Stratosphere discussion 2020

[Chris W]

CT, as seemed possible there's been a release of cold at 500mb at least but it's gone out into the Pacific:
https://earth.nullschool.net/#current/w ... 04,-67.607

[Cyclone Tracy]

Yes, that looks to be a strong tropospheric Rossby wave. The stratospheric polar vortex though has never been stronger in recorded time for this time of year. When the stratospheric warming switch gets flicked during November, the impact on the mid latitudes will be fascinating with a strong La Nina in the mix.

[Cyclone Tracy]

One of the strongest seasonal polar vortexes on record is starting to warm with a propagating Rossby wave in the lower stratosphere heading for NZ around 7th November on the NASA GEOS model. Another significant wave heading equatorward between Africa and OZ at the same time. Stratosphere is starting to call the shots, upper cut off lows, troughs, storms and rain events in order for the NZ region if that verifies.

[Cyclone Tracy]

The Polar vortex is about to be the strongest it's ever been recorded (1979 to 2020) in mid November. Equatorial heat flux has significantly dropped off and the ozone chemistry is not normal. The ozone hole is enormous for November. The final warming of the vortex normally occurs in the 3rd week of November, this year looks like mid December. In my opinion La Nina has stopped heat flux propagating poleward and is the smoking gun. The polar vortex death warming being one month later than normal will have large impacts for NZ weather in the new year.

[Awhituobs]

http://m.weatherzone.com.au/news/theres ... lia/532865

[Cyclone Tracy]

Interesting indeed. As I mentioned in an earlier post ( viewtopic.php?p=195904#p195904 ) there really isn't a year we can look back at during the satellite era (1979 -2020) when the the polar vortex has been this strong with a La Nina event. Already November has shown that the stronger polar vortex will trump a La Nina pattern for NZ and push the Hadley cell equatorward allowing the polar troughs to move up. The stratospheric polar vortex is calling the shots at the moment with an unsettled trough parade coming up in the 2nd half of November.

[Kentish Kiwi]

Interesting indeed. As I mentioned in an earlier post ( viewtopic.php?p=195904#p195904 ) there really isn't a year we can look back at during the satellite era (1979 -2020) when the the polar vortex has been this strong with a La Nina event. Already November has shown that the stronger polar vortex will trump a La Nina pattern for NZ and push the Hadley cell equatorward allowing the polar troughs to move up. The stratospheric polar vortex is calling the shots at the moment with an unsettled trough parade coming up in the 2nd half of November.

Hi there Cyclone Tracy, I’m just trying to digest the above in relation to the weather zone article. The article seemed to suggest that the colder and longer lasting vortex this year will increase the likelihood of a positive SAM and therefore easterlies hitting the east coast of Aus, and presumably Northern NZ, compounding the pattern expected as a result of La Niña. What I gather from your post is that you expect to the colder / stronger vortex will push the Hadley cell northwards with a resultant increase in westerlies over NZ (and presumably Southern and Eastern Aus)? Effectively over-riding the expected La Niña pattern. So in a sense the opposite of what the Weatherzone article suggested?

[Cyclone Tracy]

Hi KK, My post above is referring to November, while the vortex still exists. Because the vortex is still so abnormally strong, Rossby waves will reach the mid latitudes with more punch when it has a weakening phase. We can already see this influence for the 2nd half of November on the short and medium term modelling with the Hadley cell moving north, snuffing out the La Nina influence for NZ. Beyond November will depend on how long the polar vortex survives (still unknown) but that article is speculating what may happen if a strong positive SAM comes about.

I've done some more research in the last 24 hours and in December 1973, there was a strong positive SAM of 2.17 with a very strong La Nina around -2.0c. Here is a summary from Rupert Wood with regards to December 1973's rainfall.

December 1973 rainfall summary : Rainfall was below normal over almost all the country, mainly by about 40%. It was less than half of normal over almost the whole of Northland; in the greater part of Taranaki, Wanganui and Manawatu; and also in the greater part of Otago and Southland. The only 2 periods of considerable and fairly general rain were the 17th-18th and the 24th-25th. Many stations received very little or no rain in the first half of the month. In a thunderstorm at Taupo on the afternoon of Christmas Day 30mm were recorded in half an hour.

[Awhituobs]

no, Cyclone Tracy is talking about the short term effects of the current bulb /release of cold air from the vortex affecting our weather pattern for the rest of November
ops, just cross posted

[Kentish Kiwi]

Hi KK, My post above is referring to November, while the vortex still exists. Because the vortex is still so abnormally strong, Rossby waves will reach the mid latitudes with more punch when it has a weakening phase. We can already see this influence for the 2nd half of November on the short and medium term modelling with the Hadley cell moving north, snuffing out the La Nina influence for NZ. Beyond November will depend on how long the polar vortex survives (still unknown) but that article is speculating what may happen if a strong positive SAM comes about.

I've done some more research in the last 24 hours and in December 1973, there was a strong positive SAM of 2.17 with a very strong La Nina around -2.0c. Here is a summary from Rupert Wood with regards to December 1973's rainfall.

December 1973 rainfall summary : Rainfall was below normal over almost all the country, mainly by about 40%. It was less than half of normal over almost the whole of Northland; in the greater part of Taranaki, Wanganui and Manawatu; and also in the greater part of Otago and Southland. The only 2 periods of considerable and fairly general rain were the 17th-18th and the 24th-25th. Many stations received very little or no rain in the first half of the month. In a thunderstorm at Taupo on the afternoon of Christmas Day 30mm were recorded in half an hour.

Thank you for the explanation. Interesting times. I’m moving to Sydney next week so am keeping a keen eye on how La Niña is developing and interacting with other drivers. Hoping it doesn’t lead to too much of a washout summer over there.

[jamie]

Jeepers I hope we don’t replicate that analog year of December.


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[Cyclone Tracy]

Quite a remarkable forecast projecting from GFS, an extreme positive SAM in the stratosphere stemming from the abnormally stronger vortex with no sign at the moment when it will couple down into the troposphere. It's the complete opposite to last years Sudden stratospheric warming event. Since 1957, no month in the troposphere has ever averaged a positive 5.0 SAM (AAO).

[Awhituobs]

models are showing the next high coming in next week La Nina like (ie across the south island)

[Cyclone Tracy]

This is now a historic event in recorded times (1979 to present), the polar vortex continues to defy the 40 year climatology. The ozone hole looks like the middle of winter. Temperatures at 10 hPa are starting to normalise but the mid and lower stratosphere are off the charts for cold. What is also puzzling is that the lower troposphere over the polar region is also abnormally cold and on the surface, Antarctic sea ice is also at record high levels. The connection with a strong La Nina and a lack of equatorial heat flux is still the smoking gun in my opinion. How all this finishes in the next few months is anyone's guess but the polar vortex is calling the shots at the moment and the Hadley cell remains further north for NZ.

[Chris W]

10hPa over the pole today - 19C, 70hPa -74C.

Amazing resilience of the lower vortex.

[Cyclone Tracy]

Multiple ensembles are locking onto the final warming of the stratospheric polar vortex at 10 hPa to be around the 8th to 10th of December when the wind will turn easterly. Last year was 40 odd days earlier on 30th October. The record latest in the satellite era is 15th December 2010.

With the final warming now locked in, IMO, the Hadley cell will start to head poleward in the coming weeks, enhancing a La Nina pattern in the South West Pacific from mid December.

[Chris W]

The vortex has repeatedly made a mockery of the ensembles this winter/spring, let's see if it springs one last escape act!

[Cyclone Tracy]

Final warming of the southern hemisphere's stratospheric polar vortex occurred yesterday, the wind has now turned easterly at 10 hPa. 2nd latest warming in recorded history (1979 to 2020). The latest recorded is 15 December 2010.