Sudden Stratospheric Warming Event (SH) 2019

[Cyclone Tracy]

EC 10 day outlook now projecting an atmospheric ticking timebomb. 70c + temperature gradient over Antarctica in the upper stratosphere on 30 August. It's interesting to compare it to the same time last year.

[TonyT]

EC 10 day outlook now projecting an atmospheric ticking timebomb. 70c + temperature gradient over Antarctica in the upper stratosphere on 30 August. It's interesting to compare it to the same time last year.

Looks quite ominous to me. When that propagates down into the troposphere thats going to unbalance the polar vortex in a pretty mighty way.

The media are starting to pick up on this now. Expect to see some coverage this week (Paul from the Press has been asking me about it).

[Richard]

wow, that is a huge difference. Interesting month or so ahead

[Chris W]

Popcorn at the ready

[Razor]

EC 10 day outlook now projecting an atmospheric ticking timebomb. 70c + temperature gradient over Antarctica in the upper stratosphere on 30 August. It's interesting to compare it to the same time last year.

Looks quite ominous to me. When that propagates down into the troposphere thats going to unbalance the polar vortex in a pretty mighty way.

The media are starting to pick up on this now. Expect to see some coverage this week (Paul from the Press has been asking me about it).

Interesting to follow. I have no idea what the outcome of this means other than we expect some volatility bit I get suspicious here in Canterbury that volatile westerly flows just mean a warm windy dry spring unless the flows divert to the south quadrant?

[ScottyD]

EC 10 day outlook now projecting an atmospheric ticking timebomb. 70c + temperature gradient over Antarctica in the upper stratosphere on 30 August. It's interesting to compare it to the same time last year.

In layman's terms, what does that mean? What are the implications of having that sort of temperature gradient?

[TonyT]

Interesting to follow. I have no idea what the outcome of this means other than we expect some volatility bit I get suspicious here in Canterbury that volatile westerly flows just mean a warm windy dry spring unless the flows divert to the south quadrant?

No one really knows what the outcome on the ground will be. And yes, Canterbury is often a good place to ride out volatile westerly airstreams when other parts of the country get hammered.

[TonyT]

EC 10 day outlook now projecting an atmospheric ticking timebomb. 70c + temperature gradient over Antarctica in the upper stratosphere on 30 August. It's interesting to compare it to the same time last year.

In layman's terms, what does that mean? What are the implications of having that sort of temperature gradient?

In practical terms no one really knows. It means more energy injected into the polar vortex which will make it wobble, which could mean leakage of cold air into Southern Ocean weather systems about a month down the track. Whether that translates into our weather as cold southerlies or strong westerlies or intense anticyclones is anyones guess at this stage. But generally speaking, strong temperature gradients equals strong dynamics in mid latitude weather systems.

[Richard]

Popcorn at the ready

Ive still got about 20kgs to get through

[Razor]

EC 10 day outlook now projecting an atmospheric ticking timebomb. 70c + temperature gradient over Antarctica in the upper stratosphere on 30 August. It's interesting to compare it to the same time last year.

Looks quite ominous to me. When that propagates down into the troposphere thats going to unbalance the polar vortex in a pretty mighty way.

The media are starting to pick up on this now. Expect to see some coverage this week (Paul from the Press has been asking me about it).

And the Soothsayer of the Day Award goes to....
https://i.stuff.co.nz/science/115098866 ... zs-weather

[Bradley]

In layman's terms, what does that mean? What are the implications of having that sort of temperature gradient?

In practical terms no one really knows. It means more energy injected into the polar vortex which will make it wobble, which could mean leakage of cold air into Southern Ocean weather systems about a month down the track. Whether that translates into our weather as cold southerlies or strong westerlies or intense anticyclones is anyones guess at this stage. But generally speaking, strong temperature gradients equals strong dynamics in mid latitude weather systems.

Well done Tony, they have quoted you a few times throughout the article on stuff. Fingers crossed that it eventuates now

One of the southern hemisphere's rarest phenomena may be under way in the skies above Antarctica and could be driving New Zealand's stormy August weather.

Meteorologists are debating whether a sudden stratospheric warming (SSW) began earlier this month, putting a wobble into the polar vortex of westerly winds around the Antarctic and allowing freezing air to escape more easily and head towards southern New Zealand.
Whether one is or isn't already occurring, computer models are showing a much more significant winter stratospheric warming could begin in about 10 days or a fortnight.

Only two SSWs have ever been recorded in the southern hemisphere - a major event at this time of year in 2002 and a minor one in 2010. SSWs are more frequent in the northern hemisphere in winter due to land masses close to the North Pole.

Blue Skies Weather forecaster Tony Trewinnard told Stuff that an SSW forecast late last month had begun early this month and had now probably peaked, with temperatures in the stratosphere 20km or more above the Antarctic as much as 20 degrees Celsius warmer than the long-term average.
National Institute of Water and Atmospheric Research meteorologist Ben Noll told Stuff he was unconvinced that event was particularly significant, given the temperature rise was still short of the 25C threshold for a minor SSW determined by the Japan Meteorological Agency.

A major SSW is defined as a warming of 30 to 50C at those heights, which is large enough to cause a reversal of prevailing winds through the atmosphere from westerlies to easterlies.
"Something potentially more interesting is signalled in the next 10 to 15 days, showing a warming of 40-50 degrees. If this were to occur, it would be more impressive than what has occurred so far this month in the stratosphere.

"It is worth keeping an eye on over the next week or two. [But] being a keen watcher of winter in the northern hemisphere, I have seen a number of occasions where the forecast 10 to15 days in advance was too aggressive."

The winter 2002 SSW came ahead of an unusually warm and windy September, followed by the coldest October in 20 years.

The stratosphere is the second layer of the Earth's atmosphere, in which temperatures generally increase with height due to the concentration of ozone. It extends to about 50km above the surface, and starts at altitudes of between 7 and 10km over the poles and about 17km above the equator.
Below it lies the troposphere, the layer which contains most of the weather.
Major SSWs in the northern hemisphere have percolated down through the atmosphere and reversed winter wind directions, leading to frigid easterly winds and very cold, snowy winters across Europe, including the "Beast from the East" in February and March 2018.

Trewinnard said the current SSW appeared to be driving the country's unsettled weather.Play Video
"The impact of sudden warming high in the polar atmosphere is to 'knock' the polar vortex out of shape. Over time - it takes two to six weeks - the polar vortex gets a wobble, like a spinning top, and this allows cold air from the Antarctic continent to 'leak' out into the weather systems of the southern ocean.
"Eventually this affects New Zealand as depressions and troughs of low pressure, and cells of very cold air. This can make our weather colder and stormier for a period of a month or two.

"Generally this is looking like a stormy couple of months ahead, with frequent rainfalls, cold outbreaks, and windier than normal weather for the whole country.The periods likely to see the most impact from intense weather systems are the last few days of August and the very beginning of September, and again mid-September."

Noll said stormier than normal conditions were expected into September, "and it might even last longer than that".

But even with an SSW, it didn't necessarily mean New Zealand would "feel the full impact".
"That could be over South America, or even out over the oceans."

[TonyT]

In practical terms no one really knows. It means more energy injected into the polar vortex which will make it wobble, which could mean leakage of cold air into Southern Ocean weather systems about a month down the track. Whether that translates into our weather as cold southerlies or strong westerlies or intense anticyclones is anyones guess at this stage. But generally speaking, strong temperature gradients equals strong dynamics in mid latitude weather systems.

Well done Tony, they have quoted you a few times throughout the article on stuff. Fingers crossed that it eventuates now

Thank you. The SSW event is eventuating for sure (see CT's post above) but its rather harder to try to guess what weather it will bring. I did talk at length with Paul about how being in a deep solar minimum at present probably changes the rules when comparing to the last event on 2002 (which was solar maximum) but he doesnt seem to want to go anywhere near solar cycles and weather.

[Cyclone Tracy]

Just separating this subject from day to day weather talk as it will most likely span across months. To discuss projections, predictions, observations and keep a historical reference on what impact this possible event has on NZ weather and climate.

EC this morning has upgraded the warming in the upper stratosphere over the Antarctic continent at the end of August, displaying a 80c+ temperature gradient. I've included this time last year as a reference.

GFS indicating a negative -5 SAM (AAO) between 1 and 10 hPa in the same period. The 2002 event reached a negative -6 in the upper stratosphere as the event peaked.

[RWood]

In the 2002 event, November continued the cold theme but was windier and cloudier than October. Temperatures returned to average for December, with dry sunny conditions in the east. I would certainly be happy to see a return of the weather of January-March 2003.

[snowchaser01]

https://hwe.niwa.co.nz/event/October_20 ... nderstorms

Interesting reading of what happened in late october 2002 regarding some thunderstorms around the country.

[Dean.]

August 2002 may have been the time Ashburton received 15cm of very dry snow when it was cold enough to snow to 100 metres below sea level

[Razor]

Watching with interest. Models no doubt will be volatile and inconsistent, none moreso than GFS over the last 24 hours!

[Chris W]

GFS has been struggling for weeks, so goodness knows how it will go with this into the mix.

[Cyclone Tracy]

Each set of model runs across multiple met agencies, continue to project a set of extraordinary historical anomalies. EC on this afternoon’s 00Z run just projected a +2.0c temperature at 30km (10 hPa) above the south pole on 31 Aug Then on 1 Sept, signs of the notorious elongated stratospheric polar vortex split start to appear at a lower level around 100 hPa. I’m in the process of analysing GFS, that might take a while….

It’s hard to imagine the impact of if or when it propagates into the troposphere and down to the surface. On current projections, the peak of the SSW will occur in 9 days time on 31 Aug @ 10 hPa, this is 27 days earlier than the 2002 event and it's warming is displaying a different behaviour to the 2002 event. In my opinion, based on the 10 to 14 day model projections, this event has a different finger print to 2002 and most likely a different outcome.

Lots of popcorn required for this thread….

[TonyT]

In my opinion, based on the 10 to 14 day model projections, this event has a different finger print to 2002 and most likely a different outcome.

Lots of popcorn required for this thread….

Being in the depths of the minimum of a very low solar cycle (double whammy) jet streams are already all over the place. One of the mechanisms this event is likely to affect is jet stream behaviour (triple whammy). Could be a bumpy ride.

[Cyclone Tracy]

@ 10 hPa

Latest EC run has nearly a 90c temperature gradient on 30 Aug. The map scale can only handle a 75c scale and not into a positive temperature range

GFS displaces the upper vortex centre around 20 degrees equatorward to 66 degrees south latitude on 2 Sept. It also shrinks the vortex significantly. 63 other models across the North American ensembles are pretty much the same.

This event seems to be at a greater warming intensity and at a higher altitude than 2002.

[jamie]

Very interesting to watch this unfold. Thanks for the updated CT and Tony


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[Chris W]

What might the specific cause of this warming be? If memory serves correctly last time I experienced a significant SSW in the UK (sometime around early 2012 I think) it was due to mountain torque in the Himalayas.

[Andy]

https://www.nzherald.co.nz/nz/news/arti ... d=12261051

[Cyclone Tracy]

What might the specific cause of this warming be? If memory serves correctly last time I experienced a significant SSW in the UK (sometime around early 2012 I think) it was due to mountain torque in the Himalayas.

There were strong vertical propagating planetary waves at the end of July in the upper stratosphere which seems to have made the polar vortex vulnerable. If it can't regather in time, a second round attack from planetary waves can trigger the main SSW event.

Whether mountain ranges like the Andes are part of the cause like your example of the Himalayas in the NH, is a good question. The answer might take a while to figure out