Stratosphere discussion 2020

[Chris W]

The positioning of the warming potentially initially moves the vortex more in our direction, but what that really means is a month or two off. Also, La Niña and a negative Indian Ocean dipole are different to last year. Also, the lower stratosphere doesn’t seem to follow 10hPa as well at this point. So, hmm...

Still, this is cool to see.

0AEDD41B-824A-490E-936A-D02B0EF08C04.png

[Cyclone Tracy]

2018 (11 Aug image), 2019 & 2020 EC comparison 11th Aug 00Z run for the stratospheric polar vortex temperature @ 10 hPa.

Maybe we will see some extreme events in NZ with this years SSW event, last years event and subsequent flow on effects for NZ was dissapointing to say the least!

Yes, where the jet stream positioned itself certainly had a larger impact on Australia than NZ. Last November was quite remarkable in south eastern Oz. viewtopic.php?p=186816#p186816

Still early days for this year. Equatorial heat flux seems to be driving the current modelling, whether it can maintain the surge into late August is yet to be seen. The Polar vortex can defeat these surges in late August.

[Chris W]

10hPa warming starting to downwell through 70hPa and below that level to affect the polar jet:
https://earth.nullschool.net/#current/w ... 41,-56.106

GFS models the warming to hold and strengthen through the next 10 days before dissipating, but it has pushed the dissipation back again and again.

[Cyclone Tracy]

Lower vortex loosing shape as a propagating Rossby wave launches towards SE Australia this Friday and into the Tasman this weekend.

[Cyclone Tracy]

Fascinating atmospheric battle is playing out on EC's modelling between the incoming equatorial heat flux and the stratospheric polar vortex on 28th August. The stratospheric polar vortex is the most powerful atmospheric weather system on earth, so it normally just doesn't roll over and give up in late August, which is why the sudden stratospheric warming event last year was a rare event. This EC projection is displacing it well off the south pole.

[Chris W]

Good ding-dong on the GFS as well, real popcorn time as you say!

[Chris W]

No time to post details/charts right now, but the GFS operational run is going for another major two-pronged warming at 10mb and a very warped vortex all the way down to the tropopause from about a week out through the end of the month.

Edit - here we go as the 06z (UTC) GFS run ramps it further. The ensembles are beginning the agree quite strongly about this:

98C8A098-1695-4371-A2D4-3C4E419ACEC4.png

87259E8D-7890-4771-995A-963F52F04A7C.png

[Cyclone Tracy]

Ding Ding - EC is awarding round 1 to the Polar Vortex by 31st Aug.

Round 2 coming up from 3rd Sept with an even stronger heat flux surge on both EC & GFS with some GEFS members going for the first stages of a potential SSW

[Chris W]

GFS, GEFS and EC are increasingly backing the vortex to fight back strongly early September after the current warming and through the second one early next month. Zonal wind speeds pick sharply back up and overall warming gets delayed. She’s a strong one this year.

[Kentish Kiwi]

GFS, GEFS and EC are increasingly backing the vortex to fight back strongly early September after the current warming and through the second one early next month. Zonal wind speeds pick sharply back up and overall warming gets delayed. She’s a strong one this year.

Hi Chris, have you got any thoughts on what the implications of this are for NZ through early-mid spring? Eg might you expect to see a stronger westerly influence from the vortex fighting against the emerging background of La Niña?

[Chris W]

I’m very much in the learning camp having only started to ‘study’ the stratosphere in the last year or so, but I guess it depends on where the 10hPa vortex gets steered to by warming areas and how much that downwells to lower levels and the jetstream. Looks like it might be pushed away from us so less westerly from that for a while maybe later in September, then perhaps it comes back in our direction. CT and Tony and maybe others might be able to shed more light on it. I’d guess also that the stronger the vortex stays, the more cold it locks in, so it could reserve a decent cold shot or two once it does start to break down later in spring.

[Chris W]

Total knockout to the PV, it is rock solid. Zonal winds are through the roof and temperatures remain low, and the compactness of the vortex leads to a positive SAM for a while. That warm area still lingers, it just doesn’t make much headway and really serves to strengthen the vortex by keeping it tight. Not much sign of a breakdown soon.

I’d say of the models I’ve looked at my impression is that the GFS operational run has had the best handle on things; the EC op and GEFS/GFS ensembles have been a bit more carried away with a repeat SSW idea but that has not really eventuated in the end.

[Cyclone Tracy]

The Polar Vortex wins again in the southern hemisphere, as you would expect. Sudden Stratospheric warming events remain a rare phenomenon with 2 surges of heat flux this year forced out by the vortex. Gradual weakening is now underway as the equinox approaches. This time last year, the ozone hole was under attack but things are back to normal this year.

[Awhituobs]

I see the sea ice extent is above normal for the time of year, probably related associated circulation wind patterns?

[Cyclone Tracy]

The southern hemisphere lower troposphere polar region has been mostly below average temperature for the last 5 months.

[Chris W]

Destabilisation of the lower vortex leading to the severe weather being modelled for this weekend:

B28D7AEF-A9E3-402D-B56C-BD2A7619C19D.jpeg

[Chris W]

One to watch, but the above 3D vortex chart/GFS op shows a reload for about October 5th-6th that could be just as potent. Vortex potentially getting into distress.

https://stratobserve.com/misc_vort3d

[Cyclone Tracy]

The Southern hemisphere polar vortex has been recorded by NASA at the 2nd strongest in the satellite era for September. It basically smashed any heat flux that came near it. The last time it was this strong so late in the year was 1993. November 1993 across NZ was the coldest November since 1946. The difference this year is a La Nina event is underway. When the final warming occurs in the next 6 weeks, there is a chance a surge of violent polar streamers emerge equatorward. This is one of the most volatile scenarios the mid latitudes can face in this region, surging polar air and warm moist air. It all seems calm now but this could explode if the ridge weakens through November / December.

[Richard]

I don't think it's being calm at all lately, the spring NW winds have been terrible this year

[Cyclone Tracy]

I don't think it's being calm at all lately, the spring NW winds have been terrible this year

That's why I said calm now.

[TonyT]

The Southern hemisphere polar vortex has been recorded by NASA at the 2nd strongest in the satellite era for September. It basically smashed any heat flux that came near it. The last time it was this strong so late in the year was 1993. November 1993 across NZ was the coldest November since 1946. The difference this year is a La Nina event is underway. When the final warming occurs in the next 6 weeks, there is a chance a surge of violent polar streamers emerge equatorward. This is one of the most volatile scenarios the mid latitudes can face in this region, surging polar air and warm moist air. It all seems calm now but this could explode if the ridge weakens through November / December.

Interesting but I'm not buying it. The best analogue to the current pattern is 2010/11 and the October/November was very settled that year with frequent anticyclones and warm temperatures. I'd be going for an absence of southerly quarter airflow over the next 2 months.

[Cyclone Tracy]

Yes, looking at La Nina in isolation I thought the same. I took a closer look at the Polar Vortex today and looked at the SAM projection over the next 4 weeks. Comparing 1993 to 2010 throws up a different dimension. The 1993 positive SAM outcome is very similar to the latest Access S 4 week outlook, as opposed to the very strong positive SAM of Oct/Nov/Dec 2010. I too think it will be warmer because of La Nina but it could become quite volatile rather than settled.

[Chris W]

No time for posting charts but the upper vortex is under serious pressure now, -25C air over the continent. Looks to take two major warmings over the current model run so next 10-15 days.

[Cyclone Tracy]

Shorter term, the polar vortex is about to be the strongest its ever been for the start of November. Remarkably, NASA is forecasting it to strengthen again in the next few days. This time last year the final warming had already occurred. This is going to be a rapid and hostile final warming in November. Fascinating to see what the strongest ever vortex this late does to the weather around NZ leading up to Christmas with a La Nina in the mix. We haven't seen this before in recorded times.

[Chris W]

Doubling the popcorn order.