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Interitus

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  1. Interesting answer, however wavelength and amplitude are separate distinct wave characteristics
  2. Despite the coldest March 1st in the 247 years of the daily CET, and the 2nd coldest March 2nd and March 18th, the spring to April 11th at 5.69°C is only 0.3 degrees below the long term average of 5.99°C. This seems cold in the context of warming springs in recent years, however it is a full 2.65 degrees warmer than the same period just 5 years ago in 2013. 2006 and 1996 were cooler also whilst from the 1980s, of the four years 1984-7, 1985 was marginally warmer and the other three were colder than this year.
  3. Was going to post a v-wind anomaly Hovmoller chart to illustrate this, but that tweet is conveniently in response to this -
  4. For some time the GEFS have been predicting the summer wind reversal at the end of the runs for around 13th-15th April - but the GFS has only recently consistently come into agreement about a week away - The GEOS from the 4th however still has weak westerlies (~3 m/s) for the 13th. As posted previously, not a 'final warming' but gradual dissipation with the increasing insolation, as expected. Meanwhile, an interesting paper with regards to the effects of mountains has just been published, Orography and the Boreal Winter Stratosphere: The Importance of the Mongolian Mountains - https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2018GL077098 - new so paywalled at the moment, but a pre-submission version is available here - https://atmos.washington.edu/~david/White_etal_GRL_submitted2.pdf
  5. Indeed, 2006 was marginally colder than this year to the end of March and ended up being the warmest year on record at the time (since beaten by 2014).
  6. In relation to above, unsurprising that Jason Furtado refers to the NPO as he has published some interesting papers related to it eg. Linkages between the North Pacific Oscillation and central tropical Pacific SSTs at low frequencies - http://ifurtado.org/wp-content/uploads/Publications/FurtadoDiLorenzoAndersonSchneider2012.pdf Nice collection of papers on his site http://ifurtado.org/ the Pacific Decadal Precession concept in A decadal precession of atmospheric pressures over the North Pacific is particularly interesting. Anyway another tweet on this subject - Like the anomaly charts, would be handy to find them on the CPC site
  7. Don't think we're looking at SSW effects at this stage, the chart below of 60°N zonal winds shows that for the first time since the SSW, the 150mb level wind will be weaker than at 10mb - the reduction in zonal winds associated with the negative AO is from lower levels upwards allowing a brief return of the positive vertical wind shear characteristic of the winter vortex, before the summer easterlies return -
  8. Indeed, simpler perhaps in this case just to consider it as North Pacific oscillation rather than east or west -
  9. Looks more of a negative WPO
  10. Note that this is the stratospheric Aleutian high - this is a 'normal' feature, anomalies of which give the typical displaced vortex at some point during most winters. Nice to see some more work from Stephen Colucci, author of a particularly interesting paper - Stratospheric Influences on Tropospheric Weather Systems - https://journals.ametsoc.org/doi/abs/10.1175/2009JAS3148.1
  11. Interesting that the March provisional CET to the 21st is 4.1°C The equivalent for 2013 was 3.51°C and for 2006 it was 3.11°C Not so unusual after all? This year has had frequent comparison with 1987 - this was 2.9°C
  12. Back off, Blessed Weather paraphrased the quote to infer something which was not stated - whether it is the author's or Meto's beliefs or otherwise, I quoted the blog verbatim. edit: your timings look awry, if the AAM spike early Feb is the start is the tropical forcing, how long do you think it takes to impact the strat? Looking forward to your analysis.
  13. I believe you jest, but if seeking confirmation bias it potentially misses an important point made in the blog - forget the SSW, the pattern which led to the cold spell was triggered from the tropics at the beginning of February (not preceding the SSW - this was already under way).
  14. There's no mention of tropical-strat connection, be there one or not. What the author actually says is -
  15. Thought I already said above that the 10mb wind would probably be westerly after the weakening alluded to in the various tweets? Regarding said current weakening, GEOS and GFS have consistently shown now for a number of days that it will have just one day of reversal on the 20th, which if following the common convention means there were only 19 days of westerlies at 10mb 60°N so it is part of last month's SSW and not a separate event which requires 20 days ..... Anyway, the data does tend to show that a later major warming may have a later final warming - well final wind reversal - there may not be a discernible warming spike to speak of with a dissipation of the vortex gradually warmed by the sun. But of course this also depends on definition - a late major warming may be an early final warming so breaking that rule of thumb. Heat flux will be low now throughout as little wave activity propagates when the wind speeds are weak, but basically if the SSW is early enough, the vortex can recover somewhat and be prone to further wave activity and possible earlier FW. If the SSW is later and depending on its strength, the vortex can maintain a feeble westerly for some time without strengthening appreciably before gradual dissipation. This is looking like what may happen this year, though as you mention there is another possible weakening on the forecast horizon. edit: actually there may be a group of years where the recovery from the SSW occurs at such a time that the vortex can regain some strength and not be disturbed leading to very late FW, this chart shows final reversals of 10mb wind for the dates 09/05/09, 10/05/01 and 07/05/06 which show very close similarity from time of SSW to FW -
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