発表論文

The combined influences of westerly phase of the Quasi-Biennial Oscillation and 11-year solar maximum conditions on the Northern Hemisphere extratropical winter circulation

著者
Yamashita Y., Akiyoshi H., Shepherd T. G., Takahashi M.
雑誌名
Journal of the Meteorological Society of Japan, 93(6), 629–644
DOI
10.2151/jmsj.2015-054
概要

The combined influences of westerly phase of the QBO (QBO-W) and solar maximum (Smax) conditions on the Northern Hemisphere extratropical winter circulation are investigated using reanalysis data and CCSR/NIES Chemistry Climate Model (CCM) simulations. The composite analysis for the reanalysis data indicates strengthened polar vortex in December followed by weakened polar vortex in February–March for QBO-W during Smax (QBO-W/Smax) conditions. This relationship need not be specific to QBO-W/Smax conditions but may just require strengthened vortex in December, which is more likely under QBO-W/Smax. Both the reanalysis data and CCM simulations suggest that dynamical processes of planetary wave propagation and meridional circulation related to QBO-W around polar vortex in December are similar in character to those related to Smax; furthermore both processes may work in concert to maintain stronger vortex during QBO-W/Smax. In the reanalysis data, the strengthened polar vortex in December is associated with the development of north–south dipole tropospheric anomaly in the Atlantic sector similar to the North Atlantic Oscillation (NAO) during December–January. The structure of the north–south dipole anomaly has zonal wavenumber 1 (WN1) component, where the longitude of anomalous ridge overlaps with that of climatological ridge in the North Atlantic in January. This implies amplification of the WN1 wave and results in the enhancement of upward WN1 propagation from troposphere into stratosphere in January, leading to the weakened polar vortex in February–March. Although WN2 waves do not play a direct role in forcing the stratospheric vortex evolution, their tropospheric response to QBO-W/Smax conditions appears to be related to the maintenance of the NAO-like anomaly in the high-latitude troposphere in January. These results may provide a possible explanation for the mechanisms underlying the seasonal evolution of wintertime polar vortex anomalies during QBO-W/Smax conditions and the role of troposphere in this evolution.

山下陽介「準2年周期振動と太陽11年周期が冬季北半球中高緯度の気候に及ぼす影響〜当該過程に対して対流圏の波の果たす役割の理解〜」地球環境研究センターニュース2016年2・3月号