Satellite Soil Moisture Assimilation for Improved Forecasts of the Great Plains Low-Level Jet

The U.S. Great Plains low-level jet (GPLLJ) constitutes a key source of wind and water resources in the Great Plains. It is established on greater than twenty percent of warm-season (May-September) nights and accounts for up to 70% of warm-season rainfall and 45% of the United States’ wind energy generation. In the presence of a large ridge over the central U.S. and weak flow aloft over the southern Great Plains, it can also be highly sensitive to land surface processes. Soil moisture gradients that set-up lower tropospheric temperature gradients across the region’s east-west sloping terrain can significantly impact GPLLJ strength and positioning.

In this study, we evaluate the added-value of NASA Soil Moisture Active-Passive (SMAP) soil moisture retrievals to short-term (6-30 hr) wind forecasts. We apply a weakly-coupled NASA Unified WRF-Land Information System (LIS) modeling configuration to simulate 75 GPLLJ cases between 2015-2017. The SMAP DA-related forecast improvement (or degradation) is evaluated in terms of: surface flux partitioning, sensible weather, and 0-2 km wind and thermodynamic profiles. The results are reported in the form of regional composite analyses, augmented by detailed land-atmosphere coupling diagnostics computed for specific GPLLJ cases and locations. Separately, sensitivity of the results to land surface and planetary boundary layer scheme selections will be assessed. In all cases, NOAA's Rapid Refresh (RAP) operational analysis serves as the comparative truth. To conclude, plans to extend the research to wind energy ramp event forecasts are outlined.