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Storms edited learning goals.docx

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University of British Columbia
Earth and Ocean Sciences
EOSC 114

Storms learning goals Storms: 1. Be wary of the main storm hazards. Thunderstorm Hazards: 1. Lightening 2. Tornadoes 3. Hail 4. Downpours of rain (local flooding) 5. Downbursts of air (gust fronts) Hurricane Hazards: 1. Contain thunderstorms 2. Storm surge/ costal flooding 3. High waves 4. Coastal erosion 2. Describe the different types of lightning, how they form, and what happens when they strike something. Types of lightening: 1-Cloud to cloud lightning (intracloud) (IC): occur when the voltage gradient within a cloud or between clouds overcomes the electrical resistance of the air. more common than GC lightening. 2-Cloud to ground (CG): Charge separation occurs, with positive and negative charges separate in the cloud. Charge separation occurs only in clouds are above the freezing level. less common than IC a. In order to make a spark in the air, it requires 3 billion volts/km. The more volts it has, the further it can travel b. Negative strikes - are more numerous and come from cloud base. Usually has two strokes, but can have over 10 c. Positive strikes - are less frequent,  Runaway discharge theory: electrons get sped up to near the speed of light, when they are this fast, resistance is decreased and they go faster, collide with atoms and get more electrons. 3. Recognize thunderstorms, be able to identify Tstorm components, and and explain how they evolve. Components of thunderstorms: 1. Thick clouds contain lightening and thunder 2. Cloud top is near the top of the troposphere 3. Cloud base near the ground 4. Looks like an anvil 5. Strong updrafts and downdrafts (turbulent) a. If very strong updrafts, the dome of the clouds can overshoot above the anvil 6. The main updraft (stem of the mushroom) is 15km diameter Stages of Tstroms: 1-cumulus: unstable air raises, brings water vapor from surface to troposphere, it becomes humid enough that clouds begin undergoing vertical growth at 5 – 20m/s, the temp decreases cloud extends above freezing level 2- mature: precipitation begins to fall, downdrafts form where precipitation is highest, most powerful part of storm, updrafts dominate interior of cloud, and downdrafts are outside. 3-dissipative: downdrafts occupy more of the base, and supply of water vapor is cut off, precipitation diminishes and water evaporates. Types of Thunderstorm cells: 1-Cumulonimbus (thunderstorms) are made of large cells that evolve during 15-30 minutes 2. Multicell thunderstorms - most thunderstorms contain multiple cells 3. Supercell thunderstorms - Single-cell rotating thunderstorms that cause tornadoes, large hail, lightening, rain, and strong wind  Supercells can be: a-low precipitation b-classical c- precipitation 4. Explain how storms get their energy from the sun. When happens to solar energy: 1. Reflected - either by clouds and scattered back into space, or reflected from ground 2. Absorbed - by the ground which warms the surface. It is then changed into: a. Sensible heat, which warms up the air, increasing the temperature b. Latent heat, which evaporates ware from lakes and etc., causing the humidity to increase  So both Humidity and Heat fuel storms What is the daily cycle of solar energy 1-Solar heating occurs during the day à input, charging 2. Infrared Radiation (IR) cooling occurs at night à loss 3. Greatest accumulation of heat occurs near sunset (at the end of the charging cycle) 4. Late afternoon and early evening is thus when there is most likely chance of a t-storm formation 5. Explain the main characteristics that make a supercell so much nastier than a normal Tstorm. What are supercells: Supercell Tstorms are intensely powerful storms that contain a single updraft zone. they are more violent and longer lived than any other Tstorm. It also can rotate as a Mesocyclone which can spawn tornadoes. Why are they nasty: They cause the most violent tornadoes, large hail, frequent lightning, strong winds ans mesoscale convective systems: clusters of thunderstorms (squall lines) (tropical cyclones) (lake effect) 6. Be able to recognize thunderstorms in radar and satellite images 1. Satellite: you can see the parts of the thunderstorm i.e. The oval shape of the anvil cloud, the shadow underneath the anvil, and the lumpy portion on one point of the anvil showing where the storm is the strongest 2. Radar: sees the precipitation inside the storm; mostly in the up and downdraft stem of the mushroom cloud What's DBZ: 1. The disaster intensity scale for rainfall. 2. Measured in decibels. 3. Important cause downpours of rain can cause flash floods.  By tracking past movements of radar, storm path can be tracked. 7. Explain the behavior of downbursts and gust fronts, and identify their associated cloud & dust features. Downburst: 1. They are cold (dense) air that is sinking 2. Occur when Tstorms create dense air where the rain falls. So come from anvil and are moving away from storm 3. Due to precipitation drag and evaporative cooling 4. Often invisible, so a danger to aircraft 5. The downdraft speeds are between 20 to 90 km/h Gust front: 1. Are the leading edge of straight-line winds away from storm 2. Occur when downburst air hits the ground and spreads out 3. Can cause haboobs (sand storms) if on dry ground or arc clouds if the air is moist 4. Can blow down large trees and destroy weak structures, and can affect aircraft from taking off or landing 5. The horizontal gust fronts can be up to 250 km/h 8. Describe why the fact that cold air holds less water vapour is critical in explaining how Tstorms can extract energy from humid air. Moist Energy: 1. Another fuel for storms. 2. Storms draw in the moist humid air, condense it, and then release its heat into the storm resulting in precipitation and violent winds 3. Related to Humidity, Saturation, Adiabatic Cooling, Advection, and Latent heat Humidity = amount of water vapor in the air. If too much water, it will condense into liquid, if not enough water, will precipitate into gas, this is called saturation.  Humidity Variable: Mixing Ratio (r) = the amount of water vapor divided by the amount of all other gases  Warmer air can hold more water vapor at equilibrium. Saturation relates to: 1. Condensation and Evaporation 2. If there are too many water molecules in air, the excess condenses into liquid, causing the air to become drier 3. If they are too few water molecules in the air, the evaporation exceeds condensation, and the air becomes moister. However, it may not have enough liquid water to reach the saturation value, thus it is below it  Saturation value - is the maximum humidity that air can hold and be utilized for storms Adiabatic cooling: when air rises it decreases in temp, so it can hold less h2o, so condensation occurs, which releases latent heat. Storms strengthen when latent heat turns into sensible heat. If humidity exceeds saturation, condensation occurs and releases sensible heat, reduces humidity to saturation, and creates water vapor which can turn into rain. In other words: 1. Basically when rain is evaporating in air, the air has to release more rain droplets as it gets higher, cause it is turns into vapor which cant hold as much water. 2. Also as it is rises, its saturation humidity value decreases. When it becomes smaller than the actual humidity, condensation occurs causing: a. Sensible heat to be released into the storms b. Reducing the humidity down to the equilibrium (saturation value c. Producing/increasing liquid cloud drops, which can become rain drops.  Thus together, it explains why there is so much rain in storms and how storms get its energy from moist air Warming rate : change in temp /change in time = a * rainfall rate. Average warming rate is calculated: -AT/At = a * RR - AT/At = average temperature change over time interval à average warming rate - a = 0.338 K/mm of rain for Tstorm 11 km thick - RR = rainfall rate measured by the increase of depth of water in a raingauge 9. Be able to recognize tornadoes and wall clouds. What are Tornadoes: 1-Tornadoes are violently rotating columns of air, in contact with the ground and thunderstorms 2. All violent tornadoes come from supercell thunderstorms 3. Most tornadoes are made visible by cloud-water droplets (the funnel cloud - top half of tornado) and/or dust and debris from the ground (the debris cloud - the bottom half of tornado). 4. Some tornadoes are invisible 5. Usually short lived - last only 1 to 10 km long 6. Typically have a narrow damage path - usually the width of a house 7- they travel southwest towards northeast, they come in many shapes 8- Speeds of center of tornado can be anywhere from 0 to 100 km/hr - most move somewhere in the middle What are Wall clouds: 1. An isolated lowering of cloud base beneath rising cumulus towers on the SW flank of the storm 2. Tornadoes come from the rotating wall clouds in supercells. 3-Wall cloud is a rain free cloud base  With radar – a hook can be seen, and with a Doppler image, tornado vortex can be seen. 10. Explain why supercell thunderstorms spawn the most dangerous tornadoes. Tornado Evolution from supercell storms: 1. Early -> some rotating dust and debris at ground, but no funnel visible yet. 2. Next -> funnel cloud (an actual cloud made of water droplets) grows down from thunderstorm base (often from the wall cloud). 3. Next -> funnel extends to ground and merges with debris cloud at ground to form the mature tornado. 4. Finally -> decrease into a "rope" stage (long, thin and bent or twisted). 5. During the dissipating stage of the first tornado, beware of possible new tornadoes forming nearby. 11. Relate the Enhanced Fujita scale to different amounts of damage. 1. Enhanced Fujita Scale
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