Evaluation of enhanced high resolution MODIS/AMSR-E SSTs and the impact on regional weather forecasts

The NASA Short-term Prediction Research and Transition (SPoRT) Center currently produces a high resolution sea surface temperature (SST) product for use by National Weather Service (NWS) Weather Forecast Offices (WFOs) as an operational diagnostic and also as input for their weather forecast models. This product uses Moderate Resolution Imaging Spectroradiometer (MODIS) data to produce composite SST output with spatial resolution superior to other SST data used to initialize regional weather forecast models. A six month study from February to August 2007 over the marine areas surrounding southern Florida was conducted to compare the use of the MODIS SST composite versus the Real-Time Global SST analysis to initialize the Weather Research and Forecasting (WRF) model. Substantial changes in the forecast heat fluxes were seen at times in the marine boundary layer, but relatively little overall improvement was measured in the sensible weather elements. The limited improvement in the WRF model forecasts could have been attributed to the latency of these data due to persistent cloud cover.

The SPoRT Center recently developed an enhanced high-resolution SST product which incorporates both MODIS and Advanced Microwave Scanning Radiometer-Earth Observing System (AMSR-E) data into the product algorithm to decrease the latency encountered in the original product. Comparisons of these two products with in situ buoy observations indicate that the enhanced SST composite substantially decreased the latency due to cloud cover and improved the bias and correlation of the composites at available marine point observations. While these enhancements improved upon the model errors when using the original MODIS SSTs, as well as cases when large SST errors occurred due to high latency, the overall discernable impacts on the WRF model were still somewhat limited. The original methodology to initialize the model used the most recent SST composite available in a hypothetical real-time configuration, often matching the forecast initial time with an SST field that was 5ƒ{8 hours offset. However, the MODIS composites clearly demonstrate a diurnal component to the SSTs. To minimize the differences in SST that result from the diurnal variations, the previous day's SST composite is incorporated at a time closest to the model initialization hour (e.g. 1600 UTC composite at 1500 UTC model initialization). This paper will present the methodology and verification of the enhanced SST composite product as well as results from model forecasts for June and July of 2007 when data latency was a persistent issue.