIS X Sec. 5.1
Shortwave Flux X NESDIS X Sec. 5.1
TOA Flux X NESDIS X Sec. 5.1
Cloudiness X ASOS & GOES X Sec. 5.1
Net Radiative Heating X NESDIS X Sec. 5.1
Condensation Heating X Investigator Derived X Sec. 5.1
(Vertically Integrated)
Table 5-2a identifies the Surface Budget variables and the potential data sources
for the CSA and LSA scales. Table 5-2b provides the same information for the
ARM/CART region. The data and information required for the evaluation of area-
and time-averaged land/atmosphere energy and water balances will be provided by
several GCIP Principal Research Areas and the Data Management and Service
System (DMSS). The evaluation of the energy balance is particularly dependent on
satellite products for estimates of surface variables and atmospheric radiative heating
profiles.
MODEL
VARIABLE MEASURED REMARKS DERIVED REMARKS OUTPUT REMARKS
--------------------------------------------------------------------------------------------------------------
Surface Elevation USGS/EDC
Vegetation (NDVI) X NESDIS
Precipitation X Ppt. Composite obs. X NMC Mesoscale Analysis X Sec. 5.1
Storage Snow Water Equivalent X NOHRSC X Sec. 5.1
Stream Discharge X USGS
Reservoir Storage X USGS
Water Table (Wells) X Not Applicable
Soil Moisture Not routinely X GCIP/ISLSCP joint project X Sec. 5.1
in 1977.
Surface Temperature X Surface Composite X NESDIS X Sec. 5.1
Clear sky
Albedo X NESDIS X Sec. 5.1
"Surface" Specific Humidity X Surface Composite X NESDIS X Sec. 5.1
"Surface" Wind X Surface Composite X Sec. 5.1
Sensible Heat Flux X GCIP ISLSCP joint project X Sec. 5.1
in 1977.
Latent heat Flux X GCIP ISLSCP joint project X Sec. 5.1
in 1977.
Longwave Radiation X NESDIS X Sec. 5.1
Shortwave Radiation X NESDIS
The basic strategy for the energy and water budget analyses
involves distinctly different approaches for the LSA budgets and the more
diverse ISA/SSA budgets.
OBJECTIVE: Develop a research quality mean monthly time series of
basin-averaged budget variables and use these to develop a better
documentation and understanding of the "bulk" water and energy cycles over
the CSA and LSA sub-basins of the Mississippi.
The development of LSA budget time series is a continuing activity, and will
produce a continuous time series of mean monthly budget variables. Although the
temporal and spatial resolution of these "bulk" budgets is limited, much can be
learned about continental hydrological processes by deriving budgets and validating
model results over areas that are large enough and time periods long enough to
allow accurate evaluation of the heat and water
balances of the overlying atmosphere. This derived budget data set is therefore a
basic requirement for a variety of diagnostic and model validation activities that
address the major objectives of the GCIP program.
The basic time scale for the LSA and CSA budgets is monthly. The
evaluation of the individual variables will depend heavily on operational data and
operational 4DDA variable fields. Mesoscale resolution is required to adequately
resolve the effects of terrain and to accurately resolve the irregular boundaries of a
specific drainage basin. This can be provided by the data
assimilation systems of regional mesoscale forecast models e.g. NMC Eta model, the
FSL MAPS analyses and the Canadian RFE model. However, to fully utilize all
available data and information, and meet the objectives for the budget studies, it will
be necessary to improve the 4DDA capabilities of the operational model output
available to GCIP investigators. This requires a
program of intercomparison and validation studies.
The competing methods for evaluating large-scale atmospheric vapor flux
divergence are (1) line integral computations made directly from routine 12-hourly
rawinsonde wind, humidity and temperature observations and hourly profiler wind
observations, and (2) operational 4DDA products. Intercomparison of
rawinsonde/profiler line integral results with the 4DDA fields will provide
information on the quality of the 4DDA flux fields and the impact of changes in the
data assimilation system. The choice of areas for comparison is limited by the
relatively sparse distribution of rawinsonde and profiler stations. Two areas have
been chosen for ongoing intercomparison; (1) the continental-scale geographical
area enclosed by the rawinsonde stations shown on Figure 5-1, and (2) the large-
scale profiler array in the central United States, Fig. 5-2 The ongoing
intercomparison over the profiler array will be limited to winds and velocity
divergence fields. Intercomparisons will also be done between the MOLTS and the
radiosondes in the CART/ARM hexagon since these were not included in the data
assimilation schemes of the models.
Figure 5-1 Continental Scale Area for intercomparison of atmospheric
flux-diveregence results.
Figure 5-2 Large-scale profiler array in the Central U. S.
OBJECTIVE: Develop energy and water budgets for selected ISA/SSA
in support of specific GCIP program elements.
The Implementation Plan for GCIP, Volume II, Research (IGPO, 1994a)
outlined a multi-scale research strategy for GCIP which was summarized earlier in
Section 1. The ISA/SSA budgets will be of a more specialized nature than the
routinely computed LSA budgets. They will be computed for limited areas and in
many cases for limited periods of time. They will depend to a much greater degree
on data acquired from special observing systems or networks, in some cases during
short periods of enhanced observations. Their objectives will usually be more
process oriented e.g. seasonal aspects of the hydrological cycle; development and
testing of model subcomponents; more detailed decomposition of atmospheric
budget residuals i.e. Q1, Q2, total surface storage where Q1 is the apparent heat
source and Q2 is the apparent moisture sink as defined in Appendix B of the GCIP
Science Plan (WMO, 1992).
During WY97 the geographical focus will be on the LSA-NC. The
phenomenological emphasis will be on various aspects of the cold season
hydrological cycle. It will include studies on the LSA, ISA and SSA scales. Many
of the ISA activities will continue to be focused on the ARM/CART site that
occupies almost 20 per cent of the LSA-SW. SSA studies will exploit the well
instrumented Little Washita Watershed.
b) Conduct ongoing intercomparisons of atmospheric budgets obtained
directly from observations and those computed from operational
analyses for areas shown on Fig. 5-2.
c) Continue and improve development of methods for using 4DDA
operational output, including MOLTS from the ETA, FSL and
Canadian RFE mesoscale models, to derive area averaged
surface/atmosphere budgets.
b) Develop a description of the WY 97 annual cycle of the land surface
and atmosphere hydrological and energy cycles over each LSA and the
CSA drainage area. Such descriptions can serve as "benchmarks"
forstudying interannual variability and for validation of model
simulations.
c) Continue ongoing intercomparisons between atmospheric budgets
obtained directly from observations and those computed from
operational analyses for the areas shown on Fig. 5-2.
b) Continue the routine computation of area-averaged estimates of soil
moisture and surface meteorological parameters, including fluxes, over
the Little Washita Watershed, and begin similar computations for the
ARM/CART array. Compare these values with output from operational
mesoscale models.
c) Continue evaluation of available surface/atmosphere budget
information acquired during ESOP-97 in the ISA/SSA basins of the
LSA-NC.
d) Complete planning and implementation of a program of ISA/SSA
budget computations over the LSA-E during WY 98.
2) ISA/SSA Budgets. Continue evaluation of ISA/LSA budgets within the
LSA-SW and LSA-NC. Began similar evaluation of ISA/SSA budgets
for specified areas in the LSA-E. Begin planning and implementation
of focused studies over the LSA-NW.
OBJECTIVES:
2. Establish relationships between surface conditions and boundary
layer processes, particularly as they relate to the partitioning of surface fluxes
between latent and sensible heat.
The diurnal and annual cycles have a fundamental effect on the coupling of
the surface and the Planetary Boundary Layer (PBL). The diurnal cycle itself has a
pronounced annual cycle, with maximum amplitude during the warm months, when
the land surface and atmosphere are most strongly coupled.
This element of the Diagnostics Studies PRA will progress as a phased study
of processes during different seasons over different sub-basins of the Mississippi
Basin, with the overall results integrated into a coherent picture of the seasonality of
hydrological processes over the basin. The strategy therefore involves a specific LSA
and seasonal focus at any particular time, in which is embedded limited time/space
ISA/SSA enhanced observational programs during various seasons and throughout
the entire year.
During WY 97 the focus of GCIP activities will be on warm season processes
in the LSA-SW. Within the LSA-SW region there will be concentrated data
collection and diagnostic studies over the ARM/CART site and the Little Washita
Watershed. The LSA-SW, ARM CART and Little Washita combination of activities
will provide a "nested" set of studies on scales ranging from approximately 10^3 to 10^6
km^2.
The conceptual framework for the ESOP-96 multi scale diagnostic studies of
warm season processes can be summarized as follows.
LSA-SW Setting
The variability at a point includes the effect of large-scale and small-scale
advection, and the net effect of land surface forcing on scales ranging from local to
continental. Process studies over limited time-space domains need to be interpreted
in the context of gradients associated with larger scales of continental forcing.
GCIP continental-scale data sets and derived data products will be used to
describe the general nature of the continental-scale warm season processes as they
relate to the LSA-SW, and to the ARM/CART ISA and Little Washita SSA low level
northward flowing moisture jet, which exhibits large variability on diurnal, synoptic
and interannual time scales, and the pronounced warm season diurnal cycle of
hydrologic and circulation features over the LSA-SW, which includes a nocturnal
maximum in thunderstorm and precipitation occurrence.
The routine observational system over the LSA-SW will consist of
conventional surface and upper air observations (rawinsonde, wind profilers), aircraft
observations, and NEXRAD observations of precipitation. These observations will be
assimilated by 4DDA methods into regional mesoscale models to provide operational
analysis/forecast products on a grid mesh of a
few tens of kilometers. The availability of routine three-hourly regional mesoscale
model analyses will provide an improved description of many features of this
continental scale diurnal mode, and contribute to an improved documentation of its
effect on LSA-SW hydrology.
The routine observations from the national networks will be supplemented by
regional observational systems within portions of the LSA-SW. Notable among
these are the following:
2) Observations from the DOE ARM/CART area (~300 km x 200 km)
which includes portions of Oklahoma and southern Kansas. These
observations have been focused on atmospheric radiation processes, but
will also provide continuous observations of soil moisture profiles at a
steadily increasing number of sites and high frequency rawinsonde
observations (three-hourly) from five sites during the 3-week ARM-
CART Intensive Observational Periods.
3) A relatively dense network of continuous surface meteorological and
soil moisture/temperature profile observations over the Little Washita
Watershed.
The observations from the ARM/CART array will provide data required for
process studies and more detailed intercomparisons and validation of both surface
and atmospheric model subcomponents. Among the major enhancements to the
operational data which will be available from the ARM/CART area are the following:
2) Soil moisture measurements. Continuous automated soil moisture
measurements in the ARM/CART site were initiated in the spring of
1996 with the installation of instruments at sites. An additional 15
sites are scheduled to be instrumented prior to April, 1997, thus
providing a large scale but sparse array of soil moisture monitoring sites
over the ARM/CART site beginning in April 1997.
3) Aerosol concentration measurements from the ARM/CART central site.
These data will provide important information on the effect of aerosols
on the radiation balance.
4) PBL Structure. Detailed monitoring of the PBL structure will take
place during the three-week intensive observational periods, when
rawinsondes will be launched eight times daily from the ARM/CART
central facility and four profiler sites. These data will provide the
time/space sampling required to characterize the detailed structure of
the PBL, and evaluate the heat and moisture budgets on this spatial
scale during different seasons.
Little Washita Watershed Setting
A relatively dense network of continuous automated soil moisture measurement
sites will be established over the Little Washita Watershed. This will provide a more
dense network of soil moisture profile measurements than will be available from the
ARM/CART network. The existing meteorological observations over the basin will
also beevaluated and upgraded if necessary to provide the data needed to quantify
the surface fluxes over the watershed.
In order to model the annual cycle of surface fluxes, it is crucial that the
processes of both warm and cold season hydrology be documented and understood.
Therefore, in WY 97 the regional focus will shift to the LSA-NC where the
phenomenological focus will be on cold season hydrology. Cold season processes of
central importance include the following:
2) The effect of frozen ground on infiltration and soil moisture loss;
3) The evolution of the soil moisture field during the period between
initial freeze-up and to final thaw and snow melt;
4) The processes of snow accumulation, sublimation, ripening and melt,
which involves terrain effects, wind redistribution, vegetation
(interception) and advection associated with both local patchiness and
large-scale circulation.
Table 5.1a Energy and Water Budgets Variables: Atmospheric Profiles CSA & LSA Scales
________________________________________________________________________________________________________
Table 5.2a Energy and Water Budget Variables: Surface CSA & LSA Scales
______________________________________________________________________________________________________________
5.1.2 Basic Strategy
5.1.2.1 LSA and CSA Budgets
![[flux]](images/flux.gif)
![[profiler]](images/profiler.gif)
5.1.2.2 ISA/SSA Budgets
5.1.3 WY 97 Activities:
1) LSA and CSA Energy and Water Budgets
a) Continue routine assembly of area averaged mean monthly LSA and
CSA energy and water budget variables as the data become available
(one to 7 months after observation time depending on the variable and
source of the data) for all sub-basins (Missouri (upper and lower), Red-
Arkansas, Ohio, and Upper Mississippi) (Fig. 5-3) as well as for the
two intercomparison areas (Fig. 5-1).
5.1.4 WY 98 Activities:
1) LSA and CSA Budgets.
a) Continue the routine evaluation of mean monthly budget time series
for all LSAs and the CSA.
2) ISA/SSA Budgets.
a) Continue compilation of area averaged surface/atmosphere energy and
water budgets for the area within the LSA-NC ISA/SSA and continue
four station ARM/CART rawinsonde array during the seasonal three
week intensive observational periods.
5.1.5 Outlook for WY 99
1) LSA Budgets. Mean monthly LSA budget time series will be extended
into WY 98. The third year (WY 99) annual cycle will be analyzed
and compared with the first years' results. Results of diagnostic studies
will be used to develop improved estimates of budget variables and to
upgrade earlier budget estimates.
5.2 Land-Surface Boundary Layer Coupling
1. Develop an improved documentation and understanding of the
processes controlling the seasonal cycle of fluxes of water and energy across
the land/atmosphere interface and within the planetary boundary layer.
Surface fluxes, including evaporation, are at the end of a long chain of
processes and interactions involving cloudiness (which affects surface net radiation),
soil water content (which is dependent on rainfall), and vegetative cover. The
planetary boundary layer can act as a governor on the transfer process at the surface.
In turn, the boundary layer response depends on the partitioning between surface
latent and sensible heat fluxes.
5.2.1 Warm Season Processes
1) The Oklahoma Mesonet
ARM-CART Setting
1) Data for the evaluation of the surface radiation balance and surface
fluxes. These data will be provided from a number of different ARM
instrument systems and sites. Emphasis will be placed on instrumental
calibration to assure that the measurements are consistent, compatible
and reliable.
There will likely be several intense synoptic or mesoscale events which will
pass across the ARM/CART site during the these intensive observing periods. These
occurrences will be viewed as "targets of opportunity" and designated for special
study.
5.2.2 Cold Season Hydrology
1) The effect of snow cover on PBL structure and surface transfer
processes;
A prerequisite for the improvement of the modeling of cold season hydrological
processes is an improved data base of relevant parameters. A program of ISA/SSA
studies aimed at a better documentation and understanding of these processes,
comparable to the LSA program for the study of warm season processes, will be
developed during WY 96 for the LSA-NC. The enhanced winter observing period
(ESOP-97) will include improved documentation of snow cover, snow water content,
vertical variation of snow thermal properties, snow albedo, soil water content and
soil temperature over one or more ISA/SSA in the Upper Mississippi Basin. The
enhanced
observational program will supplement routinely available information from in-situ,
aircraft and satellite observations from the basin.
![[subbasins]](images/subbasins.gif)