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  • Gwo And Global Angular Momentum


    Message added by Paul

    Please be aware that these comments were copied here from another source and that the date and time shown for each comment may not be accurate.

    Glacier Point said:
    Where do you see the GWO going in the next few days Mark ? If it's back to phase 1-2, some support for Icelandic block, phases 3-4 and more of the Atlantic influence perhaps ?

    Ok I will start a new thread for dicussions along this line and perhaps I will draw on some ideas expressed in the stratospheric thread and artic sea ice thread. I guess you would be the best person to explain all this GP but for those who don't know this thread is about global angular momentum and how it oscialltes up and down (Global Wind Oscillation) along the lines discussed by Ed Berry.

    Angular momentum is of course a measure of the turning force in the winds, so could perhaps be considered a measure of the strength of low pressure systems, but also relates to how much the jetstream undulates and how much blocking we have.

    The budget of angular momentum goes up and down as energy is lost as weather systems crash into mountains and increases as cold air meets warm. Each phase of increasing and decreasing momentum suggests different types of weather for the UK. Looking at the current GWO plot we see a liklihood of going into phases 3 and 4 based on how it usually cycles round.

    This implies increasing angular momentum as the various torques including mountain torque diminish (i.e those things which take energy out are not active).

    This is certainly true of mountain torque.

    For frictional torque and gravity wave torque then the jury is out.

    Overall it looks like global angular momentum is on the increase.

    The tendecy during december has been upwards.

    Short term I think we are looking at phases 3-4 and more of an Atlantic influence. What I am guessing at though is that low pressure systems crossing the US will increase mountain torque, equally the jet stream across india is not a weak flabby one which might increase asian mountain torque. The strong jet in the western pacific along with OLR charts suggest strong trade winds with a stationary high to the north east of Australia and convectional activity to the north west of Australia. So back to phase 1-2 fairly quickly I think afterwards.

    All maps are available in the link below.

    PSD Map room for AAM

    I am sure GP will tell us what he expects from the MJO and convectional activity in the pacific and how and if he expects rossby wave development as a result. It is those Rossby waves which in part will affect the stratospheric vortex and the low angular momentum could be linked to a more blocked pattern and sea ice build up to our north which I talked about in associated threads.

    What we should always remember though that this a complex interaction of parts of which the stratosphere plays a large part during the winter.

    Please note that this post and subsequent comments have been copied from the forum, so the dates/times of the comments are not correct.

    Edited by Paul

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    I am not sure I really agree about the vortex at lower levels. Certainly there is some cold air and a deep circulation at 30hPa but it all looks pretty weak at 100hPa. Vorticity at the tropopause is very messy indicative of a weak vortex.

    Analysis out of Japan also shows a very weak vortex.

    Heat flux also looks to be fairly flat line.

    The thing about the average of zonal winds at this time of the year is that it is the average of years when both the vortex is still active and when it has already broken up. You would expect it to be above or below the average with average indicating a weak vortex at lower levels. There are indications though that it will strengthen and we might be in for a late break up of the vortex.

    We wait to see which way it goes.

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    For the first time since early February, NWP forecast tools are suggesting a northern block to develop across the Barents Sea to Greenland. How much credance can we give this ?

    During March and April, complex dynamical processes (torques and eddies) in the atmosphere have worked to add westerly winds to the overall global circulation indicative of a shift in the synoptical pattern from La Nina to neutral ENSO. The net impact of these processes has seen the Global Wind Oscillation ladder up in phase space 3-4-5 (Nino like).

    http://www.cdc.noaa.gov/map/images/gcm/gwo_40d.gif

    However, since late April / early May the westerly wind input has temporarily declined. As nature abhors a vacuum, easterly winds have begun to progressively replace the westerlies and significant easterly wind tendency has developed in the circulatory pattern. This has largely been driven by frictional torques:

    http://www.cdc.noaa.gov/map/images/reanaly...ltauf.90day.gif

    Mountain torques are following the lead:

    http://www.cdc.noaa.gov/map/images/reanaly...ltaum.90day.gif

    and tendency in earth angular momentum is sharply down:

    http://www.cdc.noaa.gov/map/images/reanaly...teaam.90day.gif

    The MJO after almost completing a full orbit has beat the retreat in phase 7 - a sure sign of negative (easterly) tendency in the atmopshere:

    http://www.bom.gov.au/bmrc/clfor/cfstaff/m...Last40days.html

    Where the GWO goes in the next 10 days will have a large influence on the global weather patterns. Given that both frictional and mountain torques are negative and likley to remain so for several days (some suggestion of frictional torques heading upwards) and lack of tropical intertia c/o a lack of convective activity, I think we will see the GWO orbit in medium amplitude phase 0 and 1.

    Composite reanalysis for phase 0 at 500hPa identify a large negative anomaly in the eastern North Atlantic and height rises further north and north-west which is consistent with the NWP outputs.

    Phase 1 reanalysis suggests the low to become stationary and fill with a height rise over continental Europe - something of a progressive pattern which should result in warmer, drier weather developing from the south and pushing northwards towards day 10 (mid month onwards) - note the trough persisting over Scandinavia.

    Today's ECM 00z (08/05/09) has a similar evolution t144 onwards and I think this is very plausible. Whilst it looks very likely to become unsettled mid next week onwards, this should only last a few days in the south and indications to me that we should see conditions improve from next weekend onwards provided that we do not see the GWO stall in phase 0.

    Longer term, even though the atmosphere is becoming more Nina like, I think this is only temporary state and the overall building of warmer SSTAs across large parts of the Indian and Pacific Ocean are likely contribute to increasing westerly (Nino) tendency in the pattern as we head into June, as is the state of the polar atmosphere which remains more conducive to sustained warm and dry periods June through August.

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    Have you guys ever pondered putting on an afternoon lesson somewhere where the rest of us could come along and attempt to be shown some of the bigger picture ? .. I think theres a lot of people who'd pay good money for this... just a sugestion.

    sam

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    Have you guys ever pondered putting on an afternoon lesson somewhere where the rest of us could come along and attempt to be shown some of the bigger picture ? .. I think theres a lot of people who'd pay good money for this... just a sugestion.

    sam

    I agree, I have a Bsc in Phys Geo and spent most of that doing meteorology and atmospheric science and some of this os over the bonce.....some well written guides would come in really really handy!

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    the idea of some kind of meet up, mind you it would need paying for, has been discussed on the open forum and elsewhere, both for synoptic meteorology and the teleconnections side.

    There are enough quite well qualified people to make it feasible.

    Best you pm Paul and see if it could be put up to test reaction.

    I would be happy to do day to day synoptic meteorology.

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