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UNC-Chapel Hill GEOG 111 - Exam 3 Study Guide

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GEOG 111 1nd EditionExam # 3 Study Guide Lectures: 21 - 33Lecture 21 (October 17)Most missed from exam 2:#6 – The lapse rate is the rate of temperature drop with increasing altitude. Which of the following situations is associated with the highest rate? Clear day#16 – What time of the year should a sea breeze be the strongest? Spring#17 – Surface winds over land blow at a 30-45 degree angle with respect to the isobars over a long distance.#27 – If the temperature of the air decreases, the saturation vapor pressure will decrease and the vapor pressure will be unaffected.#30 – The 500 mb heights are greatest over the low latitudes.Forced liftingI. Forced lifta. Orographic lifting – tends to be cloudier and more wet on wind-ward side of a mountain rangei. Air lifts on one side of a mountain  reaches its saturation level  clouds/precipitation form  air sinks down the other side of the mountain  warming and drying out as it goes downb. Frontal lifti. Two air masses with different densities that do not mix (warm air moves up and over the cold air)ii. Two scenarios:1. Warm air is stable – as warm air is forced upward it’s cooling adiabatically and will eventually cool to saturation  light precipitation2. Warm air is unstable – same except when air reaches saturation  convection  thicker clouds/ heavier rain/thunderstormsc. Low level convergence- forced liftingi. Converging at low levels in the atmosphere, it needs an outlet, must convect upward1. Ex. Clouds from the sea-breeze frontd. Upper level divergence- forced liftingi. Opposite of convergenceii. If air is pulling apart from itself, eventually there will be no air left in the area of divergenceiii. Accelerating winds exiting a trough cause air to rise1. Forces air upward through the columnLecture 22 (October 20)Clouds and PrecipitationI. Cloudsa. Cloud typesi. Cirrus- high, cold, wispy ii. Cirrocumulus- high, fine grained appearance, bubble-like clouds interwoven withblue sky1. Rising motion with cloud elements, sinking motion surrounding cloud elements2. Variations in vertical and horizontal air motions (would make for a bumpy plane ride)iii. Cirrostratus - high, very thin, instead of streaks it is covering the whole sky in a layered fashion1. Ring-like appearance around the sun2. Mini-rainbow; diffraction of light (sun dogs)iv. Contrails – high, trail of cloud consisting of liquid water1. Condensation and largely deposition2. Water vapor comes out and instantaneously turns to ice crystals3. The relative humidity is close to 100%v. Altocumulus – middle clouds, warm, similar to cirrocumulus just lower in the columnvi. Altostratus – middle clouds, warm, thicker, lower in atmosphere so block out sunlight more than cirrostratus1. Ring around sunvii. Stratus- low level, stratified, effectively block out the sun1. Can produce drizzle, but not measurableviii. Nimbostratus- low, thicker, darker, producing precipitation1. Streaked appearance ix. Stratocumulus – low, stratified, not thick, connected with a stable atmosphere (air doesn’t want to move vertically)x. Cumulus – low level, unstable atmosphere (air is lifting), daytime heating when the relative humidity is high, vertical development, late morning hours in Carolina summerxi. Cumulonimbus – largest cloud, dark bottom, thunderstormII. Precipitationa. Requires the development of droplets/snowflakes that are 100 times bigger than cloud water droplets/ice crystalsb. Most of the time, clouds don’t have precipitationc. Two processes for growing hydrometeors (scientific term for precipitation)i. Bergeron – grows ice crystals through multiple processes involving all three states of water1. Requires a cold cloud where ice crystals, water vapor and super-cooled water coexist2. Processesa. Deposition of vapor  ice crystal growthb. Freezing also occurs but deposition is the dominant processc. Evaporation of cloud water  vaporsi. RH < 100%d. So ice crystals grow at the expense of cloud watere. Rising air motions keep growing snowflake aloft until it becomestoo heavyi. Snowflake gets so heavy that it falls against the gradient  melts and falls to Earth as rain or if the atmosphere iscold enough, as snowLecture 23 (October 22)Hydrometeors and Precipitation RatesI. Two processes for growing hydrometeors (review)a. Bergeron – grows ice crystals through multiple processes involving all 3 states of water// often produces ice crystals that act as seeds for growing hydrometeors below in the warmer portions of cloudsi. Requires a cold cloud (temperature < -10 C) where ice crystals, water vapor and super-cooled water coexist1. High level clouds (cirrus and cirrostratus)2. In the coldest time of the year (winter) the Bergeron process may occur in lower altitude clouds as well and can even create snowii. Processes:1. Deposition of vapor  ice crystal growth (vapor to ice)a. Freezing also occurs but mainly deposition2. Removal of water around ice crystal so relative humidity drops3. Evaporation of cloud water  vapor 4. So ice crystals grow at the expense of cloud water5. Rising air motions keep growing snowflake aloft until it becomes too heavyiii. The Bergeron process provides a distinct glazed and/or streaked appearance in cloudsb. Collision-coalescence – hydrometer grows as it collides with smaller droplets through the skyi. It is the only precipitation formation process that operates in warm cloudsii. Can supplement the Bergeron process in cold clouds (e.g. super-cooled droplets colliding)iii. Large cloud droplet falls through smaller cloud droplets accumulating them along the wayiv. Often contributes to the seeder-feeder process: process in which you have precipitation forming from the Bergeron (seeds) and Collision-coalescence process (warmer droplets that are feeding the seeds)1. Two scenarios:a. Rain droplets from melted snowflakes (seeds) are fed by the warm cloud water dropletsb. Cloud water droplets freeze on falling snowflakes, in a process called rimingi. The snowflakes grow in size as it falls through the warmer part of the cloudII. Controls on precipitation rate (amount of precipitation/time)a. Amount of water vapor condenses/deposited out of atmospherei. Air temperature (higher temp ~ higher SVP) and proximity to warm body of water (how much water is available)ii. Rate of lifting1. Convective lift can be 10-50 times faster than frontal liftb. Distinguish between two precipitation typesi. Stratiform (from


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