Preliminary Evaluation of the Atmospheric Infrared Sounder Water Vapor Over China Against High‐Resolution Radiosonde Measurements
The accuracy of the Atmospheric Infrared Sounder (AIRS) water vapor product in China is as yet unknown due to the lack of collocated in situ sounding observations. Based on high‐resolution soundings at 1400 Beijing time from 113 radiosonde sites across China, along with the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Global Positioning System (GPS) data sets, a preliminary assessment has been conducted of AIRS water vapor mixing ratio (q) and precipitable water vapor (PWV) products in June 2013 and June 2014. Comparison between AIRS and radiosonde data suggests that the correlation coefficient (R) and mean bias of these two q products in China exhibit a distinct geographical dependence (with the highest R values in northwest China). This suggests that the AIRS q product tends to be underestimated in southeast China where cloud cover prevails, but overestimated in northwest China where cloud cover is sparse. With regard to the height‐resolved distribution, the q products from both AIRS and radiosondes tend to decrease with increasing altitude, irrespective of the particular region. The spatial distribution of AIRS PWV is consistent with that from radiosonde‐derived PWV, except in south China where the AIRS PWV data set is considerably underestimated. The accuracy of the AIRS water vapor product tends to be impaired under highly cloudy conditions, corroborating the notion of clouds affecting the retrieval of AIRS PWV. Our findings highlight the importance of afternoon sounding measurements in validating AIRS data and call for the improved understanding of the role of water vapor in the context of global climate change.