Even though the Polar Vortex is becoming stronger before the Winter Season 2021/2022 begins, it is already experiencing its first stratospheric heating event. The Polar regions are experiencing an unusually early warming event, with more warming expected to follow in the later months.
The Polar Vortex plays a key role in the cold season. It is strongly connected to all levels of the atmosphere, from the ground upwards to the stratosphere. Any major power shift or disruption of the Polar Vortex could have a profound impact on weather development. We monitor the activity high in the stratosphere regularly and take notice.
Before we explain what’s up with the Polar Vortex, our weather, and why it is so important, let’s quickly find out what the Polar Vortex is. This is what we try to do in all of our winter articles. Knowledge is powerful and essential. It can help you understand everyday weather events once you see how they fit into the larger picture.
HIGH OVER THE NORD
The troposphere, the lowest layer in the atmosphere, is where all clouds and weather are found. It can reach upto 8 km (5 mi) above the polar regions and around 14-16km (9-10 miles) above the tropics.
Above it is the stratosphere, a deeper layer. This layer is approximately 30 km thick and very dry. This is the Ozone Layer. The image below shows the layers of the atmosphere. You can see the troposphere at the bottom and the Stratosphere above it.
These layers are very important, because when you hear meteorologists and climatologists talk about the polar vortex and its influence, in most cases they mean the higher altitude – stratospheric part. The polar vortex, however, covers most of the atmosphere’s bottom.
The stratospheric Polar Vortex is spinning high above our weather but it is still directly connected with the lower part of the atmosphere and can influence our daily weather as one large hemispheric circulation.
How does the polar vortex form? As we enter autumn each year, the polar regions get less sunlight. This causes the north pole to cool down. The atmosphere further south, even though the polar regions are cooling down, is still warm because it continues to receive solar energy. On the image below, you can see when the polar region receives little to no solar energy.
The pressure drops as the temperature drops in the polar regions. The process is identical in the stratosphere. As the temperature drops above the pole, and the difference in temperature towards the south increases a large low-pressure (cyclonic), circulation starts to develop across the Polar stratosphere.
The image below shows a typical Polar Vortex at 30km/18.5miles elevation (10mb level) close to the top of stratosphere during high pressure. Winter season.
The polar vortex acts as a large cyclone that covers the entire north pole and the mid-latitudes. It is present at all levels from the ground up, but it can take on different shapes at different altitudes.
The next image below shows the polar vortex at an even lower altitude, approximately 5km/3miles. It shows the true size of the Polar Vortex closer to the ground (cold colours). Due to the increased terrain/ground influence, and the dynamic from many weather systems, the polar vortex becomes more deformed the closer we get to the ground.
Be aware of its cold “arms” extending into the lower latitudes, also bringing along colder air into the region.
We have created a high-resolution video below that will give you an even better idea. It shows the Stratospheric Polar Vortex spinning above the Northern Hemisphere at approximately 30km/18.5miles elevation.
Video of the December 2020 to Jan 2021 period, taken from NASA GEOS-5 Data. The vorticity parameter is a simplified way to show the energy of the Polar Vortex. The polar vortex covers a large portion of the Northern Hemisphere. You can see how the stratospheric “anti-vortex”, deformed and attacked the Polar Vortex, spinning in the opposite (clockwise) direction over the North Pacific.
The main message of the video is that the Polar Vortex does not consist of one winter storm that moves from the Midwest into the northeastern United States. It is a large cyclonic area spinning across the entire Northern Hemisphere at close to 50km/31miles above the stratosphere.
A strong polar vortexStrong polar circulation can be seen even at lower levels. This can often lock the cold air into the Polar regions, creating milder Winters for most of Europe and the United States. However, it can also cause a decrease in the temperature. Polar Vortex collapseIt is as dynamic as it sounds. As the higher pressure falls, the cold air from the polar regions is pushed out into the United States and/or Europe.
A rise in temperature and pressure in the stratosphere is what usually causes a polar vortex to collapse. Sudden Stratospheric Warming is also known as this. It is a sudden increase in temperature in the stratosphere, as the name implies. Further information about the SSW events and how they affected the Winter season will be provided further below.
POLAR VORTEX – COLD SEASON 2021/2022
We typically view the polar vortex at the 10mb level in the stratosphere. It is about 28-32km (17-20 mile) in altitude. This altitude is considered to be in mid-stability and gives a good representation about the general dynamics of stratospheric vortex.
The strength of the polar vortex can be measured by the power of its winds. Usually, this is done is by measuring the zonal (west to east moving) wind speeds around the polar circle (60°N latitude). Below is a forecast for the 10mb winds.
We have a fairly consistent cooling trend at this time of year over the polar areas. This usually means higher pressure and stronger winds. The image below shows the forecasted wind speed in the stratosphere. The polar vortex is currently stronger than usual.
The stratospheric Polar Vortex appears to be in a good place at the moment. It has a classic, circular shape and a stable, broad wind field. A semi-persistent area of high-pressure is found in the North Pacific.
This temperature will be the norm for the Arctic region this time of year. The cold of the polar vortex at 10mb level is reaching below -80°C and is still cooling at this point in time.
We can see a fascinating progression in the pressure anomalies across the polar regions over the past two month. The vertical pressure anomalies are shown in the image. You can see the strong high-pressure buildup that occurred in October and which also spread into the stratosphere. This caused a slight disruption in the polar vortex. However, pressure has been dropping in the stratosphere and connecting downwards over the past few months.
We now turn our attention to the forecast for the next few day. The ECMWF ensemble forecast shows the pressure anomaly at 500mb. This is located at approximately 5km elevation and shows the state the lower-level polar vortex. It is evident that the polar circulation can be quite dynamic, with many waves and low-pressure system. This shows that there is a connection to strong stratospheric pole vortex in core. However, the pressure over Polar Regions is usually lower than normal.
Despite the core connection, strong wave dynamics are maintaining their momentum, preventing cold air from being fully locked out in the Polar regions. The Atlantic high-pressure system helps to transport cold air into Europe. We also have a ridge that runs over the western United States, which helps to bring down the colder air to the eastern and central United States.
This dynamic pattern is also evident in the temperature forecast. It is possible to see colder air over Europe (especially Scandinavia), as well as over most of Canada, the northeastern United States and Canada. A large area of high-pressure over the United States is expected to bring warmer than usual air mass to most of the country’s western and southern regions.
We will continue to see activity in the stratosphere. The high-pressure area is shifting over the North Pacific. As the image below shows, this will help push the core polar vortex further towards Siberia. The wind field will also become more oval and deformed, spreading the shape.
The temperature forecast also shows the shift of the core. It shows the core moving over Scandinavia and towards Siberia. It is also slightly changing in shape as it is being pressed from the Pacific side.
You can also look at the vertical pressure profile to see the expected changes from lower levels to the stratosphere. This image basically shows the pressure anomalies with altitude over the North Hemisphere (40-80°N). We can see the stronger low-pressure region (polar vortex), in the upper stratosphere. This area extends down, connecting with lower levels at around 120-180 degree longitude. It is located in Siberia, East Asia region.
We see a disconnect in the Atlantic region, where there is a high-pressure area, and a weak link to the Canadian portion of the lower vortex.
We can see the 500mb pressure patterns in week 2 December. It shows that the low pressure region is present from Siberia into East Asia. This is the main connection point of the stratospheric Polar Vortex. However, we can see that there is a stronger core than Canada and an extension (arm) of the polar vortex into Europe.
Temperature-wise we see colder air being closer to low-pressure areas. Due to the North Atlantic region’s high pressure system, we see a trend towards colder temperatures across Europe. The expanding high-pressure area in the USA is causing warmer than usual temperatures to prevail over the west. The middle of next weeks will bring cold air to the east and central parts of the United States.
The next map below is very special because it tracks the wave activity (energy around the Northern Hemisphere). It shows the heat flux at the border of the troposphere & stratosphere. The main takeaway is the obvious strong wave activity over Siberia and the North Pacific, and the core stratospheric vortex breaking down into two units, as shown above.
The polar vortex is a large high pressure system that hovers over the North Pacific. This can be seen in the midstratosphere, towards the middle of the month. This is due to the strong wave activity in the North Pacific. The polar vortex is being pressed against, changing its form from the classic circular to more elliptical.
Temperature-wise in stratosphere, this suggests a possible warming wave in the east-Asia region and the Pacific. Although the current forecast does show some slight warming wave trends, it is not in the right range. The latest forecasts show that a warming wave is initiating.
This graphic gives a unique perspective on the weather connection and stratosphere. The next image below shows the high-pressure anomaly rising from the ground and reaching into the stratosphere between October and November.
Later in the month, low-pressure began to dominate the polar region. The forecast shows that lower pressure will reach the lower levels from the stratosphere, connecting both layers more directly. Despite this connection and the pressure dropping over the polar regions, there is enough “resistance” in the pattern below to still allow colder air to reach Europe and the eastern United States at the moment.
However, with strong momentum above, a large-scale long-term and severe winter outbreak is unlikely to occur. It can become difficult for lower levels to maintain a very disruptive circulation if the Polar vortex in the stratosphere continues its power.
ECMWF POLAR VORTEX – FORECAST
The extended range forecast from ECMWF shows trends in new warming waves over the Pacific Canada region. Below is a mid-December ensemble forecast. It shows the temperature anomaly below the 10mb level (30km/18.5miles). Extended forecasts are not perfect, so we only look at the trend.
This trend is a clear indicator that the polar Vortex will likely make some disruption attempts in the next weeks. We will monitor the situation closely as these are powerful forces that could change the course of Winter 2021/2022, if they are strong enough.
We can see the warm signal in late December and a high pressure area in the North Pacific region. This is the area to be most focused on as it is where the polar vortex expands and presses against a high-pressure region in the stratosphere.
It is difficult to predict what weather effects these scenarios might have. These stratospheric effects and their effects can be much more unpredictable than it might seem. The model cannot accurately forecast the surface, and then add the effects from above. We can only observe trends at this time, which show early warming dynamics appearing from the Pacific side.
Below you will find the ECMWFlong term stratospheric prediction. It displays the wind speed of the stratospheric vortex, which directly correlates with its strength. A major stratospheric heating event usually involves a reversal in winds in the stratosphere (negative numbers).
We can see a noticeable weakening of polar vortex in the late December and early January 2022. Although there is no major polar vortex event, this forecast does indicate potential disruption for the vortex. We do have individual calculations which go into the negative numbers (SSW). This is the most likely time for a major stratospheric temperature increase to occur in this Winter.
The best example of such a change in the course of winter was last Winter. You’ll see below how this major stratospheric phenomenon changed the weather patterns in the North Hemisphere in January. It was later discovered to be the main reason for the cold arctic eruption in the southern United States at the end of February.
WINTER SEASON STRATOSPHERIC WORMING
Officially, a polar vortex collapsing is called “The Polar Vortex Collapse”. Sudden Stratospheric WarmingEvent (SSW). It is exactly as the name implies. It is a sudden temperature increase in the polar stratosphere during cold seasons. Warming the stratosphere can mean that the polar vortex is weakening and could also collapse under rising pressure during a warming episode.
The source of warming is usually energy from the bottom. Strong weather systems can deflect a lot more energy upwards into space, disrupting its dynamics.
Below is an image showing vertical wave propagation in the 2008/2009 cold saison. It shows energy transport at the vertical levels. The red areas show energy moving from the lowest levels to the stratosphere, disrupting circulation. This energy is the main reason for a warming event.
This can cause a chain reaction that can disrupt the jet stream and create a high-pressure zone above the Arctic circle. This can allow the cold arctic air to flow into Europe and the United States. Below are two SSW examples from the excellent SSW analysis site at ESRL/NOAA. The image shows the SSW events during the 1984/1985 winter seasons and 2008/2009 winter seasons.
The top row shows the stratospheric conditions with warming anomalies and a polar vortex divided into two parts. The bottom row displays the temperature anomalies at the surface that followed these events. It includes the very cold winter in 1985, and the cooler weather after 2009’s SW event.
If we look closer at the 1985 global warming event, you can see the stratospheric temperature (red colors), as it progressed down over time. It quickly connected with the lower layers of atmosphere, raising pressure above the North Pole in January and into February. This event allowed the colder air to escape into central and western Europe, and the northern United States during that winter.
Below you will find the surface temperature anomalies from 0-30 Days after the SSW Event in 1985. It is possible to see a very cold signal coming from northern and central Europe. This is also true for most of the United States. The strong high-pressure system that generated the stratospheric warm event caused western polar regions to be warmer than normal.
We can see a fascinating picture if we add all Stratospheric Warming Events from the past decades and examine the weather 0-30 Days after these events.
Below is the average temperature between 0 and 30 days after an SSW event. The United States has the most cold signal, as does Europe, with the exception being the southeast. Note: This is an average image of many SSW-related events. Each individual stratospheric heating event is unique and does not necessarily indicate a strong winter pattern.
Below you will see the average pressure anomalies, which indicate the increase in surface pressure after the SSW events. The pressure tends drop over Europe, the western Atlantic and other regions. This is due to a highly disrupted circulation. It allows colder polar breezes to move freely out of the polar regions.
Below are snow anomalies that show an above-average amount of snowfall across much of the eastern United States as well as Europe. This is a natural response because, after major stratospheric heating, the colder air has a more direct path towards the south and into these areas.
MAJOR STRATOSPHERIC WARMING EVENT – 2021
We have witnessed significant stratospheric warmth this year, beginning in January. The entire sequence began in December, and it has changed the weather patterns for the remainder of Winter.
The polar vortex was very strong in early December. It reached speeds of over 40m/s (90mph). The polar vortex began weakening towards the middle of December and even further in late December. The graph below shows how the zonal winds became negative in January due to the collapse of the polar vortex.
The temperatures at the 10mb elevation, which is at approximately 30km/18.5miles in altitude, are shown below. Because there is less influence of the terrain and weather fronts at this altitude, the polar vortex here is more circular.
A warming sequence began in December and spread from Europe into central Asia. It was threatening to engulf the outer layers of the Polar Vortex. As the pressure rose in the stratosphere above the North Pacific and east Asia, the cold-core of polar vortex was becoming more oval.
Just two days later, a strong warming wave reached its peak over Siberia, with maximum temperatures in the wave reaching up to +5°C. In normal conditions, the temperatures here are over 30-40°C lower, so this was a very significant warming wave in development.
This was because the actual polar Vortex at this altitude (30km/18.5miles), looked more triangular rather than the usual healthy circular shape. The image below illustrates vorticity, or to reduce it, the energy of polar vortex. It can be clearly seen that it was being drained from energy by a strong (barely noticeable) wind. Anticyclonic systemOver the North Pacific, and East Asia
The preliminary date for the Sudden Stratospheric Warming Event was January 5th. This is because the winds around the Polar Circle have reversed from being predominantly easterly to being mainly westerly.
The stratospheric warmth wave has covered the entire North Pole of the stratosphere, effectively splitting up the cold-core polar vortex.
One part of the splitpolar vortex moved over North America while the other moved over the European sector. This didn’t directly impact the surface weather because it was at stratospheric elevation. As you’ll see, the domino effect began, and higher pressure was moving to lower levels.
Below you can see the NASA temperature analysis from the polar stratosphere. This SSW event caused a large temperature rise at the 10mb (30km level) in January 2021. This is a strong warming event. Temperatures remained above normal through February.
The stratosphere and the stratosphere are connected. Winter weatherIt is helpful to have more specific images on hand. It is especially useful if you combine time and altitude.
Below is an image of the atmospheric pressure index. The image below shows an atmospheric pressure index. Blue colors indicate lower pressure, while red colors indicate higher pressure. In early 2021 we can see the lower part of the atmosphere, from the ground to the middle stratosphere (30km/18.5miles).
The stratosphere can show strong positive values in January due to the stratospheric heating event. The high-pressure effect was gradually lowering over time, reaching its lowest levels by mid- to late January. This continued well into February, influencing Weather circulationEven though the stratospheric heating was already over.
Strong high-pressure systems over the Arctic can disrupt the weather circulation and open up the possibilities of the Arctic. Cold airFrom the Arctic to the mid-latitudes. Below is an image showing the anomalies in surface temperature between January and February 2021. High pressure over the polar regions caused temperatures to rise that were higher than normal. Siberia was exposed to very cold Arctic air. Some colder air was also transported into western Canada, the south-central United States and the Texas February cold air epidemic.
We also did an analysis of the winter period January-February 2021. It shows the sea-level pressure anomaly. It shows a strong high-pressure system over the North Pole. This dominant high pressure system is a result of the stratospheric warm event and the collapse of the Polar Vortex. It changed the circulation and dispersed colder air towards the south.
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*Winter 2021/2022* Final seasonal forecast shows the colder than expected La Nina having a strong influence as we head into the winter season
Source: Severe Weather