Influence of Arctic Oscillation towards the Northern Hemisphere Surface Temperature Variability under the Global Warming Scenario

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Future projection of the Arctic Oscillation (AO) signature and its significance towards the northern hemispheric surface temperature trend have been examined using 20 state-of-the-art Atmosphere-Ocean General Circulation Model (AOGCM) outputs forced under the IPCC SRES-A1B and 20C3M emission scenario. Models are mostly successful in simulating the observed AO structure and the corresponding surface temperature variability. It is found that while AO exhibits a large positive trend, especially during the autumn season with a relatively smaller trend during the winter and spring seasons. In all seasons the interannual variance in AO remains the same for both scenarios. These features in the timeseries leads to two distinct patterns of temperature variability. One is the "polar amplification" pattern due to the long-term anthropogenic forcing, which is much larger in its amplitude. Another is related to the natural variability of the AO, which is confined over the land surface and is marked by a dipole pattern of temperature between the Eurasian continent and Greenland. It is argued that the gradual trend in the AO is not a result of enhanced natural variability of the AO dynamics itself, but rather a result of the large anthropogenic forced linear trend projected onto the mean climatological state of the Arctic region. Distinguishing these two patterns of warming is crucial for detecting the signal of future global warming trend over the Eurasian continent and other regions.

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