E. K. Semenov

Vertical circulation in the tropical atmosphere during extreme El Niño-Southern Oscillation events

Scenarios for the development of large-scale vertical circulation anomalies during warm and cold phases of El Niño-Southern Oscillation are generalized based on the NCEP/NCAR reanalysis data for 1958-1998. Composite models of the cells of vertical circulation in the monsoon and trade-wind regions of the tropical Pacific are obtained for the first time for El Niño and La Niña separately. An unprecedented shift of the ascending branch of the zonal Walker circulation from the “maritime continent” of Indonesia to the east, to the central and eastern Pacific, was observed during the warm phase over the tropical Pacific; this shift was accompanied by an abrupt increase in the tropical cyclogenesis activity in the southern Pacific zone of convergence. On the contrary, during the cold phase, the ascending motions in the region of the summer Australian monsoon are subject to abrupt intensification. The reconstruction of the vertical meridional circulation during the warm phase manifested itself in the almost complete disappearance of the Hadley classic circulation over the central Pacific, characteristic of the trade-wind intertropical convergence zone (ITCZ), and in its replacement by the latitudinal monsoon circulation typical of the ITCZ over the Indian Ocean. During a cold phase, the Hadley circulation is both restored and intensified.

Synoptic conditions of the formation of a catastrophic flood on the Amur River in 2013

Considered are the synoptic mechanisms of the catastrophic flood formation on the Amur River in summer 2013; these enabled revealing the set of reasons responsible for the unprecedented rise of the water level. Demonstrated is the primary importance of the series of polar-front cyclones of the unprecedented duration and intensity being the main circulation link of the summer Far Eastern monsoon. It is revealed that the intensification of monsoon rains is associated with the active participation of the marine tropical air from the Pacific Ocean in frontal processes. The simultaneous deepening of the monsoon low over the land and the strengthening of the subtropical high over the ocean became a reason for the dramatic intensification of the moisture-laden monsoon flow.

On the problem of subtropical anticyclone regeneration as a factor of its stabilization (Case study for the summer of 2010)

The detailed investigation of conditions of the durational stabilization of subtropical anticyclone in the unusual region of the temperate zone is carried out and the reasons for its multiple regeneration are revealed. Separated are five periods of the subtropical anticyclone regeneration associated with the entering of active and relatively anticyclones of middle and high latitudes developed at the rear of cyclonic series into its circulation. All invasions were divided into three types depending on the trajectories of the movement of active anticyclones: the polar invasion from the north and northwest, the ultrapolar invasion from the east and northeast, and the western invasion from the Atlantic Ocean and Baltic Sea. The instability index introduced by V.P. Dymnikov was used for the quantitative estimation of the blocking process lifetime. It is demonstrated that this index is informative enough and could be used for the lifetime forecast of concrete quasistationary regimes of atmospheric circulation.

Monsoon circulation over the Amur River basin during catastrophic flood and extreme drought in summer

Two opposite Far East monsoon summer seasons over the Amur River basin are investigated which caused the extreme drought and fires in 2008 and catastrophic flood in 2013. It is shown that in the low-water summer of 2008 due to blocking processes, polar-front cyclones were almost absent over the Amur, were short, had fuzzy frontal systems, and did not bring precipitation. The summer monsoon circulation was suppressed, and in the Amur region continental air masses dominated over marine tropical air. On the contrary, the summer of 2013 was characterized by unprecedented cyclonic activity and the sharp strengthening ofthe moisture-laden monsoon flow from the ocean. As a result, the intensification of summer monsoon precipitation and the Amur flood were observed. It was established that the Far East summer monsoon anomalies are associated with the large-scale transformation of atmospheric circulation over the Asia-Pacific region.

Synoptic mechanisms of winter warming in the Arctic

Considered is the case of abnormally warm weather in the western sector of the Russian Arctic in winter 2011/12. The synoptic analysis is carried out using the daily data of macro-scale reconstruction of atmospheric circulation that resulted in the intensive advection of warm air to the Arctic basin and large-scale anomalies of air temperature. As a result, the area of the ice cover of the Barents and Kara seas was the least ever observed over the history of routine remote observations.

Meteorological and synoptic aspects of the formation and evolution of the Novorossiysk Bora

The genetic and synoptic classifications of the Novorossiysk Bora are created using the data of daily observations at the Novorossiysk meteorological station and other available synoptic information. Obtained are the quantitative criteria of these classifications, and on this base worked out are the basic scenarios of the generation and evolution of this dangerous phenomenon on the Black Sea coast of Russia. According to the genetic classification, the Bora was divided into four types: frontal, air-mass, monsoon, and gravity. Quantitative criteria worked out for each type can be used for the more accurate forecast of this destructive phenomenon near Novorossiysk. According to the synoptic classification, four classes were distinguished: Azores, North Atlantic, Siberian, and Arctic.

The warm winter in the Russian Arctic and anomalous cold in Europe

Considered are synoptic mechanisms of the formation of abnormally warm weather and high anticyclones in the Russian Arctic as well as the generation of the series of cold cyclones in the middle troposphere over southern Europe in January–February 2012. Obtained are the typical schemes of thermobaric fields of the macro-scale reconstruction of atmospheric circulation and of the set-in of the eastern air transport from Siberia to the central and southern areas of the European part of Russia and to the Mediterranean countries. Proposed is an algorithm for predicting processes of atmospheric blocking with the help of quantitative criteria that enable to assess the existence, intensity, and lifetime of the circulation impeding the westerlies.

The use of integrated circulation index for the description of synoptic situations in the Pacific Ocean tropics during El Niño-Southern Oscillation extreme events

The potential of Petrosyants-Gushchina integrated circulation index in respect to the problem of synoptic analysis in low latitudes is considered. The compositional models of synoptic situations, which led to the formation of extreme conditions in weather and climate over the Pacific Ocean, are constructed using the computed indices according to the data of NCEP/NCAR reanalysis for 1950–2002 separately for El Niño and La Niña events. It is demonstrated that the barometric circulation pattern of synoptic processes in tropics, being reproduced using indices, indicates the main peculiarities of atmospheric circulation in low latitudes and can be the quantitative indicator of the whole circulation system of El Niño-Southern Oscillation over the Pacific Ocean.

Analyzing the vortex as an integral formation: A case study for the blocking anticyclone of 2010

The peculiarities of blocking conditions and weather anomalies over the East European Plain in the summer of 2010 are considered using the EOF analysis and vorticity equation. The EOF analysis simulates the time series of the anticyclone as a whole using the principal modes of temporal variability. The vorticity equation is transformed into the specific form which enables assessing the contribution of different factors to the development and lasting existence of blocking conditions.

Large-scale moisture exchange in the tropical atmosphere during the extreme El Niño-Southern oscillation events

The generalization of scenarios of the development of large-scale moisture exchange is carried out separately for the warm and cold phases of the El Niño-Southern Oscillation (ENSO) event using the NCEP/NCAR and GPCP reanalysis data. Obtained are the composition models of the integral water vapor transport for the monsoon and trade-wind regions of the Pacific and Indian oceans. It is demonstrated that the monsoon circulation is suppressed during the El Niño and is replaced by the trade wind in the Indian Ocean and the trade wind is suppressed and replaced by the monsoon circulation in the Pacific Ocean. During the La Niña, the opposite picture is observed: the monsoon circulation intensifies in the Indian Ocean and the trade wind, in the Pacific Ocean. It is revealed that the South Pacific convergence zone is the main object of large-scale moisture exchange during ENSO: it moves unprecedentedly to the east of the Pacific Ocean during the warm phase and maximally approaches the northeast of Australia and Indonesia during the cold phase. The intensification of the convergence zone in the mentioned regions is accompanied by the active tropical cyclogenesis, intensive cloud formation, and heavy rains.