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 50hPa levels, the quasi geostrophic potential vorticity, the quasi geostrophic potential vorticity gradient ,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 in the westerly and easterly phase of quasi biennial Oscillation, were calculated and analyzed. The mechanism of Rossby wave breaking during five days before to five days after the wave break were analyzed. The Results show that in the anticyclonic breaking event over west Asia in the QBOe, the poleward displacement of jet in the upstream of trough to upper latitude over the Europe is more consistent than for the QBOw. Whereas in the cyclonic break in the westerly phase, jet on the upstream of trough over the west of Mediterranean sea displace to lower latitude over the Europe more than that pf the easterly phase. Therefore in the anticyclonic wave breaking over the west Asia in the QBOe compared that of to QBOw, the amplitude of the waves increase. The QBOe in the anticyclonic breaking causes increasing altitude on the upstream trough over the Europe and decreasing altitude on the downstream trough over the east Europe and Mediterranean and also causes increasing altitude over the east of Atlantic ocean. In the cyclonic breaking, QBOe causes increasing altitude on upstream of trough over the west of Mediterranean and decreasing altitude on the downstream of trough over the east of Mediterranean region.
In the anticyclonic wave breaking on the west Asia and east Mediterranean in the QBOe, anomaly jets velocity and following the formation of critical latitude on north Europe is stronger than the critical latitude in the QBOw. The QBOe causes poleward displacement the jets and critical latitude as compared to that of the QBOw. In the anticyclonic wave breaking over west Asia, formation of extended ridge over Atlantic ocean and Europe causes settlement of the narrow trough on the west Asia. In the QBOe, the jet intensifies over north of Europe and critical latitude on the upstream of trough form stronger, QBOw. Equatorward wave activity flux due to anticyclonic breaking in the QBOe is more than that of the QBOw. Therefore the anticyclonic wave breaking in QBOe is stronger than QBOw.
In the cyclonic waves breaking, jets on the upstream of trough over Europe and jet on the downstream of trough over east Mediterranean are formed across north westerly- south easterly. In the QBOe, jet on the upstream of trough intensifies on the upper latitude as compared to the QBOw. Following this the critical latitude have poleward displacement. In the QBOe, north westerly-south easterly slope of trough is more than QBOw and the trough on the Mediterranean and east Europe has lower altitude compared to that for the QBOw. The poleward wave activity flux due to cyclonic wave breaking is more in QBOe compared to that for the QBOw. Therefore the cyclonic wave breaking is stronger in QBOe compared to that for the QBOw.
Whereas in the anticyclonic wave breaking over west Mediterranean in the QBOw compared to that for the QBOe and the meridional gradient of quasi geostrophic potential vorticity is stronger and meridional wave activity flux is more. Therefore the anticyclonic wave breaking over west Mediterranean in the QBOw is stronger compared to that for the QBOe.