Observing System Simulation Experiments for a COSMIC Follow-On Mission

The six-satellite COSMIC GPS radio occultation (RO) mission was launched in April 2006. It is designed to have a five-year mission life. We can anticipate gradual degradation of the COSMIC constellation after 2011. With the significant positive impacts of COSMIC on operational weather prediction, climate studies, and ionospheric research and space weather forecasting, there is strong interest in developing a COSMIC follow-on mission to continue the provision of GPS RO data to support weather, climate and ionospheric science objectives. Taiwan's National Space Organization and NOAA/NESDIS have started the planning process for a COSMIC follow-on mission, known as the COSMIC-II. Preliminary design of COSMIC-II calls for a 12-satellite constellation, tracking radio signals from GPS, GALILEO, and GLONASS, using an advanced RO receiver. In this paper, we perform a series of observing system simulation experiments (OSSE) to examine the potential impact of constellation design on the analysis and prediction of tropical cyclones. Using the example of Typhoon Shanshan (2006), we consider several options of constellation design. The first option is to keep all the 12 satellites in high latitude inclination (72 degree), like the current COSMIC constellation. We find such constellation design yields significant imbalance in terms of data density between the tropics and high latitudes. There are three times more GPS RO soundings over the polar regions than over the tropics. The second option is to place 8 satellites in 72 degree inclination and 4 satellites in 24 degree inclination. With such option, we obtain a much more homogeneous data distribution around the globe. The second option also provides a significantly greater impact on the analysis and prediction of tropical cyclones. We are in the process of conducting additional OSSEs for other storms, and with other possible constellation options. These results will be reported at the workshop.