V. Air Pressure and motion A. Air pressure is the weight of air at any particular point. It is also called atmospheric pressure. The units are given in the ESRT in millibars and inches of mercury and as atmospheres. A barometer is a tool used to measure pressure, Air pressure depends on how tightly packed the molecules are and how heavy they are. Weather unit

B. Units of air pressure: page 13 ESRT For standard, sea level pressures, the air pressure will be found on this chart. Weather unit

C. What’s a ‘rising’ barometer’? When air is ‘heavy’ it pushes down (and around) on objects. The mercury will ‘rise’ in the vacuum tube. So a rising barometer means good weather. When air is ‘light’, it does not push down as much and the mercury in the barometer will ‘fall’ in the vacuum tube. Moist tropical air is lighter than cold, dry air from Canada An actual LOW PRESSURE SYSTEM is a storm, not a light air mass!!!!!!! Weather unit

Heavy Air: (high pressure) D. Remember…… Heavy Air: (high pressure) cold, because the molecules are close together. Dry, because nitrogen and oxygen are heavier than water vapor. Light Air: (low pressure) warm; the molecules have more energy and are farther apart. moise, because water vapor is a very light molecule. Weather unit jason.org

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E. The reason some air is light and some air is heavy is due to the unequal heating of the atmosphere due to our round rotating planet. ffden-2.phys.uaf.edu Weather unit

Air flows from areas of high pressure to areas of low pressure. VI. Why wind? A. Air pressure and wind Air flows from areas of high pressure to areas of low pressure. Air flows from regions of cold, dry air to regions of warm, moist air. Descending air means clear skies. Ascending air happens at fronts nd in very warm, wet air (afternoon thunderstorms, hurricanes) Weather unit

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B. Isobars Weather maps show pressure patterns using isobars. (lines that connect points of equal air pressure) The closer the isobars are on the map, the greater the change in pressure and the faster the wind is blowing. Weather unit

https://courseware. e-education. psu https://courseware.e-education.psu.edu/public/meteo/meteo101demo/Examples/Images/Section2/contour_tool_p0207.swf allows students to practice making isobars. It will convert from station model pressure to millibars for them and draw the lines for them to check Weather unit

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C. Comparing high pressure to low pressure High pressure system air is heavy, and is probably sinkin, creating convection. High pressure air ALWAYS blows outward. For the Northern Hemisphere, it also makes a clockwise rotation. LOW PRESSURE SYSTEM has air that is lighter and is probably rising, creating convection. Air is blowing inward and counterclockwise (in N.H.) and up. Weather unit

D. The jet stream :discovered by WWII pilots flying cross country. It is a high ribbon of wind that separates the polar air from the warmer tropical air in the mid-latitudes. The jet stream is caused by interactions in upper levels of the troposphere. Most active during our winter season; cold, dry Canadian air meets warm, moist air of the Gulf of Mexico. the jet helps determine the weather patterns for the country. Weather unit

http://vortex.plymouth.edu/make.html Weather unit

What are 2 characteristics of heavy air? Of Light air? Self-check: What are 2 characteristics of heavy air? Of Light air? What air is rising: heavy or light? High pressure or low pressure? Why does wind blow? Does it blow from high to low or low to high? Can you draw wind around a high? Around a low? Which way do storms move across the US? Weather unit