[A-AS09] Stratosphere-troposphere Processes And their Role in Climate

[AAS09-04] Sea-land-breeze gravity waves robustizing equatorial stratospheric QBO: 1. JRA-55 data analysis

Shin-Ya Ogino¹, *Manabu D. Yamanaka^2,3,1 (1.Japan Agency for Marine-Earth Science and Technology, 2.Research Institute for Humanity and Nature, 3.Professor Emeritus of Kobe University)

Keywords:quasi-biennial oscillation, diurnal-cycle sea-land breeze circulation, JRA-55

The quasi-biennial oscillation (QBO) appearing robustly in the equatorial stratosphere has been explained by the wave-mean flow interaction, but requested bidirectional (east/westward propagating) waves generated in the troposphere have never been ascertained. Here we show from objective re-analysis data (JRA-55) that the sea-land breeze circulations (SLBCs) are the bidirectional (land/seaward) waves maintaining QBO. The pressure coordinate and velocity data are converted to quasi-vertical (log-pressure) ones, and zonal and vertical wind deviations from each diurnal means are regarded as diurnal wave components, based on comparisons with some radiosonde data over IMC. The global diurnal tides, which make ocean-side variations much weaker than land-side ones, are omitted by a longitudinally 30°-high passed filter. We obtain that the zonal momentum associated with components propagating in the same direction as the stratospheric mean flow is selectively absorbed to produce directly about 30% of the mean zonal acceleration of QBO.