Relation Between the Interannual Variability in the Stratospheric Rossby Wave Forcing and Zonal Mean Fields Suggesting an Interhemispheric Link in the Stratosphere

Yuki Matsushita, Daiki Kado, Masashi Kohma, Kaoru Sato
2019 Annales Geophysicae Discussions  
<p><strong>Abstract.</strong> Focusing on the interannual variabilities in the zonal mean fields and Rossby wave forcing in austral winter, an interhemispheric coupling in the stratosphere is examined using reanalysis data: the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2). In the present study, the Eliassen-Palm (EP) flux divergence averaged over the latitude and height regions of 50°&amp;ndash;30°&amp;thinsp;S and 0.3–1&amp;thinsp;hPa, respectively, are
more » ... respectively, are used as a proxy of the Rossby wave forcing, where the absolute value of the EP flux divergence is maximized in the winter in the Southern Hemisphere (SH). The interannual variabilities in the zonal mean temperature and zonal wind are significantly correlated with the SH Rossby wave forcing in the stratosphere in both the SH and Northern Hemisphere (NH). The interannual variability in the strength of the poleward residual mean flow in the SH stratosphere is also correlated with the strength of the wave forcing. This correlation is significant even around the equator at an altitude of 40&amp;thinsp;km and at NH low latitudes of 20&amp;ndash;40&amp;thinsp;km. The temperature anomaly is consistent with this residual mean flow anomaly. The relationship between the cross-equatorial flow and the zonal mean absolute angular momentum gradient (<span style="text-decoration: overline"><i>M</i></span><sub><i>y</i></sub>) is examined in the meridional cross section. The <span style="text-decoration: overline"><i>M</i></span><sub><i>y</i></sub> around the equator at the altitude of 40&amp;thinsp;km is small when the wave forcing is strong, which provides a pathway for the cross-equatorial residual mean flow. These results indicate that an interhemispheric coupling is present in the stratosphere through the meridional circulation modulated by the Rossby wave forcing.</p>
doi:10.5194/angeo-2019-99 fatcat:cvnyb6zb2vfadjwapegjmnxkuy