Surface Temperature of the Arctic: Comparison of TOVS Satellite Retrievals with Surface Observations

Abstract

Surface temperature is a fundamental parameter for climate research. Over the Arctic Ocean and neighboring seas conventional temperature observations are often of uncertain quality, however, owing to logistical obstacles in making measurements over sea ice in harsh environmental conditions. Satellites offer an attractive alternative, but standard methods encounter difficulty in detecting clouds in the frequent surface-based temperature inversion and when solar radiation is absent. The Television and Infrared Observation Satellite (TIROS) Operational Vertical Sounder Polar Pathfinder (TOVS Path-P) dataset provides nearly 20 yr (1979?98) of satellite-derived, gridded surface skin temperatures for the Arctic region north of 60°N. Another dataset based on surface observations has also recently become available. The International Arctic Buoy Program/Polar Exchange at the Sea Surface (IABP/POLES) project provides a gridded near-surface air temperature dataset based on optimally interpolated observations from Russian drifting ice stations, buoys, and land stations from 1979 to 1997. In this study these two datasets are compared and areas with large differences (4 to 6 K) are found in both winter and summer. Over the ice-covered Arctic Ocean in both seasons TOVS temperatures are substantially colder than POLES and over the Greenland?Iceland?Norwegian (GIN) Seas TOVS is warmer. Using point measurements from manned ice stations and ships it is found that POLES is too warm (?2 K on average) in January. The bias is larger (?4 K) in regions where the primary source of data is buoys, which contain warm biases in winter owing to the insulation effect of snow covering the sensors. The difference between skin and 2-m temperatures accounts for approximately 1 K of the January discrepancy between POLES and TOVS. Over the GIN Seas in both seasons POLES is much too cold (?7 K) where values are based primarily on analyses from the National Centers for Environmental Prediction (NCEP). In July the TOVS temperatures are approximately 6 K too cold over ice-covered regions owing to poor retrievals when cloud cover exceeds 95%. When overcast retrievals are removed, this difference is reduced to 2 K. Therefore it is recommended that TOVS retrievals be rejected in summer when the retrieved cloud cover is over 95%. Decadal trends also differ greatly between POLES and TOVS primarily owing to the discontinuation of ice station data in the POLES dataset after 1991. Large positive trends in POLES over the central Arctic during spring are absent in TOVS in part because POLES relies on buoy data during the latter third of the data record.