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UNC-Chapel Hill GEOG 111 - Wind

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GEOG 111 1st Edition Lecture 16 Outline of Last Lecture I. Air PressureII. Winda. Wind systemsOutline of Current Lecture I. Winda. Wind systemsb. Factors affecting windCurrent LectureI. Wind- generated by pressure differencesa. Common wind systemsi. Monsoon -seasonal reversal of winds1. Ex. In India- Occurs due to thermal differences between land and water2. Winds blow in opposite direction at the changing of the seasons3. Land warms much quicker than water so we have higher pressures over water and lower pressure over land in the summera. Air wants to move from higher to lower pressure4. Summer: hot land  low pressure  onshore flow of air starting at the end of May moisture/lift/raina. Warmest month is May because a lot of energy is going into the sensible heat flux; very dryb. Convergence is necessary for cloud and rain development5. Winter: cooler land  higher pressure  offshore flow of air  dry air from inland areasii. Sea-land breeze1. Pressure gradient force2. Occurs on a daily basis3. Land warms much quickly than ocean; winds move inland; clouds form over the beach4. Strongest in summertime when there’s more daytime heating5. Creates a thermal circulation pattern because at night the land cools faster than the water so a cloud will form over the water insteadiii. Valley-mountain breeze1. Upslope flow- mountains facing the sun heat more intensely than shaded valley areas. This develops thermal low during the day which produces a valley breezeThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.2. Mountain breeze/cold air drainage- opposite phenomenon; radiational cooling at night; radiational fog; cold air drainage into the valley; frost can occur at the bottom of the valley (called a frost hollow)b. Factors affecting windi. Pressure gradient- wind blows from high to low pressure1. Shallow pressure gradient  low wind speed2. Steep pressure gradient  high wind speedii. Global circulation1. Low pressure system at equator/winds are moving into the low pressuresystem causing converginga. Large scale convection cell is occurring in upper troposphere iii. Coriolis Effect- moving objects are slightly deflected1. In Northern hemisphere  particles will move West to East2. Causes the most deflecting at the poles (none at the equator)/increases with increasing latitude3. Increases with the speed of the air parcel 4. Takes place regardless of the direction of motion5. Only changes direction doesn’t affect speediv. Geostrophic wind- only occur in upper atmosphere where there’s no friction1. Occurs when pressure gradient force = Coriolis force2. Wind begins to move parallel with the isobars3. Winds are particularly strong where isobars are close together (where isoheight gradient is strongest)v. Friction- in lower atmosphere/surface not in upper1. By slowing the wind down, friction causes a decrease in the coriolis force thus air moves slightly towards low pressure2. The greater the friction, the greater the cross-isobar flow3. Different ways of measuringa. Gust factor- a rapid increase in wind speedi. As friction increases, wind speed decreases, gust factor increasesii. Ex. In forest will be highiii. Ex. At airport will be lowb. Wind fetch- how far wind can travel over a distancei. As fetch increases, wind speed increases, gust factor decreasesii. Ex. In forest will be lowiii. Ex. At airport will be high4. Topographic constrictions- provides a Bernoulli effecta. Wind and water gaps in mountain ridges- forces air flow in gaps/high wind speedsb. Between tall buildings- forces air flow between streetsvi. Cyclonic flow- counterclockwise circulation around cyclone (low pressure system), converging, and rising  clouds and precipitation1. This lift drives a lot of severe weathervii. Anticyclonic flow- clockwise, diverging, sinking motions (air from upper atmosphere moves to surface), winds move away from high pressure system  clear


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