Assessing the potential of the Atmospheric Infrared Sounder (AIRS) surface temperature and specific humidity in turbulent heat flux estimates in the Southern Ocean

Surface air temperature (T-A), sea surface temperature (T-O), and surface specific humidity (q(a)) satellite retrievals from the Atmospheric Infrared Sounder (AIRS) are compared with shipboard measurements across Drake Passage for the period from September 2002 to June 2007. The objective is to evaluate whether AIRS retrievals, in conjunction with microwave sea surface temperatures from the Advanced Microwave Scanning Radiometer (AMSRE), can provide sufficiently accurate parameters to estimate sensible and latent heat fluxes in the data-limited Southern Ocean. The collocated data show that both AIRS T-A and T-O are colder than those from shipboard measurements, with a time mean bias of -2.03 degrees C for TA and -0.22 degrees C for T-O. Results show that air-sea temperature difference (T-A-T-O), q(a), and relative humidity (RH) are the major factors contributing to the differences between satellite and shipboard temperature measurements. Differences in AIRS and shipboard T-A (Delta T-A) decrease with increasing T-A-T-O, and Delta T-A increases with increasing RH, whereas differences in AIRS and shipboard T-O (Delta T-O) increase with both increasing T-A-T-O and increasing q(a). The time mean q(a) from AIRS is lower than the shipboard qa by 0.69 g/ kg. Statistical analyses suggest that T-A-T-O, cloud, and q(a) are the major contributors to the qa difference (Delta q(a)). Delta q(a) becomes more negative with increasing T-A-T-O and increasing cloud fraction. Delta q(a) also becomes more negative as q(a) increases. Compared with T-A, T-O, and T-A -T-O, from the National Centers for Environmental Prediction/National Center for Atmospheric Research Reanalysis (NCEP), AIRS-derived and AMSRE-derived variables show more small-scale spatial structure, as is also typical of the ship observations. Although AIRS qa gives a better representation of the full range of values of shipboard qa, its deviation from shipboard qa is relatively large compared to NCEP q(a). Compared with several existing gridded flux products, turbulent fluxes estimated from AIRS and AMSRE data using bulk algorithms are better able to represent the full range of flux values estimated from shipboard parameters.