Validation of AMSU measurements in lower stratosphere using COSMIC radio occultation data: preliminary results

Global Positioning System (GPS) Radio Occultation (RO) data from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission is used to validate the measurements of advance microwave sound unit (AMSU) on different NOAA satellite platforms due to high accuracy and stability of RO data in lower stratosphere. The atmospheric temperature profiles derived from COSMIC RO data are combined with the AMSU radiative transfer model to simulate the microwave brightness temperatures (Tb). The comparison of the matched simulated and observed Tb of AMSU in lower stratosphere show that RO data can be used as an independent reference to valid the measurement of AMSU on different NOAA platforms. The preliminary validating results from one year's Tb comparisons show that all the measurement of AMSU on three NOAA satellites in lower stratosphere are underestimated, and the Tb bias on NOAA18 is more significant than those on NOAA15, 16. The bias of AMSU measurements in lower stratosphere is more significant in polar region during the winter time, especially in south pole region the variation range of Tb bias on NOAA18 about 1.8 K. Combining with the variation of Tb bias and the samples' distribution within 24 hours, it implies that the significant solar radiation difference might be the main cause for large Tb bias in polar region.