Stratosphere temperature watch - 2016/17

[bluearmy]

14 hours ago, Summer Sun said:

 

Pedantic I know but the Berlin chart is he previous days 12z not the 00z run. 

As far as current nwp is concerned, zonal flow 500/300hpa continues to be stronger days 7/10 than now which explains the mobility showing. Thereafter expect the reversal high up to makes itself felt lower down as zonal flow relaxes to become very slack and HLB establishes more widely in the trop. 

[phil nw.]

Yes the charts below show the result of the recent warming and now maybe the final one as zonal winds at all levels are shown to decrease as we go forward into March.No surprise of course at this time with the Sun again above the horizon for a time in the Arctic and the Polar night almost at an end.

and as mentioned in the Model thread later frames in the 500hPa charts now showing the start of what could well be the commencement of the final trop.vortex breakup.

[Matthew.]

Great charts above. Just comparing the zonal winds to March last year and am I right in thinking last year was a major SSW whereas this year looks just a normal event?

[Interitus]

16 hours ago, Matthew Wilson said:

Great charts above. Just comparing the zonal winds to March last year and am I right in thinking last year was a major SSW whereas this year looks just a normal event?

Last year was a large major SSW, but because the winds didn't return to westerly it doesn't count as a major midwinter warming but as a final warming instead. Not sure what a 'normal' event is, but this forecast 2nd SSW of the winter is dragging on for ages and is even maybe not a certainty having vanished within 10-days on yesterday's ECM, and not on last night's GFS 0z as plotted on the weatheriscool site. Bear in mind that the GFS at one point had a reversal with a split vortex for as early as the 14th February to generally by the 18/19th for a number of runs.

[Gray-Wolf]

http://www.atmos-chem-phys.net/17/615/2017/

"Stratosphere–troposphere coupling is investigated in relation to middle atmospheric subtropical jet (MASTJ) variations in boreal winter. An exceptional strengthening of the MASTJ occurred in association with a sudden equatorward shift of the stratospheric polar night jet (PNJ) in early December 2011"

For those who haven't seen it yet I thought this might be useful?

I had worried about impacts on the QBO on the MJO and so on weather generally but this opens up the topic further.

[Summer Sun]

 

[Gael_Force]

Is anybody discussing this in a more in depth medium than twitter? 

 

[Summer Sun]

 

[Frostbite1980]

2 hours ago, Summer Sun said:

 

I didn't think the warming in early December was a SSW......a bit misleading??

[Interitus]

12 hours ago, Frostbite1980 said:

I didn't think the warming in early December was a SSW......a bit misleading??

Not a full SSW and it was generally in late November anyway - this was when the minimum wind speed was recorded and although 10mb temperatures peaked in the first week of December, the vortex was already cooling and strengthening lower down.

edit: He's been taken to task to explain it in subsequent tweets and apparently "it was kind of a remnant of more robust warming earlier in November". Hmm.

Edited February 25, 2017 by Interitus

[Dennis]

Bullseye

[Summer Sun]

 

[Interitus]

On 3/2/2017 at 15:01, Summer Sun said:

 

But the next day -

Hard to make any meaningful predictions with such variable output, but it also raises questions about what would be assumed to be downward propagation. How does this manifest itself, and is that what is being witnessed in the second image or is it just coincident with tropospheric variability giving polar height rises for the trop and lower strat?

[Weather-history]

On 18 February 2017 at 20:46, Summer Sun said:

 

Have we actually had an official SSW event this year? The one above looks like it was over egged by the models again. I think that has been the story of the season, predictions so far out haven't quite come out at the time.

[Interitus]

1 hour ago, Weather-history said:

Have we actually had an official SSW event this year? The one above looks like it was over egged by the models again. I think that has been the story of the season, predictions so far out haven't quite come out at the time.

Following the 10mb 60°N zonal wind reversal criteria, there was an SSW on 1st February according to the ECM analysis at the time (?? m/s) and the MERRA2 reanalysis (-0.63 m/s), but wind speed just fell short on NCEP/NCAR reanalysis, with reversal at 62.5°N (-0.89 m/s) but not 60°N (+1.48 m/s). This was forecast reasonably well.

A follow-up 2nd wind reversal or separate SSW - arbitrary criteria based typically on being at least 20 days apart - has been repeatedly forecast but hasn't happened. However, not sure that this is all down to poor modelling or just a bit of luck. With the event in the image above, on the 26th February the ECM analysis was 0.53 m/s, MERRA2 was 0.72 m/s and NCEP/NCAR 1.87 m/s. Fine margins.

[bluearmy]

7 hours ago, Interitus said:

Following the 10mb 60°N zonal wind reversal criteria, there was an SSW on 1st February according to the ECM analysis at the time (?? m/s) and the MERRA2 reanalysis (-0.63 m/s), but wind speed just fell short on NCEP/NCAR reanalysis, with reversal at 62.5°N (-0.89 m/s) but not 60°N (+1.48 m/s). This was forecast reasonably well.

A follow-up 2nd wind reversal or separate SSW - arbitrary criteria based typically on being at least 20 days apart - has been repeatedly forecast but hasn't happened. However, not sure that this is all down to poor modelling or just a bit of luck. With the event in the image above, on the 26th February the ECM analysis was 0.53 m/s, MERRA2 was 0.72 m/s and NCEP/NCAR 1.87 m/s. Fine margins.

All a bit technical rather than practical though. It isn't whether it's 65 N or 55N , its more how big any reversal is and how effectively it can propagate down to the trop. Is there that much difference between +1 m/s and -1 m/s? Clearly they flow in opposite directions but so weak as not likely to have much effect. and the actual flow at exactly 60N is again surely not as relevant as the magnitude of any reversed flow anywhere between 50 and 70N.

[Interitus]

On 3/7/2017 at 08:31, Interitus said:

Following the 10mb 60°N zonal wind reversal criteria, there was an SSW on 1st February according to the ECM analysis at the time (?? m/s) and the MERRA2 reanalysis (-0.63 m/s), but wind speed just fell short on NCEP/NCAR reanalysis, with reversal at 62.5°N (-0.89 m/s) but not 60°N (+1.48 m/s). This was forecast reasonably well.

 

Fell short on the JRA-55 also, apparently.

[summer blizzard]

Looking at the stratospheric forecast in terms of zonal winds it looks like the current uptick has no legs and we quickly see a weak stagnation. I would suggest that the next strong wave 1/2 will probably finish the job and hence i would expect a final warming to occur late in the month (only a week or two earlier than normal). 

[Interitus]

On 3/7/2017 at 15:48, bluearmy said:

All a bit technical rather than practical though. It isn't whether it's 65 N or 55N , its more how big any reversal is and how effectively it can propagate down to the trop. Is there that much difference between +1 m/s and -1 m/s? Clearly they flow in opposite directions but so weak as not likely to have much effect. and the actual flow at exactly 60N is again surely not as relevant as the magnitude of any reversed flow anywhere between 50 and 70N.

Yes, possibly. Where it does become interesting is in the future when composites and research make use of SSW events, usually little thought is given to the actual details, just whether it was a 60°N 10mb reversal.

Edited March 12, 2017 by Interitus

[Gray-Wolf]

I take it we're done here? Are we just to expect the vortex to fade away from here on in?

Meanwhile how is our QBO reversal coming along? I do not know what another failure to do so would signal for forecasting beyond 2 days as we've seen repeatedly over winter?

So QBOe allows for a wonkier polar Jet and more SSW's or is that not true under these new low ice forced wonky jet/SSW's?

[stodge]

18 hours ago, Gray-Wolf said:

I take it we're done here? Are we just to expect the vortex to fade away from here on in?

Meanwhile how is our QBO reversal coming along? I do not know what another failure to do so would signal for forecasting beyond 2 days as we've seen repeatedly over winter?

So QBOe allows for a wonkier polar Jet and more SSW's or is that not true under these new low ice forced wonky jet/SSW's?

This morning's GFS 00Z OP has a stronger warming at the turn of the month which is presumably our "final warming" working through.

[Interitus]

5 hours ago, stodge said:

This morning's GFS 00Z OP has a stronger warming at the turn of the month which is presumably our "final warming" working through.

The average date of 10mb wind reversal in the MERRA-2 reanalysis data is 12th April. Research shows that sometimes the final warming occurs first in the mid-stratosphere eg 10mb and other years in the upper stratosphere and working down. Hardiman et al. categorise the FW by which level they occur at first - 1mb or 10mb, and suggest that this has implications for tropospheric effects and forecasting - http://onlinelibrary.wiley.com/doi/10.1029/2011JD015914/epdf

[Interitus]

On 3/8/2017 at 20:28, summer blizzard said:

Looking at the stratospheric forecast in terms of zonal winds it looks like the current uptick has no legs and we quickly see a weak stagnation. I would suggest that the next strong wave 1/2 will probably finish the job and hence i would expect a final warming to occur late in the month (only a week or two earlier than normal). 

It depends on how a final warming is defined, but only 3 times in the MERRA data since 1979 has the 10mb 60°N wind become easterly in March and remained so onwards for the rest of the summer.

Last year was the earliest on 05/03, a whole two weeks earlier than 19/03/86, then 24/03/85. Further to the previous post that the average 10mb 60°N wind speed becomes easterly on 12th April, the actual average date is 17th April.

The latest are 09/05/09 (after record SSW in Jan), 10/05/01 and finally 13/05/81.

Looking at the analogues, the suspicion is that this year it will probably be at least a month away, towards the end of April.

 

 

[summer blizzard]

5 hours ago, Interitus said:

It depends on how a final warming is defined, but only 3 times in the MERRA data since 1979 has the 10mb 60°N wind become easterly in March and remained so onwards for the rest of the summer.

Last year was the earliest on 05/03, a whole two weeks earlier than 19/03/86, then 24/03/85. Further to the previous post that the average 10mb 60°N wind speed becomes easterly on 12th April, the actual average date is 17th April.

The latest are 09/05/09 (after record SSW in Jan), 10/05/01 and finally 13/05/81.

Looking at the analogues, the suspicion is that this year it will probably be at least a month away, towards the end of April.

 

 

Interesting. I had no idea that the final warmings occurred so close to the mean.

[Interitus]

On 3/7/2017 at 08:31, Interitus said:

Following the 10mb 60°N zonal wind reversal criteria, there was an SSW on 1st February according to the ECM analysis at the time (?? m/s) and the MERRA2 reanalysis (-0.63 m/s), but wind speed just fell short on NCEP/NCAR reanalysis, with reversal at 62.5°N (-0.89 m/s) but not 60°N (+1.48 m/s). This was forecast reasonably well.

A follow-up 2nd wind reversal or separate SSW - arbitrary criteria based typically on being at least 20 days apart - has been repeatedly forecast but hasn't happened. However, not sure that this is all down to poor modelling or just a bit of luck. With the event in the image above, on the 26th February the ECM analysis was 0.53 m/s, MERRA2 was 0.72 m/s and NCEP/NCAR 1.87 m/s. Fine margins.

The finalised MERRA-2 figures give an SSW on 01/02/17 by just -0.07 m/s!

26/02/17 was +0.8 m/s