Climate Data Records Using Radio Occultation And Coordination with Other Upper Air Observing Systems such as GRUAN and GSICS

Radio occultation (RO) using Global Navigation Satellite Systems (GNSS) has the potential to provide measurements of atmospheric refractivity and temperature that meet stringent accuracy requirements needed for climate studies. Small (< 0.1 K, ~0.05% refractivity) inter-satellite measurement biases have been demonstrated by comparing measurements from closely collocated soundings obtained from different RO instruments. However, detailed analyses of the physical retrieval scheme for RO reveals several potential sources of measurement bias that potentially affect long-term climate observation. These biases may vary with geophysical conditions, such as the state of the ionosphere, or the vertical structure of the stratosphere. We have undertaken a detailed study of GNSS RO measurement biases under NASA's Earth System Data Records Uncertainty Analysis program. In this talk, we discuss means of determining upper bounds on retrieval biases that are robust to varying geophysical conditions. We will present recent results that characterize key sources of uncertainty, such as small-scale ionospheric structure and stratospheric variability. Finally, we present the status of plans to coordinate RO with other upper air observing systems such as GRUAN (GCOS Reference Upper-Air Network) and GSICS (Global Space-based Inter-Calibration System).