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Geopotential height of the SH polar vortex has Positive correlation with the AAO

An incredible correlation between vertical geopotential height and the phase of the AAO.

Amazing l have never noted that before. A light bulb moment.

When geopotential height between surface to 100 hPa is positive . The AAO index is negative.
When geopotential height between surface and 100 hPa is negative. The AAO index is positive.

Some convincing proof that the condition of the polar vortex affects our weather.
I will put this geopotential height anomaly in the polar vortex on my weekly observation  round.

https://www.cpc.ncep.noaa.gov/products/precip/CWlink/daily_ao_index/hgt.aao.shtml

timeseries june to sept pv geoht

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New understanding of the drivers behind hot and dry conditions over Australia’s north-east

Posted by BCG on 14th March 2019

http://www.climatekelpie.com.au/index.php/2019/03/14/new-understanding-of-the-drivers-behind-hot-and-dry-conditions-over-australias-north-east/

Predicting temperature extremes and dry conditions over spring and summer is vital for agriculture, water supplies, bushfire risk and human health. But to make accurate predictions the Bureau of Meteorology needs to better understand the climate drivers behind such extremes.

Bureau researchers have recently identified how wind patterns in the stratosphere around Antarctica can drive hot and dry conditions over southern Queensland and northern New South Wales.

This research was undertaken by the Forewarned is Forearmed (FWFA) project, which is part of the Federal Government Rural R&D for Profit program. FWFA is supported by the Bureau, a range of Rural R&D Corporations, Universities and state government agencies.

While most weather systems like storms, rain and high pressure systems are found in the troposphere, the relatively turbulent first layer of the atmosphere, the stratosphere above it is known for its stable air flows. Commercial airplanes target this layer to find jet streams for a smooth and efficient flight.

A key feature of the stratospheric circulation is the development of the wintertime polar vortex, whereby Antarctic circumpolar westerly winds (extending up to 40-50 km altitude) seasonally strengthen from autumn to winter as the polar cap region seasonally cools. The vortex weakens and breaks down during late spring as the polar cap warms up. In some years the vortex warms up and breaks down early, which can lead to hot and dry conditions on Australia’s surface during late spring-summer.

The early weakening of the polar vortex results in a strong downward air flow and a lack of clouds over eastern Australia (Figure 1) via another large-scale circulation that Australian farmers already know – a negative Southern Annular Mode (SAM) according to Bureau researcher Dr Eun-Pa Lim.

“A negative SAM is responsible for bringing hot and dry conditions to eastern Australia in our warm seasons” says Dr Lim. “Anything we can do to improve our ability to predict SAM will help people on the land to prepare for and manage these conditions. The long time–scale of the polar vortex weakening, which spans several months, means if we can capture it in our model, we can potentially predict low SAM conditions during late spring as early as late winter.”

Figure 1. A strong weakening of the polar vortex and the associated negative Southern Annular Mode leads to an abnormally strong downward air flow and a lack of clouds (orange indicates less than average cloud cover) over eastern Australia, which results in higher than average temperatures and dry conditions. This plot shows the cloud cover variation in late spring-early summer following the early break down of the polar stratospheric vortex.

But just what is a polar vortex and how does it influence Australia’s climate?

The abnormal weakening of the polar vortex and its downward coupling in spring to summer can be visualised in Figure 2. During winter the westerly winds associated with the SH polar vortex are stronger than usual in the upper stratosphere (as shown in orange), which can allow more atmospheric waves to propagate from the lower atmosphere into the stratosphere. Because these vertically propagating waves act to weaken the upper stratospheric westerlies, the polar vortex starts to weaken from early spring. As the vortex weakens over time, the weakening signal descends (shown in blue). The impact is felt at ground level from October to January.

Figure 2. When the abnormal polar vortex weakening happens, generally the vortex is abnormally strong during winter (shown in orange) and then weakens rapidly in spring. The process of weakening of the westerly winds descends after September (blue). Exact timings of the strengthening of the winter polar vortex and its subsequent weakening in spring to early summer can vary year-to-year.  Wind (m/s) is measured as being stronger or weaker than the average.

Impact on Australia’s climate

Developing an index to measure polar vortex weakening and strengthening has been a vital part of the Bureau’s recent research and has made it possible for them to study the impact of these events on Australia’s seasonal conditions.

“The Bureau has developed the stratosphere-troposphere (S­‑T) coupled mode index to identify these events and quantify their strength,” says Dr Lim. The index is based on monthly average wind data (1979-2017) over the Antarctic sub-polar region (55° to 65° South) at all available vertical levels from the surface to 50km altitude.

The index allows the Bureau to measure whether the polar vortex weakening is progressing at its usual pace. A high index means unusual weakening which leads to faster vortex breakdown. The strongest weakening event occurred in 2002 (Figure 3), which was related to the strongly negative SAM in spring 2002 that is believed to have played a more important role in driving hot and dry conditions than the relatively weak El Niño observed in the same year.

Figure 3. The Bureau have developed the S-T coupled mode index to identify polar vortex weakening (in red) and strengthening (in blue) events. The strongest vortex weakening event on record occurred in 2002 (based on monthly average wind data from April 2002 to March 2003 compared to wind data of all years).

Hot conditions

The Bureau’s S-T coupled mode index also highlights other less dramatic, but still significant, polar vortex weakening/strengthening events. By comparing historic temperatures and rainfall for the October to January period with the index the Bureau have found a very strong correlation between the polar vortex weakening and hot and dry seasonal conditions in southern Queensland and northern NSW.

For instance, maximum temperatures (Tmax) in the nine polar vortex weakening years (Index ≥ 0.8) were 1.2°C to 1.8°C warmer over southern Queensland and northern NSW than in the other 29 years studied between 1979 and 2017 (Figure 4). At the same time rainfall was 0.4 to 1.2 mm per day lower; that’s around 12 to 36mm a month.

Figure 4. The October to January mean maximum daily temperature is between 1.2°C and 1.8°C warmer and rainfall is 0.4 to 1.2 mm/day lower over southern Queensland and northern NSW during the nine identified polar vortex weakening years than in all the other 29 years.

“When you consider the seven hottest years (the top 20 per cent) – they are over four times more likely to occur when it is a polar vortex weakening year than a non-weakening year,” says Dr Lim.

“The research demonstrates that the Antarctic polar vortex is an important driver of heat and rainfall extremes in subtropical eastern Australia during late spring to summer.”

“The Bureau’s new ACCESS-S seasonal forecast system has a high level of skill in predicting S-T coupling from the beginning of September, which will improve our ability to predict temperature and rainfall extremes for the spring and early summer in polar vortex weakening years,” she said.

This result of the Bureau’s research implies that if land managers can be warned in September that they are likely to face hot and dry conditions through to January due to the polar vortex weakening, it will put them in a better position to make timely decisions such as how to manage livestock numbers, pastures and their supply of supplementary feed.

Lastly, since the beginning of spring 2018 the stratospheric polar vortex has been stronger than usual, which is likely to have somewhat mitigated the hot and dry conditions promoted by the development of El Niño over Queensland and northern NSW. This was something we could be thankful for during the tough dry spring of 2018”

Eun-Pa Lim, 03 9669 4000, eun-pa.lim@bom.gov.au

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Troposphere height

Links , pictures, research, information.

troposphere rheemoclineatmosphere temperature layers with,height

In no specific order.

Theory. Height of the troposphere

http://www-das.uwyo.edu/~geerts/cwx/notes/chap01/tropo.html

extract

‘The height of the tropopause depends on the location, notably the latitude, as shown in the figure on the right (which shows annual mean conditions). It also depends on the season (1, 2). Thus, it is about 16 km high over Australia at year-end, and between 12 – 16 km at midyear, being lower at the higher latitudes. At latitudes above 60� , the tropopause is less than 9 -10 km above sea level; the lowest is less than 8 km high, above Antarctica and above Siberia and northern Canada in winter. The highest average tropopause is over the oceanic warm pool of the western equatorial Pacific, about 17.5 km high, and over Southeast Asia, during the summer monsoon, the tropopause occasionally peaks above 18 km. In other words, cold conditions lead to a lower tropopause, obviously because of less convection.

Deep convection (thunderstorms) in the Intertropical Convergence Zone, or over mid-latitude continents in summer, continuously push the tropopause upwards and as such deepen the troposphere. This is because thunderstorms mix the tropospheric air at a moist adiabatic lapse rate. In the upper troposphere, this lapse rate is essentially the same as the dry adiabatic rate of 10K/km. So a deepening by 1 km reduces the tropopause temperature by 10K. Therefore, in areas where (or at times when) the tropopause is exceptionally high, the tropopause temperature is also very low, sometimes below -80� C. Such low temperatures are not found anywhere else in the Earth’s atmosphere, at any level, except in the winter stratosphere over Antarctica.

On the other hand, colder regions have a lower tropopause, obviously because convective overturning is limited there, due to the negative radiation balance at the surface. In fact, convection is very rare in polar regions; most of the tropospheric mixing at middle and high latitudes is forced by frontal systems in which uplift is forced rather than spontaneous (convective). This explains the paradox that tropopause temperatures are lowest where the surface temperatures are highest.

The tropopause height does not gradually drop from low to high latitudes. Rather, it drops rapidly in the area of the subtropical and polar front jets (STJ and PFJ respectively in the Figure on the left), as shown in the Palmen-Newton model of the general circulation (Fig 12.16 or Fig on left). Especially when the jet is strong and the associated front at low levels intense, then the tropopause height drops suddenly across the jet stream. Sometimes the tropopause actually folds down to 500 hPa (5.5 km) and even lower, just behind a well-defined cold front. The subsided stratospheric air within such a tropopause fold (or in the less pronounced tropopause dip) is much warmer than the tropospheric air it replaces, at the same level, and this warm advection aloft (around 300 hPa) largely explains the movement of the frontal low (at the surface) into the cold airmass, a process called occlusion (Section 13.3) (4).

 

 

………

Google search.. ‘pictures tropopause height’

https://www.google.com/search?q=picture+tropopause+height&tbm=isch&source=univ&client=firefox-b-d&sa=X&ved=2ahUKEwjlnsDf-bDjAhVDfX0KHcEUAu0QsAR6BAgEEAE&biw=1025&bih=491

………..

 

 

 

 

 

 

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Stratospheric warming and a central polar vortex split in the Southern Hemisphere 2019

source

https://www.cpc.ncep.noaa.gov/products/intraseasonal

The above animation shows 2 warmings spots .. (edit.. sorry ONE warming spot , movinv west to east)at about latitude 60s commencing the first week of June 2019 .

They appear to be fully formed a few weeks later in the last week of June. The week of this post.

The AAO was positive during the month of June 2019 but is forecast by half the ensemble models to go strongly negative in the coming weeks.

I am not sure of the link between the Stratosphere warming and the AAO but will be on the look out.

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This post is in progress. Check the comments section below for further entries. Click on the title of this post to load further information if necessary

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Sudden stratospheric warming event.. Northern Hemisphere Jan 2019

We are talking about what’s going on in the upper air ( stratosphere) over the ARCTIC POLAR REGION.  A sudden up welling of warm air is called a stratospheric warming.

The event sends ‘shock waves’  across the globe.

Michael Ventrice from Weather company is reporting and following this event on twitter.

MJVentrice   @ twitter

On January 6th 2019..Michael posted

“The split of the Stratospheric Polar Vortex is now taking place.”

jan 6 2019 polar vortex split

 

JANUARY 10th…….. Michael posted

“Classic downward propagation of anomalous warm air following the SSWE”

polar temperature anomaly jan 10 _2019

JANUARY 11th 2019..Michael Ventrice from weather company and twitter .. posted

“The next step of a SSWE is the downward propagation of warmth into the troposphere. During this downward step, there is cooling over the Polar stratosphere, with warming over the equatorial Stratosphere. This tends to suppressed significant MJO activity moving for a couple months”

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TODD CRAWFORD IS ALSO TWEETING AND FOLLOWING THE SSW

Todd Crawford @tcrawf_nh Jan 10

MICHAEL VENTRICE POSTS 12 th January 2019.

The effect on the equatorial troposphere.

Michael posts

“It’s not often you get 15m/s+ westerly wind anomalies in the lower troposphere over the equatorial Date Line. This translates to 10m/s+ actual westerlies in this region, qualifying this as a true Westerly Wind Burst. Some discussions with at on this

event being the strongest WWB in this region of the world in our archives. I’d have to run an analysis to confirm, but I trust Paul. In the coming months, we should see a response in the Pacific Ocean in which grows El Nino later this Summer into Fall.

PAUL ROUNDY said

“Astonishing thing about that figure is that some people still think that WWBs are not associated with the MJO (because they are using the RMM index instead of focusing on the lower tropospheric wind). Upper trop flow and OLR signals occasionally distort the index.”

850hpa zonal wind anomalies_equator_ 11th dec 2018 to 6 jan 2019

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Another researcher of SSW on twitter to follow..       WILLIAM SEVIOUR

@WillSeviour


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Thanks to Michael and his followers

@MJVentrice

Meteorological Scientist | PhD in Tropical Meteorology from | 2018 Chair of

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POLAR VORTEX

A video explaining the polar vortex in the Northern hemisphere

polar vortex video
source
http://globalnews.ca/news/1114911/words-the-winter-of-2013-2014-have-taught-us/

‘Polar vortex’ pushes dangerously cold temps into U.S. Midwest

THIS LINK HAS 2 EDUCATIONAL VIDEOS ON THE NORTHERN HEMISPHERE POLAR VORTEX

http://globalnews.ca/news/1063597/polar-vortex-pushes-dangerously-cold-temps-into-u-s-midwest/

CHICAGO – A whirlpool of frigid, dense air known as a “polar vortex” descended Monday into much of the United States, pummelling parts of the country with a dangerous cold that could break decades-old records with wind chill warnings stretching from Montana to Alabama.