2007年3月に生じた成層圏惑星規模波下方伝播イベントの力学と予測可能性 --上部成層圏循環の安定性解析--

Abstract

Dynamics of quasi-stationary precursory signal in the upper stratosphere related to adownward propagating event of stratospheric planetary waves observed in early March2007 is examined using a non-divergent barotropic model. It is found that obtainedunstable modes for basic states comprised of zonally varying 5-hPa streamfunction fieldof an ensemble mean forecast attain local maximum in growth rate with an e-foldingtime of about 1.3 days and become stationary prior to the downward propagating event.Moreover, the fastest growing modes have predominant planetary-scale structure similarto the precursory signal. Hence, it is suggested that the barotropic instability inherent tothe distorted polar vortex in the upper stratosphere determines whether planetary wavesincoming from the troposphere are eventually absorbed in the stratosphere or emitted downward into the troposphere.