Stratosphere Discussion 2012-13

[chionomaniac]

Polar vortex becoming much colder/stronger than average in the middle to upper stratosphere.

The polar vortex is about to pop in the middle stratosphere. If we see any form of the reversed mean zonal winds propagate to the trop, then I dare say that the AO forecasts will start to look a lot different as well!

[wxmx]

Polar vortex becoming much colder/stronger than average in the middle to upper stratosphere.

Look at 2009 and 2010 around this time.

[Big O]

Look at 2009 and 2010 around this time.

I don't see those years on the posted graphic. What does it show, and what does it mean? SSW or Major Stratospheric Warming? Turn to much colder long term?

[QVectorman]

The newest ECMWF strat. temp forecast shows a ~+48C warming at 10mb from Dec. 29 through Jan. 2 and a ~+42C warming from Jan1 to Jan 2 at 90N. There is also a wind reversal forecasted to take place Jan 2 at 1mb and 10mb at 60N. This should qualify as a MAJOR SSW since only a +25C temp change is required over a week period for a minor SSW and I believe the wind reversal is extensive enough to qualify also. If not it is still a minor SSW. The EP vector is also forecasted poleward at least at 90N which is a good signal that the SSW will in fact allow arctic air to spill southward.

[wxmx]

It's definitely an MMW on the Euro. We'll see if it holds, and if so, if it propagates and if so, where are the favored areas for cold...but so far, so good.

[thunderbolt]

It's definitely an MMW on the Euro. We'll see if it holds, and if so, if it propagates and if so, where are the favored areas for cold...but so far, so good.

hey wx what is the lag time before we will see the effects of the mmw?i thought i read it takes about 15 to 20 days is this true? and the last big

question will the cold come to our side of the world?thanks chris

[turtlehurricane]

Look at 2009 and 2010 around this time.

It makes sense that a strengthening polar vortex would be prone to breaking down, perturbations induced by Rossby and gravity wave forcing can more easily lead to instability since there's more energy to work with.

[wxmx]

There's still much uncertainty to adventure a forecast 15-30 days out ... signals aren't that clear cut to lean toward a p or np event (propagating, non propagating). EP stratospheric flux appears to change to a bit more poleward around the central date of warming...best correlation is a few (5-10) days before the warming onset, but it's better than a persistent equatorward flux. My WAG is that if it propagates to the mid levels of the troposphere, it would first translate into an EPO ridge followed by a NAO ridge...with the mean trough in the western half of the CONUS ~2 weeks from now, swinging east in ~3 weeks...but that's a very low confidence guess.

[tacoman25]

There's still much uncertainty to adventure a forecast 15-30 days out ... signals aren't that clear cut to lean toward a p or np event (propagating, non propagating). EP stratospheric flux appears to change to a bit more poleward around the central date of warming...best correlation is a few (5-10) days before the warming onset, but it's better than a persistent equatorward flux. My WAG is that if it propagates to the mid levels of the troposphere, it would first translate into an EPO ridge followed by a NAO ridge...with the mean trough in the western half of the CONUS ~2 weeks from now, swinging east in ~3 weeks...but that's a very low confidence guess.

I agree that is the most likely scenario. I made a similar guess in the medium range discussion thread.

[Isotherm]

IF the stratosphere does anything to help out the pattern, and that is a big "if" in itself, folks shouldn't be expecting those effects for at least 2 weeks, probably 3 weeks. Looks to me like the next 7-10 days are cold in the Mid-west/Northeast, then we moderate above normal as the EPO/PNA ridging break down w/ no blocking. Then it remains to be seen if the strat warming can force another -AO episode, which would have its impacts later in Jan into Feb. Strat warming or not, the statistics for -AO Nov/Dec argue for another burst of -AO regime during the DJF period.

[wxmx]

I am currently teaching myself about the PV/stratosphere relationship, and from what I understand stratospheric warming helps break down the PV. Can someone explain how that actually works?

The weakening/breakdown of the stratospheric PV is the cause of the stratospheric warming. That breakdown may or may not propagate to the troposphere... people tend to focus on the temperature, but that's just a collateral, the main issue is the weakening or reversal of the westerlies associated with the PV. What causes this weakening/reversal? Tropospheric long Rossby waves traveling upward whose genesis is mainly from orographic causes or land/sea temperature contrasts. Dissipation of this energy is what causes the deceleration of the flow. You can get a better understading of the basics in this wikipedia article.

[thunderbolt]

thanks for the response wx . I was looking at the mjo and looks like it is going in to phases 5-6 ( per the euro model) and some of its emsembles have them going into phase7 by mid month or so. the nao and ao looked to going from poss to neutral at the same time. the question that i have does the stratosphere warming have any influence on any of this indices

[It's Always Sunny]

The weakening/breakdown of the stratospheric PV is the cause of the stratospheric warming. That breakdown may or may not propagate to the troposphere... people tend to focus on the temperature, but that's just a collateral, the main issue is the weakening or reversal of the westerlies associated with the PV. What causes this weakening/reversal? Tropospheric long Rossby waves traveling upward whose genesis is mainly from orographic causes or land/sea temperature contrasts. Dissipation of this energy is what causes the deceleration of the flow. You can get a better understading of the basics in this wikipedia article.

Thanks for responding. I understand that aspect of it but I think my main question is if stratospheric warming alters the upper tropospheric temperature gradient in the Arctic resulting/assisting in a weakening PV which would allow cold air to stream south? It's the only thing that seems reasonable to me but there's a good chance that is incorrect because the stratosphere is a very stable layer so a mix down effect is unlikely.

[Amped]

GFS consistently splitting the PV up to 100mb in the long range and showing a Greenland block in both the stratosphere and troposphere, mostly after day 10. The cross polar flow is still working it's way down at the end of the run.

[wxmx]

If it propagates to the troposphere it definitely affects the AO and the NAO.

thanks for the response wx . I was looking at the mjo and looks like it is going in to phases 5-6 ( per the euro model) and some of its emsembles have them going into phase7 by mid month or so. the nao and ao looked to going from poss to neutral at the same time. the question that i have does the stratosphere warming have any influence on any of this indices

[wxmx]

Not sure I understand...would your question refer to the mechanism that allow the propagation to the troposphere of a stratospheric warming event?

Thanks for responding. I understand that aspect of it but I think my main question is if stratospheric warming alters the upper tropospheric temperature gradient in the Arctic resulting/assisting in a weakening PV which would allow cold air to stream south? It's the only thing that seems reasonable to me but there's a good chance that is incorrect because the stratosphere is a very stable layer so a mix down effect is unlikely.

[It's Always Sunny]

Not sure I understand...would your question refer to the mechanism that allow the propagation to the troposphere of a stratospheric warming event?

Lol alright I don't think I'm making the connection as to how stratospheric warming helps weaken the PV. I get how stratospheric warming is caused (Rossby waves propagated upwards and such) but how does this all allow the PV to weaken to allow cold air to usher into the mid latitudes? I thought it was maybe because the upper air temperature gradient was altered around the Arctic due to such warming aloft which would result in a pressure gradient change that would allow cold air to stream down. I hope tjhis makes more sense.

[wxmx]

Lol alright I don't think I'm making the connection as to how stratospheric warming helps weaken the PV. I get how stratospheric warming is caused (Rossby waves propagated upwards and such) but how does this all allow the PV to weaken to allow cold air to usher into the mid latitudes? I thought it was maybe because the upper air temperature gradient was altered around the Arctic due to such warming aloft which would result in a pressure gradient change that would allow cold air to stream down. I hope tjhis makes more sense.

As I said before...warming is a consequence, not a causal. Rossby waves energy is dispersed in the stratosphere (maybe even the mesosphere), causing the mean flow to decelerate, that means the polar night jet weakens and the PV is distorted/displaced/split...as a consequence, the air temps abruptly soars several tens of degrees kelvin. After wind reversal (from westerly to easterly) occurs, planetary waves are blocked to move upward anymore, so the remnant energy must move downard across the entire stratosphere column, disrupting the previously stacked stratospheric PV. Then we get to the part of the p vs np warming events into the troposphere. In the propagating events, the deceleration/reversal and consequent disruption of the tropospheric PV continues...allowing high amplitude waves distort the theoretical near circular PV, displacing the cold air from the high latitude and let it spill south. So it's all about wind speed/direction, not temperature.

[griteater]

As I said before...warming is a consequence, not a causal. Rossby waves energy is dispersed in the stratosphere (maybe even the mesosphere), causing the mean flow to decelerate, that means the polar night jet weakens and the PV is distorted/displaced/split...as a consequence, the air temps abruptly soars several tens of degrees kelvin. After wind reversal (from westerly to easterly) occurs, planetary waves are blocked to move upward anymore, so the remnant energy must move downard across the entire stratosphere column, disrupting the previously stacked stratospheric PV. Then we get to the part of the p vs np warming events into the troposphere. In the propagating events, the deceleration/reversal and consequent disruption of the tropospheric PV continues...allowing high amplitude waves distort the theoretical near circular PV, displacing the cold air from the high latitude and let it spill south. So it's all about wind speed/direction, not temperature.

To this end, what would we specifically want to see in the graphs below (this is the 0 day to 10 day Euro)? Would we want to see reversal of the winds in the troposphere around 60N? Also, how strong and at what levels of the troposphere would they need to be in order to be considered significant?

[Lorenzo]

Do you have any thoughts on the Propagation of the upcoming event wxmx?

[It's Always Sunny]

As I said before...warming is a consequence, not a causal. Rossby waves energy is dispersed in the stratosphere (maybe even the mesosphere), causing the mean flow to decelerate, that means the polar night jet weakens and the PV is distorted/displaced/split...as a consequence, the air temps abruptly soars several tens of degrees kelvin. After wind reversal (from westerly to easterly) occurs, planetary waves are blocked to move upward anymore, so the remnant energy must move downard across the entire stratosphere column, disrupting the previously stacked stratospheric PV. Then we get to the part of the p vs np warming events into the troposphere. In the propagating events, the deceleration/reversal and consequent disruption of the tropospheric PV continues...allowing high amplitude waves distort the theoretical near circular PV, displacing the cold air from the high latitude and let it spill south. So it's all about wind speed/direction, not temperature.

Spot on. Thanks again, and have a Happy New Year!

[wxmx]

Tropospheric wind anomalies are never as strong as stratospheric anomalies, but they are quite persistent, usually lasting several weeks. That' s how we know it was a propagating event.

To this end, what would we specifically want to see in the graphs below (this is the 0 day to 10 day Euro)? Would we want to see reversal of the winds in the troposphere around 60N? Also, how strong and at what levels of the troposphere would they need to be in order to be considered significant?

[wxmx]

Do you have any thoughts on the Propagation of the upcoming event wxmx?

I' m leaning toward propagting but I' ll be more certain in 2-3 days.

[turtlehurricane]

Sudden stratospheric warming underway! These maps are kinda annoying at the beginning of a new year since they're so thin, but you can still easily see the temperature and wind anomaly reversal.

 

 

[okie333]

January 10 0Z analysis...