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131 GEO Weather and Climate Study Guide for the Final Exam Exam Date: Tuesday, May 13, 8:00 10:00 AM Notes: This review guide is not all-inclusive. However, it does cover most of the topics and concepts you can expect to see on the exam. Remember, a limited number of questions may be included from the Homework 3 assignment! 1. Properties of Water - Know the concept of phase change in water (melting, freezing, sublimation, condensation) Phase changes occur as a result of changes in temperature (temperature is a measure of the speed of motion of atoms and molecules, their kinetic energy. Phase changes take energy to occur, one calorie is the amount of energy required to raise the temperature of one gram of liquid water 1C. The calorie is a unit of heat/kinetic energy. Melting- phase change from solid to liquid. Must raise the temperature of ice to the melting point (32F;0C) by adding 0.5 calories per gram per degree, this is specific heat of ice. Freezing- phase change from liquid to solid. In order for water to freeze, it must lose 80 calories per gram of water to its surroundings. In this case energy is being transferred from the ice to the air, so this warms the air. Sublimation- ice goes straight to gas state. No liquid Deposition- gas goes straight to ice state. No liquid In essence, these processes represent two phase changes in one, and do the number of calories involved equals the sum the two 590 calories/g + 80 calories/g= 670 cal/g - Know difference between: humidity, relative humidity, and specific humidity. HumidityRelative Humidity- How much vapor the air can hold before condensation occurs. We can sense relative humidity because we can feel it. RH is based on air temperature because temperature is a measure of the amount of energy available for evaporation to occur (it controls the amount of water vapor that can be pumped into the air). Specific Humidity- The mass of water vapor per mass of air at any specified temperature. Can be thought of in terms of density because density equals mass/volume. - Can you do a simple calculation of relative humidity if given values for the actual water vapor content of air and the maximum water vapor capacity of the air at a given temperature? RH= Actual vapor (g)/capacity or potential vapor (g) x 100 - Can you do a simple calculation of specific humidity if given values for the mass of water vapor (in grams) in the air and the mass of air (in kilograms) containing that water vapor at a given temperature? Specific Humidity = mass of water vapor (g)/ mass of air (kg) - That sling psychrometer thingy... sounds like what David used to kill Goliath! Measures relative humidity 1) Dry Bulb- measures actual temperature 2) Wet Bulb- gauze on the end that is soaked in pure water. As water evaporates from the gauze, the temperature decreases because evaporation causes cooling. The more evaporation that occurs, the more the temperature drops Slinging the psychrometer causes air to flow across the wet bulb and this stimulates the effect of wind. - Oh, and then there's that wet bulb depression thing... The difference between the wet bulb and the dry bulb temperature is called the "wet bulb depression" The greater the wet bulb depression, the lower the RH This is because the lower the amount of moisture in the air, the greater the amount of evaporation that will occur- and the more the temperature will drop on the wet bulb thermometer. On the other hand, if the air is humid, very little evaporation will occur and the wet bulb and dry bulb temperatures will be very close. - What is a dew point? Is there any similarity with a condensation level? Dew point is the temperature at which the RH reaches 100%. The point at which clouds begin to form, the condensation level, is when the elevation has reached the dew point. 2. Atmospheric Moisture - Clouds and Fog - How does condensation and sublimation fuel storms? Heat energy released by sublimation and condensation intensifies the low pressure, which increases the pressure gradient, and thereby increases wind velocity. It also enhances uplift by warming the air, which enhances the rate of condensation - What processes can produce fog? (advection, evaporation, upslope movement, radiation) All of the above can produce fog - What kinds of clouds are there? How do we name them? Where and how are they formed? Clouds are first determined by their altitude and then their shape. - Why do islands typically have clouds above them? - What in the world does a DAR, MAR, and ELR have to do with a cumulonimbus cloud?? Cumulonimbus clouds form in absolutely unstable air so the ELR has to be greater than the DAR which has to be greater than the MAR. - Know the different kinds of freezing precipitation Freezing rain forms when rain drops freeze on contact with a cold surface. Sleet is formed when rain freezes while falling to the ground Rime ice is formed when cloud droplets freeze on contact with a surface- but also trap air in between the droplets making the ice opaque. Snowflakes are formed by deposition Hail forms in the rising and descending currents of a cumulonimbus cloud. As water droplets are carried to high altitude, they freeze. As they fall toward the bottom of the cloud, a new layer of water envelops the hail stone. Hail forms most often in summer, because convectional heating forms cumulonimbus clouds - What kind of lapse rate would represent cumulonimbus cloud development? (review the diagram showing fields of stability, instability and conditional stability) MAR - Condensation trails (aka contrails) can be useful weather indicators what's up with that? The moister the air the longer contrails will persist. The longer they persist indicates that the weather will change soon because moisture is moving into the region. 3. Weather - What is an air mass? How does is acquire its characteristics? large A mass of air that is characterized by relatively uniform temperature and moisture characteristics in any horizontal direction at any given altitude. - What are the various atmospheric lifting mechanisms? (convergent, convectional, orographic, frontal) - Cyclones and anticyclones know how they circulate and whether the air movement is up or down... northern vs. southern hemisphere. What if a tornado encountered a zone of cyclonic circulation (where would the strongest winds be generated?) Anticyclones are high pressure systems that are created by upper air convergence and subsidence favoring their formation. Cold, dry air flows downward, outward, and clockwise (in the Northern hemisphere), produces clear skies. Cyclones are warm, moist areas of low pressure. In effect, they are storm systems that produce precipitation. Air flows inward, upward and counterclockwise in the northern hemisphere - Know how the weather will change as a front passes over (i.e., temperature, pressure, humidity, kind of precipitation). Cold frontCold air overtakes warm air Average speed=25 mph (fastest front), potential for intense thunderstorms due to the rapid uplift as air plows into the warm air, forcing it to rise quickly. As the front approaches, the pressure falls as warm air rises and condensation occurs along the frontal boundary. Wind shifts from SW as the front approaches to NW after it passes, temperatures drop after the front passes and relative humidity and dew point drop after the front passes; skies clear. Warm FrontWarm air replaces cold air; cool air before passage and warm air after Travels at an average speed of 15 mph. The warm air gently rises up and over the cold air as it overtakes the cold air. Because the rate of uplift is slower, rainstorms are generally less intense than those associated with cold fronts. Winds are generally from an easterly direction prior to the passage of a front, and from the south/southwest after. Humidity and dew point increase after the front passes. - Does the process of occlusion usually occur in the middle stages of a mid-latitude cyclonic storm? Occluded fronts occur when three air masses meet-cold, warm and cool. The process of occlusion usually occurs in the latter stages of a mid-latitude cyclonic storm. Occlusion causes the warm air mass in between the cooler air masses to be lifted upward off the ground. - What is frontolysis? frontogenesis? Frontolysis is the birth of a thunderstorm or a cumulonimbus cloud Frontogenesis is the death of a thunderstorm - Know the rules of thumb regarding lightening hazards (i.e., 30 second rule and number of seconds between lightening strike and thunder vs. distance) Count seconds and dived by 5 to determine the distance in miles. - Updrafts and downdrafts... microbursts and macrobursts. Know how these form and with what they are associated. Downdrafts- during the mature stage entrainment of dry air leads to evaporation and cooling in parts of the cloud creating a downdraft. Downdrafts can be enhanced by falling precipitation. When downdrafts hit the ground and flow outward they create a gust front that can be attributed to Microbursts, winds extending < 4km (2.5 miles) at the surface, and macrobursts, winds extending > 4 km at the surface. Updrafts are fed by gust fronts. - Know the stages of thunderstorm development (growing stage, mature stage, dissipating stage) Thunderstorms are formed from mT air masses, not fronts. The cumulus stage is the growing stage with limited vertical development because water initially evaporates into dry air, continued evaporation increases moisture content; condensation releases latent heat that feeds upward growth. No down drafts, lightning, thunder, or precipitation occurs during the growing stage. The mature stage is the entrainment of dry air leading to evaporation and cooling in parts of the cloud, the downdraft which are 18 degrees cooler. Downdrafts are enhanced by precipitation, lasts for about 30 minutes; this is the most intense stage with rain, thunder, and lightning. The dissipating stage has downdrafts forming throughout the cloud, decreases updrafts and shuts off moisture supply. - Tornadoes know aspects of them that were discussed in class - What happens to cP air masses as they are carried toward North America from Asia by the Aleutian Low? Become mP air masses by becoming unstable after crossing the ocean - Do you know what proportion of hurricanes produce tornadoes in the U.S.? 1/4 - Rossby waves low pressure cells are generated from them and the polar jet stream too. Rossby Longwaves are waves that form along the Polar Front and are comprised of a series of ridges and troughs. - Did I mention that you'll need to know all about occluded fronts?? Occluded fronts occur when three air masses meet-cold, warm and cool. The process of occlusion usually occurs in the latter stages of a mid-latitude cyclonic storm. Occlusion causes the warm air mass in between the cooler air masses to be lifted upward off the ground. There are two types of occlusion: Cold type- cold air forces warm air up and over cooler air; when over, warm air is above the surface. Temperature changes from cool to warm to very cold. Pressure changes from high to low to high. Relative humidity and dew point decreases. Warm type- a cool (mP) air mass overtakes a warm air mass (mT) that is located adjacent to a cP air mass. As with a cold type occluded front, the warm air is uplifted off the ground producing widespread precipitation and rapidly changing weather. 4. Water and Atmospheric Moisture - Name the 4 oceans; How much of the surface of the earth is covered by the oceans? Atlantic, Pacific, Indian, Arctic Oceans 75%. - Where is the freshwater contained? (glaciers, surface, soil, groundwater) - Where is most of the fresh surface water contained? (ice sheets and glaciers) ... View Full Document

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