Evaluation of Near-Surface Specific Humidity and Air Temperature From Atmospheric Infrared Sounder (AIRS) Over Oceans

Abstract

The state of the near-surface atmosphere, especially air temperature (AT) and specific humidity (SH), has profound effects on human health, ecosystem function, and global energy flows. Accurate measurements of AT and SH are essential for weather forecasting, climate modeling, data assimilation, and trend assessment. The Atmospheric Infrared Sounder (AIRS) provides global estimates of near-surface AT and SH estimates, with continuous improvements in accuracy leading to significant reductions in error rates. However, existing studies have not systematically validated AIRS near-surface products in both temporal and spatial perspectives, especially over oceans. This study aims to address this gap by using the International Comprehensive Ocean–Atmosphere Data Set as a ground-based reference to evaluate AIRS near-surface AT and SH over the ocean from the V7 Level 2 product. Our results show an overall underestimation of near-surface AT and SH. Spatially, higher uncertainties, indicated by high root-mean-square error, near land were found. In terms of seasonality and diurnal variation, we found that the products perform better during winter and at night on a global scale, although there are regional exceptions. In terms of temporal variation, the estimation errors show remarkable stability over a 20-year period, demonstrating the ability of AIRS to capture general temporal characteristics. These findings underscore the importance of validating and understanding the retrieval uncertainties of AIRS near-surface products, paving the way for improved climatological applications.