Quasi-two-day wave amplification through interhemispheric coupling during the 2010 austral summer

Abstract

A quasi-two-day wave (QTDW) event during January-February 2010 is investigated using the MERRA-2 reanalysis dataset. MERRA-2 data reveals the growth of the QTDW westward propagating wavenumber 3 preceded by a weak westward wavenumber 4. The diagnostic analysis suggests that the QTDW growth near tropical stratopause is mainly supported by barotropic (BT) instability in the presence of the summer easterly jet. BT instability during this event is suggested to be linked to the planetary wave breaking (PWB) in the winter hemisphere. The connecting link between the two appears to be the inertial instability (II) supported by the cross-equatorial transport of potential vorticity in association with PWB in the winter hemisphere which is consistent with the previous studies. Signatures of II are evident from the MERRA-2 temperature and wind anomalies in the vicinity of cross-equatorial transport of potential vorticity. One important observation brought out in this study is that the strength of meridional wind anomalies in the regions of the II appears to control the meridional curvature of the zonal mean zonal wind and, hence, BT instability of the jet. Overall, the temporal evolution of the QTDW at tropical stratopause during this event is consistent with the episodes of PWB, strength of meridional wind anomalies around the II and meridional curvature of zonal mean zonal wind. The latitude-altitude growth of the QTDW W3 in the zonal wind conforms to the location of critical layers and region of negative meridional gradient of potential vorticity.