Polar Phenomena

Polar Phenomena

In the Polar Regions you can experience a whole range of weather and light related phenomena that are not normally seen, or at least not as often, in other parts of the World.

Aurora

The aurora borealis (northern lights) and its southern equivalent aurora australis (southern lights), surround both the north and south magnetic poles. They are best seen on a cold clear night and often appear as hanging curtains of light in the sky. Sometimes they ripple and move quite quickly across the sky. These lights occur when highly charged particles from solar winds interact with elements in the Earth’s magnetic fields. As these electrons enter the Earth’s atmosphere, they collide with oxygen and nitrogen atoms anywhere up to 200 miles above the Earth’s surface. The colour of the aurora depends on which atom is struck and at what altitude. A red colour of light usually means that oxygen atoms have been hit more than 150 miles above the Earth’s surface while a blue colour indicates nitrogen being struck up to 60 miles in altitude. Probably the most common colour of the northern lights is green, the result of the electrons hitting oxygen atoms up to 120 miles above the Earth.

People have been fascinated by auroras for thousand of years and most of the native peoples of the Arctic have traditional beliefs relating to the lights in the sky. The Cree in the north of the Canadian province of Quebec believe that the lights are the spirits of their ancestors and by rubbing their hands together as they watch them, the spirits will dance in the sky. A traditional belief amongst the Saami in Scandinavia is that the lights are the tail of an arctic fox that extends upwards into the sky.

Halos & Parhelia

Parhelia at Halley Antarctica
Halos of light around both the sun and the moon can be seen anywhere but they are most commonly viewed in polar skies. They occur mainly when high thin clouds containing millions of ice crystals cover the sky. The crystals act like small lenses refracting and reflecting sunlight between their faces. The halos vary in size and structure, sometimes appearing as a complete arc while on other occasions only part of the arc will be visible. The bright areas on the sides are known as parhelia and also sometimes called ‘sun dogs'. Arcs also form at the top of the 22 degree halo and these are called an upper tangent arc if they form above and a lower tangent arc if they form below. There are many other forms of arcs that form far more rarely around the 46 degree sun halo these can be a once in a lifetime viewing. It is also possible to have low level parhelia forming in the presence of Diamond Dust, which is the presence of low levels of ice crystals on calm clear cold days in polar regions. The air around you sparkles with ice crystals. Sun halos and sun dogs are used by many of the Arctic’s native peoples in their traditional weather forecasting as both parhelia and sun dogs are often associated with imminent bad weather.

Sun Pillars

These vertical pillars of light rising from the sun are usually seen just after sunrise or before sunset. This phenomenon occurs when snow or ice crystals form in high cirrus or alto clouds. The ice crystals which have plate or column shapes reflect the sunlight towards the observer. The width and shape of a sun pillar varies according to the type and orientation of the ice crystals, their height in the sky, and the distance from the observer, as well as the height of the light source. Plate shaped ice crystals normally only produce sun pillars visible on the ground, when the sun is within 6° of the horizon. Light reflected off column shaped crystals can form pillars visible on the ground when the sun is higher but not usually when the sun is more than 20° above the horizon. Light pillars can also form around the moon or any source of bright outside light at night.

Nacreous Cloud

Nacreous Cloud Antarctica
Also known as Polar Stratospheric Clouds, These clouds form in the Polar winters at very high altitudes, 9-16 miles high (15 to25km) and at temeratures lower than -78C. Believed to be ice and Nitric acid, these react to produce clorine & bromine, from CFCs, which directly destroy ozone molecules, so they are believed to be implicated as a cause of the ozone holes. Because the stratosphere is so high, these clouds receive sunlight from below the horizon and glow in mother of pearl colours, best seen two hours after sunset or before dawn.

 

Boiling Water in Freezing Air

When boiling water at a temperature of +100° C (+212°F) is thrown into very cold air, say below -40°C / F, it can result in a very dramatic visual effect. The hot water vaporises instantaneously into a cloud of steam while some of the water droplets are turned directly into small pieces of ice.

Frost Smoke

Frost smoke, also called sea smoke is a fog of ice particles that forms when air from the cold surrounding land and frozen water is over the warmer open water and the moisture condenses, forming a low band of fog.

Polar Night

The term ‘polar night’ usually refers to the period of the winter where in Polar Regions the sun is not visible above the horizon. Although it is called the ‘polar night’ the name is misleading because it is not dark the whole time. There can be quite light periods with a red glow along the horizon around the middle of the day and there is also a long period of twilight. The length of the polar night depends on the latitude. The closer to the ‘pole’ you are, the longer the period of polar night. A community on the Arctic Circle would expect not to see the sun for about 20 hours, while in Thule region of north Greenland, the world’s most northerly natural community, the polar night lasts four months. At the actual Poles, this winter dark period lasts for 179 days. Nature however, balances things out and for every day when the sun doesn’t rise above the horizon there is a corresponding day of ‘midnight sun’ in the summer when the sun doesn’t set.

Ice Blisters

Ice blisters are generally found in the early winter on rivers or other confined bodies of water. They are usually formed by fast moving water flowing under the ice in a confined space. The resulting pressure forces the ice canopy on the river upwards. The ice blisters that form as a result of this often have a conical or elongated dome shape which can be up to 3 metres high and 15 metres long.

 

Related links

Sun Halos

Nacreous Clouds

Ice Blisters


Text © B & C Alexander