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  1. Thought I cleared up this (EA)MT nonsense?
  2.   From the MERRA data, for SSW in January & February, the peak in average 60-90°N 10mb polar cap temperature is 235.08 K (-37.92°C) occurring on day of reversal. The most recent available GEOS 60-90°N 10mb forecast for 08/02 is 241.79 K (-31.21°C), warmer than 12 of 17 SSW and 7th warmest Jan/Feb period behind (max dates) 23/01/09 - 251.83 K - SSW (as per 60°N 10mb wind) 29/02/80 - 247.42 K - SSW 27/02/99 - 243.41 K - SSW 05/02/81 - 243.16 K - NO SSW (+0.6 m/s) 02/01/85 - 242.92 K - SSW 30/01/95 - 242.83 K - SSW (-0.02 m/s!)
  3.   Well if we go by the original definition of SSW when first observed by Scherhag in the 1950s as "explosive warmings in the stratosphere" then this is absolutely a SSW befitting the acronym, that it doesn't fulfil one metric used by Charlton and Polvani (commonly referred to as CP07) for their particular study of reanalysis data is neither here nor there. I linked the Defining Sudden Stratospheric Warmings paper by Amy Butler et al previously and urge everyone interested to read it - and the supplement paper They point out the benefits and simplicity of CP07, but also some misconceptions and drawbacks, in short (tl;dr) -  
  4. Interesting as usual Recretos, though it does assume that those forecasts are correct and moreover, that the SSW is actually finished - there is a good chance that it isn't. Simply, the strength of the vortex meant it was unlikely to reach wind reversal in one go. It may be surprising but the 10-day 10mb 60°N wind reduction from  22/1/16 to 1/2/16 of about 53 m/s in this 'minor SSW' is the 3rd greatest behind only 26/2/07 only just ahead with 54 m/s and 28/1/09 with 68.21 m/s, which both occurred during full SSW. Actually, there were a number of other greater 10-day drops in Jan 2009 - the fact is as the wind reduction suggests, that no other year compares to that event, dropping from in excess of 68 m/s to -30 m/s more or less one attempt. It was 68.48 m/s 16 days before reversal - the average speed at this stage before SSWs is only about 28 m/s. As pointed out previously, the earliest an SSW has occurred after winds in the 75 m/s region like this year on 22/1 was a month later in Jan/Feb 1989 which incidentally was the second behind 2009 at 16 days to reversal with 49.74 m/s. Only Jan 1985 and March 1988 were also above 40 m/s at this stage (all 4 were splits). Recent years like Jan 2006 or Jan 2013 were only 28-29 m/s.  
  5. Indeed and briefly returning to the discussion regarding mountain gravity waves, the cooling of rising air that these stationary waves cause allows researchers to predict quite accurately where the polar stratospheric clouds (PSC) may form and allow their study - see eg That was coauthored by Andreas Dornbrack who will be a familiar name to many on this thread for his stratosphere potential vorticity charts amongst others - but a large part of his work has involved both gravity waves and stratospheric clouds over Scandinavia. For PSC type 1, synoptic conditions (eg vortex position like now) are favourable 36% of the time in January, with gravity waves contributing only a further 6%. However for the colder PSC type 2 the temperatures are rarely low enough over Scandinavia and it is suggested that the presence of these clouds is almost always due to mountain waves -
  6. It's not quite as clear as the original thought experiment makes it seem. Theory and modelling shows that actually, slowing the earth's rotation leads to a warming at higher latitudes and slight cooling of the tropics such that the equator-pole temperature gradient is reduced. The jet stream and westerly winds increase in strength and shift northwards of the UK. By 72 hour day length the meridional Ferrel cell circulation ceases and the Hadley cell reaches 40-50°N ie southern UK would be bordering on subtropical region. Beyond a 144 hour day length there is a single tropic to polar Hadley cell circulation reaching 70°N and the jet now confined to the high Arctic weakens with greatly reduced available angular momentum - see eg
  7. At face value 97/98 like this year was a strong El Nino, but stratosphere wise 97/8 was quite different and there was no SSW in Feb 98. After a strong early season in October and first half of November a series of warmings nearly caused technical SSW on 7th January, down to 2 m/s from which the vortex never properly recovered. The maximum 10mb 60°N speed of the whole season was on November 30th at just under 47m/s while the average from December 1st to today 28th January was 21.7 m/s. Contrast with 1988/9 where the winter average to 28th Jan of 54 m/s was higher than the 97/98 max, and the second strongest to this point almost identical to 1980/81. This year is 3rd to this point just a little less on about 53.7 m/s so a similar strat, but here's a thing, 1988/9 was a strong La Nina.
  8. According to the MERRA data, the 60°N 10mb wind speed achieved its 3rd highest value (data since 1979) on 22/01/16 of 75.31 m/s behind 75.65 and 75.35 m/s on 16th and 21st of January 1989. The good news - these 1989 winds were followed by a split SSW. The bad news - it was a month later on 21st February.
  9. In meteorological terms, mountain waves or orographic gravity waves (OGW) are small scale features with horizontal wavelengths typically in tens to a few hundred kilometres with geopotential amplitudes of a few hundred metres i.e. temperature amplitude perturbations typically much less than 10K. As such they are often not even resolved in global models because of horizontal and vertical resolution and are included by parameterisation, much like cumulus convection for example. Here is an example of modelling differences between a 15km and 50km horizontal resolution - They are typically visualised by removing global atmospheric motions and temperatures, here is a filtered satellite image showing numerous waves, but not just orographic, also from frontal systems etc. Compare for similarity with Recretos' NH image from GEOS modelling a few posts back. Here is the mesoscale modelling overview high up in the strat at 2.5hPa, and a cross-section for the OGW produced over the east of Greenland showing vertical windspeeds (coloured contours, red rising motion) and potential temperature contours (orange lines). Note in this example the maximum temperature amplitude of about 3K and limited extent of the wave train.   (above images from Limpasuvan etal The OGW propagation is dependent on a number of factors, basically the speeds and direction of lower tropospheric wind over the mountains, then suitable winds in the higher troposphere eg jet stream, and then also the stratosphere jet. Alignment of all three is important. Mountains perpendicular to the wind are good - most notable perhaps the Andes in the SH but in the NH Greenland, Norway, Rockies, Urals, Arctic Islands and those of northern half of Asia. The Himalayas and Tibetan massif though highest are not usually the best because of latitude and general east-west orientation and have been considered more important for OGW from tropical cyclones. Another factor also is that these waves can be affected by lee cyclogenesis as the coriolis force affects the flow over larger mountain systems. So these waves don't 'directly' appear on upper air charts of temperature, but that is not to say they are unimportant as the wave breaking can cause strong deceleration of stratosphere jet. Also in slightly alternative approaches to the subject, they impact on nodes of vortex resonance and flow stability. According to Albers & Birner, OGW contributes >30% of the total wave driving in the JRA-25 and >10% in ERA-interim reanalysis products for the critical areas of the stratosphere, north of 40°N and 30-50km altitude, thus the region of the vortex edge. The model difference may be differences in parameterisation, but whatever numerous studies show that handling of the wave drag can make the difference between an SSW being modelled or not (particularly with regards to 2009 for example). So what are we seeing in current Berlin ECMWF images like this? - Clearly in terms of geopotential heights there is primarily a planetary wave 1 forcing on the vortex from the semi-permanent Aleutian high (ignore the transient high on the Atlantic side, though it may be important later on!), but also following the geostrophic wind flow round the vortex shows that there is clearly a single global wave 1 in temperature amplitude, warming over Asia as the air approaches the high, and cooling on the Atlantic side. The temperature amplitude on the 60°N circle shows that it is over 20K (i.e over 40K between coldest and warmest) and as this is not incident with the vortex the actual temperature amplitude is greater than this - This scale is very different from mountain torque. Planetary Rossby waves don't just advect warmer and importantly lower potential vorticity air from lower latitudes, they cause baroclinic forcing which induces vertical motion in the vortex flow. Harvey & Hitchman in their climatology of the Aleutian High describe the typical situation quite simply - There are plenty of papers that look at this in (much!) more detail, but it is shown well in early modelling work by Hsu for example, here particles tracing a vortex trajectory not too disimilar to present - ...and the associated vertical motion (2km in this example so a 20K range) Here is a real example from O'Neill<2800%3AEOTSDN>2.0.CO%3B2 which may help the 3d picture. The images are fairly complex, a description is included, first showing an unperturbed vortex then with baroclinic forcing, showing distortion of the potential temperature fields which affects the isentropic flow - notice how the ends of the flow arrows are lower in the centre (north) between vortex and anticyclone than the outside (south) showing the adiabatic descent/ascent. The air parcels don't stay at one pressure level remember! Ultimately, this may lead to a wave 1 forced SSW with descending air parcel trajectories such as this over Switzerland from 2008 - Note the lower vortex was cold and displaced over Bern, but the higher vortex showed descent from 41km to 36.7km i.e ~40K warming, see description included - Finally, for those keeping up, there is fairly neat way of identifying areas of descent/ascent warming/cooling from the geopotential charts. Here for example, GFS charts from instantweathermaps a couple of days ago are forecasts for 10mb and 100mb - As should be clear by now, there is differential forcing between the two levels, with the prominent anticyclone at 10mb displacing the vortex centre some distance from the vortex centre at 100mb. If we overlay the charts we can approximate the highly baroclinic areas by looking at where the isohypses (lines of equal geopotential) at the two pressure levels are near perpendicular to each other (red for descending/warming air, blue for ascending/cooling) - When combined with the temperature forecast it can be seen that they align quite well -   Hope this was interesting and clears up some obvious confusion.    
  10. Which pressure level is this Omega chart?
  11. Once again, where is the mountain torque event?
  12. Good post Recretos, though with a warming like 2009 there was nothing ambiguous about an easterly zonal wind component in excess of 30 m/s on 28th January. Also for those that might not be sure,  counterintuitively the 50% north and east directions of a 10 m/s sw wind are 7.07 m/s
  13. The origin of the torpedo can be seen in this post which relates the possibility and impact of northward propagating atmospheric angular momentum anomalies. However a search for the term 'torpedo' shows that it then took on a life of it's own such that it was responsible for just about any potential cold spell on the horizon, quite amusing -
  14. There is repeated mention of mountain torques in this thread. Where are these being seen and what have they got to do with stratosphere warming?