Abstract
Abstract. An interesting occurrence of a Rossby wave breaking event observed during the VORCORE experiment is presented and explained. Twenty-seven balloons were launched inside the Antarctic polar vortex. Almost all of these balloons evolved in the stratosphere around 500K within the vortex, except the one launched on 28 October 2005. In this case, the balloon was caught within a tongue of high potential vorticity (PV), and was ejected from the polar vortex. The evolution of this event is studied for the period between 19 and 25 November 2005. It is found that at the beginning of this period, the polar vortex experienced distortions due to the presence of Rossby waves. Then, these waves break and a tongue of high PV develops. On 25 November, the tongue became separated from the vortex and the balloon was ejected into the surf zone. Lagrangian simulations demonstrate that the air masses surrounding the balloon after its ejection were originating from the vortex edge. The wave breaking and the development of the tongue are confined within a region where a planetary Quasi-Stationary Wave 1 (QSW1) induces wind speeds with weaker values. The QSW1 causes asymmetry in the wind speed and the horizontal PV gradient along the edge of the polar vortex, resulting in a localized jet. Rossby waves with smaller scales propagating on top of this jet amplify as they enter the jet exit region and then break. The role of the QSW1 on the formation of the weak flow conditions that caused the non-linear wave breaking observed near the vortex edge is confirmed by three-dimensional numerical simulations using forcing with and without the contribution of the QSW1.
Highlights
Towards middle latitudes (e.g. Polvani and Plumb, 1992; Waugh and Polvani, 2010)
We present high-resolution simulations using the method of contour advection with surgery (CAS) to demonstrate that air masses enclosing the balloon after its ejection were pulled off the vortex edge
The second objective of this paper is to study the role of the QSW1 and the asymmetry that this wave produces, in both the wind and the horizontal PV gradient, along the vortex edge on the location of the wave breaking event that was observed
Summary
The data used in this study are taken from measurements made during the VORCORE experiment This experiment took place in the Antarctic polar vortex for the period between September 2005 and February 2006. We use data from the National Center for Environmental Prediction (NCEP) Final Analysis (FNL from Global Forecasting System (GFS)) to initialize a threedimensional model that use potential temperature as a vertical coordinate. This model will be presented in Sect. For the purpose of the model, these data are interpolated on 8 isentropic levels ranging from 350 K–700 K
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