knocker

How do different pathways connect the stratospheric polar vortex to its tropospheric precursors? Abstract Processes involving troposphere–stratosphere coupling have been identified as important contributors to an improved subseasonal to seasonal prediction in the mid-latitudes. However, atmosphere models still struggle to accurately predict stratospheric extreme events. Based on a novel approach in this study, we use ERA5 reanalysis data and ensemble simulations with the ICOsahedral Non-hydrostatic atmospheric model (ICON) to investigate tropospheric precursor patterns, localised troposphere–stratosphere coupling mechanisms, and the involved timescales of these processes in the Northern Hemisphere extended winter. We identify two precursor regions: mean sea level pressure in the Ural region is negatively correlated with the strength of the stratospheric polar vortex for the following 5–55 d with a maximum at 25–45 d, and the pressure in the extended Aleutian region is positively correlated with the strength of the stratospheric polar vortex the following 10–50 d with a maximum at 20–30 d. A simple precursor index based on the mean pressure difference of these two regions is very strongly linked to the strength of the stratospheric polar vortex in the following month. The pathways connecting these two regions to the strength of the stratospheric polar vortex, however, differ from one another. Whereas a vortex weakening can be connected to prior increased vertical planetary wave forcing due to high-pressure anomalies in the Ural region, the pathway for the extended Aleutian region is less straightforward. A low-pressure anomaly in this region can trigger a Pacific–North American-related (PNA-related) pattern, leading to geopotential anomalies of the opposite sign in the mid-troposphere over central North America. This positive geopotential anomaly travels upward and westward in time, directly penetrating into the stratosphere and thereby strengthening the stratospheric Aleutian High, a pattern linked to the displacement towards Eurasia and subsequent weakening of the stratospheric polar vortex. Overall, this study emphasises the importance of the time-resolved and zonally resolved picture for an in-depth understanding of troposphere–stratosphere coupling mechanisms. Additionally, it demonstrates that these coupling mechanisms are realistically reproduced by the global atmosphere model ICON. https://wcd.copernicus.org/articles/4/1071/2023/

https://confluence.ecmwf.int/display/FUG/Section+8.2.6+Madden-Julian+Oscillation+Output

The links between the Madden-Julian Oscillation and European weather regimes Abstract Skillful weather forecasting on sub-seasonal timescales is important to enable users to make cost-effective decisions. Forecast skill can be expected to be mediated by the prediction of atmospheric flow patterns, often known as weather regimes, over the relevant region. Here, we show how the Grosswetterlagen (GWL), a set of 29 European weather regimes, can be modulated by the extra-tropical teleconnection from the Madden-Julian Oscillation (MJO). Together, these GWL regimes represent the large-scale flow characteristics observed in the four North Atlantic-European classical weather regimes (NAE-CWRs), while individually capturing synoptic scale flow details. By matching each GWL regime to the nearest NAE-CWR, we reveal GWL regimes which occur during the transition stages between the NAE-CWRs and show the importance of capturing the added synoptic detail of GWL regimes when determining their teleconnection pattern from the MJO. The occurrence probabilities of certain GWL regimes are significantly changed 10–15 days after certain MJO phases, exhibiting teleconnection patterns similar to their NAE-CWR matches but often with larger occurrence anomalies, over fewer consecutive MJO phases. These changes in occurrence probabilities are likely related to MJO-induced changes in the persistence and transition probabilities. Other GWL regimes are not significantly influenced by the MJO. These findings demonstrate how the MJO can modify the preferred evolution of the NAE atmospheric flow, which is important for sub-seasonal weather forecasting. https://link.springer.com/article/10.1007/s00704-020-03223-2

Lubbly jubbly to end the week

Just had a quick scamper through the Mod. thread and I know not why but “Other than that Mrs. Lincoln, how was the play?” flashed into my mind.

I can't remember the last time I've seen so much frenzied .......

It is because the low deconstructs as the jet hits the buffers of the block to the east and rapidly veers

Shortwaveitus - an endemic disease that tends to proliferate in winter months. There is no known cure but can be treated with copious amounts of Diazepam and plenty of bed rest.

Sacre bleu.......we are on course for possible the shortest winter on record

Put simply the ecm next week has intense trough development in the Atlantic driven by a strong jet which at the same time amplifies the Euro ridge which effectively mixes out the colder air in the west, including the UK and isolates the colder air to the east. Original post: https://community.netweather.tv/topic/99584-model-output-discussion-into-winter/?do=findComment&comment=4965504

Put simply the ecm next week has intense trough development in the Atlantic driven by a strong jet which at the same time amplifies the Euro ridge which effectively mixes out the colder air in the west, including the UK, and isolates the colder air to the east.

The dash to make a silk purse out of a pigs ear is now well underway

And nobody was listening

Yes when something looks odd the first question should be why?

Surface chart

I take it you do appreciate that currently the analysis has a warm front edging slowly north on Sunday into the cold air so the ens not too surprising

Well now the moderate rain here has turned to moderate snow for a while this morning. A good example of evaporative cooling

Game over.....just as well close the mod. thread for the rest of the winter

A short summary of the MJO MJO_summary.pdf

Time to wheel out "Will it Snow" by John once again https://community.netweather.tv/learning/basics/will-it-snow-by-john-holmes-r96/

Oh God............just when I thought things couldn't get any worse in here

There is a strong rumour doing the rounds that this thread is going to be renamed the gymkhana thread.

I didn't say alone and bluearmy has pre-empted my reply which i have made in more detail elsewhere

Not necessarily

Not even with a strat/trop coupling?