Observing System Simulation Experiments (OSSEs) to Assess the Potential Impact of Proposed Observing Systems on Global NWP and Hurricane Prediction

Observing System Simulation Experiments (OSSEs) can be used to assess various strategies to mitigate or avoid the potential for satellite data gaps or evaluate benefits of new data streams that could improve the operational weather forecast. With support in part by funding from the Disaster Relief Appropriations Act of 2013, we are conducting preliminary OSSEs with existing OSSE systems, and building an advanced “next-generation” global OSSE capability to investigate the impact of additional global navigation satellite system radio occultation satellites and a global system of geostationary hyperspectral sounder instruments in a scenario where no afternoon polar orbiting satellites are assimilated.

Preliminary OSSEs evaluated the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC-2) equatorial and polar components using NOAA's current global OSSE system and assimilating simulated radio occultation observations. The results of this experiment showed that increasing the number of assimilated radio occultation satellites from 6 to 18 improved weather forecasts: 18 satellites were better than 12 satellites; 12 satellites were better than 6 satellites. We also conducted a preliminary regional hurricane OSSE. Since the structure of hurricanes cannot yet be represented realistically in global models, we developed a dedicated regional hurricane OSSE capability to assess the impact of these data. This experiment showed that short-range forecasts improved as the number of satellites increased from 6 to 30. More rigorous OSSEs are being conducted with the advanced next-generation global OSSE system.

We completed preliminary OSSEs to evaluate the potential impact of geostationary hyperspectral sounder instruments on global model forecasts and regional model hurricane forecasts. The results of the global experiments showed a significant improvement in forecast accuracy over the Southern Hemisphere, but the forecast accuracy did not improve over the Northern Hemisphere. Due to the relatively coarse horizontal resolution used to simulate the atmosphere and the relatively coarse horizontal and temporal resolution of the data used in the data assimilation system, these results may not fully represent what could be achieved from an advanced geostationary sounder. Decisions should be based on the experiments with the new global OSSE system, which are just beginning. The results of the regional model hurricane experiments were mixed. They indicate some potential to improve hurricane forecasts if the frequency of observations increases. However, the results of both the global and regional model OSSEs are not final; experiments directed at severe local storms have not yet been conducted; and more research is needed to improve the application of these instruments for weather prediction and to determine if a significant impact over the Northern Hemisphere is possible. We are conducting this research using both global and regional forecast systems and are using findings from the preliminary experiments to guide the more advanced and comprehensive OSSEs in progress.5 on 8-18-2015-->