Influence of the equatorial QBO on the winter circulation in the Northern Hemisphere (Invited Speaker)

The relation of the tropical stratospheric quasi-biennial oscillation (QBO) to extratropical circulation in both the stratosphere and troposphere has been the subject of numerous observational and modeling studies over the last quarter century. This talk will review some current studies aimed at understanding the possible QBO links with the winter circulation in the extratropical Northern Hemisphere. Four approaches will be briefly reviewed:

(i) Simple analyses of the dependence of the observed extratropical seasonal mean fields on the QBO phase. A comparison will be presented of results with traditional QBO indices (e.g. the raw seasonal-mean 40 hPa near-equatorial zonal wind) and indices based on the height-time wind variations as filtered by a neural-network based nonlinear principal component analysis.

(ii) Analysis of the QBO-extratropical connection in extensive seasonal hindcast runs. These integrations with standard weather forecast models include the QBO only in the initial conditions and are likely to feature tropical stratospheric zonal-mean circulation that relaxes quickly to an unrealistic near-steady state. The improvement in skill that adding a statistical correction based on QBO phase makes to such forecasts will be investigated. This forecast framework may provide a method to help extract the extratropical effects attributable to the QBO from unrelated internal variations in the atmosphere-ocean system.

(iii) Analysis of the QBO-extratropical connection in seasonal hindcast integrations performed with an atmospheric global model with realistic tropical stratospheric wind evolution imposed via an artificial momentum source.

(iv) Analysis of the QBO-extratropical connection in multidecadal integrations of a global model with realistic QBO wind variations imposed in the tropical stratosphere.