NOTE: The nws-changes mailing list is no longer active. The list archives are made available for historical reasons.
2003/03/25 DM 03-03.28 - NOTICE OF INTENT TO CHANGE OPERATIONAL ETA MODEL NOXX10KWBC 252022 DATA MGT MESSAGE 03-03.28 TO AWIPS/NOAAPORT USERS.. FAMILY OF SERVICES/FOS/SUBSCRIBERS... EMERGENCY MANAGERS WEATHER INFORMATION NETWORK /EMWIN/ NATIONAL WEATHER SERVICE /NWS/ CUSTOMERS... WAFS USERS... GTS USERS... NWS FAX CHART USERS FROM RTH WASHINGTON DATA MANAGEMENT SUBJECT NOTICE OF INTENT TO CHANGE OPERATIONAL ETA MODEL ADDITIONAL INFORMATION ABOUT THESE CHANGES WILL BE PROVIDED AS IT BECOMES AVAILABLE. Brief Description of Changes: - Modifications of the cloud microphysics and radiation, including perpetual cycling of the new cloud microphysical fields in the Eta Data Assimilation System (EDAS) - Extension of 06z/18z Eta runs to 84-h; - Assimilation of GOES cloud-top pressure information into the EDAS - Assimilation of the Stage IV precipitation data into the EDAS - Assimilation of super-observations of radial wind data from the NEXRAD 88D radar network into the EDAS - Update radiance processing in the EDAS to keep current with GDAS (Global Data Assimilation System) radiance processing - Extended output: hourly posting of model products (not on AWIPS), including more fields that describe different aspects of grid-resolved and parameterized (convective) clouds The Technical Procedures Bulletin describing these changes in detail can be found at http://wwwt.emc.ncep.noaa.gov/mmb/tpb.spring03/tpb.htm Reasons for Changes: - Cloud microphysics: In November 2001, the Eta model resolution was increased from 22 km / 50 levels to 12 km / 60 levels (Rogers et al., 2001) and a new grid-scale microphysical parameterization (Ferrier et al., 2002) was implemented. Although timely changes were made in the precipitation assimilation method of Lin et al. (2001) to account for the new microphysics, the model restart files remained unchanged. This meant that model input and output and the posting of forecast fields were not treated in a manner consistent with the new microphysics, but rather consisten with the previous microphysics package (Zhao et al., 1997). The forecast code has now been changed to include the expanded model restart files, which include additional arrays used in the Ferrier microphysics. Old arrays associated with the Zhao microphysics were removed. These modifications allow the new clouds simulated at the end of a 3-h forecast to be read in at the start of the next 3-h forecast during the EDAS thus allowing full and consistent cycling of the cloud quantities. - Extension of off-time runs to 84-h At the request of NWS field forecasters and NCEP service centers, the 06z/18z eta runs, currently run out to 48-h, will change to be identical to the 00z/12z forecasts, which are run to 60-h in one model execution with an extension to 84-h. The off-time Eta output beyond 48-h will only be available from the NCEP and NWS ftp servers at this time until DRG requests and proper user notification can be accomplished. - Use of GOES cloud top pressure data in the Eta DAta Assimilation System (EDAS) The hourly, 10-km cloud-top pressure data, derived from the GOES-8 and GOES-10 sounder radiances, give us valuable information on what the model cloud field should be like (i.e. no cloud) above the cloud top, but reveal little below the cloud top level. In the assimilation of these data, we use them mainly to remove spurious cloud above the observed cloud top level, while making small adjustment to the moisture field at the level of observed cloud top (if the model is sub-saturated there). This means that the cloud-top pressure assimilation tends to reduce the amount of cloud in the model. Prior to running each 3-h EDAS forecast, a preprocessing program reads in 3-h of GOES cloud-top data and distributes the observations into the appropriate assimilation hour and horizontal grid box within the Eta domain. At each physics time step during the EDAS forecast, condensate (water or ice) is removed from the model above the GOES cloud top level, or removed from the entire column if the satellite data indicate that this point is cloud-free. The water vapor mixing ratio is also set to no more than grid-scale saturation for those grid points where the satellite observations indicate that no cloud is present. To prevent grid-scale saturation at these locations, water vapor is also removed by setting the specific humidity to ice saturation at -10C or water saturation at warmer temperatures. At the model level closest to the observed cloud top, subsaturated air is moistened at a rate that just brings it to saturation in one hour. If there is a need to create a cloud layer in the precipitation assimilation procedure where no forecast cloud is present, it is created by moistening the air below the satellite-observed cloud top. - Assimilation of Stage IV precipitation data into the EDAS Since its implementation in July 2001, the precipitation assimilation scheme in the EDAS used the NCEP Stage II hourly precipitation analysis as the source of observed precipitation. In the new package, the NCEP Stage IV precipitation analysis will be the principal source of the precipitation input and supplemented by Stage II. Both analyses are produced at NCEP, and they are based on hourly radar and gauge observations. The NCEP Stage IV analysis merges the regional multi-sensor precipitation analyses produced by the twelve River Forecast Centers (RFC) within the CONtiguous US (CONUS). It benefits from some manual quality control performed at the RFCs, and is generally considered to be of higher quality than the Stage II product. It is, however, not as timely as the Stage II, which is produced at NCEP at approximately 40 minutes after the top of the hour. The timeliness of the Stage IV depends on the transmission of the regional analyses, which is generally delayed several hours. The latest available Stage IV analyses often have only partial coverage since analyses from RFCs arrive at different times of the day. Prior to the model integration for each 3-h EDAS segment, the available Stage II/IV analyses for that time period are collected to produce a merged analysis by using Stage IV values when available. Data gaps are filled in with available Stage II data. If there is no Stage IV data available at all for that hour, then Stage II alone is used. If both analyses are not available, which often occurs during the last hour of the operational EDAS due to time constraints, then no precipitation data is assimilated. - Assimilation of super-observations of radial wind data from the NEXRAD 88D radar network into the EDAS Radial wind data from the network of 88D radars across the US are assimilated into the EDAS using the 3DVAR analysis. The raw data are obtained from the NWS multicast and merged into a composite data set (super observations) at a coarse spatial resolution of 1 km in the radial direction and 6 degrees in the azimuthal direction, using any 88D scan taken within 1.5 h of the analysis time. The vertical component of the radar beam width is assumed to increase with radar range at a rate of 20 m km-1, which is roughly 20% larger than the actual beam width in order to account for some uncertainty in beam propagation. Winds at all model levels intercepted by the radar beam are adjusted so the observation is as close as possible to an acceptable range of wind speeds derived from straight-line fits of the radial wind observations. In this way, all winds out to the maximum range of the radar are used. All the quality marks of wind observations derived from VAD (velocity- azimuth display) analyses are colocated in the vertical in 500-m bins with the corresponding radial winds. The radial winds are not used if there is no VAD observation or if the VAD observation failed its quality-control (QC) check. This approach combines the QC algorithm for removing radial winds contaminated by birds with other checks used on the VAD winds. The radial winds are not used if: 1) the beam envelope extends below the Eta model terrain height, 2) the super observation error is larger than 6 m s-1, or 3) it fails the same gross checks used for conventional wind fit to the first guess. - Modification of radiance processing in the Eta 3DVAR analysis The assimilation of radiances in the 3DVAR analysis is done with codes adapted from the global model 3DVAR. The radiance processing code has been updated to reflect changes previously made to the global system. These changes include a more sophisticated quality control of microwave channel data, which allows more data to be used over both land and water, and the inclusion of NOAA-16 infrared channels (currently turned off). - Model products: Responding to frequent requests for hourly output of gridded products from the operational eta, the following output grids will be created on an hourly basis out to 36-h: - 32-km Lambert conformal grid over the Northern Hemisphere (grid 221). - 40-km Lambert conformal grid over the CONUS (grid 212). - 90-km polar-stereographic grid over the Northern Hemisphere (grid 104). - 11.25-km polar-stereographic grid over Alaska (grid 242). - 12-km Lambert conformal grid over the CONUS (grid 218). - 1/8-degree resolution in latitude and longitude over the CONUS for the land surface products (the so-called NLDAS grid). Contingent upon available resources on the NCEP and NWS TOC servers, these grids will be accessible via anonymous ftp from these servers. There will be no changes to any Eta model output available on AWIPS. The ability to output additional output fields from the grid-scale parameterization and the land-surface model has been included in this implementation, including mixing ratio of rain and snow on pressure and model levels, cloud top and bottom pressures of grid-scale and convective (both deep and shallow) clouds, and liquid volumetric soil moisture. Updated on-line inventories of output grids will be available at http://wwwt.emc.ncep.noaa.gov/mmb/mmbpll/etax.gridinv/ . The Eta model product generator has been extended to allow creation of output grids using nearest-neighbor interpolation from the native Eta grid, instead of bilinear interpolation for all fields except precipitation, for which a budget interpolation is done. For this implementation, this type of interpolation will be applied only to the new 1/8 latitude / longitude NLDAS grid over the CONUS, which contains a myriad of land-surface model output fields. Schedule for change: Final testing : Ongoing since 21 September 2002 Expected implementation : May 2003 Description of testing: Most of the individual components of this change package were tested using EMC's 32-km EDAS/Eta parallel system; details of this individual tests can be found on the EMC parallel web page (http://wwwt.emc.ncep.noaa.gov/mmb/mmbpll/paralog/). Since 21 September 2002 the full package of changes has been undergoing real-time testing at 12-km resolution. The description and evolution of this parallel test is documented on the EMC parallel web page at http://wwwt.emc.ncep.noaa.gov/mmb/mmbpll/paralog/paralog.etax.cloudrad.html. On this page one can find links to the following web sites: 1) parallel 12-km run compared to operational Eta-12 at http://wwwt.emc.ncep.noaa.gov/mmb/mmbpll/etapllsup12.etax/ 2) parallel 12-km run compared to operational Eta-12, GFS and NGM at http://www.emc.ncep.noaa.gov/mmb/mmbpll/etapll/ Statistical summaries: - 30-day time series of operational and parallel eta-12 forecasts vs observation (RAOB and surface) verification statistics at http://wwwt.emc.ncep.noaa.gov/mmb/mmbpll/mmbverif.etax/ - Averaged verification of precipitation and against rawinsonde / surface data at http://wwwt.emc.ncep.noaa.gov/mmb/mmbpll/pll12stats.etx/ Anticipated impact of forecasts: Based on both the daily observations of forecasts and the objective verification statistics, the changes described above will lead to slight improvements in model QPF and upper air predictions of temperatures, heights, RH, and winds. The performance of the parallel eta at the surface (10-m winds, 2-m temperatures) has been mixed. During September-November 2002, only minor differences in surface forecasts between the operational and parallel Eta runs were observed. Starting in mid-December 2002, an noticeable cold bias in Eta-12 parallel 2-m temperatures was observed in the Western and Eastern U.S, especially over northern latitudes. A series of sensitivity runs with modifications to the model radiation and/or cloud physics were performed. One test, using the Xu and Randall (1996) cloud fraction formulation, but modified such that a cloud fraction of 1.0 (total overcast) is achieved once the forecast relative humidity (RH) exceeds the threshold for the onset of grid-scale condensation (equal to 97.7% for the 12-km operational Eta and parallel Eta) was made. This run improved the consistency in the representation of cloud coverage between the radiation and the microphysics, and yields more reasonable near- surface temperatures that agree better with current operations. An additional advantage of this version of the model code is that the higher cloud fractions should also reduce the warm-season warm bias in surface temperatures by increasing the in-cloud absorption of solar radiation. Therefore this change was included in the Eta-12 change package, because it is expected to improve model performance over all seasons. Field evaluation: Datasets and webpages were available for download and review, respectively. An appendix in the TPB is dedicated to forecaster feedback. At the moment, there is only one entry in the Appendix. We will leave this open for additional entries for 60 days. Points of Contact: Eric.Rogers@xxxxxxxx 301-763-8000 ext 7227 Brad.Ferrier@xxxxxxxx 301-763-8000 ext 7290 Geoff.DiMego@xxxxxxxx 301-763-8000 ext 7221 Approvals: NCEP EMC NCO Director: Director: Director: Future changes: Testing of a new radiation parameterization are planned for 2003, in conjunction with a new convective parameterization scheme which emphasizes parcel dynamics and unifies deep and shallow convective schemes. Implementation of these and other changes are planned for the winter of 2003-2004. References: Ferrier, B. S., Y. Jin, Y. Lin, T. Black, E. Rogers, and G. DiMego, 2002: Implementation of a new grid-scale cloud and precipitation scheme in the NCEP Eta model. Preprints, 15th Conf. On Numerical Weather Prediction, San Antonio, TX, Amer. Meteor. Soc., 280-283. Lin, Y., M. E. Baldwin, K. E. Mitchell, E. Rogers, and G. J. DiMego, 2001: Spring 2001 changes to NCEP Eta analysis and forecast system: Assimilation of observed precipitation data. Preprints, 14th Conf. On Numerical Weather Prediction, Fort Lauderdale, FL, Amer. Meteor. Soc., J92-J95. Lin, Y. L., R. D. Farley, and H. D. Orville, 1983: Bulk parameterization of the snow field in a cloud model. J. Climate Appl. Meteor., 22, 1065-1092. Rogers, E., T. Black, B. Ferrier, Y. Lin, D. Parrish, and G. DiMego, 2001: Changes to the NCEP Meso Eta Analysis and Forecast System: Increase in resolution, new cloud microphysics, modified precipitation assimilation, modified 3DVAR analysis. NWS Technical Procedures Bulletin. [Available at http://wwwt.emc.ncep.noaa.gov/mmb/mmbpll/eta12tpb/ or from the National Weather Service, Office of Meteorology, 1325 East-West Highway, Silver Spring, MD 20910]. Xu, K.-M., and D. A. Randall, 1996: A semiempirical cloudiness parameterization for use in climate models. J. Atmos. Sci., 53, 3084-3102. Zhao, Q., T. L. Black, and M. E. Baldwin, 1997: Implementation of the cloud prediction scheme in the Eta model at NCEP. Wea. Forecasting, 12, 697-712. Zhao, Q., and F. H. Carr, 1997: A prognostic cloud scheme for operational NWP models. Mon. Wea. Rev., 125, 1931-1953. FOS/NOAAPORT AND NON-AWIPS CUSTOMERS - IF YOU HAVE ANY QUESTIONS REGARDING THIS NOTICE... PLEASE CONTACT DATA MANAGEMENT LOWER CASE EMAIL NWS.DM/AT SYMBOL/NOAA.GOV DATA MANAGEMENT TELECOMMUNICATION OPERATIONS CENTER RTH WASHINGTON SENDS ---------- End Forwarded Message ----------
nws-changes archives: