The Plunger Hypothesis: an overview of a new theory of stratosphere-troposphere dynamic coupling

Abstract:

I will demonstrate the advantages of a new method of quantifying polar stratosphere-troposphere coupling by considering large-scale movements of mass into and out of the polar stratosphere. This project aims to use these mass movements to explain pressure and temperature anomalies throughout the polar troposphere and lower stratosphere in the aftermath of extreme stratospheric events. We hypothesise that these mass movements are induced by deposition of momentum by breaking waves in the stratosphere, slowing the wintertime polar vortex, and so are associated with sudden stratospheric warmings (SSWs). Such a mass movement in the upper stratosphere acts to compress the polar atmosphere below it in the manner of a plunger. In this way the pressure anomaly in the upper polar stratosphere 'controls' the pressure and temperature anomalies below by adiabatic compression of the polar atmospheric column. Better understanding this method of control will allow us to use stratospheric data to improve medium-range forecasting ability in the troposphere.

One of the key innovations featured in this project is considering pressure and temperature fields at fixed geopotential surfaces, allowing for the easy observation of mass movement into and out of a polar cap region (which we have defined as north of 65N) as a function of altitude. Reanalysis data considered in this manner demonstrates a relationship between tropospheric pressure anomalies and stratospheric anomalies in the polar cap, and so a way to predict tropospheric variability given stratospheric information. This work forms part of a three and a half year PhD project.