World geography

The Troposphere

This is the lowest part of the atmosphere - the part we live in. It contains most of our weather - clouds, rain, snow. In this part of the atmosphere the temperature gets colder as the distance above the earth increases, by about 6.5°C per kilometre. The actual change of temperature with height varies from day to day, depending on the weather.

The troposphere contains about 75% of all of the air in the atmosphere, and almost all of the water vapour (which forms clouds and rain). The decrease in temperature with height is a result of the decreasing pressure. If a parcel of air moves upwards it expands (because of the lower pressure). When air expands it cools. So air higher up is cooler than air lower down.

The lowest part of the troposphere is called the boundary layer. This is where the air motion is determined by the properties of the Earth's surface. Turbulence is generated as the wind blows over the Earth's surface, and by thermals rising from the land as it is heated by the sun. This turbulence redistributes heat and moisture within the boundary layer, as well as pollutants and other constituents of the atmosphere.

The top of the troposphere is called the tropopause. This is lowest at the poles, where it is about 7 - 10 km above the Earth's surface. It is highest (about 17 - 18 km) near the equator.

Layers of the atmosphere: troposphere,stratosphere, mesosphere and thermosphere. Earth's atmosphere has a series of layers, each with its own specific traits. Moving upward from ground level, these layers are named the troposphere, stratosphere,mesosphere, thermosphere and exosphere.

The Tropic of Cancer is the most northern latitude on the Earth where the sun can appear directly overhead. The Tropic of Capricorn is the most southern latitude on the Earth where the sun can appear directly overhead. TheTropic of Cancer is currently positioned at approximately 23.4 degrees north of the

The Tropic of Cancer is significant to Earth's geography because, in addition to being the northernmost point where the sun's rays are directly overhead, it also marks the northern boundary of tropics, which is the region that extends from the equator north to the Tropic of Cancer and south to the Tropic of .

latitude. [ lăt′ĭ-tōōd′ ] A measure of relative position north or south on the Earth's surface, measured in degrees from the equator, which has a latitude of 0°, with the poles having alatitude of 90° north and south. The distance of a degree of latitude is about 69 statute miles or 60 nautical miles (111 km).

Longitude is measured by imaginary lines that run around the Earth vertically (up and down) and meet at the North and South Poles. These lines are known as meridians. Each meridian measures one arcdegree of longitude. The distance around the Earth measures 360

Latitude and longitude are angles that uniquely define points on a sphere. ...Latitudes of +90 and -90 degrees correspond to the north and south geographic poles on the earth, respectively. Longitude is defined in terms of meridians, which are half-circles running from pole to pole.