[A-AS05] Stratosphere-troposphere Processes And their Role in Climate

[AAS05-13] Downward Propagation of Planetary Wave Packets from the Stratosphere to the Troposphere During Northern Hemisphere Winter

*Matsuyama Yuya¹, Toshihiko Hirooka² (1.Department of Earth and Planetary Sciences, Graduate School of Science, Kyushu University, 2.Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University)

Keywords:planetary wave packet, downward propagation, wave activity flux

Downward propagation of planetary wave packets from the stratosphere to the troposphere is often observed during Northern Hemisphere winter and their influence on the tropospheric circulation has been also reported by various authors. Recent observational studies show that the downward propagation into the troposphere frequently occurs over the North America centered around 90W. Hence, we investigate the frequency distribution of downward propagation events of planetary wave packets and its relationship to the background field using the Japanese 55-year Reanalysis (JRA-55) data. We calculate Plumb’s (1985) wave activity flux (WAF) and extract the downward propagation events over the analysis period (1958-2016) based on a specified criterion value for the vertical component of WAF at 30 hPa. Next, we investigate the longitudinal location of each downward propagation event and classify it into eight sectors of 45 degrees along the longitudinal circle to make a composite analysis of the classified events. Resultantly, around 500 events are extracted during the analysis period and it is found that about more than 80% of the events occurred in three sectors between 135W to 0E; these events are shown to be intimately related to the development of the Aleutian High in the stratosphere, which is located in the west of the downward propagation region. As for the other events, a developed anticyclone was also observed in the west of each downward propagation region.