Winds of Winter
By Ved Dubhashi
We might never get our hands on a copy of Martin’s “Winds of Winter”, but a shift in global weather phenomenon has ensured that some of us in the mid-latitudes have gotten a good taste of winter after a long hiatus. As the nation continues to remain in lockdown, a week of icy weather did more to lift the spirits of people of all ages than Christmas or Sinterklaas. As the mercury dropped below zero and stayed there for quite some time, it elicited a glimmer of hope; perhaps Elfstedentocht could happen? Shops sold out skates across the country, for those who couldn’t get their hands on a pair, struck deals with friends to borrow. For a brief moment in time, amidst a pandemic, the entire country was united and happy, ironically by the winter wind’s churlish chiding.
Last month, aficionados of cold weather revelled in the snow. Femke, a Masters student at TU Delft, smiles as a wave of nostalgia engulfs her as she recalls the times she spent as a child building a snowman with her family, often piling the snow high enough to make the sculpture taller than herself. “We would wait until the ice was thick enough before venturing out to ice skate on the fens and small lakes”, she goes on to add, “Sometimes the stretch of water from my home to my grandparent’s house would be frozen, and I’d skate till there for some hot pea soup and back again”. Gijs, also a masters student, is in the final leg of his thesis. Like Femke, he recollects that during his childhood, snow and ice skating were always part of the winter equation-“there was no question about it, going skating with friends and playing ice hockey was a significant part of growing up”. Gijs and his brother went on to participate in the Dutch National Championships for winter sports. With time Gijs and his friends got busy with studying, and the snow made rare appearances. His affinity for snow is apparent in his voice. He believes that it offered a feeling of relaxation and an opportunity to bond with friends and family. When winter came marching in, Gijs made it a point to skate with his girlfriend this time around. His appetite for adrenaline also came in handy as he believes that driving a car in the snow is fun. He hopes his work at Zero Emission Fuels and the collective global effort will resolve climate change. Gijs and Femke’s experience is a poignant reminder that climate change is real, and the effects are etched in the minds of young people.
Albeit the Netherlanders met this event with great cheer and spirits, it begets the question: why did this happen? A simple why can send a flurry of people searching across the web for the right answer. But if memory serves correctly, the last time a similar event took place was in 2014. It shows that maybe this might not be an isolated event but fits into a pattern that coincides with the weakening and collapse of the polar vortex. A term that is regularly thrown about in conversations about extreme weather patterns, sometimes correctly, at times misappropriated.
What is the polar vortex?
A phenomenon first described in 1853, the polar vortex is a high-velocity circulation of cold air at the north and south poles. It begins at the tropopause and extends high up into the stratosphere. Typically, the temperatures inside this low-pressure region can plunge to -70C with wind speeds of up to 320 km/hour.
Why does it exist?
As with all weather phenomena on the planet, the polar vortex is driven by the sun’s differential heating of the earth’s surface. This unequal distribution of thermal energy results in alternating low and high-pressure zones that comprise circulation cells. These cells are responsible for transporting energy from the equator to the poles, thus reducing the temperature gradient between the equator and the poles. Each cell roughly spans around 30 degrees latitude in the southern and northern hemispheres, beginning from the equator and moving poleward: Hadley cell, Ferrell cell and the Polar Cell.
Named after it’s discoverer, the Hadley cell is responsible for the trade winds or the easterlies; this loop forms as warm air rises, creating a low-pressure zone at the equator. This air cools as it reaches the upper extents of the troposphere and is pushed polewards in either direction (North & South) by the rising hot air from the lower altitudes. The Coriolis effect imparts an eastward component to this moving bulk of air, which results in the subtropical jet streams. The cooler air starts settling down at 30 degrees N and S latitudes as it collides with the colder air from the polar regions, which results in a high-pressure zone in the tropics. Similarly, we have the Ferrell cell in the temperate latitudes followed by the poles’ polar cell. The warm air rising from the Ferrell cell meets the cold front from the poles. This contributes to the formation of a region of warm air (low pressure) surrounded by cold air, resulting in the polar vortex formation.
The Coriolis effect comes into play yet again and causes this mass of air to rotate from west to east as it moves towards the low-pressure zone in the stratosphere. The polar vortex is essentially a cyclone in the upper atmosphere with some of the planet’s freezing winds.
Why is the polar vortex weakening?
Ideally, the polar vortex’s cold wind is kept within the arctic circle by the polar jet stream—the latter acts as a fence. Unfortunately, due to global warming, the temperature gradient responsible for the jet streams decreases, weakening the air currents. Consequently, it allows the colder winds from the polar vortex to descend into lower latitudes such as Northern Europe and Central America, resulting in cold icy winters. But this is only possible when the polar vortex weakens and splits into smaller low-pressure cells. Scientists believe rising ocean temperatures can be a cause for sudden stratospheric warming events. For example, the North Atlantic warm ocean current appears to feed warmer air to the polar regions, which leads to a weakening of low-pressure areas in the stratosphere that can split the polar vortex into two or smaller cells. Combined with a weaker jet stream and multiple cold air cells, winter winds are ready to descend into the lower latitudes. Winter is here.
For a good part of the Netherlands, the snow last month was akin to having a slice of the past or reliving a lost aspect of their childhood. Albeit many cannot skate or build a snowman that often anymore, some remain hopeful for Eflstedentocht.