[Gwo And Global Angular Momentum]

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.

[Gwo And Global Angular Momentum]

One of the key things about Spring and Early summer is that the jet stream begins to shift North. Typically in the region of the UK there is a northern arm and a southern arm to the jet and where ever they occur you often get wet and windy weather. Due to the low global angular momentum (la nina like) state of the climate then the jet stream is currently further south than it would normally be. This is born out by the ITCZ being relatively far south across Africa for this time of year.

I tend to think that we get two periods of about a month of wet weather as the jet stream moves north. During la nina those months might be April and June with August and October being wet as the jet comes back south. During el nino those months may be earlier for instance March and April. Ideally you would want a transition from la nina to el nino during spring which would push the jet north quickly, limiting the about of wet weather.

One of the best teams for predicting la nina and el nino are the Australians who tend to look at the SOI (Southern Ocean Oscillation Index) as a pre cursor to the state of equatorial water temperatures in the Pacific (which is what la nina and el nino are). During the last month we have seen a significant change and although this was enhanced by some strong activity through phase eight of the MJO it should be noted that the recently dominate pacific trade winds have been over come.

I will take time for the MJO signal to travel around the world again and to some extent you might expect some change at this time of year, but I still see some significance that may not yet be reflected in the models.Warm water volumes should be declining somewhat now so a full on el nino seems unlikely but the changes seem to be significant even though global angular momentum is on the low side.

Since the stratospheric vortex has never really recovered from the mid winter disruption we have had an unusually spring like late winter season with very little pattern blocking. Significantly the North Atlantic storm channel has been open for over a month and this has had an impact on ice formation to our north especially in the Barents sea area (yes I do know all the caveats surrounding the following chart but it goves an indicator).

This is perhaps not good news for snow lovers for next winter in the UK although the snow fields of Asia may still be quite late clearing leaving us watching for a beast from the east as a source of cold next winter. Coming back to the storm channel being open and how weather patterns seem to be to be limited to a two month period then the current pattern should not have that much more to run. I put this down to the rossby wave lengths (number of undulations of the jetstream around the world) tending to change with time and season.

In conclusion I am quite hopeful for a drier spring season than usual with temperatures beginning to catch with the norm from here on in. I am also rather hopeful that with plenty of cold air to the north due to the low angular momentum conditions and with the jetstream beginning to come north more quickly we may have an interesting storm season ahead (although it may be shorter than usual?). We might also see a Hot month mid summer instead of barely escaping the clutches of the jet stream last year. I reserve the right to completely change my mind though if the SOI changes, or the stratospheric vortex reforms, or any one of a number of variables change.

[Gwo And Global Angular Momentum]

My take would be that Low angular momentum means less energy going into the jet stream. This would suggest to me that during a low angular momentum period the jet stream tends to stay south and not arch northwards leading to high latitude anticyclones. This means that low angular momentum is not good for a particular type of blocking. Typically we get cold periods due to being north of the jetstream, but the Atlantic storm track is rarely disrupted.

A strong la nina period which is associated with low angular momentum however means trade winds tend to be strong across the Pacific. This leads to a stationary anticyclone north of the equator which by nature of the fact it does not move can cause extra tropical blocking to its north. Unfortunately this type of blocked pattern is not often conducive to cold weather in the UK with I think high pressure in the north pacific, low pressure in north west Canada and high pressure again in north east Canada. All this does depend on the season and number of Rossby waves around the globe, hence why Glacier Point uses re- analysis to show the effect during any particular month.

You might think that a strong el nino period would give you the opposite effect, but what you get is a strong jet blasting across the Atlantic with the UK ending up with a largely wet winter. You will get periods where the jet arches northwards but any anticyclone tends to get undercut or blown away by the strong jet. In contrast to the fixed anticyclone north of the equator in the Pacific you tend to get Thunderstorm activity (MJO) moving west to east across the equator, again not giving a very fixed pattern.

The point about the QBO and its direction is that stratospheric anomalies tend to be transmitted down to the troposphere during a easterly QBO rather more than a westerly one. This is not well explained why in literature but seems to reflect the fact that north pole stratospheric winds (stratospheric vortex) may be pulling in the opposite direction to equatorial stratospheric winds (QBO). I also think the actual nature of the Stratospheric disturbance plays a part. Split vortexes tend to lead to a lot of blocking, displace vortexes lead to less blocking and completely disrupted vortexes give very little blocking, but tend to reinforce low angular momentum. We have actually gone through all three of these phases with different results.

[Gwo And Global Angular Momentum]

Current Analysi of the stratosphere.

5 Days out.

From this I would take a strong signal for blocking in the northern Pacific and a secondary weaker signal for blocking in the north Atlantic. This kind of shows up on the GFS blocking maps.

8 DAYS OUT

How does it compare to ECM and GFS forecasts.

Clearly the strong signal is across the other side of the world and we are more likely to be influenced by GWO and as a downstream product of the strong signal in the pacific.

GWO is now headed strongly into phase 1 and there are clear indications that Global Angular momentum is likely to tank. I see this as an indication that we are never going to be far away from being north of the jet stream, but indications are that we might just miss out on the really cold stuff. Spring weather with a misture of cold and mild seems in order.

[Gwo And Global Angular Momentum]

Events in the stratosphere are pretty unusual and the tropospheric response should be linked to the specifics of the type of event going on. To my way of thinking there are three distinct types of event that can occur in the stratosphere.

1) A split Vortex with both displaced southwards much like we have now.

2) A single vortex displaced southwards, much like we will have in a few days.

3) A complete disruption of the vortex which I think may be on the cards after that.

Lets look at now.

Temps and the vortex

Signals for high pressure as a result

Lets move on 5 days and we see one part of the vortex collapsing as they both rotate around. Unfortunately that collapsing bit moves nearer to the UK and seems likely to give us some more atlantic type weather untill early next week.

Further out and that second part of the vortex collapses leaving just one part displaced southwards. Vorticty charts suggest here we could be in for another cold period with a risk of snow.

Even further out and we have to start looking upward in the stratosphere for clues and you need to go almost all the way up to the 5hPa layer before you start to see any kind of vortex reforming.

Giving very little vorticity in the stratosphere for a period. Meaning other signals will take priority over the stratosphere.

Those signals will most likely involve the GWO which you would expect to head into phase 1 and 2 but seems to be stubornly stuck in 3 4 and 5.

I am not really convinced about mountain torque reducing angular momentum which if I understand things correctly means as a cyclone crosses one of the great mountain ranges it transfers momentum to the earth ,taking it away from the atmosphere. My take on this would be although the mourtain torque is falling it is still positive and as such we still have some time before angular momentum falls away. Perhaps this is something for Glacier Point to elaborate on.

Cyclically it looks like warm water ought to be on the decline in the Pacific, but we do have a stalled MJO in phase 6 so maybe this will come into play. SST's I think will have their day this year if things really calm down so we ought to be thinking about high pressure maybe to the north of the warm spots in the atlantic.

The upshot of this is that models are likely to struggle a bit with the transitioning phases in the stratosphere and globally we might expect some high impact weather this year as a result of this event.

[Gwo And Global Angular Momentum]

There are times when the Global wind oscillation is not the whole story and I suspect we have such a period coming up. It is not that its wrong just that there can be some delayed actions from the patterns that occur as a result.

First let us have a quick review of where we think we are. GWO shows we are drifting into phase 1, perhaps spiking as ed berry puts it is a better word although.

Long Paddocks SOI figures show that the pacific trade winds have been somewhat intermittent, showing that the la nina phase at the moment is pretty weak.

1-Jan-2009 1012.26 1002.65 23.56 12.82 14.72

2-Jan-2009 1011.35 1003.55 15.03 12.60 14.81

3-Jan-2009 1012.38 1004.40 15.88 12.42 14.85

4-Jan-2009 1012.21 1004.95 12.49 12.91 14.89

5-Jan-2009 1013.74 1005.60 16.63 13.70 14.95

6-Jan-2009 1013.60 1005.70 15.50 14.38 14.93

7-Jan-2009 1013.45 1006.10 12.91 14.76 14.76

8-Jan-2009 1010.79 1005.40 3.68 14.37 14.57

9-Jan-2009 1008.14 1004.25 -3.39 13.78 14.37

10-Jan-2009 1008.39 1003.60 0.85 13.33 14.22

11-Jan-2009 1011.14 1003.20 15.69 13.47 14.21

12-Jan-2009 1011.61 1006.60 1.89 13.27 13.96

13-Jan-2009 1011.89 1007.60 -1.50 12.88 13.74

14-Jan-2009 1012.16 1006.90 3.07 12.94 13.56

15-Jan-2009 1013.66 1007.35 8.01 13.15 13.38

16-Jan-2009 1014.60 1006.00 18.80 13.44 13.33

17-Jan-2009 1014.59 1007.30 12.63 13.25 13.28

18-Jan-2009 1012.88 1007.60 3.16 12.60 13.20

This also coincides with a pick up in MJO activity as the wave finally comes round again.

Phase 8 where the MJO is currently is usualy the end of the cycle and we might expect la nina and the trade winds to pick up again.

Understanding what is going on Torque wise is rather more tricky. Moutain torque does not suggest any spectacular change in angular momentum, however as GP points out the frictional torque has picked up. Gut feeling tells me that the spike into DWO 1 will lead to a signifcsnt drop in angular momentum coming up (Read a blocked pattern). Normally I would guess that the current pattern is here to stay, but I don't think so and I think most of the models may be perfroming poorly at more than a week out. Ed berry suggest a transitional change and when he talks about winter storm developments focusing on the Plains I cannot help thinking mountain torque and sinking angular momentum.

Now for the fly in thointment so to speak and here I am looking at the stratosphere forecasts.

That looks a lot like a split stratospheric vortex and if that comes off then all bets are off. Current vorticity charts suggest a deep low for the central plains of the US, meaning winter will reallly start over there and a lot of energy will go into the jet stream as a result. High pressure ridging north in the Atlantic would not be an unexpected result although it does depend on how the jet reacts (it could just blast across the atlantic).

Despite my inital argument that the stratosphere was spoiling things there is some symmetry between what the GWO tells us and the ECM stratospheric forecasts. Cooler northerly perhaps on its way then ?

[Gwo And Global Angular Momentum]

That slightly tricky to answer. Lets try to answer the second question first.

Fast, zonally oriented Rossby wave dispersion occurs in phase 5. (Amplified Jet)

An extended Pacific Ocean jet stream and southward shifted storm track is observed in phase 7 (strong flat jet over the pacific)

A retracted Pacific Ocean jet stream is a key feature in the total field is observed in phase 3 (Weak pacific jet)

Phase 1 has enhanced subtropical jets and closed lows in the subtropics.

Angular momentum being added usually results in a stronger jetstream I think.

As for how angular momentum is measured and what level then I think it is from the winds at all levels up to 10hPa with those at the jet stream level being important.

GP will probably have a few more details.

[Gwo And Global Angular Momentum]

East asian mountain torque looks to be dropping off and I cannot quite see where the next reduction in angular momentum is going to come from. High pressure looks to cover the big mountain ranges in the short term, so I could see a bit of a stall in phase 4 or 5 as a result. Stratospheric modelling would appear to me to be divergent with weather modelling so am undecided beyond about 5 days out as to whether it will move into phase 7 and 8 at that point. I suppose the MJO going into phase 7 and 8 could disrupt the trade winds somewhat which might help to break the pattern. SOI (Southern Oscillation Index) has remained positive which would tend to indicate continued la nina conditions (east to west trade winds) over riding the MJO convective activity.