A Climatological and Process-Based Evaluation of AIRS Tropospheric Thermodynamics over the High-Latitude Arctic

Measurements from space borne sensors have the unique capacity to fill spatial and temporal gaps present from the ground-base atmospheric observing system. This is especially true over the high latitude Arctic polar region, where observing stations are limited to pan-Arctic landmasses and infrequent field campaigns. The hyperspectral infrared sounder instrument AIRS, housed on the Aqua satellite and polar-orbiting within the A-Train satellite constellation, has provided radiances and retrieved thermodynamic profiles from the global atmosphere twice daily since its launch in 2002. These measurements are critically important for weather prediction models as background observations for the data assimilation cycles. Likewise, retrievals of thermodynamics from AIRS over the Arctic have been used to quantify and improve the understanding of important processes and features of the sparsely observed Arctic atmosphere.

However, a detailed investigation into the accuracy of AIRS thermodynamic profiles over the high-latitude Arctic is lacking. In this study, we have compiled a wealth of radiosounding profiles from long-term Arctic land stations, including from intensive icebreaker-based field campaigns, which we use to evaluate daily mean thermodynamic profiles from the satellite sensor. Results indicate that while the mid- to upper-troposphere temperature and specific humidity are relatively well captured by the satellite, the lower troposphere is susceptible to specific seasonal, and even monthly, biases. These differences across the lowest atmospheric levels have a critical influence on the lower tropospheric stability structure. The relatively coarse vertical resolution of AIRS retrievals, together with infrared retrievals through persistent low Arctic cloud layers, lead to artificial thermodynamic structures that fail to accurately represent the lower Arctic atmosphere. These thermodynamic errors are likely to introduce artificial errors in the boundary layer structure and associated physical processes.