Uncertainties of Temperature Measurements on Snow-Covered Land and Sea Ice from In Situ and MODIS Data during BROMEX

The Bromine, Ozone, and Mercury Experiment (BROMEX) was conducted in March and April of 2012 near Barrow, Alaska, to investigate impacts of Arctic sea ice reduction on chemical processes. During BROMEX, multiple sensors were deployed to measure air and surface temperature. The uncertainties in temperature measurement on snow-covered land and sea ice surfaces were examined using in situ data and temperature measurements that were derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) and are part of the Terra and Aqua ice-surface temperature and land-surface temperature (LST) standard data products. Following an 24-h cross-calibration study, two Thermochrons (small temperature-sensing devices) were deployed at each of three field sites: a sea ice site in the Chukchi Sea, a mixed-cover site, and a homogeneous tundra site. At each site, one Thermochron was shielded from direct sunlight and one was left unshielded, and they were placed on top of the snow or ice. The best agreement between the Thermochron- and MODIS-derived temperatures was found between the shielded Thermochrons and the Aqua MODIS LSTs, with an average agreement of 0.6 degrees +/- 2.0 degrees C (sample size of 84) at the homogeneous tundra site. The results highlight some uncertainties associated with obtaining consistent air and surface temperature measurements in the harsh Arctic environment, using both in situ and satellite sensors. It is important to minimize uncertainties that could introduce biases in long-term temperature trends.