Harmonic analysis of climatological temperature over Antarctica: present day and greenhouse warming perspectives

On the basis of ERA40 and NCEP/NCAR Reanalysis (NNR) and simulations from CCCma, CCSM, CSIRO, HadCM3, MIROC-MEDRES and GFDL, which support the Intergovernmental Panel on Climate Change (IPCC) 4th Assessment Report (AR4), we demonstrated that the amplitude of the annual and the semi-annual harmonics delivered by the ERA40 and NNR is dominated by distinct seasonal variability. The maximum first harmonic amplitude of near surface temperature 2-metre air temperature (t2m) according the NNR is located over the Plateau of East Antarctica, whereas analyses for ERA40 show maximum amplitude over the west Antarctic ice sheet. The spatial pattern of the first harmonic of t2m in NNR more closely corresponds to station observations, suggesting that the seasonal cycle of t2m over Antarctica may be biased in ERA-40. A comparison between the global climate models (GCMs) and NNR demonstrates that the models satisfactorily simulate the amplitude of the first and second harmonics; however, the modelling results differ among themselves in terms of the amplitude values. Larger seasonal variability is identified for CCCma, HadCM3 and MIROC-MEDRES with values as high as 20 °C over the Antarctic plateau. We have further identified that the CSIRO GCM does not reproduce the seasonal amplitude of t2m as compared to other models, which is primarily due to its overestimation of the cloud cover and weak seasonal changes of precipitation. Calculations of the harmonic analysis based upon greenhouse warming (GW) conditions reveal that there is no substantial seasonal difference between the amplitude of the first harmonic as projected by GW and present day (PD) simulations over the Antarctic continent. Over the polar ocean, however, the amplitude of the first harmonic is reduced in all climate models under future conditions. In order to narrow down the uncertainties on future climate projections, analyses of the cloud forcing which include the short- and long-wave radiation and the surface mass balance (SMB) may provide substantial information on the cause of the discrepancies as simulated by climate models over the Antarctic region.

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