The Northern Hemisphere is the northern half of the Earth (map). It begins at 0° or the equator and continues north until it reaches 90°N latitude or the North Pole. The word hemisphere itself specifically means half of a sphere, and since the earth is considered an oblate sphere, a hemisphere is half.
Geography and Climate of the Northern Hemisphere
Like the Southern Hemisphere, the Northern Hemisphere has a varied topography and climate. However, there is more land in the Northern Hemisphere so it is even more varied and this plays a role in the weather patterns and climate there. The land in the Northern Hemisphere consists of all of Europe, North America and Asia, a portion of South America, two-thirds of the African continent and a very small portion of the Australian continent with islands in New Guinea.
Winter in the Northern Hemisphere lasts from around December 21 (the winter solstice) to the vernal equinox around March 20. Summer lasts from the summer solstice around June 21 to the autumnal equinox around September 21. These dates are due to the Earth's axial tilt. From the period of December 21 to March 20, the northern hemisphere is tilted away from the sun, and during the June 21 to September 21 interval, it is tilted toward the sun.
To aid in studying its climate, the Northern Hemisphere is divided into several different climatic regions. The Arctic is the area that is north of the Arctic Circle at 66.5°N. It has a climate with very cold winters and cool summers. In the winter, it is in complete darkness for 24 hours per day and in the summer it receives 24 hours of sunlight.
South of the Arctic Circle to the Tropic of Cancer is the Northern Temperate Zone. This climatic area features mild summers and winters, but specific areas within the zone can have very different climatic patterns. For example, the southwestern United States features an arid desert climate with very hot summers, while the state of Florida in the southeastern U.S. features a humid subtropical climate with a rainy season and mild winters.
The Northern Hemisphere also encompasses a portion of the Tropics between the Tropic of Cancer and the equator. This area is usually hot all year and has a rainy summer season.
The Coriolis Effect and the Northern Hemisphere
An important component of the Northern Hemisphere's physical geography is the Coriolis Effect and the specific direction that objects are deflected in the northern half of the Earth. In the northern hemisphere any object moving over the Earth's surface deflects to the right. Because of this, any large patterns in air or water turn clockwise north of the equator. For example, there are many large ocean gyres in the North Atlantic and North Pacific- all of which turn clockwise. In the Southern Hemisphere these directions are reversed because objects are deflected to the left.
In addition, the right deflection of objects impacts the flows of air over the Earth and air pressure systems. A high pressure system for example is an area where the atmospheric pressure is greater than that of the surrounding area. In the Northern Hemisphere, these move clockwise because of the Coriolis Effect. By contrast, low pressure systems or areas where atmospheric pressure is less than that of the surrounding area move counterclockwise because of the Coriolis Effect in the Northern Hemisphere.
Population and the Northern Hemisphere
Because the Northern Hemisphere has more land area than the Southern Hemisphere it should also be noted that the majority of Earth's population and its largest cities are also in its northern half. Some estimates say that the Northern Hemisphere is approximately 39.3% land, while the Southern half is only 19.1% land.
Wikipedia. (13 June 2010). Northern Hemisphere - Wikipedia, the Free Encyclopedia. Retrieved from: http://en.wikipedia.org/wiki/Northern_Hemisphere