In situ observed relationships between snow and ice surface skin temperatures and 2 m air temperatures in the Arctic

To facilitate the construction of a satellite-derived 2 m air temperature(T_2 m) product for the snow- and ice-covered regions in theArctic, observations from weather stations are used to quantify therelationship between the T_2 m and skin temperature(T_skin). Multiyear data records of simultaneous T_skinand T_2 m from 29 different in situ sites have been analysed forfive regions, covering the lower and upper ablation zone and the accumulationzone of the Greenland Ice Sheet (GrIS), sea ice in the Arctic Ocean, andseasonal snow-covered land in northern Alaska. The diurnal and seasonaltemperature variabilities and the impacts from clouds and wind on theT_2 m–T_skin differences are quantified.T_skin is often (85 % of the time, all sites weighted equally)lower than T_2 m, with the largest differences occurring when thetemperatures are well below 0 ^∘C or when the surface is melting.Considering all regions, T_2 m is on average0.65–2.65 ^∘C higher than T_skin, with the largestdifferences for the lower ablation area and smallest differences forthe seasonal snow-covered sites. A negative net surface radiation balance generally coolsthe surface with respect to the atmosphere, resulting in a surface-drivensurface air temperature inversion. However, T_skin andT_2 m are often highly correlated, and the two temperatures canbe almost identical (<0.5 ^∘C difference), with the smallestT₂–T_skin differences around noon and early afternoon duringspring, autumn and summer during non-melting conditions. In general, theinversion strength increases with decreasing wind speeds, but for the siteson the GrIS the maximum inversion occurs at wind speeds of about5 m s⁻¹ due to the katabatic winds. Clouds tend to reduce the verticaltemperature gradient, by warming the surface, resulting in a mean overcastT_2 m–T_skin difference ranging from −0.08 to1.63 ^∘C, with the largest differences for the sites in thelow-ablation zone and the smallest differences for the seasonal snow-coveredsites. To assess the effect of using cloud-limited infrared satelliteobservations, the influence of clouds on temporally averagedT_skin has been studied by comparing averaged clear-skyT_skin with averaged all-sky T_skin. To this end, wetest three different temporal averaging windows: 24 h, 72 h and 1 month.The largest clear-sky biases are generally found when 1-month averages areused and the smallest clear-sky biases are found for 24 h. In most cases,all-sky averages are warmer than clear-sky averages, with the smallest biasduring summer when the T_skin range is smallest.