A.1. Introduction

The Task Group met on March 25-26, 1996 at the Illinois State Water Survey in Champaign, Illinois. The group focused on the existing infrastructure and ongoing projects in the LSA-NC. The recommendations primarily address those scientific issues that relate to snow and frozen ground processes and that can take advantage of the existing infrastructure and ongoing projects.

A.2. Relevant Issues

A series of presentations were given. These presentations highlighted a number of issues that are pertinent to the recommendations. These issues are as follows:

A.3 Scientific Themes

The scientific issues raised in the two workshops can be organized around the following themes, based on the strategy for experimental design.

A.3.1 Land Surface Model Physics

This includes frozen soil processes, snowpack maturation and melt, and the energy budget at the snow-atmosphere interface. This could also include the issue of small (field)-scale snow patchiness. In situ measurements of relevant variables at one or more sites during ESOP-97 and ESOP-98 can provide the basis for studies to improve model parameterizations and for model intercomparison studies to identify model deficiencies.

A.3.2 Land Surface Modeling of SubGrid

Scale Heterogeneity Effects - this is most relevant during snowmelt when the change in albedo can exert a profound influence on the surface-atmospheric energy exchange. The modeling of the grid-averaged energy budget is a particularly challenging problem during partial snow cover conditions when the albedo may vary from less than 0.20 to greater than 0.80 within a grid square. A model intercomparison study based on data collected in a focus study area the size of a numerical weather prediction (NWP) model grid square (40 km x 40 km) can be envisioned. However, the limited financial resources that are available may make it difficult to collect sufficient data to accurately characterize grid-averaged properties.

A.3.3 Monitoring of the Land-Surface State

Studies of the LAS-NC region as a whole will require accurate measurements of the condition of the land-surface, particularly soil moisture, soil temperature, and snowpack characteristics. NWP models will be able to capitalize on improvements in land-surface modeling only to the extent that accurate operational monitoring of the land-surface condition is available to initialize model runs. Appropriate studies under this theme include removal of biases that are present in situ snow measurement datasets, improvement of satellite snow products, algorithm development for improvement of NEXRAD products, and soil moisture initialization algorithms.

A.4. Recommended Activities

The recommended activities are described the three general areas of land-surface model physics, validation of land surface modeling of sub-grid scale heterogeneity.

A.4.1 Land-Surface Model Physics

The important cold season processes to be modeled include:

Table A-1  Variables Required for Land Surface Model Intercomparison Studies

Forcing measurements (30 minute resolution) U component wind speed at 10 m V component wind speed at 10 m Temperature at 2 m Specific humidity at 2 m Surface pressure Surface skin temperature Precipitation Surface Radiation - downward shortwave Surface Radiation - downward longwave Validation Surface Radiation - upward longwave Surface Radiation - net radiation (measured) Streamflow Soil moisture (profiles) Soil temperature (profiles) Surface latent heat flux Surface sensible heat flux Set up for Experiment Vegetation type and characteristics Site Site Description Surface Radiation - upward shortwave (albedo) Soil characteristics Wilting point Rooting zone Field capacity

Specific activities that are recommended are:

A.4.2 Validation of Land Surface Modeling of Subgrid-Scale Heterogeneity

The issue of heterogeneous snow cover, soil moisture, and land surface characteristics should be addressed partially by the collection of data in a focus area of the approximate size of a NWP model grid square (40 x 40 km). Two sites in southern Minnesota, the Cottonwood basin and the Le Sueur Basin, may be suitable for such studies. Both are of an appropriate size and shape and there are existing data collection efforts that can contribute to GCIP goals. However, it will be necessary to collect substantial additional data to describe the heterogeneity of the surface. A working group should be formed to establish specific requirements for data collection. A challenge is to design an experiment to effectively study subgrid-scale heterogeneity that is cost efficient. The following issues must be addressed in order to meet relevant scientific objectives: Specific activities that are recommended include:

A.4.3 Monitoring of the Land Surface State

Studies of the water and energy budgets during the cold season in the LSA-NC will require detailed and accurate data on snow distribution and magnitude and on soil moisture. Although WSR-88D precipitation estimates provide the desired high spatial resolution, the operational algorithms used to relate radar return to precipitation rate are not valid for snow events with the exception of the MSP radar. It may be possible to acquire the raw radar data and reprocess through more appropriate algorithms for the ESOP-97 and ESOP-98 time periods of interest. However, the cost of this is substantial and may exceed the limits of expected funds. Thus, when considering the LSA-NC as a whole, data on snow may be limited to in situ measurements by NWS cooperative observers, satellite observations, and airborne gamma radiation measurements. Each of these sources of data has limitations as follows: Specific activities that are recommended include: