Winter: The Coldest Season

Winter, the coldest season of the year, comes between autumn and spring. It is associated with plunging temperatures and icy weather, but its impact and timing change according to location. The farther an area lies from the equator, the colder temperatures it experiences. Temperatures in equatorial regions stay relatively constant despite the shifting seasons. This is because, due to the curve of the Earth, the equatorial areas get more sunlight, according to the Atmospheric Radiation Measurement (ARM) program.

Shifting time frames

Most people think the coldest season begins during the winter solstice, but there are in fact two definitions of winter.

Astronomical winter — what most people think of as winter — is defined by Earth's position around the sun and ranges from the winter solstice to the vernal equinox. The winter solstice marks the time when sun passes directly over the equator. In the Northern Hemisphere, it falls around December 21, and in the Southern Hemisphere it occurs around June 21, according to the National Weather Service (NWS). It is the shortest day of the year, and has been noted and celebrated by a wide variety of cultures around the world. [Gallery: Images of Stunning Snowy Landscapes]But anyone who regularly engages in winter sports might tell you that winter weather tends to fall before the middle of December or June. Meteorological winter falls sooner, spanning the three-month period from December to March, according to NOAA. It is based on the annual temperature cycle and the calendar rather than Earth's journey around the sun.

Winter in the hemispheres

People living in the Northern Hemisphere are more likely to experience a colder winter than those in the Southern Hemisphere. In fact, all of the coldest countries in the world are located in the Northern Hemisphere. These include Kazakhstan, Russia, Greenland, Canada, the United States, Iceland, Finland, Estonia and Mongolia, according to Earth & World. (Though not a country, Antarctica, in the Southern Hemisphere, is technically the coldest region on Earth.)So why do so many countries in the Northern Hemisphere get much colder than those in the Southern Hemisphere? This occurs because there are a few major differences between the two hemispheres when it comes to factors that affect climate: the size of a land mass, how close the land is to a polar region and the amount of ocean coverage.

First, there are larger masses of land at higher latitudes in the Northern Hemisphere, even within the Arctic Circle, such as Greenland, the northern parts of Norway, Sweden, Finland and Iceland and the frigid tundras of North America, Europe and Asia. In contrast, the bigger land masses in the Southern Hemisphere are closer to the equator and no countries are located on or below the Antarctic Circle — only the frozen unpopulated continent of Antarctica.

Another important temperature moderator is the ocean. Oceans cover 81 percent of the Southern Hemisphere, compared to only 61 percent in the Northern Hemisphere, according to the book "Atmospheric Temperature Profiles of the Northern Hemisphere" (Springer, 2012). All of this water, which stores and conducts heat better than land, helps keep temperatures somewhat warmer and more stable.Winter brings many changes to the world around it. During winter, some animals migrate, which means moving to another area for a season's time. Usually, animals go south to warmer areas during the winter. In response to global warming, some bird species now arrive in spring breeding grounds earlier, and lay eggs earlier, according to a report by the World Wildlife Fund (WWF). In Europe, some birds that normally migrate have stopped migrating altogether, according to the report.