Title : Rapid Arctic warming and its link to the strength of westerly jet stream over West Asia
Abstract:
Rapid sea-ice loss and warming of the Arctic within the past few decades may have been contributing to changes in the strength and location of midlatitude jet streams. Using ERA-Interim data for the period 1979-2018, warming of the Arctic compared to midlatitudes and its impact on jet stream over West Asia are investigated. Pre- and post-Arctic amplification periods are defined as 1979-1993 and 2004-2018, respectively. It is found that interannual variability of near-surface temperature is much stronger in the Arctic compared to that in lower latitudes, suggesting that climate of the Arctic has been more significantly affected by natural climate forcing. A decrease of near-surface temperature variability in the Arctic is identified in winter, spring and summer in the post-Arctic amplification period when a larger area of open ocean has been exposed to the atmosphere. In both pre- and post-Arctic amplification periods, near-surface temperature variabilities in spring and summer were less than half as much of variability in winter, implying that generally there are more extreme weather events in the Arctic during winter compared to warm seasons. In contrast to the warm-Arctic cold-continent pattern observed in parts of North America and East Asia, West Asia has been warmed in recent decades. In winter of the post-Arctic amplification period, maximum mid-tropospheric meridional wave extent over West Asia is increased by 4.5º and moved to lower heights compared to the pre-Arctic amplification period. Following a decrease in the meridional temperature gradient, jet stream at the upper troposphere over West Asia is reduced in the post-Arctic amplification period in all seasons except autumn. Throughout the troposphere, the least warming trend over West Asia is occurred in autumn, which is contributing to the least decrease in the strength of synoptic eddies over West Asia during the post-Arctic amplification period. As synoptic eddies can influence the strength of the zonal jet by acting as an eddy-driven component of the jet, the strength of the jet stream over West Asia has not changed considerably in autumn during the post-Arctic amplification period.
