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2. 2 Web Address For comprehensive information about: NOAA Network Profilers and RASS Boundary-layer profilers Surface-based estimates of total precipitable water vapor from GPS Go to: http://www-dd.fsl.noaa.gov/profiler.html

3. 3 Introduction to NAOS NAOS - North American Atmospheric Observing System Program to make recommendations on the configuration of the upper air observing systems over North America and adjacent water areas NAOS Council has representatives from 15 agencies in U.S., Canada, and Mexico to identify issues, set priorities, coordinate work of the program, and seek financial support NAOS Test and Evaluation Working Group –Assesses potential effects of proposed observing systems and configurations on the overall efficacy of forecasting services. –Assessments involve tests of hypotheses concerning the sensitivity of forecast accuracy to specific mixes of observing systems. –Assessments must also consider utility of data to field forecasters, who use them subjectively, and to the climate community.

4. 4 Hypothesis 1 It will be possible to reduce the number of rawinsondes in the U.S. network without noticeably reducing forecast accuracy provided that the sites removed have substitute observing systems already in place. Test in two steps: Identify rawinsonde sites close to busy hub airports. At these sites withhold rawinsonde and all potential substitute observations for the periods covered by the sensitivity test. Compare forecasts generated from reduced data set with operational forecasts. Restore all substitute observations but continue to withhold rawinsondes. Compare these forecasts with operational forecasts.

5. 5 Selection criteria for matching raob sites and hub airports 1) Average number of ascents or descents per day (fewer on weekends) 2) Distance from the airport to the raob site 3) Expected similarity in climate between the airport and raob site 4) Average number of points in aircraft "slant” sounding 5) Impact of deletions on overall uniformity of rawinsonde distribution 6) Don't touch GCOS sites.

6. 6 Match-ups RaobAirport# Ascents and Descents / week Salem ORPortland~100 Oakland CASan Francisco>500 Desert Rock NVLas Vegas>100 Salt Lake City UTSalt Lake City50-80 Santa Teresa NMWhite Sandsprofiler Denver CODIA~500 Fort Worth TXDallas/Fort Worth~ 80 Topeka KSKansas City(MCI)40-70 Chanhaussen MNMinneapolis (MSP)~ 20 Buffalo NYToronto25-30 Peachtree City GAAtlanta~ 50 Slidell LANew Orleans~ 75 Miami FLMiami (MIA)~ 65 Upton NYNew York City (JFK)>150

7. 7 Test Status for Hypothesis 1 May 1999 NASA has donated computer time on its 32- processor Cray J-90. Wintertime tests (late Dec 97 until mid-Feb 98) have been completed on the J-90 computer with NCEP’s global spectral model and Eta model. Tests with the RUC-2 model are in progress.

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