Abstract
The Arctic sea ice region is the most visible area experiencing global warming-induced climate change. However, long-term measurements of climate-related variables have been limited to a small number of variables such as the sea ice concentration, extent, and area. In this study, we attempt to produce a long-term temperature record for the Arctic sea ice region using Special Sensor for Microwave Imager (SSM/I) Fundamental Climate Data Record (FCDR) data. For that, we developed an algorithm to retrieve the wintertime snow/ice interface temperature (SIIT) over the Arctic Ocean by counting the effect of the snow/ice volume scattering and ice surface roughness on the apparent emissivity (the total effect is referred to as the correction factor). A regression equation was devised to predict the correction factor from SSM/I brightness temperatures (TBs) only and then applied to SSM/I 19.4 GHz TB to estimate the SIIT. The obtained temperatures were validated against collocated Cold Regions Research and Engineering Laboratory (CRREL) ice mass balance (IMB) drifting buoy-measured temperatures at zero ice depth. It is shown that the SSM/I retrievals are in good agreement with the drifting buoy measurements, with a correlation coefficient of 0.95, bias of 0.1 K, and root-mean-square error of 1.48 K on a daily time scale. By applying the algorithm to 24-year (1988–2011) SSM/I FCDR data, we were able to produce the winter-time temperature at the sea ice surface for the 24-year period.
Highlights
The increasing emission of man-made greenhouse gases has caused global warming of 0.8 ◦C since 1900 [1,2,3], but the temperature increase is not the same everywhere over the globe
As expected, increased precipitation is noted in the Arctic [11], mainly due to the increased local evaporation caused by the sea ice loss [12]
Aiming at producing long-term snow/ice interface temperature (SIIT) over the Arctic sea ice, we develop an algorithm for retrieving the SIIT from Sensor for Microwave Imager (SSM/I) TB data, by counting surface and volume scattering effects on the measured TBs, which were examined in the previous study [22]
Summary
The increasing emission of man-made greenhouse gases has caused global warming of 0.8 ◦C since 1900 [1,2,3], but the temperature increase is not the same everywhere over the globe. The aforementioned sea ice decline, changes in the Arctic hydrological cycle, and influences on the mid-latitude weather are all related to the SIIT because the SIIT is the variable that can give information on the thermal state of the ice. In this study, we propose an algorithm to produce the long-term SIIT from SSM/I microwave (MW) measurements, which can penetrate the snow layer without much interference. Aiming at producing long-term SIIT over the Arctic sea ice, we develop an algorithm for retrieving the SIIT from SSM/I TB data, by counting surface and volume scattering effects on the measured TBs, which were examined in the previous study [22] For this objective, we introduce a correction factor to remove surface and volume scattering influences from measured TBs. Subsequently, the radiative transfer equation is solved for the physical emission temperature from SSM/I (or SSMIS alike) TBs only using the correction factor and combined Fresnel equation. The obtained long-term SIIT will certainly help to understand how the global warming has influenced the Arctic climate change in the past decades
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