5.11 THE FORECASTING OFHAZARDOUS WEATHERCONDITIONS IN UKRAINE CAUSEDBY SOUTHERN CYCLONES
Geyko Ludmila
State Hydrometeorological Service,Kiev, Ukraine
Savchenko Ludmila
Ukrainian HydrometeorologicalCenter, Kiev, Ukraine
Introduction
The weather conditions of the Ukrainianterritory have been depended on manycirculation processes over the Europeand Asia. The geographical position ofthe country and atmospheric processeshas caused a great variability of climaticconditions and sufficiently greatfrequency of hazardous weatherphenomena. Some times thesephenomena (heavy rainfall, snowdrift,strong winds, etc.) become ascatastrophe and have produced seriousdamage.
Hazardous weatherphenomena
As a rule the hazardous weather phenomena inUkraine are conditioned by movement of southernor southwestern cyclones on its territory. Soevery fourth case of the hazardous weatherphenomenon and every second case of the stormwind call forth by Mediterranean cyclones. It wasestablished that the majority of cyclones over theUkrainian territory are the southern orMediterranean cyclones (49.1% from generalnumber of cyclones over Ukraine). The frequencyof these cyclones (%) is almost identical for coldand warm periods of year.
(frequency)
Cyclones trajectory
The scheme of highfield in the beginningof cyclonedevelopment whenmeridional flow overthe Europe
The scheme of highbaric field at thebeginning of cyclonedevelopment whenlatitudinalreconstruction of highfield deformation takeplace over the Europe
Factors for successful forecast ofMediterranean cyclone entrance
It is necessary to take into consideration the followingfactors for successful forecast of Mediterranean cycloneentrance to the Ukrainian territory. Southwesterncyclones arise on the southern periphery of the upper-level cold trough situated over the Mediterranean Sea,than these cyclones move under southeastern part ofthe trough.
At the first phase the cyclone is the faint wave on thepolar front over the southern coasts of Europe. Themain factors of the cyclones' evolution are the stateand location of the upper-level trough and thepenetration of the cold to the south at the rear oftrough. As a rule the second cyclone moves after thefirst often along the same trajectory. Sometime thethird cyclone appears turned round the trough on theits southern and southeastern periphery.
Main types of synoptic situations ofMediterranean cyclones
It is possible to distinguish five main types of synopticsituations of Mediterranean cyclones movement toUkraine 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 ofthe Black Sea;- stationary of cyclone over the eastern part of theBlack Sea on the southwestern periphery of theblocking continental anticyclone.
Cold invasion
The intensity of the cold invasion to the cyclone rear, thespreads of cold to its southern periphery determine thedegree of distortion and bend of cyclone trajectory tothe north or north-east. The geographical positions ofthe cold advection area, the trajectory turning pointand the active warmth curries out have determined thefuture evolution of cyclones. It is possible to note thetypical cases.
Typical cases
The Balkan cyclone entries to the Danube mouth whenthe cold flows to the north of Adriatic Sea and theAdriatic bora have begun. If the cyclone move over theIonic Sea then it pass over the Bosphor and get out tothe Black Sea.
The cyclone trajectory is like this when the cold flowsacross the Danube valley.
Cyclone going out to the Black Sea abruptly rise to theNorth when at the same time the cold flows along theDnister valley (at the eastern side of Carpathians) andwarm flow in front of cyclone to the eastern part ofUkraine. The form and structure of the cold area overthe Europe characterize the intensity of cold flow.
Groups of Mediterraneancyclones
It is possible to distinguish three groups of Mediterraneancyclones when the Carpathians exert influence on theevolution of the baric field.
I. The cyclones moving from the Hungary lowland acrossnorthern part of Carpathians to the Poland, Byelorussiaand north of Russia.
II. The cyclones moving across the central part ofCarpathians on the Ukrainian territory and then on theEuropean part of Russia. The centers of these cyclonespass across Ukraine.
III. The cyclones move from the Low-Danube lowland innortheastern direction.
Sometime the mountain influence on the baric fielddeformation when the cyclones do not move directlyacross Carpathians.
The cyclone trajectories over the Ukraine territory
Conclusions
The Mediterranean cyclones are pretty difficult forforecasting. In some case they get the developmentand move to the Ukrainian territory but in the othercase they end the existence and stay nearly on thesame place when the thermodynamic conditions arethe identical. Therefore it is very necessary to makecareful analysis every case of these cyclones and toelaborate the definite recommendations, to bring tolight the essential factors that determine of thecyclones' evolution before and after their entrance toUkrainian territory. The above mentionrecommendations can promote to increase theaccuracy of cyclone warning and weather advisory inUkraine.