Characterization of Himawari-8/AHI to Himawari-9/AHI infrared observations continuity

As the 'twin imagers', Himawari-8/AHI and Himawari-9/AHI are both the new generation imagers operated by the Japan Meteorological Agency (JMA). After more than 7 years of operation, Himawari-8/AHI turned into stand-by status and Himawari-9/AHI began operation as the successor. To continuous users of both imagers, it is essential to characterize continuity of Himawari-8/AHI to Himawari-9/AHI observations, which can provide beneficial information to quantitative retrieval and satellite assimilation algorithm developer. In this research, cross-comparison are performed to Himawari-8/AHI and Himawari-9/AHI infrared (IR) observations, and 'observation minus background (O - B)' characters of two imagers under clear-sky condition over ocean are also compared. The results are as follows: 1) Himawari-8/AHI and Himawari-9/AHI IR observations are in good consistency with largest absolute bias less than 1.437 K and RMSE below 1.663 K. Biases and RMSEs for Himawari-8/AHI and Himawari-9/AHI channel 7 show obvious diurnal variation character and RMSEs for all channels have evident temporal cycle variation characteristics, with cycle time of about 10 days; 2) IR observations of Himawari-8/AHI are more closed to RTTOV simulations under clear-sky condition than those of Himawari-9/AHI, especially for channels 7, 9 and 16. Dependence of O - B biases and RMSEs for two imagers IR channels on satellite scan angles are almost identical.