عنوان مقاله [English]
In the present study, using the ERA-INTERIM reanalysis data for geopotential height, horizontal wind speed and relative vorticity at 300, 200, 150, 100 and 50- hPa levels, the wave activity and wave activity flux for cyclonic and anticyclonic Rossby wave breaking events that occurred over Europe during the winter time 1979-2018, were calculated and analyzed. Results showed that in anticyclonic (cyclonic) wave breaking evnts, a narrow (wide) trough with north-east/south-west (north-west/south-east) axis and associated potential vorticity with values around 5-8 (4-6) 1e6PVU are extended from Europe to the west (east) of Mediterranean.
In the anticyclonic wave breaking evnts, the wave amplitude and their associated potential voriticity are higher compared to cyclonic events and also the associated jet streams form in higher latitudes over Europe and the Mediterranean. It appears that intensification of the trough and its extention to lower latitudes over the Mediterranean is associated with intensification of the ridge over northwest of Europe. While in cyclonic wave beaking events the insification of the trough over the east of Europe is associated with intensification of the ridge in lower latitudes over the west of the Mediterranean. The waves in anticyclonic wave beaaking evsnts move to lower latitudes over the Mediterranean, while in cyclonic wave beakings the waves move to north of Europe.
Therfore, the anticyclonic (cyclonic) wave breaking evnts, are generally associated with equatorward (poleward) flux of wave activity, downstream of the trough in latittudes lower (higher) than 40N, which causes the intensification (weakening) of synoptic waves over the Mediterranean and west of Asia.
Also, the value of equiatorward wave activity is 1.5 times compared to those of poleward fluxes. It was also found that, in anticyclonic wave breakings the downward wave activity flux is around twice, when compared to cyclonic wave breaking events.
Our esults showed that During anticyclonic wave breaking, the equitaorward of wave activity flux at 40N over west of Europe is larger than its value over the East Mediterranean and west of Asia. While during cyclonic wave breaking events the poleward flux of wave activity over west of Europe is negligible and even over east of Europe and west of Asia becomes equitorward. It seems that the reason is due to the existence of a ridge over Euroasia which results to the formation of a blocking over east of Europe and consequentlt causes the intensification of throughs in lower latitudes. As such, in addition to the lesser number of cyclonic wave breakings compared to those of anticyclonics, the cyclonic wave breaking events are relatively weaker than anticyclonic breakings over Europe.