Evaluation and Application of Precipitable Water Vapor Product 1 from MERSI-II onboard the Fengyun-3 D Satellite 2

The evaluation of precipitable water vapor (PWV) derived from the advanced Medium Resolution Spectral Imager 10 (MERSI-II) onboard FengYun-3D is performed with the PWV from Integrated Global Radiosonde Archive (IGRA) based on 11 626 sites (54214 match-ups) in total during 2018-2021. The averaged PWVs from MERSI-II and IGRA both present the 12 distribution opposite to latitude, with great PWV mostly found in the tropics. In general, a good consistency exists between 13 the PWVs of MERSI-II and IGRA, and their correlation coefficient is 0.9400 and root mean squared error (RMSE) is 0.31 14 cm. The peak values of mean bias (MB) and the mean relative bias (MRB) are 0.00 cm and -2.38%, with the standard 15 deviations of 0.25 cm and 16.8%, respectively. For most sites, the PWV is underestimated with the MB between -0.28 cm 16 and 0.05 cm. However, there is also overestimated PWV, which is mostly distributed in the surrounding areas of the Black 17 Sea and the middle of South America. The peak values of MB are found in February and July over the Southern and 18 Northern Hemisphere, respectively. More than 66.91% of retrievals falling within the except error (EE) envelope during all 19 months. Overall, the MRB and RMSE become larger with the increasing temporal and distance discrepancy, and it is 20 contrast for EE and correlation coefficient. Besides, the distance discrepancy impacts the evaluation more. The application of 21 PWV product over Qinghai-Tibet Plateau shows that the transport of water vapor along the Brahmaputra Grand Canyon is 22 obvious and it is more significant in July. 23