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Physical Initialization for Regional Spectral Model Summary

Learn about the implementation of Physical Initialization (PI) in the Regional Spectral Model (RSM) to improve precipitation simulations. See results over U.S., Mexico, and South America domains using different data sets and procedures.

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Physical Initialization for Regional Spectral Model Summary

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  1. Physical Initialization for the Regional Spectral Model Ana Nunes, John Roads and Masao Kanamitsu Scripps Experimental Climate Prediction Center (ECPC)La Jolla, California, USA anunes@ucsd.edu NCEP CDWorkshop

  2. Summary PHYSICAL INITIALIZATION FOR THE REGIONAL SPECTRAL MODEL Although atmospheric analyses and reanalyses are now providing physical realistic fields for many variables, precipitation remains problematic. Physical initialization (PI) has been proposed as a methodology for improving precipitation and related hydroclimatological simulation skill. For this reason, the Scripps Experimental Climate Prediction Center (ECPC) is now implementing a PI procedure in the Regional Spectral Model (RSM). We summarize here some of the improvements obtained for climate simulations over two distinct domains: (1) U. S. and Mexico during a Southwest-Mexico monsoon season; and (2) South America during the rainfall season of the Amazon region and increased activity of the South Atlantic Convergence Zone. NCEP CDWorkshop

  3. Model PHYSICAL INITIALIZATION FOR THE REGIONAL SPECTRAL MODEL The Scripps ECPC RSM, described previously by Juang and Kanamitsu (1994); Anderson et al. (2001); and Roads (2003), used for these experiments had 60-km resolution and 28 levels in the vertical. A Mercator projection was used for the projection of the regional grid. The RSM is a primitive equation model, with similar physics as the driving NCEP-DOE reanalysis II (R-2) Global Spectral Model as reported in Kanamitsu et al. (2002). NCEP CDWorkshop

  4. Data Set PHYSICAL INITIALIZATION FOR THE REGIONAL SPECTRAL MODEL RSM initial and boundary conditions were obtained from the coarser-scale R-2 reanalysis (1.875° resolution) and 28 vertical levels. Daily rain rates were provided by the Climate Prediction Center (CPC) precipitation analysis (see Higgins et al., 2001) over the U. S. domain. R-2 precipitation fields were used for the rest of the model domain, including Mexico. The CPC precipitation was provided on a regular grid of 0.25º. SSM/I-OLR precipitation estimates were used in the simulations over South America. The SSM/I-OLR estimate was provided on a Gaussian grid of 0.7º. The NOAA/NESDIS SSM/I algorithm (Ferraro and Marks, 1995) was used to estimate the rain rates. All rainfall fields were bi-linearly interpolated to the regional model’s grid. SST (1 degree resolution) was taken from the PIRCS data set. NCEP CDWorkshop

  5. PI Procedure PHYSICAL INITIALIZATION FOR THE REGIONAL SPECTRAL MODEL This scheme basically adjusts the humidity profile using the difference between the “observed” and predicted rain rates as factor of this adjustment. In order to provide consistent temperature profiles, the cumulus and large-scale precipitation parameterizations are then immediately called. This methodology differs from the used by the FSU Nested Regional Spectral Model (Nunes and Cocke, 2003), where a modified Kuo parameterization is the convection scheme, however the general PI procedure follows the same structure as shown in Fig. 1. “OBSERVED” RAIN RATES TIME STEP ASSIMILATED PI-ANALYSIS PHYSICAL INITIALIZATION SCHEME FORECAST DAY -1 ANALYSIS DAY 0 ANALYSIS Fig. 1 - General overview of the PI procedure considering a continuous data assimilation system. NCEP CDWorkshop

  6. RSM 60-km Experiments PHYSICAL INITIALIZATION FOR THE REGIONAL SPECTRAL MODEL The experiments were performed during the summertime. U. S. and Mexico: - July-August-September, starting at July 1st, 1999 at 0 UTC. South America: - January, starting at January 1st, 1999 at 0 UTC. The control simulations were not initialized. In the PI simulations, the rain rates were updated every 24 hours, and the moisture adjustment took place every time-step which was 3 min. The boundary conditions were updated every 6 hours. NCEP CDWorkshop

  7. U. S. and MexicoMonthly Accumulated Precipitation (mm)July 1999 SAS Verification RAS NCEP CDWorkshop

  8. U. S. and MexicoMonthly Accumulated Precipitation (mm)August 1999 SAS Verification RAS NCEP CDWorkshop

  9. U. S. and MexicoMonthly Accumulated Precipitation (mm)September 1999 SAS Verification RAS NCEP CDWorkshop

  10. South AmericaMonthly Accumulated Precipitation (mm)January 1999 SAS Verification RAS NCEP CDWorkshop

  11. Evaluation PHYSICAL INITIALIZATION FOR THE REGIONAL SPECTRAL MODEL A preliminary evaluation of the PI scheme results was based on spatial correlation coefficient (r) and bias given by: The variables x and y represent the predicted and observed precipitations, and the subscript i, the grid point on the Mercator projection. NCEP CDWorkshop

  12. U. S. and MexicoSpatial Correlation CoefficientJuly 1999 NCEP CDWorkshop

  13. U. S. and MexicoSpatial Correlation CoefficientAugust 1999 NCEP CDWorkshop

  14. U. S. and MexicoSpatial Correlation CoefficientSeptember 1999 NCEP CDWorkshop

  15. U. S. and MexicoBias: July 1999 SAS RAS NCEP CDWorkshop

  16. U. S. and MexicoBias: August 1999 SAS RAS NCEP CDWorkshop

  17. U. S. and MexicoBias: September 1999 SAS RAS NCEP CDWorkshop

  18. South AmericaSpatial Correlation CoefficientJanuary 1999 NCEP CDWorkshop

  19. South AmericaBias: January 1999 SAS RAS NCEP CDWorkshop

  20. U. S. and Mexico850 hPa Temperature (K)July 1999 SAS R-2 RAS NCEP CDWorkshop

  21. U. S. and Mexico500 hPa Temperature (K)July 1999 SAS R-2 RAS NCEP CDWorkshop

  22. U. S. and Mexico300 hPa Temperature (K)July 1999 SAS R-2 RAS NCEP CDWorkshop

  23. U. S. and Mexico850 hPa Temperature (K)August 1999 SAS R-2 RAS NCEP CDWorkshop

  24. U. S. and Mexico500 hPa Temperature (K)August 1999 SAS R-2 RAS NCEP CDWorkshop

  25. U. S. and Mexico300 hPa Temperature (K)August 1999 SAS R-2 RAS NCEP CDWorkshop

  26. U. S. and Mexico850 hPa Temperature (K)September 1999 SAS R-2 RAS NCEP CDWorkshop

  27. U. S. and Mexico500 hPa Temperature (K)September 1999 SAS R-2 RAS NCEP CDWorkshop

  28. U. S. and Mexico300 hPa Temperature (K)September 1999 SAS R-2 RAS NCEP CDWorkshop

  29. South America850 hPa Temperature (K)January 1999 SAS R-2 RAS NCEP CDWorkshop

  30. South America500 hPa Temperature (K)January 1999 SAS R-2 RAS NCEP CDWorkshop

  31. South America300 hPa Temperature (K)January 1999 SAS R-2 RAS NCEP CDWorkshop

  32. U. S. and MexicoJuly 1999 NCEP CDWorkshop

  33. U. S. and MexicoAugust 1999 NCEP CDWorkshop

  34. U. S. and MexicoSeptember 1999 NCEP CDWorkshop

  35. South AmericaJanuary 1999 NCEP CDWorkshop

  36. Conclusions PHYSICAL INITIALIZATION FOR THE REGIONAL SPECTRAL MODEL Preliminary evaluations of the PI implementations indicate that the RSM was able to successfully assimilate the merged precipitation analysis and SSM/I estimates as well. The correlation coefficients exceeded 0.9 and the spin-up problem was noticeably reduced during the continuous assimilation period. The temperature fields are not degraded by using a rainfall nudging and they are well correlated with the R-2 fields. We are now attempting to implement a physically initialized analyses as part of our effort to develop useful downscaled reanalysis fields NCEP CDWorkshop

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