GEOG 111 1st Edition Final Exam Study Guide Weather forecasting Forecast skill o Accuracy depends on Proximity to forecasting location Size of the region How well the forecaster knows the climatology and recognizes its patterns o 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 forecast o Weather models computers that use physics to simulate atmospheric conditions of the future o 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 tuned o Forecaster knowledge something to keep in mind when reading forecasts Pattern recognition experienced forecasters in an area can recognize patterns and question models Water in the Atmosphere Phase changes of water o 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 in thunderstorm 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 heating Relative humidity and dew point temperature o 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 saturated o 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 high Sensible and latent heat fluxes o 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 effect o Sensible heat evaporation water vapor latent energy that rises condensation heat is released cloud sensible heat Vertical Air Motions Adiabatic temperature changes o 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 compresses o 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 much Types of lifting Convective lift buoyant air parcels rise as they remain relatively warmer less dense than their surroundings Forced lift o Orographic lifting tends to be cloudier and more wet on wind ward side of a mountain range o 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 upward o Upper level divergence forced lifting Accelerating winds exiting a trough cause air to rise Forces air upward through the column Atmospheric 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 atmosphere o ELR DALR WALR absolutely unstable convection o DALR ELR WALR conditionally unstable convection IF atmosphere is saturated o DALR WALR ELR absolutely stable no convection no matter what because thermal is cooler than surrounding air and resists vertical air motions inversion stability Instabilityo If a thermal is rising and reaches an inversion the thermal will stop rising and atmosphere regains stability Circumpolar Vortex Jet Stream Circumpolar vortex CPV The Circumpolar Vortex river of air that meanders around Earth s poles o There is much day to day and week to week variability in the character of the CPV o Ridges and troughs propagate downstream Jet stream o Jet stream the geographic place in the atmosphere where winds blow the strongest Occurs where the north south temperature gradient is the strongest Seasonal changes in the strengthen positioning of CPV and jet stream o 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 persistent R ships between surface and middle tropospheric features Cyclones Anticyclones and Troughs ridges Wave Cyclones Wave cyclone fronts and air masses warm cool sectors Wave cyclones o Where do they occur Along a front where there is a temperature gradient Fronts encourage the lifting of air clouds and precipitation Middle troposphere around cold front is much colder The ELR tends to be steeper Beneath the jet stream aloft and downstream of a trough Wind directions vertical air motions o When there is a front there will always be a temperature inversion Cooler air beneath relatively warmer air o More