Evaluation of Total Precipitable Water over East Asia from FY-3A/VIRR Infrared Radiances

Satellite retrieval of atmospheric water vapor is intended to further understand the role played by the energy and water cycle to determine the Earth's weather and climate. The algorithm for operational retrieval of total precipitable water (TPW) from the visible and infrared radiometer (VIRR) onboard Fengyun 3A (FY-3A) employs a split window technique for clear sky radiances over land and oceans during both day and night. The retrieved TPW is compared with that from the moderate resolution imaging spectroradiometer (MODIS) onboard the Terra satellite and data from radiosonde observations (RAOB). During the study period, comparisons show that the FY-3A TPW is in general agreement with the gradients and distributions from the Terra TPW. Their zonal mean difference over East Asia is smaller in the daytime than at night, and the main difference occurs in the complex terrain at mid latitude near 30°N. Compared with RAOB, the zonal FY-3A and the Terra TPW have a moist bias at low latitudes and a dry-bias at mid and high latitudes; in addition, the FY-3A TPW performs slightly better in zonal mean biases and the diurnal cycle. The temporal variation of the FY-3A and the Terra TPW generally fits the RAOB TPW with the FY-3A TPW. The FY-3A TPW is more accurate at night, while the Terra TPW is more accurate during the daytime. Comparisons of correlations, root mean square differences and standard deviations indicate that the FY-3A TPW series is more consistent with the RAOB TPW at selected stations. As a result, the FY-3A TPW has some advantages over East Asia in both spatial and temporal dimensions.