OBJECTIVE: Provide a better description and understanding of the factors which control the mean annual cycle and interannual variability of hydrological processes over the Mississippi River Basin.

The core diagnostics activities consist of three interrelated program elements:

A description of the activities within each of these program elements is given in the following sections.

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:

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.

Table 5.1a  Energy and Water Budgets Variables:  Atmospheric Profiles CSA & LSA Scales

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 5.1b  Energy and Water Budget Variables:  Atmospheric Profiles ARM/CART Region for ESOP-96

MEASURED DERIVED MODEL VARIABLE R.* E.* REMARKS R.* E.* REMARKS OUTPUT REMARKS -------------------------------------------------------------------------------------------------------------- Water Vapor (q) X X RWS-NWS,ARM include IOP X Sec. 5.1 Dry Static Energy (CpT+qZ) X X Investigator Derives X Sec. 5.1 Wind X X RWS-NWS,ARM include IOP Sec. 5.1 Profilers; NEXRAD Water Vapor Flux X X Investigator Derives X Sec. 5.1 Dry Static Energy Flux X X Investigator Derives X Sec. 5.1 Vapor Flux Divergence X X Investigator Derives X Sec. 5.1 Energy Flux Divergence X X Investigator Derives X Sec. 5.1 Longwave Flux X X NESDIS;CAGEX X Sec. 5.1 ARM database Shortwave Flux X NESDIS;CAGEX X Sec. 5.1 ARM database TOA Flux X NESDIS;CAGEX X Sec. 5.1 ARM database Cloudiness X X GOES-ASOS;Sfc Composite X Sec. 5.1 ARM database Net Radiative Heating X NESDIS;CAGEX X Sec. 5.1 ARM database Condensation Heating X Houze (WSR-88D) Aerosol Concentration X ARM Central Site X database ------------ * R. - Routine * E. - Enhanced

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.

Table 5.2a  Energy and Water Budget Variables:  Surface CSA & LSA Scales

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

Table 5.2b  Energy and Water Budget Variables:  Surface ARM/CART Region for ESOP-96

MEASURED DERIVED MODEL VARIABLE R* E* REMARKS R* E* REMARKS OUTPUT REMARKS ----------------------------------------------------------------------------------------------------------------- Surface Elevation X Sec. 5.8 Task 5.8.5 Vegetation (NDVI) X Sec. 5.8 Task 5.8.2 Precipitation (Liquid) X ESOP-96 Precip Composite X Sec. 5.4 Task 5.4.1 X Sec. 5.1 15min,hrly,daily) Sec. 5.4 Task 5.4.2 Stream Discharge X USGS & USACE daily stream flow Sec. 5.9 Task 5.9.1 Reservoir Storage X Sec. 5.9 Task 5.9.1 Water Table (Wells) X Sec. 5.9 Task 5.9.1 Soil Moisture Sec. 5.7 Task 5.71 Little Total Column X Washita & ARM/CART data X Sec. 5.1 Profile X OK Mesonet Surface Temperature X ESOP-96 Hrly. Sfc. X NESDIS & CAGEX X Sec. 5.1 Composite Table 7.5 Clear sky Albedo X ARM/CART Sec. 5.6 X 2-D Grid ARM/CART X Sec. 5.1 Task 5.6.1 "Surface" Specific Humidity X ESOP-96 Hrly. Sfc. X Sec. 5.1 Composite Table 7.5 "Surface" Wind X ESOP-96 Hrly. Sfc. X Sec. 5.1 Composite Table 7.5 Sensible Heat Flux X LWW & ARM/CART flux sites Latent heat Flux X LWW & ARM/CART flux sites X 2-D Grid ARM/CART X Sec. 5.1 Longwave Radiation X Sec. 6.4 ARM/CART X NESDIS & CAGEX X Sec. 5.1 2-D Grid ARM/CART Shortwave Radiation X Sec. 6.4 ARM/CART X X NESDIS & CAGEX X Sec. 5.1 2-D Grid ARM/CART ------------- * R - Routine * E - Enhanced

5.1.2 Basic Strategy

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. LSA and CSA 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. ISA/SSA Budgets

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.

5.1.3 WY 97 Activities:

5.1.4 WY 98 Activities:

5.1.5 Outlook for WY 99

5.2 Land-Surface Boundary Layer Coupling


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.

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.

5.2.1 Warm Season Processes

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:

ARM-CART Setting

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:

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.

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.

5.2.2 Cold Season Hydrology

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:

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.

5.2.3 Near Term Activities

WY 97 Activities:

WY 98 Activities: WY 99 Outlook:

Emphasis will be placed on a synthesis of the results from the warm season and cold season analyses. New studies will be undertaken in the LSA-E, and planning for studies over the LSA-NW will be completed.

5.3 Diagnostic Studies of Long-Lasting Hydrological Regimes

OBJECTIVE: Provide more complete descriptions and understanding than previously available of the initiation, evolution and decay of long lasting (months) continental-scale anomalous hydrologic regimes; particularly, as they relate to budget derived evapotranspiration and surface and subsurface storage.

The profound societal impacts of anomalous large-scale hydrological regimes is well illustrated by the series of major regional fluctuations which have occurred during the past quarter century. Of particular significance to GCIP are the upper Midwest drought of 1988 and the more recent winter and spring wet spell which culminated in the catastrophic 1993 summer floods in the upper Mississippi River Basin. These two contrasting lengthy, continental-scale anomaly regimes will be a focus of these studies during WY 97 and WY 98.

We anticipate that these studies will serve as "benchmark cases" for use in subsequent simulation experiments and continental-scale validation of land- atmosphere hydrological subcomponents. The relevant questions can be addressed most effectively if the diagnostic studies are carried out in tandem with activities of the GEWEX Numerical Experimental Group (GNEG) and the Pan American Climate Studies (PACS) Program.

Because of the global component of these studies, they will be carried out as a joint effort of GCIP and the PACS Program. The effort will bring together global and regional mesoscale modeling groups and the land surface parameterization communities.

The development of large-scale anomaly patterns will be examined in the context of the annual cycle; e.g. what was the "cold season carry-over" contribution to anomalies during the growing season? Underlying these studies is the important question of the relative roles of regional surface anomalies and remote forcing in the perpetuation and intensity of the anomalous regime and the question of the extent to which positive feedback between anomalous land surface conditions and an anomaly-sustaining atmospheric circulation exist during these regimes. Is such feedback a significant factor in the evolution of land surface anomalies, or is it easily overpowered by other influences, e.g. a remote response to large-scale SST anomalies? Are changes in precipitation recycling over the continent an important factor?

WY 97 Activities:

GCIP-GNEG-PACS joint planning activities will continue. This will include specifying the required data sets. The feasibility of generating EDAS reanalysis data sets for the appropriate periods will be examined. Diagnostic studies based on output from the NMC global reanalysis project will be initiated.

The GCIP-PACS joint study of the North American Monsoon System will be initiated.

WY 98 Activities:

Diagnostic studies of the 1988 and 1993 anomaly regimes will extend into WY 98 and new studies of large-scale anomaly regimes which occurred during the 1995 to 1997 WYs will be initiated.

WY 99 Outlook:

Continuation of the new studies of large-scale anomaly regimes which occurred during 1995-1997 with emphasis on the interactions among the large scale atmospheric circulation features and the ISA/SSA, LSA and CSA hydrology.