M14 Middle Atmosphere Science

IAMAS (Meteorology)



27-Jun-2015, 16:30 - 18:00


 
Abstract content:

Combined influences of westerly phase of the QBO and 11-year solar maximum on theNorthern Hemisphere extratropical winter circulation

The combined influences of westerly phase of the quasi-biennial oscillation (QBO-W) and 11-year solar maximum (Smax) on the Northern Hemisphere (NH) extratropical winter circulation are investigated using reanalysis data and Chemistry Climate Model (CCM) simulations. The polar vortex was strong in December during QBO-W and Smax conditions. In December, the dynamical processes of planetary wave propagation and meridional circulation induced by QBO-W conditions around the polar vortex are similar in character to those induced by Smax conditions, and both processes may work in concert to strengthen the polar vortex during QBO-W and Smax conditions. The strengthened polar vortex in December during QBO-W and Smax was occurred simultaneously with the development of a north-south dipole tropospheric circulation anomaly in the Atlantic sector similar to the North Atlantic Oscillation (NAO), which lasted from December to January. The structure of the north-south dipole anomaly has a zonal wavenumber 1 (WN1) component, where the longitude of the anomalous ridge overlaps with that of the climatological ridge in the North Atlantic in January. This implies the amplification of the WN1 wave and results in the enhancement of upward WN1 propagation from the troposphere into the stratosphere in January, leading to the weakened polar vortex in February–March. These results may provide a possible explanation for the mechanisms underlying the complex seasonal evolution of NH wintertime polar vortex anomalies during QBO-W and Smax conditions and the role of the troposphere in this evolution.

 
Author(s):
Y. Yamashita1, H. Akiyoshi1, T. Shepherd2, M. Takahashi3.
1National Institute for Environmental Studies, Center for Global Environmental Research, Tsukuba, Japan.
2University of Reading, Department of Meteorology, Reading, United Kingdom.
3University of Tokyo, Atmosphere and Ocean Research Institute, Kashiwa, Japan.

 

Keywords:
quasi-biennial oscillation (QBO)     11-year solar cycle     North Atlantic Oscillation (NAO)