Articles | Volume 16, issue 8
Research article
20 Apr 2016
Research article |  | 20 Apr 2016

Influence of the sudden stratospheric warming on quasi-2-day waves

Sheng-Yang Gu, Han-Li Liu, Xiankang Dou, and Tao Li

Abstract. The influence of the sudden stratospheric warming (SSW) on a quasi-2-day wave (QTDW) with westward zonal wave number 3 (W3) is investigated using the Thermosphere–Ionosphere–Mesosphere Electrodynamics General Circulation Model (TIME-GCM). The summer easterly jet below 90 km is strengthened during an SSW, which results in a larger refractive index and thus more favorable conditions for the propagation of W3. In the winter hemisphere, the Eliassen–Palm (EP) flux diagnostics indicate that the strong instabilities at middle and high latitudes in the mesopause region are important for the amplification of W3, which is weakened during SSW periods due to the deceleration or even reversal of the winter westerly winds. Nonlinear interactions between the W3 and the wave number 1 stationary planetary wave produce QTDW with westward zonal wave number 2 (W2). The meridional wind perturbations of the W2 peak in the equatorial region, while the zonal wind and temperature components maximize at middle latitudes. The EP flux diagnostics indicate that the W2 is capable of propagating upward in both winter and summer hemispheres, whereas the propagation of W3 is mostly confined to the summer hemisphere. This characteristic is likely due to the fact that the phase speed of W2 is larger, and therefore its waveguide has a broader latitudinal extension. The larger phase speed also makes W2 less vulnerable to dissipation and critical layer filtering by the background wind when propagating upward.

Short summary
The influences of sudden stratospheric warming in the Northern Hemisphere on quasi-2-day waves are studied with both observations and simulations. We found the energy of W3 is transferred to W2 through the nonlinear interaction with SPW1 and the instability at winter mesopause could provide additional amplification for W3. The summer easterly is enhanced during SSW, which is more favorable for the propagation of quasi-2-day waves.
Final-revised paper