Ch 13 summaryI have learned that air pressure is the pressure which is exerted by air above it and at sea level it is 1 kilogram per square centimeter. Gas molecules are not bound but they can move freely and fill the available space. For example when a gas is filled in a container then it collides with the walls of container and exert outward pressure. That outward pressure is called air pressure. In atmosphere there is no boundary so air confined between earth surface and from upper side by gravitational force. Different units like millibars is used to measure air pressure and instrument used for this purpose is called mercury barometer which contain mercury in it but now modern instrument are used like aneroid barometer that do not have mercury in them and this can be connected to instrument called barograph for recording mechanism. Air moves horizontally and vertically and this mechanism is called wind. The lines that are connecting places of equal atmospheric pressure are known as isobars. Air moves from higher pressure to lower pressure. Ifearth did not rotate then air moves straight but as earth rotates so air is effected by pressure gradient force which is the imbalance of movement of air due to unbalanced force in one direction, Coriolis Effect which is produced due to the rotation of earth and causes the wind to not cross the isobars at right angles and last factor that effects the movement of air is friction which slows the movement of air. Pressure centers are the areas that are most common on weather map. Cyclones are the centers oflow pressure while anticyclones are high pressure. From outer isobars to center in a cyclone pressure decreases but in anticyclones are case is reverse. Rising air produces clouds and causes precipitation while subsidence produces clear skies. In tropical regions, receives more solar radiation but radiated less space while Polar Regions receive less solar energy but they lost more.To balance this warm air is transferred towards poleward while cold air is transferred toward equatorward. Equatorial low is the pressure zone which is near the equator and air is rises there and in intertropical convergence zone wind is coverage’s and this is the low pressure zone and subtropical high is the center of subsidence zone which produce hot, arid conditions. Winds produced by locally generated pressure gradient are known as local winds. In coastal areas, land is more heated in summer during days so air above the surface heats, expands, and rises and creates an area of lower pressure. So for cooling the areas, cool air moves toward warm areas. That cool breeze is called sea breeze. Sea breeze starts developing before noon and develop completely mid- to late afternoon. Air on valley floor are less heated while air on slopes of the mountains is more heated. Warm air is less dense so it glides up along the slope and generates a breeze which is known as valley breeze. In evening cool air is produced by mountain slopes which is dense and drains downslope into the valley. That breeze is known as mountain breeze. Chinooks are Warm, dry winds. These winds sometimes move down the eastern slopes of the Rockies. Santa Ana is the wind that occurs in southern California. Direction and speed of wind is measured by an instrument known as wind sock. Wind vane can also be used to determine wind direction while speed can also be determined by cup anemometer. When wind blow more in one direction than in other direction then it is called prevailing wind. Precipitation do not occur same in different areas. Regions withhigh pressure and diverging winds remain mostly dry. While the areas with low pressure and its converging winds receive ample precipitation. I have learned that that wind is not same everywhere. Some areas experience hot wind while some experience cool. Trees can play an important role in cool wind. The areas with trees experience mostly cool air while areas with less tress mostly have hot wind. So we should try to plant more trees to make our atmosphere cool.I have a question for you what other steps should be taken to keep our atmosphere