A Description of the Air Force Real-Time Nephanalysis Model

Abstract

The Air Force Global Weather Central (AFGWC) Real-Time Nephanalysis (RTNEPH) is an automated cloud model that produces a 48-km gridded analysis of cloud amount, cloud type, and cloud height. Its primary input is imagery from polar-orbiting satellites. Six main programs make up the RTNEPH. These are the satellite data mapper, the surface temperature analysis and forecast model, the satellite data processor, the conventional data processor, the merge processor, and the bogus processor. The satellite data mapper remaps incoming polar-orbiter imagery to a polar-stereographic database. The surface temperature model produces an analysis and forecast of shelter and skin temperatures for comparison to satellite-measured infrared (IR) brightness temperatures. The satellite data processor reads in the new satellite data and produces a satellite-derived cloud analysis. The conventional data processor retrieves and reformats cloud information from airport observations. The merge processor combines the satellite- and conventional-derived cloud analyses into a final nephanalysis. Finally, the bogus processor allows forecasters to manually correct the nephanalysis where appropriate. The RTNEPH has been extensively redesigned, primarily to improve analyses of total and layered cloud amounts generated from IR data. Recent enhancements include the use of regression equations to calculate atmospheric water vapor attenuation, an improved definition of surface temperatures used to calculate cloud/no-cloud thresholds for IR data, and the use of Special Sensor Microwave/Imager (SSM/1) data to further improve the calculation of infrared cloud/no-cloud thresholds. Planned enhancements include the processing of geostationary satellite data, more sophisticated processing of visible data, and a higher-resolution satellite database for the archiving and processing of multispectral satellite data.