The vertical connection of the quasi-biennial oscillation- modulated 11 year solar cycle signature in geopotential height and planetary waves during Northern Hemisphere early winter

We analyzed observational geopotential height data to provide some new insights on the 11 year solar cycle signal in the Northern Hemisphere early winter and its modulation by the quasi-biennial oscillation (QBO). The signals are strongest in the upper stratosphere. When the QBO is in its easterly phase (QBOe), it appears to move gradually eastward and poleward, resulting in a predominantly positive signal over the pole, with a weaker vertically connected negative signal over the Icelandic Low. When the QBO is in its westerly phase (QBOw), the polar stratospheric signal is mainly negative and appears connected to a negative anomaly in the troposphere over the Aleutian Low. A spectral analysis of the stratospheric response in planetary waves showed a reduction of wave number 2 power under QBOe and an enhancement of wave number 3 under QBOw. These responses are characterized by an overall increase/decrease in wave activity at middle to high latitudes rather than a latitudinal shift of wave activity. There is no clear stratosphere-troposphere connection under QBOe, but under QBOw, there is a vertically coherent increase in wave power at wave numbers 1–3 with a period of 5.6–6.9 days. We suggest that the differences in response under QBOe and QBOw can be explained through differences in initial vortex strength, resulting in either a stronger influence from the low-latitude upper stratosphere (QBOe) or from the troposphere (QBOw) on the polar stratosphere.