The relationship between transient wave interference, tropical convection, the stratosphere, and Arctic warming

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Wednesday, 7 January 2015
Michael Goss, Pennsylvania State University, University Park, PA; and S. B. Feldstein

A "stationary wave index" (SWI) daily timeseries is developed by projecting the daily 300-hPa stream function anomalies onto the climatological stationary wave pattern over the Northern Hemisphere. This index is used to analyze relationships between transient interference with the stationary wave pattern, tropical convection, the stratosphere, and Arctic warming, both in the context of an idealized dynamical model, and in ERA-Interim reanalysis data.

In the observations, it is found that, prior to positive (negative) SWI events, Madden-Julian Oscillation (MJO) phase 5 (1) -like convection is present over the tropics. Furthermore, it is found that in the two weeks prior to positive (negative) SWI events, the stratospheric polar vortex edge tends to become more (less) meridionally amplified with (without) wave breaking. Finally, we show that during and after a positive (negative) SWI event, the Arctic surface air temperatures tend to warm (cool). Physically, we interpret the evolution of a positive SWI event as follows (opposite features are observed for negative SWI events). First, enhanced localized tropical convection over the western tropical Pacific and Maritime Continent weakens the subtropical jet in the western Pacific. This is followed by the growth of eddies (of all wavenumbers) in the midlatitudes,. These enhanced eddies constructively interfere with the climatological stationary wave pattern to result in a "positive SWI event," and the changes in the stratosphere and the Arctic. These reults provide further support for the TEAM mechanism of Lee et al. (2011). The sensitivity of the relationship between tropical convection and Arctic warming to the state of the stratosphere is examined with the dynamical model.