5.11 THE FORECASTING OF HAZARDOUS WEATHER

CONDITIONS IN UKRAINE CAUSED BY SOUTHERN CYCLONES

Geyko Ludmila

State Hydrometeorological Service, Kiev, Ukraine

Savchenko Ludmila

Ukrainian Hydrometeorological Center, Kiev, Ukraine

Introduction

The weather conditions of the Ukrainian territory have been depended on many circulation processes over the Europe and Asia. The geographical position of the country and atmospheric processes has caused a great variability of climatic conditions and sufficiently great frequency of hazardous weather phenomena. Some times these phenomena (heavy rainfall, snowdrift, strong winds, etc.) become as catastrophe and have produced serious damage.

Hazardous weather phenomena

As a rule the hazardous weather phenomena in Ukraine are conditioned by movement of southern or southwestern cyclones on its territory. So every fourth case of the hazardous weather phenomenon and every second case of the storm wind call forth by Mediterranean cyclones. It was established that the majority of cyclones over the Ukrainian territory are the southern or Mediterranean cyclones (49.1% from general number of cyclones over Ukraine). The frequency of these cyclones (%) is almost identical for cold and warm periods of year.

(frequency)

Period Trajectory

from South-West

from South

from the Black Sea

April-September

11.4% 11.1% 0.8%

October-March

12.9% 11.9% 1.1%

Cyclones trajectory

The scheme of high field in the beginning

of cyclone development when

meridional flow over the Europe

The scheme of high baric field at the

beginning of cyclone development when

latitudinal reconstruction of high field deformation take place over the Europe

Factors for successful forecast of Mediterranean cyclone entrance

It is necessary to take into consideration the following factors for successful forecast of Mediterranean cyclone entrance to the Ukrainian territory. Southwestern cyclones arise on the southern periphery of the upper-level cold trough situated over the Mediterranean Sea, than these cyclones move under southeastern part of the trough.

At the first phase the cyclone is the faint wave on the polar front over the southern coasts of Europe. The main factors of the cyclones' evolution are the state and location of the upper-level trough and the penetration of the cold to the south at the rear of trough. As a rule the second cyclone moves after the first often along the same trajectory. Sometime the third cyclone appears turned round the trough on the its southern and southeastern periphery.

Main types of synoptic situations of Mediterranean cyclones

It is possible to distinguish five main types of synoptic situations of Mediterranean cyclones movement to Ukraine that depend on upper-level trough location:- across the Danube mouth to the north;- across the Carpathians to the north;- across Aegean Sea and straits to the north-east;- across Ionic and Aegean Seas, Turkey to the east of the Black Sea;- stationary of cyclone over the eastern part of the Black Sea on the southwestern periphery of the blocking continental anticyclone.

Cold invasion

The intensity of the cold invasion to the cyclone rear, the spreads of cold to its southern periphery determine the degree of distortion and bend of cyclone trajectory to the north or north-east. The geographical positions of the cold advection area, the trajectory turning point and the active warmth curries out have determined the future evolution of cyclones. It is possible to note the typical cases.

Typical cases

The Balkan cyclone entries to the Danube mouth when the cold flows to the north of Adriatic Sea and the Adriatic bora have begun. If the cyclone move over the Ionic Sea then it pass over the Bosphor and get out to the Black Sea.

The cyclone trajectory is like this when the cold flows across the Danube valley.

Cyclone going out to the Black Sea abruptly rise to the North when at the same time the cold flows along the Dnister valley (at the eastern side of Carpathians) and warm flow in front of cyclone to the eastern part of Ukraine. The form and structure of the cold area over the Europe characterize the intensity of cold flow.

Groups of Mediterranean cyclones

It is possible to distinguish three groups of Mediterranean cyclones when the Carpathians exert influence on the evolution of the baric field.

I. The cyclones moving from the Hungary lowland across northern part of Carpathians to the Poland, Byelorussia and north of Russia.

II. The cyclones moving across the central part of Carpathians on the Ukrainian territory and then on the European part of Russia. The centers of these cyclones pass across Ukraine.

III. The cyclones move from the Low-Danube lowland in northeastern direction.

Sometime the mountain influence on the baric field deformation when the cyclones do not move directly across Carpathians.

The cyclone trajectories over the Ukraine territory

Conclusions

The Mediterranean cyclones are pretty difficult for forecasting. In some case they get the development and move to the Ukrainian territory but in the other case they end the existence and stay nearly on the same place when the thermodynamic conditions are the identical. Therefore it is very necessary to make careful analysis every case of these cyclones and to elaborate the definite recommendations, to bring to light the essential factors that determine of the cyclones' evolution before and after their entrance to Ukrainian territory. The above mention recommendations can promote to increase the accuracy of cyclone warning and weather advisory in Ukraine.