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UNC-Chapel Hill GEOG 111 - Final Exam Study Guide

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GEOG 111 1st EditionFinal Exam Study GuideWeather forecastingForecast skillo Accuracy depends on: Proximity to forecasting location Size of the region How well the forecaster knows the climatology and recognizes its patternso Weather models accuracy decrease with time Should be trusted 3-5 days into the future but after that it’s better to rely on climatology Forecast specificity- 3 resources in making forecasto Weather models- computers that use physics to simulate atmospheric conditions of the futureo Climatology- tell what conditions you would normally expect Usually a good starting point for weather forecasters and may indicate that a weather model needs to be tunedo Forecaster knowledge- something to keep in mind when reading forecasts Pattern recognition- experienced forecasters in an area can recognize patterns and question modelsWater in the AtmospherePhase changes of watero Phase changes of water Melting/evaporation (sublimation) is a cooling process/absorbs heat and creating latent energy Condensation/freezing (deposition)- latent heat released o Effects/examples Melting- cools- snow melt inhibits temperature rises; warming not observed in Arctic until snow has melted (around July) Freezing- warming- latent heat going back to sensible energy; surface temperature hangs at 32 until all of the water has frozen and then the temperature continues to drop Evaporation- cooling- cooling when it starts to rain; falling through an atmosphere that’s not saturated Condensation- warming – convection/lifting; adds buoyancy to updrafts inthunderstorm or hurricane. Nocturnal temperature drop decreases/stops when dew forms Sublimation- cooling – cooling when it starts to snow Deposition – warming – ice fogs which are common in high latitudes; contrails Sensible and latent heatingRelative humidity and dew point temperatureo Relative humidity = vapor pressure/saturation vapor pressure * 100% Can range from close to 0% to 100% Desert environments are very far from being saturated In contrast, once VP = SVP = 1  relative humidity 100% and atmosphere is saturatedo Dew point temperature- the temperature to which the air must be cooled in order to reach saturation DPT is much higher in the summer than winter (in Eastern U.S.)- Pacific ocean is much cooler than Atlantic so there’s not nearly as much evaporation and dew point is not nearly as highSensible and latent heat fluxeso Two types of heat transfer: Sensible heat flux- the rate at which heat that can be sensed moves from one place to another- Heat flux- quantity of heat moved across a unit area per unit time (e.g. watts/m^2)o Contributing processes: Conduction- molecule by molecule heat transfer- Thermal conductivity- the ease with which heat conducts through a material Convection-heat movement through bodily movement; warmer moves upward- Example: Air moving from warmer to cooler Advection- horizontal movement of heat through wind circulation or ocean currents- Example: southerly winds advect warm air northward Latent heat flux- heat movements through phase changes in water- Example: in the process of evaporation, heat goes into a latent (or hidden) form as it is absorbed and creates a cooling effecto Sensible heat  evaporation  water vapor (latent energy) that rises  condensation (heat is released)  cloud + sensible heatVertical Air MotionsAdiabatic temperature changeso Adiabatic processes- changes in the temperature of the air but no changes in energy/heat- An air parcel is forced upward  it expands and cools (no heat has been removed)  continued lifting, it continues to expand and cool- When air is lifted in the atmosphere it cools adiabatically- In contrast, sinking air compresseso Vertical temperature patterns Lapse rate- the rate of change of temperature with height- Average: 5.6 F degrees of cooling per 1000 feet Inversion- temperature profiles are inverted from the normal- Temperatures rise with altitude rather than fall which is typical- Takes place on relatively clear nights where wind is not blowing very muchTypes of lifting Convective lift- buoyant air parcels rise as they remain relatively warmer (less dense) than their surroundings Forced lifto Orographic lifting – tends to be cloudier and more wet on wind-ward side of a mountain rangeo Frontal lift Two air masses with different densities that do not mix (warm air moves up and over the cold air)o Low level convergence- forced lifting Converging at low levels in the atmosphere, it needs an outlet, must convect upwardo Upper level divergence- forced lifting Accelerating winds exiting a trough cause air to rise- Forces air upward through the columnAtmospheric stability (do not need to know values of ELR/DALR/WALR); however need to identify r-ships between stability and vertical temperature changes.- Stability of atmosphereo ELR > DALR > WALR: absolutely unstable  convectiono DALR > ELR > WALR: conditionally unstable  convection IF atmosphere is saturatedo DALR > WALR > ELR: absolutely stable  no convection no matter what because thermal is cooler than surrounding air and resists vertical air motions; inversion = stability- Instability- o If a thermal is rising and reaches an inversion, the thermal will stop rising and atmosphere regains stabilityCircumpolar Vortex & Jet StreamCircumpolar vortex (CPV)- The Circumpolar Vortex – river of air that meanders around Earth’s poleso There is much day to day and week to week variability in the character of the CPVo Ridges and troughs propagate downstreamJet streamo Jet stream – the geographic place in the atmosphere where winds blow the strongest Occurs where the north-south temperature gradient is the strongestSeasonal changes in the strengthen/positioning of CPV and jet streamo Climatology of circumpolar vortex Winter/Early Spring- Fastest winds- Most expansive (i.e. jet stream closest to Carolina)- Weather most changeable Summer/Early Fall- Weakest winds- Most contracted- Jet stream to the North (in Canada)- Pressure gradient much weaker- Weather most persistentR-ships between surface and middle tropospheric featuresCyclones/Anticyclones and Troughs/ridgesWave CyclonesWave cyclone, fronts, and air masses (warm & cool sectors)- Wave cycloneso Where do they occur? Along a front where there is a temperature gradient Fronts encourage the lifting of air  clouds and


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