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