stratospheric meteorology Interpreting stratospheric temperature flux charts

[Vorticity0123]

Hi all, 

 

Now that winter is approaching, the stratospheric polar vortex is starting to take shape again. This also marks the time when the interest in stratospheric meteorology starts to increase again, due to its coupling with the weather in the troposphere etc. 

 

While looking at the stratospheric charts of the ECMWF from the Freie Universitat Berlin (or FU berlin in short), I came across a chart (heat flux charts) which I was so far unable to interpret.

 

The type chart is given below:

 

Heat flux wave 1 forecast of ECMWF, 12 UTC November 8 run, T+240.

 

The chart is coincident with Wave 1 activity, which is expected to be present at the top of the stratosphere at around 70 N (zonal average). 

 

http://users.met.fu-berlin.de/~Aktuell/strat-www/wdiag/figs/ecmwf1/ecmwfzm_ha1_f240.gif

 

From what I could guess so far, I would say that the chart shows the covariance of horizontal, meridional wind with temperature. Assuming that the meridional wind is postive toward the pole, my guess would be that positive (orange) colours indicate transport of positive temperature anomalies toward the pole (in other words: a positive heat flux from lower to higher latitudes). This would in turn bring warm air from the midlatitudes toward the pole (in the chart above). 

 

Below is a representation of how this would look like at 1 hPa pressure level at the same timeframe:

 

Geopotentials 1 hPa level, ECMWF, 12 UTC November 8 run, T+240.

 

The black circle shows the line of 70 N around the pole. The arrows indicate temperature fluxes (if done properly). A possible interpretation would be that the heat flux in the first chart indicate a flux of warm air entering the vortex from one side (since it is only prevalent in 1 wave). This would then be from the Eurasian side (the arrow with a box around it), since the temperature gradient would be the most sharp at that area.

 

My question is: is the way of reading the charts given above correct? Does the heat flux chart presented in the first image indeed represent the transport of heat poleward and vice versa? And is the way of application to the final chart also correct?

 

Many thanks in advance for taking the time to answer these rather technical questions!

 

Regards,

 

Vorticity.

 

*Edited to change thread tag.

Edited November 28, 2014 by Vorticity0123

[lorenzo]

For Heat Flux charts I relate activity to the NAM, also working on getting my head round the Berlin charts still and this is after a few years of looking at them, good to see a thread examining these. More than happy to be corrected as essentially this is thinking out loud and putting together bits and pieces.

 

These charts are a challenge and I think some degree level study would have helped here, however it is probable that all have simplistic explanations / readings.

 

For above I view the positive anomalies representing heat flux as a result of the wave activity, with the standing wave introducing heat anomalies into the stratosphere. For the second chart the Wave 1 location is the lead for the introduction of this flux.

 

The important point I think is that any monitoring of heat flux ,with respect to vortex events,  has to consider that activity has to be sustained and daily analysis cannot always tell the whole story.

 

Waugh & Polvani paper here describes the impacts http://www.phys.ocean.dal.ca/people/po/Whistler/waugh.pdf

 

Tiffany Shaw has written many papers relating to this, also from earlier this year an interesting one on how the stratospheric bias within models imprints onto the Atlantic, again good to see academics working on exactly what the Atlantic Jet is doing.

From the abstract.

 

The impacts are reminiscent of different phases of the North Atlantic Oscillation. In particular, extreme positive (negative) heat flux events in the stratosphere are associated with an equatorward (poleward) jet shift in the North Atlantic basin. The metric is used to evaluate troposphere-stratosphere coupling in models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5). The results show that models with a degraded representation of stratospheric extremes exhibit robust biases in the troposphere relative to ERA-Interim. In particular, models with biased stratospheric extremes exhibit a biased climatological stationary wave pattern and Atlantic jet stream position in the troposphere. In addition, these models exhibit biases in geopotential height and zonal wind extremes in the North Atlantic region.

 

 http://onlinelibrary.wiley.com/doi/10.1002/2013JD021191/abstract

 

In general the thoughts are then that positive heat flux events in the stratosphere are related to an equatorward shift in the jet, with the opposite being true and a polar shift for low heat flux events.

 

JMA site is also useful for seeing the temperature changes over a weekly periods and these can be viewed in combination with the EP Flux over 100hPa to determine wave impact and where this is decelerating the mean vortex.

 

 

http://ds.data.jma.go.jp/tcc/tcc/products/clisys/STRAT/index.html#monit_nh

 

Loads of other data on there to also consider.

 

The composites within (W&P) show when recorded over a longer timescale that high heat flux events precursor a stronger vortex, low heat flux precursor to a colder vortex regime. In turn these then imprint on NAM. With a drop in NAM following high heat flux events.

 

Also looking at the heat flux across wave 1 and 2 on berlin another thing to compare is the momentum flux.

 

Day 10 this morning shows considerable heat flux in the upper stratosphere.

 

Hope that was of some help, would be good to get a professional meteorologist to go through the Berlin site and annotate all the charts into a guide. But I guess that would take away some of the mystery.

 

All in all, it's not a happy vortex this season and we have really decent wave activity with a good background to these repeating and sustaining. If ever the atmosphere was pre-conditioned to an SSW or EVE then this year is it. Fascinating to watch where this activity is almost head to head with the classic VI period.

 

 

[Tyfelin]

Hi Lorenzo. I originally posted this question on the start thread, and got to take a few sips from the firehose that is Recretos :-)

I'm trying to Interpret the wave 1 and 2 charts as frequently posted by yourself, Matt etc. I know how Fourier analysis works, so I'm good the concept of waves 1, 2, 3. And I can spot the phenomena easily enough on a chart which displays the height of a geopotential surface. But I'm really struggling with this type of chart:

https://f1.nwstatic.co.uk/forum/uploads/monthly_11_2014/post-15767-0-96037400-1415857618.jpg

I understand the axes. And I can see that in this view you're looking at the phenomenon happening through a deep layer of atmosphere. But how do I interpret this as a wave? What are the units on the third axis, delineated by the colour scheme?

Any help appreciated. Sure I'll get to the heat flux data at some point!

Tyfelin

[lorenzo]

Look on the strat thread for the MERRA dataset here you can download all the respective W1-3 amplitudes in meters.

The above demonstrates the amplitude of w1 across the latitude and pressure level from upper to mid to lower strat.

JMA Site has a plot of wave 1 to 3 activity. Keeping it simple these are posted to show disturbances on the vortex. Wave 1 activity displacement vortex and wave 2 splits.

[Tyfelin]

That's a great help. Cheers.

[Vorticity0123]

For Heat Flux charts I relate activity to the NAM, also working on getting my head round the Berlin charts still and this is after a few years of looking at them, good to see a thread examining these. More than happy to be corrected as essentially this is thinking out loud and putting together bits and pieces.

 

First of all, lots of thanks for putting up such an elaborate post. I was rather busy during the past few weeks, so that explains the rather late timing of my post, please forgive me for that.

 

Agreed on the first comment, those charts definitely require some advanced knowledge, starting from the representation of a flux in terms of variances. And that only just explains what is indicated on one axis of the graphs, nothing more in detail yet.

 

The point of view I was looking from was somewhat incomplete, as the part I only took in consideration in my initial post was the horizontal wave propagation. In other words, the transport of heat from the equator to the poles and vice versa while keeping the pressure level (or height) steady. But of course vertical wave propagation (thus the transport of heat toward higher/lower altitudes) is also a part of stratospheric meteorology. The combination of horizontal (East-West, North-South) wave propagation and vertical (altitudinal) wave propagation is quite a challenging subject to get my head around, let alone the figures on the FU Berlin site.

 

This new insight does help me somewhat in getting the insight in what is meant with vertical wave propagation. So if I am correct, a flux of warm air toward the pole at, for example, 10 hPa over the USA translates into troughing in that position at the same position at a height of 500 hPa. Judging from simplicity, I would think it would be the other way around (WAA at 10 hPa causes WAA at the surface), but it is clear that this line of thinking is not elaborate enough.

 

Also thanks for the cool plots from JMA, these plots do indeed give a nice insight. From the JMA profiles at the given time it does seem that the polar vortex is being pushed away from USA (given the continuous warming at that region). It is also interesting to see that the Western Pacific has been heating at 10 hPa over the past couple of weeks (given the image, if my way of reading is correct).

 

About the Northern Annular Mode, it seems to be quite a difficult subject (never heard of it before), but I found a good article about it here:

 

http://www.atmos.colostate.edu/ao/introduction.html

 

One question about the NAM-part of your post: you mention that high heat flux activity leads to a stronger vortex. On the other hand, low heat flux activity relates to a colder vortex. But if the vortex is stronger (i.e. deeper), the polar vortex is also colder in general. Would high heat flux activity lead to a weaker (warmer) vortex instead?

 

This polar vortex is definitely in a much different state compared to last year, great to watch it unfold this year. Furthermore, perhaps even better (from a personal point of view), is that, slowly but surely, the concept of stratospheric meteorology is slowly becoming more clear for myself. This forum provides an excellent place to build on this knowledge.

 

Regarding winter prospects, let the polar vortex be quickly weakened by these atmospheric waves, and then we could well be facing a vastly different winter compared to last year.

 

Hopefully this thread could turn into a very informative thread regarding stratospheric chart interpretation. I realize that a large part of the post is a little bit off-topic in that sense, but it appears to me that it is necessary to understand the concepts in order to be able to interpret the stratospheric charts in a reliable way. So probably when I have more time, I’ll try to give a more sophisticated look at these charts.  

 

Once again my gratitude for your very extensive post!

 

And last but not least, any feedback from all sides is greatly appreciated!

[Vorticity0123]

To give a first go for interpreting stratospheric figures, I will start with a rather difficult series of graphs, being the zonal mean winds and fluxes chart from FU Berlin. The graph (or better, set of graphs) is given below.

 

Zonal mean winds and fluxes at 60N, as of 10-11-2014 (ECMWF-run)

 

Due to the complexity of the lower three charts, and due to my very basic understanding of the stratosphere, only the two upper charts will be explained here. The explanation may not be without errors, so any comments or improvements would be greatly appreciated. 

 

To start with the first one, the chart shows the zonal mean wind at 1 hPa level (being at the top of the stratosphere) at 60 N latitude. The term zonal mean indicates that one measures a quantity at all points at a given latitude, essentially circling the earth, and averages these. For example, consider the wind at 60 N from 0E to 180E (the eastern part of the Earth) to be 10 m/s (westerly winds), and from 180W to 0W (the western part of the earth to be 20 m/s (westerly winds). This would result in a zonal average wind of 15 m/s. 

 

For anybody willing to learn more about zonal averaging, a good read can be found here:

 

http://disc.sci.gsfc.nasa.gov/giovanni/additional/users-manual/G3_Zonal_Mean

 

Note that a positive wind means a wind blowing from west to east. No meridional wind component (northern- or southern component) is being taken into account in the calculation of the zonal mean wind. The black line on the first two graphs shows the forecast for the zonal mean wind up to 10 days out.

 

The zonal averaged wind at 1 hPa tells something about the strength of the stratospheric polar vortex. When the zonal mean wind is very high and positive, it means that the stratospheric polar vortex is rather strong (deep). However, when the zonal mean wind is very low or even negative (easterlies), the stratospheric polar vortex is in a much weakened state, and is highly susceptible to wave breaking activity.

 

The second figure shows the zonal mean wind at 10 hPa and 30 hPa levels, which are closer to the surface than the 1 hPa level. In short, the same rules apply as indicated in the 1 hPa zonal mean wind profile, except for the fact that one is looking at a lower altitude.

 

Finally, for an interpretation and intercomparison of these zonal average winds between this and last year, please take a look at the post from Chionomaniac below:

 

https://forum.netweather.tv/topic/81567-stratosphere-temperature-watch-20142015/page-29

 

Hopefully this information can help some to gain a little understanding in what all these mysterious stratospheric charts mean. And please do not hesitate to correct me, because, as noted before, my understanding of stratospheric meteorology is very basic at best. Finally, any additions or new information to make it easier interpreting these charts is greatly appreciated  .

 

Sources:

http://disc.sci.gsfc.nasa.gov/giovanni/additional/users-manual/G3_Zonal_Mean

http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/

https://forum.netweather.tv/topic/81567-stratosphere-temperature-watch-20142015/page-29

Edited November 28, 2014 by Vorticity0123