Changes in atmospheric circulation regimes

Some experts (e.g. Wu et al. 2005) consider Atlantic water warming and ice extent reduction as major causes of recent changes in atmospheric circulation regimes in Northern Eurasia: appearance of long-lived low atmospheric pressure patterns during warm part of year and a high ones - during cold period over Arctic Shelf Seas. Deepest SLP depression was observed over Northern Siberia in September 2005 and October 2006 (Pokrovsky 2006). Low atmospheric pressure anomaly in early autumn led to appearance of a more strong meridian flow and as a consequence to delay in autumn development in Northern Eurasia. Extremes in anomalies of atmospheric pressure field, which spread over vast territory, prevents a normal zonal atmospheric flow across Siberia from west to east and can cause a flow of opposite direction in Eastern and Western Siberia. Inflow of warm and humid air masses from Pacific Ocean and South-East Asia is a main reason of sudden spring warming in Eastern Siberia. Catastrophic flood in Lena river basin, which was occurred in May 2001, is an example of dangerous consequence of circulation regime development related to a negative pressure anomaly. Extreme low and vast SLP anomaly last September-October (2006) caused a huge vortex spread over most part of Northern Asia. A winter of 2005/2006 demonstrated the extreme high atmospheric pressure and height field anomalies in troposphere, which blocked a normal zonal flow in Northern Eurasia and generated intensive cold air outbreaks to Eastern/Southern Europe and to Central Asia. As a result, a winter of 2005/2006 was most severe among others during last 50 years.

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