Assimilation of diverse metorological datasets with a four-dimensional mesoscale analysis and forecast system

The station-nudging approach of the NCAR/ATEC Real-time FDDA and forecast system (RTFDDA) provides a flexible method for incorporating all observations taken at irregular times and spatial locations. New unconventional data sources were introduced to the system, and many model features were refined to improve the RTFDDA analyses and forecasts. A set of eight comparison experiments were conducted to investigate the RTFDDA model response to the assimilation of the observations from satellite wind measurements and wind-profiler networks, from upperair and surface platforms, and from temperature and moisture observations and wind observations. It can be concluded that, 1) Adding new data sources will always reduce the error, though to varying extents, no matter which variable is provided; 2) observations that are well distributed temporally and spatially appear to perform better than those clustered in time and space; 3) upperair wind observations are most important and effective in driving the model toward the correct evolution (This indicates that data sources such as NESDIS satellite winds, FSL wind profilers and the FSL ACARS aircraft observations are especially valuable); and 4) surface observations (of temperature, moisture and winds) are critical to maintaining the proper evolution and accuracy of the model surface states and the physical structure of the lower troposphere; and lastly and interestingly, the simulations that employ the complete set of observations tend to produce the best analyses and forecasts. Finally, we noted that, although the above conclusions appear to be robust for this case, it is important to investigate how the value of the each platform changes with synoptic weather and geographic locations by conducting more numerical experiments. The second group experiment mentioned earlier is one effort aiming at this. Also more complete data sources were tested in the second set. The result from this set of experiments will be reported at the conference and future publications.