Abstract
Abstract. This paper reviews the development of the global navigation satellite system (GNSS) radio occultation (RO) observations assimilation in the Global/Regional Assimilation and PrEdiction System (GRAPES) of China Meteorological Administration, including the choice of data to assimilate, the data quality control, the observation operator, the tuning of observation error, and the results of the observation impact experiments. The results indicate that RO data have a significantly positive effect on analysis and forecast at all ranges in GRAPES, not only in the Southern Hemisphere where conventional observations are lacking but also in the Northern Hemisphere where data are rich. It is noted that a relatively simple assimilation and forecast system in which only the conventional and RO observation are assimilated still has analysis and forecast skill even after nine months integration, and the analysis difference between both hemispheres is gradually reduced with height when compared with NCEP (National Centers for Environmental Prediction) analyses. Finally, as a result of the new on-board payload of the Chinese FengYun-3 (FY-3) satellites, the research status of the RO of FY-3 satellites is also presented.
Highlights
The radio occultation (RO) is an innovative limb sounding technique for probing the atmosphere
Compared to the results provided by the advanced numerical weather prediction (NWP) centres, most of our results are based on a relatively simple experimental system in which the effect of RO data might be amplified, but its contribution is distinguished from other types of data assimilated into the data assimilation system
Even we use ECMWF and NCEP analyses to evaluate the model performance, because Global/Regional Assimilation and PrEdiction System (GRAPES) is a developing system and the types of observations assimilated in GRAPESVar are still limited, whereas the analyses from advanced NWP centres include a large amount of information from satellite remote sensing data; as a result, it is easier to identify the problems of GRAPES when the simulations are compared with these analyses
Summary
The RO is an innovative limb sounding technique for probing the atmosphere. It was originally used to investigate the atmosphere of Mars in the early 1960s (Fjeldbo and Eshleman, 1968); it was not used to probe the Earth’s atmosphere for two reasons. The RO technique can precisely measure the delay of a radio signal as it travels from a GNSS transmitter to a receiver in a low-orbit satellite. As radiance data require bias correction, GNSS-RO data can help to “anchor” these biases These radiance observations “anchored” by GNSS-RO observations indirectly spread this information with better horizontal resolution (Collard and Healy, 2003). The COSMIC mission launch enables the operational assimilation of RO data, because COSMIC consists of six low-orbit satellites and can provide relatively more RO sounding profiles (approximately 2000 profiles daily) in near real time (Anthes et al, 2008). Highlights of the status of FY-3 RO are presented here
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