Polar Vortex

[NYCSuburbs]

After all of the PVs stuck over Canada/Alaska this winter, there's some things I'm trying to better understand about them:

What makes the bigger, stronger PVs usually develop over the northern latitudes as opposed to further south? Especially this winter there were a lot of them that were stuck over the same region; is it known what determines the direction of their motion? Also, is there a difference between for example a big Canadian PV and a cutoff low drifting slowly through the US?

[nzucker]

After all of the PVs stuck over Canada/Alaska this winter, there's some things I'm trying to better understand about them:

What makes the bigger, stronger PVs usually develop over the northern latitudes as opposed to further south? Especially this winter there were a lot of them that were stuck over the same region; is it known what determines the direction of their motion? Also, is there a difference between for example a big Canadian PV and a cutoff low drifting slowly through the US?

I think the development of the fall polar vortex is usually highly dependent upon stratospheric temperatures. We had very cold stratospheric temperatures in November 2011 which allowed for an abnormally cold/strong PV that was difficult to disturb compared to Winters 09-10 and 10-11. Also, I think the Pacific pattern (MJO-driven usually) is responsible for the extent to which the PV can descend into Central Canada/Hudson Bay region and bring colder than normal temperatures to the CONUS.

[Geos]

The strength of the zonal jet stream kept the PV going strong as well. A fast zonal jet stream will prevent ridges from the mid-latitudes from coming to far north and introducing warmer air. La Nina was partially to blame for the zonal flow this winter.

A fast zonal jet stream around Antarctica during its winter is quite common, actually that's the way it always is. In the southern hemisphere the jet stream is positioned over the Southern Ocean and does not interact with land masses at all to speak of. Westerly winds can maintain their speed going around the continent with minimal friction effects over the ocean. The Antarctic PV doesn't weaken until spring arrives.

[usedtobe]

The strength of the zonal jet stream kept the PV going strong as well. A fast zonal jet stream will prevent ridges from the mid-latitudes from coming to far north and introducing warmer air. La Nina was partially to blame for the zonal flow this winter.

A fast zonal jet stream around Antarctica during its winter is quite common, actually that's the way it always is. In the southern hemisphere the jet stream is positioned over the Southern Ocean and does not interact with land masses at all to speak of. Westerly winds can maintain their speed going around the continent with minimal friction effects over the ocean. The Antarctic PV doesn't weaken until spring arrives.

This is not always true. There is also an antarctic oscillation, the southern annular mode which is analogous to the northern annular mode.

http://www.jisao.washington.edu/aao/

http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch3s3-6-5.html

The polar vortex can weaken in the southern hemisphere if the stratosphere warms and you get downwelling. The southern annular mode phase can be positive or negative which has implications about the jet stream in the same way the northern annular mode does.

[Geos]

This is not always true. There is also an antarctic oscillation, the southern annular mode which is analogous to the northern annular mode.

http://www.jisao.washington.edu/aao/

http://www.ipcc.ch/p.../ch3s3-6-5.html

The polar vortex can weaken in the southern hemisphere if the stratosphere warms and you get downwelling. The southern annular mode phase can be positive or negative which has implications about the jet stream in the same way the northern annular mode does.

Thanks for clearing that up!