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Montclair EAES 104 - 6Extreme_Weather_Lecture_Outline

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Extreme Weather Chapter 10 Climate and Weather Related to HazardsChapter 15 Thunderstorms and TornadoesChapter 14 Hurricanes and Nor’easters: The Big WindsEarth CyclesGreenhouse EffectWeatherWeather is the condition of the atmosphere at a particular time and place. It refers to such conditions of the local atmosphere astemperature,atmospheric pressure,humidity (the amount of water contained in the atmosphere),precipitation (rain, snow, sleet, & hail),wind velocity.Water Vapor in the AtmosphereWater can exist in all 3 states at the normal range of earth temperature and pressure.Whenever matter changes from one state to another, energy is either absorbed or released.From liquid to gas - evaporation - heat energy is absorbedFrom gas to liquid - condensation - heat energy is releasedThe Hydrologic CycleRelative HumidityTherefore, relative humidity can be changed by...Changing the water vapor content.Add water, increase relative humidity.subtract water, decrease relative humidity.Changing the temperature.Increase temperature, decrease relative humidity.Decrease temperature, increase relative humidity.Adiabatic ProcessesUpward movement of air results from:Convergence lifting - when flowing air masses of equal density converge and are forced upward.Convective (Density) lifting - When warm, low-density air rises convectively and displaces cooler, denser air.Orographic lifting - When flowing air is forced upward over a mountain range.Frontal lifting - when two flowing air masses of different density meet.Warm Front: Warm air mass advances rapidly.Cold Front: Cold air mass advances rapidly.Atmospheric StabilityAtmospheric stability is a property of air that describes its tendency to remain in its original position or sink (stable) or to rise (unstable) once the initial lifting force ceases.Two assumptions:Lifting processes force air upward.Rising air does not mix substantially with the surrounding atmosphere.A parcel of air forced to rise will expand and cool adiabatically.WindCoriolis EffectDue to the rotation of the earth on its axis.Deflects all free moving objects to the right of their path in the Northern Hemisphere and to the left in the Southern Hemisphere.Deflection increases with wind speed.Deflection is strongest at the poles and weakens equator ward.Convergent and Divergent FlowIn the Northern HemisphereAround a low pressure cell (rising air), an inward counterclockwise flow develops near the ground surface; Centers of low pressure are called cyclones = convergent flowAround a high pressure cell (sinking air), an outward clockwise flow develops near the ground surface. Centers of high pressure are called anticyclones = divergent flow.Right Hand Rule for Rising or Falling Air in the Northern Hemisphere (Left Hand Rule for the Southern Hemisphere)Vertical FlowCenters of low pressure: Net upward movement of air, often resulting in cloud formation and precipitation. Low pressure center generally related to unstable conditions and stormy weather. Around a surface low air is spiraling inward, which leads to an upward flow of air at the center and divergence aloft.ThunderstormsViolent, local atmospheric disturbance that mostly last only 30 minutes, but can create several dangerous phenomena:Torrential rain: usually intense, but short in duration - flash flooding and slope failure in mountainous terrain is often associated with this type of precipitation.High wind: Winds at the surface beneath a thunderstorm can reach well over 50 mph (80 kph).Hail: falling at several meters per second, hail stones can result in extensive damage to crops and property in just a few minutes and can injure or kill.Lightning: every year in the U.S., lightning is responsible for an average of almost 100 deaths and 300 injuries. Lightning frequently starts fires which threaten homes, businesses, and lives. Power and communication outages caused by lightning (as well as wind) can result in large scale disruption of everyday activities.Tornadoes:Thunderstorms: Ingredients for Cooking up the StormAll thunderstorms require three ingredients for their formation:Sources of moisture: It is estimated that there are as many as 40,000 thunderstorm occurrences each day world-wide, most occurring in latitudes near the equator. Late afternoon hours in Spring and summer bring the greatest risk of thunderstorms to most of North America.A Lifting Mechanism: Cold air pushing under warm air along a cold front is a common lifting mechanism.Atmospheric InstabilityLife Cycle of A ThunderstormCumulus Stage: A cumulus cloud begins to grow vertically. Air within the cloud is dominated by updraft.Mature Stage: The storm is at its most intense stage of development and is now a cumulonimbus cloud. The top of the cloud reaches the tropopause where upward motion is hindered and the cloud spreads out horizontally. Strong updrafts and downdrafts coexist. The mature air mass thunderstorm contains heavy rain, thunder, lightning, and produces wind gusts at the surface.Dissipating Stage: The thunderstorm enters the dissipating stage as the supply of warm moist air is depleted. Air currents within the convective storm are now mainly downdrafts. Light rain and weak outflow winds may remain for a while during this stage, before leaving behind just a remnant anvil top.LightningLightning occurs when thunderstorms concentrate positive electrical charges in the upper part of cumulonimbus clouds and negative charges in the lower part. When the difference in the charge become great enough to overcome air resistance, a sudden and visible violent electrical discharge occurs in the form of a lightning stroke. The electrical discharge can be within clouds and/or between the cloud and ground.ThunderThe lightning heats the surrounding air to about 30, 000 degrees Celsius, which expands at supersonic speeds, creating the mighty crashes we recognize as thunder.Lightning and thunder happen at exactly the same time, but you see the lightning before you hear the thunder because light travels faster than sound.HailFlash FloodsA short lived upstream flood characterized by rapidly rising, high velocity water.TornadoesA tornado is a violently rotating funnel of air spawned from supercell thunderstorms.3 main atmospheric conditions must occur simultaneously to produce a tornado1. a northerly flow of warm, moist air from the Gulf of Mexico2. a cold, dry air mass rapidly moving southward from Canada or the Rocky Mountains3. strong easterly jet streamThese three air


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Montclair EAES 104 - 6Extreme_Weather_Lecture_Outline

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