Current Projects

I am currently investigating the effect ENSO has on the polar vortex. It has long been thought that WENSO results in a weaker polar vortex, and CENSO results in a stronger polar vortex. But a problem many have encountered is that it is difficult to differentiate between these ENSO effects and those of the QBO in observational data, as the QBO also affects the polar vortex. Westerly QBO, like CENSO, forces a stronger vortex, and Easterly QBO, like WENSO, forces a weaker vortex. The paper published in October 2007 in JGR-Atmospheres details how one can separate the two influences. I found that the magnitude of the signal due to the influence of QBO is comparable in magnitude to that of ENSO. A caveat is that ENSO only modulates the vortex under WQBO and no QBO however, not under EQBO. Similarly, QBO more strongly modulates the vortex under CENSO and noENSO than under WENSO.

After that I studied the mechanism(s) through which ENSO might modulate the vortex. The dominant mechanism is an enhancement of wave-1 without too large a drop in wave-2. This occurs when WENSO induces the PNA pattern in the North Pacific. The reason that ENSO doesn't modulate the vortex under EQBO, and the reason that QBO doesn't modulate the vortex as strongly under WENSO, is that the PNA pattern was not excited in WENSO months that were also EQBO months in the observational record. All of this is described in a paper published in September 2008 by JGR-Atmospheres.

Since then, I've studied in a more systematic way the mechanisms through which the troposphere can affect the stratosphere. Both the wave-1 and wave-2 components of the climatological wintertime stationary eddy field of the Northern Hemisphere are low over the North Pacific and high over Eastern Europe. Because of this, a high anomaly over Eastern Europe or a low anomaly over the North Pacific will constructively interfere with the climatological planetary waves and enhance wave driving of the polar vortex. Variability in these two locations are separate pathways through which the troposphere can affect the vortex. The ENSO and October Eurasian snow cover influence on the vortex manifests itself through these pathways. 40% of seasonal vortex variability is associated with these two pathways and the QBO. All of this is described in a paper submitted in December 2008 to Journal of Climate.

Most recently I have investigated why ENSO's teleconnections seem different based on QBO phase. EQBO at 70hPa leads to a weaker teleconnection in the North Pacific than WQBO. Part of this may be due to a direct affect of the QBO on the North Pacific. In particular, the QBO seems to lead to a horseshoe shaped pattern response, not the vortex response, in the North Pacific. This horseshoe response can then alter the propagation, and the subsequent extratropical growth, of the wavetrain associated with anomalous ENSO convection, offering an additional explanation of how the QBO can modulate ENSO teleconnections. A description of this work can be found in a paper submitted in November 2009 to Geophysical Research Letters.









The difference plot and climatology. The movie .