Stratosphere Temperature Watch

[cooling climate]

What I would like to know is, which comes first the blocking or the SSW. Too my untrained eye, it appears we need blocking in place for a SSW event to take place?

Mountain torques etc giving rise to ridging forcing warm air into the Arctic stratosphere

causing greater geopotential height anomalies causing blocking. Whether this propagates

down to the troposphere is another question.

[UV-RAY]

Mountain torques etc giving rise to ridging forcing warm air into the Arctic stratosphere

causing greater geopotential height anomalies causing blocking. Whether this propagates

down to the troposphere is another question.

But the way I see it is, you need the blocking in place for any warming to take place, So which is the more dominant factor, the established blocking or the warming. One needs each other?

[chionomaniac]

But the way I see it is, you need the blocking in place for any warming to take place, So which is the more dominant factor, the established blocking or the warming. One needs each other?

Most of the studies on this have shown that the stratosphere needs to be 'preconditioned' to allow a SSW but that this has not been exclusively so. My guess is that we are more likely to see wave breaking into the stratosphere from more blocked scenarios so quite often the situations will go hand in hand.

[snowmadchrisuk]

Can anybody Explain the reasons in 2002 why a major warming was observed in the southern-hemisphere ? Can't really find much information to explain why it happened ?

[chionomaniac]

Can anybody Explain the reasons in 2002 why a major warming was observed in the southern-hemisphere ? Can't really find much information to explain why it happened ?

Out of all the SSWs that is probably the most researched. I am sure if you google it you will be able to find more info.

No SSW likely here though looking at latest charts. However the upper warming is putting considerable pressure on the vortex which is being transmitted to lower levels. I see the first signs of a possible split bring forecast on the ECM and if so it looks far more favourable than the GFS at 100hPa.

[karyo]

Out of all the SSWs that is probably the most researched. I am sure if you google it you will be able to find more info.

No SSW likely here though looking at latest charts. However the upper warming is putting considerable pressure on the vortex which is being transmitted to lower levels. I see the first signs of a possible split bring forecast on the ECM and if so it looks far more favourable than the GFS at 100hPa.

It's a significant warming at the 10hpa level but doesn't seem to have a big impact on the 30hpa level.

http://wekuw.met.fu-berlin.de/~Aktuell/strat-www/wdiag/ts.php

Karyo

[chionomaniac]

It's a significant warming at the 10hpa level but doesn't seem to have a big impact on the 30hpa level.

http://wekuw.met.fu-berlin.de/~Aktuell/strat-www/wdiag/ts.php

Karyo

The GFS suggests a greater warming at the 30 hPa level than the ECM. This is certainly worth watching to see if the vortex splits lower down.

[chionomaniac]

This is an interesting chart at day 10 and is at variance with the ECM at 1 hPa.

The reason that it is interesting is because it suggests that mean zonal winds are about to reverse at this level. The higher pressure over Alaska will displace the lower pressure over Scandinavia which will fill if this was to run to T+300. The high would travel further over the North Pole whilst a new area of lower pressure develops over the Pacific.

Now if this occurs at the 1 hPa level it would definitely have consequences to the vortex lower down the stratosphere and would increase the chances of mean zonal wind reversal there as well. Let us hope that it is there tomorrow and the ECM swings back the same way.

[chionomaniac]

Both the GFS and ECM are going with a split from the troposphere into the stratosphere as a result of the warming projected in the mid to upper stratosphere. I am still cautiously optimistic of a reversal of mean zonal winds at the 1hPa level which may filter down. Both the GFS and ECM hint at a squeeze on the vortex which may shift the vortex centre from the pole as the original vortex centre reduces and a new one sets up. We shall see.

Lower down we see that the GFS and ECM both agree on a split.

However until the potential vorticity drops completely between the split vortices then there will be no permanent height rise in between.

So much to watch in the coming days.

[Great Plum]

Hi,

As a novice here, I see that the 6z GFS shows no split in the vortex (that I could see)... Is it running with the latest projections with warming?

[chionomaniac]

Hi,

As a novice here, I see that the 6z GFS shows no split in the vortex (that I could see)... Is it running with the latest projections with warming?

Hi GP,

The 6Z GFS run did show signs of an upper split but it wasn't complete. And that is exactly the thing that I mentioned wrt the upper potential vorticity charts. In order to get the better chance of a full split and therefore higher latitude blocking we need to see two distinct areas of potential vorticity rather than a squashed oval shape.

[bluearmy]

Hi GP,

The 6Z GFS run did show signs of an upper split but it wasn't complete. And that is exactly the thing that I mentioned wrt the upper potential vorticity charts. In order to get the better chance of a full split and therefore higher latitude blocking we need to see two distinct areas of potential vorticity rather than a squashed oval shape.

as the berlin output is derived from the ecm 12z data, might we expect to see a better fist of seperating that vorticity tomorrow or at least stretching it further ???

[chionomaniac]

as the berlin output is derived from the ecm 12z data, might we expect to see a better fist of seperating that vorticity tomorrow or at least stretching it further ???

Yes, I know exactly what the 100hpa T+240 chart will look like already. Figure of 8.

[chionomaniac]

Yes, I know exactly what the 100hpa T+240 chart will look like already. Figure of 8.

....Of sorts..

Until we see the Potential vorticity seperate into two orange balls we will get no sustained heights builing north

[BLAST FROM THE PAST]

....Of sorts..

Until we see the Potential vorticity seperate into two orange balls we will get no sustained heights builing north

Thatlooks promising though as a projection

BFTP

[chionomaniac]

Thatlooks promising though as a projection

BFTP

Yes but that looks that it is as good as it will get. The Siberian vortex segment will increase in dominance moving more centrally.

Yet again we see distortion of the vortex shape and position but the zonal wind reduction anomalies are not propagating below the 30 hPa level, so the benefits of the latest (minor) warming are kept to the upper stratospheric levels.

[Duane S.]

Chiono, currently there appears to be (give or take) a fairly big -18 degree temperature anomaly over the pole at 10 hPA. I was wondering, does this in itself make an SSW more likely than if we were running at about average? As in.. there is more scope for a steep temp rise leading (potentially) to downward propagation and disruption OR... because the upper westerlies are established that that in itself makes disruption less likely to occur??? i.e. any warming towards the mean will likely be more gradual?

Not sure I've worded that very well but hopefully you get my gist. :unsure:

[damianslaw]

Can some moderate warming allow for a weakening PV rather than splitting? Wouldn't a weakening PV be enough to send more energy into the southern arm of the jet or allow for trough disruption caused by a sluggish atlantic...

[chionomaniac]

The problem is that the PV seems to be weakening at the top of the stratosphere - not in the lower reaches of the troposphere. This weakening is not filtering down past the 10 hPa level. What is filtering down though, is the position and shape of the vortex as this is dictated by the position and shape higher up. My guess is that if the tropospheric signal was conducive to blocking then it would occur quite readily with the minor warmings. it looks that that is not the case though and in order for any disruption to propagate down we will need a major warming - and even then that is no guarantee of latent northern blocking.

S4lancia, the lower the temperature at 10 hPa the more significant warming that would be needed to cause a reversal of mean zonal winds at this level. What tends to happen is that a series of gradual warmings incrementally raise the temperature which in turn means that a SSW gets closer the warmer the stratosphere gets. There are big SSW events as well that raise the temperature from well below average to high enough to create a reversal of mean zonal winds.

[Kentish Kiwi]

Would I be right in my thinking that the Polar Vortex has hit/is forecast to hit a level of strength and organisation that hasn't been seen since pre-2008/2009?

[chionomaniac]

Would I be right in my thinking that the Polar Vortex has hit/is forecast to hit a level of strength and organisation that hasn't been seen since pre-2008/2009?

No, the mean zonal winds were higher for a small period last winter at the 10 and 30 hPa levels.

[chionomaniac]

The strength of the upper polar vortex is set to reduce dramatically over the next day or so as the latest upper warming takes hold. This will be most pronounced at the 1 hPa level and does look like not filtering down to the troposphere. Unfortunately we are not in the best position to receive any benefits from the position of the displaced polar vortex which will be Atlantic based.

In fact the polar vortex regains its shape quite quickly following the warming and without any reduction in strength at lower levels it looks to help dictate the pattern of our weather for the foreseeable future. One can see looking at the 20 hPa level the shape, position and strength of the vortex forecast at T+240.

Probably as bad as it gets for cold lovers!

There is a chance that the jet as it travels from east to west will have a slight southerly component which could allow for colder polar to get into the mix.

One can see this chance when looking at the potential vorticity charts. If you imagine that any depressions will travel along the southern edge of the increase in potential vorticity then it is possible to make out the likely trajectories.

I certainly have not given up hope that winter is over but there are no signs of high latitude blocking that will affect us in the current charts for the foreseeable future. However I would not be surprised to see another warming on the cards come into the forecasts next week.

[Guest mycroft]

Chionomaniac.

Whats making the PV so stubbingly strong this last month,? is it the la nina or just the right synoptics in the wrong place (for us)The warming events albeit minor seem to have no effect and do not descend to lower levels this past month

Edited January 29, 2011 by mycroft

[picog]

Chionomaniac.

Whats making the PV so stubbingly strong this last month,? is it the la nina or just the right synoptics in the wrong place (for us)The warming events albeit minor seem to have no effect and do not descend to lower levels this past month

This link shows how unusually cold it is at the 30 hPa level — the "heat" definitely is staying at the top!

http://ds.data.jma.go.jp/tcc/tcc/products/clisys/STRAT/html_e/pole30_n.html

[lorenzo]

Warming is occurring up top but not going anywhere - some interesting nose dives at 1Hpa that hit a brick wall. Is QBO changing again?

Mycroft found a post from GP that explained the current PV - the QBO and La Nina got married...

The blocking signal (enhanced -ve zonal wind anomalies) peaked during October and I suspect the cold outbreak that took place then was heavily influenced by this although the blocking signal at 500 hPa and above has remained favourable since October. Looking at the periodicity, the blocking signal should come under pressure at 200hPa around the turn of the year, and then progressively weaken to a minimum in February and March as the downwelling of +ve zonal winds (weakest upwelling waves) reaches its peak intensity. This underlines the extremely long time scales for stratospheric events to impact the troposhere.

Current Winds http://www.cpc.ncep.noaa.gov/products/stratosphere/strat-trop/gif_files/time_pres_HGT_ANOM_JFM_NH_2011.gif

Current Temps http://www.cpc.ncep.noaa.gov/products/stratosphere/strat-trop/gif_files/time_pres_TEMP_MEAN_JFM_NH_2011.gif