Description of possible causes of the formation of anomalies of the cloud field over the Atlantic-European sector in the spring of 1996

Abstract

--We describe one of possible mechanisms of the formation of anomalies of the cloud field over the North Atlantic and Europe by using, as an example, the processes developed in the Atlantic-European sector during the natural synoptic season in the spring of 1996. It is shown that the anomalies of the cloud field can be classified with the use of the index of the North Atlantic oscillation and the latitude of the center of the Azorean maximum.In recent years, the economic activities in Europe seriously suffer from the detrimental effect of highly anomalous atmospheric processes [1,2]. Thus, according to the data of the agricultural authorities, a terrible drought recorded in the Crimea in 1996 had no precedents for the last 30 years. It is clear that weather anomalies of this sort require both adequate explanation and thorough analysis of the possibility of their prediction. There are numerous works devoted to the investigation of longrange correlations between the processes of anomalous heating in the tropical zone and anomalies in the atmospheric circulation at middle latitudes [3,4]. As shown in these works, the atmospheric circulation over the North Atlantic and Europe is affected by the thermal processes in the regions of atmospheric convergence over the tropical part of the Pacific Ocean and in the equatorial part of South America. These regions of negative anomalies of the outgoing long-wave radiation are well known as the "key" regions of "initial" fluctuations in the tropical zones of the Earth [5,6]. In this connection, we consider two "key" regions whose influence on the formation of the mode of circulation over the North Atlantic and Europe is decisive as shown by the recent investigations. The first of these regions is located over Southeast Asia (Indonesia and the Philippines) and the second region is located over South America to the south of the equator. In the sky maps of the world, these regions are marked as zones of elevated cloudiness. In view of the fact that strong divergence in the upper equatorial troposphere over the indicated regions promotes the intense process of convection, we conclude that the indicated "key" regions feed the Pacific and Atlantic upper tropospheric branches of the Hedleycirculation [6]. The results of last investigations of the correlations between tropical and nontropical latitudes of the Earth reveal the existence of chains of links between the "key" regions and certain regions in the North Atlantic and Europe [3][4][5]. These chains of links were discovered in the field of outgoing long-wave radiation. However, the geographic location " Translated by Peter V. Malyshev and Dmitry V. Malyshev IIDC 551.465.7.511.6