Impact of loss of U.S. microwave and radio occultation observations in operational numerical weather prediction in support of the U.S. Data Gap Mitigation Activities

As the U.S. polar-orbiting satellites NOAA-15, -18, and -19 and NASA's Aqua satellite reach the ends of their lives, there may be a loss in redundancy between their microwave (MW) soundings, and the Advanced Technology Microwave Sounder (ATMS) on the Suomi-National Polar-Orbiting Partnership (NPP) satellite. With the expected delay in the launch of the next generation of U.S. polar-orbiting satellites, there may be a loss in at least some of the U.S. MW data. There may also be a significant decrease in the number of radio occultation (RO) observations. The mainstay of the global RO system, the COSMIC constellation of six satellites is already past the end of its nominal lifetime. A replacement of RO soundings in the tropics is planned with the launch of COSMIC-2 satellites in 2016. However, the polar constellation of COSMIC-2 will not be launched until 2018 or 2019, and complete funding for this constellation is not assured. Using the NCEP operational forecast system, forecasts for March-April 2013 are carried out in which various combinations of the U.S. MW and all RO soundings are removed. The main results are that the forecasts are only slightly degraded in the Northern Hemisphere, even with all of these observations removed. The decrease in accuracy is considerably greater in the Southern Hemisphere, where the greatest forecast degradation occurs when the RO observations are removed. Overall, these results indicate that the possible gap in RO observations is potentially more significant than the possible gap in the U.S. MW data.