Weather

Weather is the condition of the atmosphere in a local environment or region over a short period of time, ranging from an exact instant to a few days. This is distinct from climate, which refers to persistent atmospheric systems over larger areas and greater time periods. The atmospheric conditions may be hot or cold, dry or humid, rainy or dry, windy or calm, cloudy or clear in combination.

The atmosphere is the envelope of air that surrounds the surface of the earth. It has four layers: They are the troposphere, the stratosphere, the mesosphere, and the thermosphere. The term atmosphere also means the weight of the air pressing against the earth at any given point on earth. At sea level the weight of the air is 14.7 pounds per square inch (1.03 kilograms per square centimeter) of surface. At places below sea level such as the surface of the Dead Sea the atmospheric pressure is greater than one atmosphere. On mountaintops the atmospheric pressure is less. This natural feature of the weight of the atmosphere at various places on the earth's surface is an important feature in the weather and in the climate.

Climate differs from weather. Weather is the immediate atmospheric conditions. Climate is the average of the weather over an area for a long period of time. Almost all weather takes place in the troposphere that extends from the surface to six to ten miles above the surface of the earth. Most of the atmosphere, water vapor and heat are in this layer.

Weather conditions involve temperature, air pressure, wind, and moisture. A weather report will combine all of these to show the weather as it is currently, or more importantly as it is expected to be in the hours or days ahead in order that people may respond appropriately.

Temperature readings measure the amount of heat in the atmosphere. The heat comes from sunlight shining on the earth. However, sunshine does not strike the earth everywhere with the same effect. At the equator the sun shines directly on the earth making the weather at the equator warm. The further from the equator and the closer to the North Pole or the South Pole the more the sun strikes the earth's surface at an angle. In addition, as the earth rotates around the sun in its yearly circumnavigation it presents either the Northern or the Southern Hemisphere to the sun more directly, which produces summer or winter.

As the sun strikes the earth's surface it may strike water or land. Since the oceans and the continents present different surfaces to sunshine the effect generates different amounts of heat. In desert regions [Page 1938]the heat is reflected away from the surface of the earth. At night the radiant heat quickly turns the desert into a chilly place. However, in land areas of moisture and extensive plant growth heat is absorbed by the plants and retained in the locality. In the oceans the heat is absorbed and distributed by currents, evaporation, and by reflection in a different pattern.

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