ERS-2 Altimetry in Operational NOAA Forecast Models

1. ERS-2 Altimetry in Operational NOAA Forecast Models John Lillibridge NOAA/NESDIS Laboratory for Satellite Altimetry David Behringer & Jean Thiebaux NOAA/NWS/NCEP Environmental Modeling Center Michelle Mainelli NOAA/NWS National Hurricane Center Remko Scharroo Delft Institute for Earth-Oriented Space Research Delft University of Technology ERS-ENVISAT Symposium 2000 Göteborg, Sweden

2. Latency of Daily ERS-2 Processing ERS-ENVISAT Symposium 2000 Göteborg, Sweden

3. Improvements to Real-Time ERS-2 Altimetry • Delft DGM-E04 Gravity Model tuned to ERS: 8/98 • Fast-Delivery wet troposphere correction: 11/98 • NOAA/Delft orbit “feedback” loop: 11/98 • Prince Albert fast-delivery data: 7/99 ERS-ENVISAT Symposium 2000 Göteborg, Sweden

4. NOAA/Delft Orbit Determination Feedback Loop ERS-ENVISAT Symposium 2000 Göteborg, Sweden

5. Reduction in Orbit Error after Altimeter Feedback Loop ERS-ENVISAT Symposium 2000 Göteborg, Sweden

6. El Niño Southern Oscillation Predictions • Coupled model based on GFDL Modular Ocean Model • Assimilates subsurface temperature (XBT, TAO) & altimetry • ENSO predictions with 6-month lead time • Compare parallel model runs: with vs. without altimetry ERS-ENVISAT Symposium 2000 Göteborg, Sweden

7. Sea Level Differences (cm) ENSO Model with Altimetry • Differences between models with/without Topex altimetry, along equator • Salinity effects in western tropical Pacific better modeled by altimetry • 10 cm differences prior to ‘97-’98 El Niño ERS-ENVISAT Symposium 2000 Göteborg, Sweden

8. ENSO Model vs. Tide Gauges • Western Pacific gauges • Model without altimetry (XBT) diverges from gauges • Model with altimetry (TPX) tracks sea level better • Lower RMS with altimetry ERS-ENVISAT Symposium 2000 Göteborg, Sweden

9. Adjusting ERS-2 with T/P Crossovers • Spline fit crossovers with t < 5 days • Hemispheric tilt from heating/cooling • Adjusted ERS-2 data retains seasonal tilt • Adjustment removes biases and geocenter offsets between missions ERS-ENVISAT Symposium 2000 Göteborg, Sweden

10. Coastal Ocean Forecast System • Regional coupled model based on Princeton Ocean Model • Assimilates SST and T/P + ERS-2 altimetry • Nowcasts & 24-hour forecasts of surface height, currents, temperature and salinity • Compare parallel model runs: T/P alone vs. T/P + ERS-2 ERS-ENVISAT Symposium 2000 Göteborg, Sweden

11. Merged ERS-2 and T/P Sea Level Deviations ERS-ENVISAT Symposium 2000 Göteborg, Sweden

12. S S T °C • Gulf Stream follows high gradient in sea surface height • Model with ERS-2 shows more realistic structure • Addition of ERS-2 gives better agreement with SST analysis ERS-ENVISAT Symposium 2000 Göteborg, Sweden

13. Hurricane Forecasting at NHC • Storm track predictions have improved, but not intensity forecast • Intensification correlated with “heat potential” not simply SST • High heat potential in warm-core eddies shed by Gulf Stream & Gulf of Mexico Loop Current • Case study: Hurricane Gordon, September 14-18 2000. ERS-ENVISAT Symposium 2000 Göteborg, Sweden

14. ERS-ENVISAT Symposium 2000 Göteborg, Sweden

15. Heat Potential Before/After Hurricane Gordon • Gordon intensified over Loop Current meander • Low heat potential feature in wake of storm • Diagnostic tool for operational forecasters ERS-ENVISAT Symposium 2000 Göteborg, Sweden

16. Conclusions • Real-time Altimetry in 10 hours with < 10 cm orbit error • ENSO model improved where salinity affects sea level • Improved Gulf Stream analyses with better mesoscale sampling • Heat potential maps aid in predictions of hurricane intensification • Future plans: • Fully implement ERS-2 in ENSO model • Assimilate altimetry directly in hurricane models • Include data from GFO, ENVISAT, JASON …. ERS-ENVISAT Symposium 2000 Göteborg, Sweden