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Posted (edited)

 

Edited by knocker

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So is it possible that the SSW that refused to down-well earlier in the season is now driving the synoptic pattern with all this northern blocking? Or is it just a naturally variable?

 

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20 minutes ago, chris55 said:

So is it possible that the SSW that refused to down-well earlier in the season is now driving the synoptic pattern with all this northern blocking? Or is it just a naturally variable?

The polar vortex has naturally warmed-out under the increasing strength and duration of sunlight, but it took longer than usual this year.

This 'final warming' (FW) typically encourages increased high latitude blocking (HLB) for a few weeks.

For many years running, we saw earlier than usual FWs with the increased HLB during late winter and early spring before a shift to a low pressure dominated Arctic (which helps bring warm, dry weather to the UK) by mid-late spring, so this year is making for quite the change of tune from what we've become used to.

It's not just the FW at play, though. There's also some powerful tropical convection, including tropical cyclone activity in the Indian Ocean, serving to pump up the HLB about as far as it can physically go at this time of year. The charts we're seeing for next week and out toward mid-May are truly sensational from a scientific standpoint, but sadly make the UK's weather liable to be unusually cool, or even cold at night, with rapid cloud build-up by day unless we see a fully unstable atmosphere with no stable 'lid' causing the cloud to spread out as it rises into it (this allows for lots of blue sky, punctuated by towering cumulus (bringing heavy showers) or cumulonimbus (bringing downpours / thunderstorms).

The HLB should start to wane by mid-May, but the questions are, how fast will that occur, and will the other driving forces support movement of high pressure across the UK from the southwest or south? Things have started to look uncomfortably 'in the balance' in that respect. It could go either way.

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16 hours ago, Singularity said:

The polar vortex has naturally warmed-out under the increasing strength and duration of sunlight, but it took longer than usual this year.

This 'final warming' (FW) typically encourages increased high latitude blocking (HLB) for a few weeks.

For many years running, we saw earlier than usual FWs with the increased HLB during late winter and early spring before a shift to a low pressure dominated Arctic (which helps bring warm, dry weather to the UK) by mid-late spring, so this year is making for quite the change of tune from what we've become used to.

It's not just the FW at play, though. There's also some powerful tropical convection, including tropical cyclone activity in the Indian Ocean, serving to pump up the HLB about as far as it can physically go at this time of year. The charts we're seeing for next week and out toward mid-May are truly sensational from a scientific standpoint, but sadly make the UK's weather liable to be unusually cool, or even cold at night, with rapid cloud build-up by day unless we see a fully unstable atmosphere with no stable 'lid' causing the cloud to spread out as it rises into it (this allows for lots of blue sky, punctuated by towering cumulus (bringing heavy showers) or cumulonimbus (bringing downpours / thunderstorms).

The HLB should start to wane by mid-May, but the questions are, how fast will that occur, and will the other driving forces support movement of high pressure across the UK from the southwest or south? Things have started to look uncomfortably 'in the balance' in that respect. It could go either way.

Gonna show my ignorance here...could this be associated with solar minimum - the jet streams tend to meander more anyway at solar minima, and it sort of depends where the meanders set yup that dictates the weather patterns? The fact that the FW took longer to materialise could also be connected?

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19 hours ago, JeffC said:

Gonna show my ignorance here...could this be associated with solar minimum - the jet streams tend to meander more anyway at solar minima, and it sort of depends where the meanders set yup that dictates the weather patterns? The fact that the FW took longer to materialise could also be connected?

What ignorance 😉 - the solar minimum is likely playing a part yes 👍 - though it's more of a winter factor acting on the polar vortex, some effect is plausible up until the FW. Perhaps the reduced geomagnetic activity does promote a later FW (as there's less energy for the ozone to take on and convert into warmth) as you suggest - of this I'm not sure; more research is needed.

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I am still not overly worried for May personally, the standing wave in the Pacific should tend to encourage more mid-lattitude blocking once the final warming effects fade. A switch into late May/early June is still probable.

I have more concern for the summer as a whole since i'm not sold on this Nino lasting and we did recently see the strongest trade burst in a good six months.

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Posted (edited)

 

Edited by knocker

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Just stumbled across this link for all things QBO-related. Has some nice data and graphics:

https://acd-ext.gsfc.nasa.gov/Data_services/met/qbo/qbo.html

qbo_plot.png

The next few months will be interesting: will we see the usual descending easterly pattern, or will we get another anomaly like 2016?

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12 hours ago, Yarmy said:

The next few months will be interesting: will we see the usual descending easterly pattern, or will we get another anomaly like 2016?

I hope we do not get another anomaly like 2016!

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I am sure we are more likely to get another anomaly now we have already had one, but I'm not sure if it will be so soon. Curious and fascinating, but rather worrying.

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Posted (edited)
On 03/06/2019 at 13:58, Woollymummy said:

I am sure we are more likely to get another anomaly now we have already had one, but I'm not sure if it will be so soon. Curious and fascinating, but rather worrying.

The general scientific concensus was that anomaly was predominately down to the preceding strong El Nino event. So unlikely to follow suit.this time around.

Safe to say though, that if the QBO does 'reverse' again this summer, that will certainly eliminate that theory!

Edited by s4lancia

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Posted (edited)

Regarding Stratosphere/Troposphere interactions these basics are useful to know IMO

Waves in the Atmosphere

There exist four basic modes of atmospheric wave propagation that are of interestin atmospheric science. The four types are:

Acoustic waves - speed controlled by temperature

Gravity waves - speed controlled by stability

Inertial waves - speed controlled by Coriolis parameter

Rossby waves - speed controlled by latitudinal variation of Coriolis

Parameter

Waves in the stratosphere and troposphere include gravity (buoyancy) waves,Rossby waves, inertia-gravity waves, forced stationary planetary waves, free traveling planetary waves, equatorial waves, and midlatitude gravity waves.

Acoustic waves ( sound waves) are longitudinal waves, in which the particle oscillation

is parallel to the direction of propagation. They derive their oscillations from

the compression and expansion of the medium due to the compression force.

Gravity waves are those whose restoring mechanism is their buoyancy or vertical

static stability. Gravity is involved in the hydrostatic balance part.

Inertio-gravity waves are those with a sufficiently long period to cause them to

"feel" the rotation of Earth (i.e., the Coriolis deflection).

Rossby waves are those whose restoring mechanism is the latitudinal (north-south)

gradient of potential vorticity. The more significant topography in the

northern hemisphere results in air parcels that are displaced north-south. Such

displacements cause changes in the planetary and relative components of vorticity

in such a way that total potential vorticity is conserved. The result is north-south

undulations that produce wave patterns around a circle of latitude.

Forced stationary planetary waves are Rossby waves with very long wavelengths

up to 10,000 km that are generated by large-scale surface topography like the Rocky

Mountains and the Himalaya-Tibet complex, or by land-sea temperature contrasts.

These waves remain stationary since the topographical features or land-sea temperature

contrasts force them not to move. Such waves propagate upward when westerly

zonal winds are weak. They deposit their momentum in the stratosphere.

Free traveling planetary waves are planetary waves of wavelengths on the order

of 10,000 km that are generated in the atmosphere at certain "natural frequencies"

wherein the atmosphere is excited at a certain frequency and generates a wave.

These waves propagate around a latitude band with a period of a few days.

Equatorial waves are mixed Ross by gravity waves that propagate eastward with a

frequency similar to the inertio-gravity waves and westward with a frequency similar

to the Rossby waves. They are driven by the change in sign of the Coriolis

parameter at the equator. A type of equatorial wave is the Kelvin wave, which propagates

eastward like a pure gravity wave with only zonal velocity. Kelvin waves

in the ocean propagate along the thermocline or region of tightest temperature gradient.

The ocean Kelvin wave is associated with the ENSO phenomenon, as these

waves propagate along the thermocline, bringing warm or cold water anomalies to

the eastern Pacific.

Midlatitude gravity waves are inertio-gravity waves that exist in the middle and

high latitudes and can propagate into the middle atmosphere.

Source – K. Mohanakumar, Stratosphere Troposphere Interactions, Springer

.

Edited by knocker

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Many thanks, for that, Malcolm. I think it ought to be pinned.:oldgood:

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Weakening of the teleconnection from El Niño‐Southern Oscillation to the Arctic stratosphere over the past few decades: What can be learned from subseasonal forecast models?

Quote

While a connection between the El Niño‐Southern Oscillation (ENSO) and the Northern Hemisphere wintertime stratospheric polar vortex appears robust in observational studies focusing on the period before 1979 and in many modeling studies, this connection is not evident over the past few decades. In this study, the factors that have led to the disappearance of the ENSO‐vortex relationship are assessed by comparing this relationship in observational data and in operational subseasonal forecasting models over the past few decades. For reforecasts initialized in December, the models simulate a significantly weaker vortex during El Niño (EN) than La Niña (LN) as occurred before 1979, but no such effect was observed to have occurred.

The apparent cause of this is the Eastern European and Western Siberian height anomalies present during ENSO. The observed LN events were associated with persistent ridging over Eastern Europe as compared to EN. Although the S2S models are initialized with this ridge, the ridge quickly dissipates. As ridging over this region enhances wave flux entering the stratosphere, the net effect is no robust stratospheric response to ENSO in the observations despite a North Pacific teleconnection that would, in isolation, lead to less wave flux for LN. The anomalies in the Eastern European sector in response to ENSO likely reflect unforced internal atmospheric variability.

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JD029961#.XP9Q-rEbx7Q.twitter

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https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018JD029368

Abstract

The Quasi‐Biennial Oscillation (QBO) is the dominant mode of interannual variability in the tropical stratosphere, with easterly and westerly zonal wind regimes alternating over a period of about 28 months. It appears to influence the Northern Hemisphere winter stratospheric polar vortex and atmospheric circulation near the Earth's surface. However, the short observational record makes unequivocal identification of these surface connections challenging. To overcome this, we use a multicentury control simulation of a climate model with a realistic, spontaneously generated QBO to examine teleconnections with extratropical winter surface pressure patterns. Using a 30‐hPa index of the QBO, we demonstrate that the observed teleconnection with the Arctic Oscillation (AO) is likely to be real, and a teleconnection with the North Atlantic Oscillation (NAO) is probable, but not certain. Simulated QBOAO teleconnections are robust, but appear weaker than in observations. Despite this, inconsistency with the observational record cannot be formally demonstrated. To assess the robustness of our results, we use an alternative measure of the QBO, which selects QBO phases with westerly or easterly winds extending over a wider range of altitudes than phases selected by the single‐level index. We find increased strength and significance for both the AO and NAO responses, and better reproduction of the observed surface teleconnection patterns. Further, this QBO metric reveals that the simulated AO response is indeed likely to be weaker than observed. We conclude that the QBO can potentially provide another source of skill for Northern Hemisphere winter prediction, if its surface teleconnections can be accurately simulated.

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https://www.esrl.noaa.gov/psd/data/correlation/qbo.data

Juli came in with 10,96. We are in the process of a declining wQBO.

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Can we get a new thread for this?? It still says 2017/18....well out of date.

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4 minutes ago, CreweCold said:

Looking at it, seems we'll go negative some time around October

In business if we do IMO, should mean some nice -ve  numbers reach the tropopause in plenty of time to do some damage.

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On 07/08/2019 at 20:16, knocker said:

Getting colder

gfs_sh-gphtemp_001hPa_20190807_f000.thumb.png.1af714f8b1d0a5d6d3c45e228ab3b6d5.pnggfs_sh-gphtemp_001hPa_20190807_f384.thumb.png.fbb707942b55b9ce208edbbba3f6b0fb.png

?

Southern hemisphere

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13 minutes ago, Interitus said:

?

Southern hemisphere

Whoops

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