Authors: Nedostrelova L.V.
Blocking as a large-scale steady atmospheric process is a main reason of weather anomalies existing at weekly and seasonal time scales. It is very interesting to study these processes in view of medium and long-term weather forecasts, atmospheric processes modelling and climate monitoring. There are presently a large number of papers considering climatic features of atmospheric blocking. However the methodological differences in methods of blocking processes detection, the lack of common methods, and differences in the length of studied periods make difficulties for a climatic generalization of blockings. This article aims, on the one part, to review the existing methods suitable for the recognition of blocking processes and, on the other part, to offer an approach which uses the dynamic nature of blocking as basis. According to Tyrlis and Hoskins (2007), the basic characteristic of blocking is considered to be potentially warmer air being found at higher latitudes, i.e. the usual situation is reversal. Also, the spatial scales and duration of real blocking are larger than those for usual synoptic processes; these characteristics can be considered as additional. As a result, an inter-pretation of the basic blocking requirement is that large-scale wave breaking at the tropopause level is occurring. If consider the evolution of Rossby waves as a usual situation for the formation of blocking anticyclone in the troposphere, the 500-hpa geopotential height map can show that a horizontal axis of the baric ridge is oriented from southern west to northern east in the case of anticyclonic wind shear and from southern east to northern west in the case of cyclonic one. Both these configurations allow the atmospheric blocking by using different approaches to the calculation of blocking indices. The proposed approach was used to study and classify atmospheric blockings in Europe during the period from 1998 to 2008.
Tags: blocking anticyclone; classification of blocking processes; dynamic approach
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