Impact of Loss of Microwave and Radio Occultation Observations in Operational Numerical Weather Prediction in Support of the US Data Gap Mitigation Activities

As the current U.S. polar-orbiting satellites in the early afternoon orbit reach the end of their life, there may be a loss in redundancy between their microwave (MW) soundings, and the Advanced Technology Microwave Sensor (ATMS) sounders on the Suomi-NPP satellite. With the expected delay in the launch of the U.S. next generation of polar-orbiting satellites, there may be a gap in the afternoon MW data.

There may also be a gap in 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 expected 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.

This paper investigates how much degradation in forecast skill will occur as a result of these possible data gaps. Using the NCEP operational forecast system as of March and April 2013, two-month forecasts are carried out in which various combinations of MW and RO soundings are removed. The main results are that the forecasts are degraded only slightly 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 more significant than the possible gap in the early afternoon orbit MW data.