Improving the impact of radio occultation observations on numerical forecasts of tropical cyclones

The Global Positioning System (GPS) Radio Occultation (RO) is an active remote sensing technique, which is complementary to passive microwave and infrared sounders and microwave imagers. Since its launch in 2006, Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) RO data have been assimilated by the National Centers for Environmental Prediction (NCEP; Cucurull et al., 2013), the European Centre for Medium-Range Weather Forecasts (ECMWF; Healy and Thépaut 2006), and other global numerical weather prediction (NWP) centers in their operational systems. The high accuracy, precision, and small biases (Anthes, 2011) make RO observations useful in calibrating microwave, infrared sounding systems, as well as radiosondes (Anthes, 2011; Ho et al., 2019). Because RO data can be assimilated without bias corrections, they can be considered “anchor references” in both NWP and climate reanalysis (e.g., Poli et al., 2010; Cucurull et al., 2014; Aparicio and Laroche, 2015), preventing the model from drifting to its own biased climate. All the centers had shown positive impacts of the COSMIC RO data on global forecasts (Anthes, 2011; Ho et al., 2019). The primary impact of RO data in global NWP systems is between 7- and 35-km altitudes (Poli et al., 2010).