[Early run up to Winter 2020/2021 discussion]

43 minutes ago, jules216 said:

You need to read the whole GSDM synoptical conundrum. As a general rule to get cold weather in to Europe in winter from AAM perspective we need a robust MJO convection to travel eastwards from Indian Ocean to Maritime continent and Western/Eastern Pacific - phases 4-8. Initially there is a rise of frictional torque followed by mountain torque events that slow that general westerlies in mid latitudes. The Rossby wave train associated with strong MJO pulses initially effect the Pacific jet stream and initially force a equatorward momentum flow at 35N which help promoting ridges to the north. It is a very complex diagnostics very much dependant on the base state of the atmosphere plus seasonal wave lengths. So AAM response in winter may be different to the summer one. We have some experts here in the forum like @Tamara or @Blessed Weather who can explain this in greater detail then me for sure

A Synoptic–Dynamic Model of Subseasonal Atmospheric Variability | Monthly Weather Review | American Meteorological Society

JOURNALS.AMETSOC.ORG

 

Thanks a lot!!! I know how the MJO modulates the mid-latitude circulation, but I am missing the connection to AAM. I will go through the article you recommend. Hezký den!

[Early run up to Winter 2020/2021 discussion]

On 18/11/2020 at 10:52, jules216 said:

The atmosphere was fully coupled with La Nina this year if we take in to account summer weather in Europe. This was the wettest summer here since 1998 and 2010 - those were also forming Ninas in spring those years. I have made a very good summer forecast locally based on this as monthly blends were exactly how the regime behaved in May,June and July, things have started to be complicated exactly in August where there was a heatwave in central Europe that lasted for nearly 3 weeks - not seen in analog blend which suggested euro trough. This is probably because of +AAM spike. This AAM spike in autumn also put La Nina off track so no early season cold shot in Europe but Euro high instead. This will be 1st La Nina that will not feature any snow here in November(Slovakia)  out of last 10! crazy if you thing this will be 1st no November snow La Nina - all 2017,2016,2011,2010,2008,2007,2005,1998,1998,1995 featured at least one if not multiple cold shots in to continental Europe in November yet this one is such an exception.

If you want to know my opinion I either dont understand AAM/GSDM at all or think its overrated, why? Because there were a good few of those last 10 La ninas that had similar MJO progress in autumn yet produced Europe cold shots, so presuming +AAM is not an exception this year and also featured in some past 10 autumn Ninas but didn't stand in the way of cold shots in November.

What I do think its more relevant is - Haddley Cell poleward expansion and cooling upper levels of atmosphere to balance out record warm troposphere. Already if you look at polar profile this autumn its nearly a continuation of last winter while we keep breaking global temperature records at surface level. These two Haddley Cell + stratosphere are easily outweighing what would you call typical atmosphere behavior driven by Pacific Ocean - ENSO. Unfortunately these effects are enhanced in boreal winter which is even worse for those of cold persuasion. 

Hey Jules,

is there any source where to gain a deeper understanding of the impact of AAM on Europe? Thanks!