Meteorology 3

Weather Basics. Energy from the sun is the main cause of all weather as the sun's rays heat the atmosphere at different rates causing different air density (and pressure) This difference in density and pressure is what causes the air to move and it is this movement of air and the moisture within it that causes winds, clouds and precipitation, we call this weather. Wind The Earth's surface is heated unevenly due to the rotation of the earth, land and oceans, and the seasons. This results in both vertical and horizontal air movement; wind being the result of the differences in air pressure. Air will always moves from high pressure to low pressure, but the rotation of the earth (coriolis) and local terrain causes the air not to flow in a straight line. In the Northern Hemisphere, air moves clockwise around high pressure and counter-clockwise around low pressure (it is the opposite in the southern hemisphere) Vertical Air Movement Uneven heating of the Earth causes the air to move vertically; generally hot air rises, cold air falls. Thermals and turbulence are often caused by ground features at different temperatures. Stable and Unstable Air The normal flow of air is horizontal, but some disturbances can cause vertical updrafts of downdrafts Stable Air - Is air that will resist these vertical movements and returns to its original horizontal level Unstable Air: Is air that tends to move even further away when disturbed by updrafts or downdrafts Stable Air Characteristics: More settled calmer conditions Light wind shear Poor visibility Haze or smog Light rain Unstable Air Characteristics: Turbulence and rough air Good visibility Showery precipitation Thunderstorms