Land surface air temperature variations over Eurasia and possible causes in the past century
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ABSTRACT In this study, the variations of annual land surface air temperature (SAT) over Eurasia and the northern part of Africa (0°–180°E, 0°–90°N) were investigated using monthly SAT data from the Climatic Research Unit, University of East Anglia for 1901–2014 and the simulations from the Geophysical Fluid Dynamics Laboratory coupled model. The observed results suggested that the SAT variations exhibited robust non‐uniform spatial features at multi‐time scales. For the variations in inter‐annual to decadal time scales (IDV), the intensity generally increased from south to north, with the strongest intensity being around Siberia and four times that of the weakest intensity found around China. The IDV leading pattern showed a north–south dipole across 40°N. The simulated results suggested that the north–south dipole and the northwards increase of the IDV were due to internal interactions within the complex nonlinear climate system, but the natural and greenhouse gas forcings could intensify the IDV. The warming trend of the SAT was generally homogeneous, but it showed distinctive multi‐decadal fluctuations in different regions. The linear secular trends and robust multi‐decadal variation around Siberia and China corresponded to the considerable acceleration and deceleration in the warming over the two regions, respectively. The warming around Siberia was mainly caused by greenhouse gases but its modulation due to natural forcing was also considerable because of the robust multi‐decadal variations. Around China, the multi‐decadal variation, contributed by the natural forcing, can explain more than half the variances in the warming. The warming trend around central Asia was intense and parabolic, and the multi‐decadal variation over there was weak and showed few modulating effects.Keywords:
Forcing (mathematics)
Surface air temperature
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Abstract Global analyses of surface mean air temperature ( T m ) are key datasets for climate change studies and provide fundamental evidences for global warming. However, the causes of regional contrasts in the warming rate revealed by such datasets, i.e., enhanced warming rates over the northern high latitudes and the “warming hole” over the central U.S., are still under debate. Here we show these regional contrasts depend on the calculation methods of T m . Existing global analyses calculate T m from daily minimum and maximum temperatures ( T 2 ). We found that T 2 has a significant standard deviation error of 0.23 °C/decade in depicting the regional warming rate from 2000 to 2013 but can be reduced by two-thirds using T m calculated from observations at four specific times ( T 4 ), which samples diurnal cycle of land surface air temperature more often. From 1973 to 1997, compared with T 4 , T 2 significantly underestimated the warming rate over the central U.S. and overestimated the warming rate over the northern high latitudes. The ratio of the warming rate over China to that over the U.S. reduces from 2.3 by T 2 to 1.4 by T 4 . This study shows that the studies of regional warming can be substantially improved by T 4 instead of T 2 .
Surface air temperature
Mean radiant temperature
Diurnal temperature variation
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