Comparison of NOAA near-surface air temperatures and MODIS ice-surface temperatures at Summit, Greenland (2008-2012)

The availability of climate-quality data from NOAA temperature sensors has enabled a detailed comparison of Moderate-resolution Imaging Spectroradiometer (MODIS) infrared-derived ice-surface temperatures (IST) at Greenland's Summit station. During a ~4.5 year period (2008-2012), 2213 IST values were compared with 5-minute average temperatures (TA) derived from 15 second observations taken by NOAA's primary 2-m air temperature sensor. These data enabled an expected small offset between air and surface temperatures to be investigated over multiple annual cycles. Our preliminary findings are: 1) that temporally-coincident IST values are colder than the 5-minute average air temperatures and also that this difference increases as temperatures decrease; 2) IST-TA differences vary little with distance in the immediate vicinity of the in situ data; 3) there is a small but detectable decrease in IST-TA as the MODIS sensor's zenith angle relative to the site increases; and 4) there is a pattern in IST-TA as the solar zenith angle changes at Summit through the year. This last result largely explains the progressive increase in the temperature difference from the NOAA reference data at colder temperatures but also indicates that the MODIS cloud mask is less effective in periods of low solar zenith angle and during the polar night.