Factors Affecting Arctic Weather and Climate
Just like other areas on Earth, a number of factors influence the Arctic climate. Weather and climate depends on a lot of variables, including latitude, temperature, and the mix of land and water. Individually the factors that affect Arctic climate are important. However, they also interact with each other to produce weather patterns and climate feedbacks, which have effects both within the Arctic region and far beyond the Arctic.
Considered together, these factors determine the Arctic Energy Budget, or the balance of heat in the Arctic region. Over the course of the year, heat moves northward into the Arctic and escapes through the atmosphere. Learn more about these factors:
The amount of sunlight hitting the Earth's surface is affected by the tilt of the Earth and its atmosphere.
—Credit: Peter Halasz.
The Arctic is sometimes called the land of the midnight sun. North of the Arctic Circle, the sun does not set for a period of time during summer, called polar day . This happens because the Earth is tilted on its axis. The length of this period of continuous daylight depends on how far north of the Arctic Circle you are. At the Arctic Circle, there is only one day of continuous daylight. This occurs at the summer solstice, usually around the 23rd of June. At the North Pole, there is almost six months of continuous daylight. The sun rises close to the spring equinox , around March 21, and does not set until the autumn equinox around September 22. In between the North Pole and Arctic Circle, the number of days of continuous daylight decreases as you get closer to the Arctic Circle. In winter, the North Pole experiences six months of continuous night. The number of days of continuous night also decreases the closer you get to the Arctic Circle. At the Arctic circle there is one day of continuous darkness.
Meteorologists look at changes in air pressure to figure out how air masses are moving and predict how weather will change.
Air pressure, or atmospheric pressure, is caused by the combined weight of a column of air directly above a point on the Earth or in the air. At high elevations such as the top of mountains, there is less air above the Earth's surface than at lower elevations such as sea level, so atmospheric pressure is lower at the top of a mountain than at sea level. Most weather maps show sea level pressure, which is the atmospheric pressure at sea level. Weather maps show atmospheric pressure using lines called isobars, which are similar to contours on a topographic map. Just as topographic contours show hills, basins, ridges and valleys, isobars show areas of high and lows pressure called highs and lows, ridges and troughs. These are formed by the circulation of the atmosphere around the Earth, and by movement of air upwards and downwards.
Changes in atmospheric pressure can indicate what the weather will be like. A decrease in pressure indicates an approaching low-pressure system, which is associated with cloudy and wetter conditions. An increase in pressure indicates an approaching high-pressure system, which is associated with clear and dry conditions. Over longer periods of time, weather maps show common patterns of high and low pressure. The names of these patterns often reflect the location of these patterns. In the Arctic, the common features are the Aleutian Low, Siberian High, Icelandic Low and Beaufort Sea High. Scientists look at the strength of these patterns to study changes in atmospheric circulation, and how these change are related to changes in temperature, precipitation and winds.
Temperature is measured using thermometers. It is often the first thing you read in a weather report, and can help you decide what clothes to wear, what activities to plan, and what gear to bring when heading outside.
Air temperature is a measure of the amount of energy held in the air. Warm air has more internal energy than cooler air. Temperature can be reported using several different scales. In the United States, the Fahrenheit scale is the most common. Internationally and in science, people use the Celsius scale.
Just like other regions of the Earth, temperatures in the Arctic tend to rise during the day, when sunlight warms the ground, and fall at night. Arctic temperatures are warmer in summer, when there is more sunlight, and colder in winter, when the region is dark.
Scientists also use temperature for monitoring changes in climate. Long-term measurements of air temperatures over many years are important for scientists to track climate change.
In this schematic drawing of North Atlantic and Arctic Ocean circulation, red arrows represent relatively warm water from lower latitudes entering the Arctic, while blue arrows show the export of colder water from the Arctic. Shaded white shows the average area covered by sea ice. Click for larger image.
—Credit: G. Holloway, Institute of Ocean Sciences, Sidney, British Columbia.
Much of the Arctic region stays warmer than scientists would expect based only on latitude. That unexpected warmth comes from the Arctic Ocean. Water has a high heat capacity, meaning that it takes a lot of energy to change its temperature. This is one reason that coastal areas tend to have mild climates: the ocean keeps them cool during the summer and warm during the winter. Land, in contrast has a lower heat capacity, so it heats up quickly during the day and cools down as soon as the sun goes down.
In most parts of the Arctic, the moderating effect of the ocean works more strongly in summer than in winter. In winter, sea ice spreads over the ocean, creating an insulating layer, like a blanket, that prevents much heat from escaping from the ocean to warm the air. That means that the air above the ice can get bitterly cold—deep below freezing—while the water underneath remains much warmer—never getting colder than the freezing point.
Ocean currents also bring heat from warmer regions into the Arctic Ocean. In the Atlantic Ocean, a current called the Gulf Stream brings warm water from the Gulf of Mexico up along the coast of North America and across the North Atlantic Ocean towards Europe. The Gulf Stream keeps places like Norway and the island of Svalbard much warmer than other places at similar latitudes in the Arctic.
Wind is the movement of air between regions of high pressure to regions of low pressure. The larger the difference between high and low pressure (shown by closely spaced isobars on a weather map), the faster the wind. Wind speed and direction is also influenced by other factors, including the Coriolis force and surface friction. The Coriolis force, caused by the rotation of the Earth, changes the direction of the wind. In the northern hemisphere, the Coriolis force deflects the wind to the right, so that winds circulate in a clockwise direction around high-pressure regions, and counterclockwise around low-pressure regions. The opposite occurs in the southern hemisphere.
Surface friction caused by the movement of air across land and ocean surfaces can also affect wind speed and direction.
Winds in the Arctic can vary a lot in strength, but they are typically light. Winds tends to be stronger in the Russian Arctic, where there are more storms, than in the Canadian Arctic. Strong temperature inversions form in winter, which slow winds near the ground. Temperature inversions are where air at the surface is cooler than the air above. These inversions disconnect the surface air from the air above.
Although Arctic winds are typically light, strong gales that can reach hurricane strength can occur and last several days. In the winter, these strong winds scour the snow from exposed areas and form large snow drifts in sheltered areas. Strong winds increases the wind chill factor. Wind chill refers to the cooling effect of any combination of temperature and wind, expressed as the loss of body heat in watts per square meter of skin surface. The body has a very thin layer of still air immediately adjacent to it called the boundary layer that helps to insulate the body from heat loss. As wind speed increases, the thickness of the boundary layer diminishes, and the rate of sensible heat loss from the body increases.
The Coriolis force explains why winds circulate around high and low pressure systems as opposed to blowing in the direction of the pressure gradient. The following figure shows how wind is deflected in each hemisphere.
Air is a mixture of gases, which includes nitrogen, oxygen, carbon dioxide and water vapor (water in its gas form). Humidity refers to the amount of water vapor in air. All air contains at least some water vapor, but the amount of water vapor changes a lot from place to place and from time to time. The amount of water vapor in air can increase when water evaporates from land and water surfaces, and as plants respire. Humidity decreases when water vapor condenses to form very small drops of liquid water, forming clouds or growing to become rain drops. Evaporation and condensation happen all the time. Sometimes more water is evaporating into the atmosphere, sometimes more water is condensing out of the atmosphere, and sometimes as much water evaporates into the atmosphere as condenses out of it. When evaporation is the same as condensation at a location in the atmosphere, scientists call the air at this point saturated.
There are several measures of the amount water vapor in air. Relative humidity is one measure often used by meteorologists and TV weather reporters. Relative humidity is the ratio of water vapor in the air to the saturated water vapor content of the air.
Overall, humidity in the Arctic atmosphere is low. In some places, Arctic air is as dry as air in the Sahara desert. Humidity tends to be higher over the oceans and in coastal areas in summer, when water vapor evaporates from the relatively warm ocean surfaces. Humidity is lower over land areas, such as Canada, where there is less water to evaporate. In winter, humidity is very low because surface temperatures are very cold and very little water evaporates into the atmosphere. At this time of year, sea ice covers much of the Arctic Ocean, preventing evaporation from ocean water. However, in areas where there is no sea ice cover in areas, there can be a lot of evaporation and fog can form, making the ocean look as if it is steaming .
Clouds are made of tiny water droplets or ice crystals that have condensed onto tiny pieces of sea salt, dust, smoke, or other particles in the air. Clouds have two major effects on weather and climate. Clouds reflect sunlight, which can keep surface temperatures cool. However, they also trap heat close to the Earth's surface, which keeps temperatures warmer. Which one of these processes wins out depends on how thick the clouds are, and a number of other factors, including cloud type and thickness, the magnitude of the solar radiation, and the albedo of the underlying surface.
In the Arctic, the cloudiest months are in summer, when the sea ice melts away and exposes open water in the Arctic Ocean. That open water adds more moisture to the air, helping to increase cloud cover. Cloud cover is least extensive in December and January, when the ice cover is at its thickest.
Precipitation is water that is deposited on Earth's surface from the atmosphere. Although we generally think of precipitation as rain or snow, hail, dew, hoar frost are also forms of precipitation. Precipitation is an important component of the hydrological cycle. It supplies water for plants to grow, soaks into the soil and feeds river and lakes, which eventually drain to the ocean. Water from plants, soil, and the oceans evaporates back into the atmosphere. There it forms clouds and returns to the Earth surface as precipitation.
Over much of the Arctic, precipitation amounts are low. Some areas are called polar deserts and receive as little precipitation as the Sahara desert. However, the Atlantic sector of the Arctic, between Greenland and Scandinavia is an exception. Storms forming in the Atlantic Ocean bring moisture up into this area, especially in winter.
Almost all precipitation in the central Arctic and over land falls as snow in winter. However, rain can occur on rare occasions during winter in the central Arctic ocean when warm air is transported into this region. Snow also falls in summer. More than half of the precipitation events at the North Pole are snowfall. Over the Atlantic sector, snow is very rare in summer.