2012 Pearson Education, Inc. Lecture Presentation Chapter 9 Atmosphere and Severe Weather 2012 Pearson Education, Inc. Learning Objectives Understand Earths energy balance and energy exchanges that produce climate and weather Know the different types of severe weather events Know the main effects of severe weather events, as well as their linkages to other natural hazards Recognize some natural service functions of severe weather 2012 Pearson Education, Inc. Learning Objectives, cont. Understand how human beings interact with severe weather hazards and how we can minimize the effects of these hazards 2012 Pearson Education, Inc. Energy Force Push or a pull Measured in Newtons (N) Magnitude measured by how much a body is accelerated Work Done when force is applied to an object that moves it a certain distance in the direction of the applied force Measured in Joules (J) Power Rate at which work is done Measured in Watts (W) 2012 Pearson Education, Inc. Energy, cont. The ability to do work Measured in exajoules (EJ) to describe global energy Types Potential - stored energy Kinetic - energy of motion Heat - energy of random motion of atoms and molecules 2012 Pearson Education, Inc. Heat Transfer Conduction Transfer through atomic or molecular interactions Two bodies in contact with one another Convection Transfer through mass movement of a fluid Hot air rises displaces cool air which falls Creates a convection cell Radiation Transfer through electromagnetic waves 2012 Pearson Education, Inc. Figure 9.3 2012 Pearson Education, Inc. Earths Energy Balance A general equilibrium between incoming and outgoing radiation Earth intercepts only a fraction of the suns radiation Suns energy drives hydrologic cycle, ocean waves and currents, and global atmospheric circulation Nearly all of the energy available at Earths surface comes from the sun Exception, heat from Earths core that drives plate tectonics 2012 Pearson Education, Inc. Heat Energy Energy transferred between two objects at different temperatures Sensible heat Heat that is monitored by a thermometer Latent heat Energy necessary to cause a change in state Example: latent heat of vaporization is energy necessary to change liquid water into water vapor 2012 Pearson Education, Inc. Electromagnetic Energy Most of the suns energy is electromagnetic Described by the wavelength Distance from one crest to the next All wavelengths are part of electromagnetic spectrum Only a small part of this is visible 2012 Pearson Education, Inc. Figure 9.5 2012 Pearson Education, Inc. Energy Behavior Redirection Reflection back to space by clouds, water, land Scattering disperses energy is many directions Transmission Energy is passed through atmosphere Absorption Alters molecules or causes them to vibrate Some of this may be re-emitted to space 2012 Pearson Education, Inc. Energy Behavior, cont. Temperature depends on amount of energy absorbed or reflected Reflection depends on albedo Describes the reflectivity of surfaces Dark woodlands reflect 5 percent to 15 percent Light grasslands reflect 25 percent Absorption Energy that is not reflected is absorbed Different objects absorb different wavelengths Hotter objects radiate energy more rapidly and at shorter wavelengths 2012 Pearson Education, Inc. Figure 9.4 2012 Pearson Education, Inc. The Atmosphere Gaseous envelope that surrounds Earth Composed mostly of nitrogen and oxygen Smaller amounts of water vapor, argon, carbon dioxide Water vapor Important for cloud formation and circulation Comes from evaporation off of Earths surface Humidity describes amount of moisture in atmosphere at particular temperature Relative humidity is the ratio of water vapor present to the amount that saturates the air Increases at night because of cooler temps, decreases during the day due to heating 2012 Pearson Education, Inc. Structure of the Atmosphere Troposphere All of Earths surface is within this layer Upper boundary is tropopause Temperature decreases with increasing altitude Clouds are present at the tropopause Figure 9.7 2012 Pearson Education, Inc. Clouds Made from very small water droplets or ice crystals that condense from the atmosphere Cumulus puffy fair weather clouds Cumulonimbus Tall, dark storm clouds 2012 Pearson Education, Inc. Figure 9.8 2012 Pearson Education, Inc. Weather Processes: Atmospheric Pressure and Circulation Atmospheric pressure also called barometric pressure Weight of a column of air above a given point Force exerted by molecules on surface In the atmosphere, pressure decreases with increasing altitude Nearly all of the weight of the atmosphere is in the lower atmosphere 2012 Pearson Education, Inc. Figure 9.10b 2012 Pearson Education, Inc. Weather Processes: Atmospheric Pressure and Circulation, cont. 1 Changes in air temperature and air movement are responsible for horizontal changes in pressure Temperature influences pressure because cold air is more dense and exerts greater pressure on surface Global variations in temperature cause global winds At equator, air is warm and low in density Creates low pressure zones at the equator Air rises, condenses, forms clouds and rain Cooler, drier air sinks at latitudes around 30 causing deserts 2012 Pearson Education, Inc. Weather Processes: Atmospheric Pressure and Circulation, cont. 2 Air movement can cause changes in pressure Convergence occurs when air flows in increasing pressure Divergence occurs when air flows out decreasing pressure At surface, air moves from surface high pressures (H) to low pressures (L) Air at low rises into atmosphere and then diverges in the upper atmosphere A surface low is often associated with a high aloft and vice versa Jet streams Narrow, fast moving jets of air caused by low pressures near the top of the troposphere 2012 Pearson Education, Inc. Figure 9.11 2012 Pearson Education, Inc. Figure 9.12 2012 Pearson Education, Inc. Unstable Air Tendency of air is to remain in place Atmospheric stability Air parcels resist movement or return to original spot after they move In unstable air, parcels are rising until they reach air of similar temperature and density Air is unstable when lighter, warm or moist air is overlain by denser cold or dry air Some air sinks and some air rises 2012 Pearson Education, Inc. Fronts Air masses do not mix, Fronts are the boundary between cooler and warmer air masses Cold front when cold air is moving into warm air Warm front when warm air is moving into cold air Stationary front where boundary shows little movement Occluded front where rapidly moving cooler air overtakes another cold air mass wedging warm air in between 2012 Pearson Education, Inc. Figure 9.13 2012 Pearson Education, Inc. Hazardous Weather: Thunderstorms Most occur in equatorial regions Most common in the afternoon or evening hours in spring or summer Three conditions necessary Warm and humid air in lower atmosphere Steep vertical temperature gradient such that the rising air is warmer than the air above it Cold air over warm air Updraft must force air up to the upper atmosphere 2012 Pearson Education, Inc. Figure 9.15 2012 Pearson Education, Inc. Thunderstorm Development Moist air is forced upwards, cools and water vapor condenses to form cumulus clouds Cumulus stage Moisture supply and updrafts continue, clouds grow A continuous release of latent heat from condensation warms the surrounding air causing the air to rise further Expanding the cloud into colder air causes water droplets to freeze Larger snowflakes fall and melt as raindrops Large droplets grow until they cannot be supported by updrafts 2012 Pearson Education, Inc. Thunderstorm Development, cont. Mature stage Downdrafts and falling precipitation leave the base of the cloud Updrafts and downdrafts are present Cloud continues to grow until it reaches the top of unstable atmosphere (tropopause) Storm produces heavy rain, lightning and thunder, and occasionally hail Dissipative stage Upward supply of moist air is blocked by downdrafts Thunderstorm weakens, precipitation decreases, and the cloud dissipates Most are air mass thunderstorms and do little damage 2012 Pearson Education, Inc. Figure 9.16 2012 Pearson Education, Inc. Severe Thunderstorms National Weather Service, classified severe if winds > 93 km (58 mi.) per hour, or hailstones > 1.9 cm (0.75 in), or generates a tornado Necessary conditions Large changes in vertical wind shear differences in wind speed and direction Greater the wind shear, the more severe the storm High water vapor content in lower atmosphere Updraft of air Dry air mass above a moist air mass 2012 Pearson Education, Inc. Severe Thunderstorm Types Mesoscale convective systems (MCSs) Most common type Very large clusters of self-propagating storms in which downdrafts from one creates a new storm Downdrafts come together to form outflow boundaries curved lines of thunderstorms that may travel long distances Squall lines Long lines of individual storm cells common along cold fronts Updrafts form anvil-shaped clouds extending ahead of the line Downdrafts surge forward as gust front in advance of precipitation Can develop along drylines Fronts with differing moisture content 2012 Pearson Education, Inc. Severe Thunderstorm Types, cont. Supercells Smaller than MCSs and squall lines, but more damaging Extremely violent and spawn most tornadoes Last from 2 to 4 hours Downbursts from thunderstorms can create: Derechos Strong, straight-line windstorms Wind gusts can be tornado strength Cause fallen trees, power outages, injuries, fatalities Microbursts Hazard for aviation 2012 Pearson Education, Inc. Hail Hard, round, irregular pieces of ice originating from thunderstorms Contain rings due to adding coatings during updrafts Hail moves up and down in lower part of the storm adding layers of liquid water which then freezes Cause mostly property damage 2012 Pearson Education, Inc. Hazardous Weather: Tornadoes Usually spawned by severe thunderstorms 19922002, killed 57 people/year Defined by vortex extending downward from the cloud and touching the ground Called funnel clouds when it does not touch ground Form where there are large differences in atmospheric pressure over short distances Figure 9.18b 2012 Pearson Education, Inc. Tornado DevelopmentOrganizational Stage Vertical wind shear causes rotation to develop within the storm Strong updrafts in advance of the front tilt the horizontally rotating air vertically Known as a mesocyclone Updrafts at rear of the storm lower part of the cloud Wall cloud Wall cloud rotates and funnel descends 2012 Pearson Education, Inc. Figure 9.19 2012 Pearson Education, Inc. Tornado DevelopmentMature Stage Visible condensation funnel extends to ground Moist air drawn upward In stronger tornadoes, smaller whirls may develop within tornado Suction vortices Responsible for the greatest damage Figure 9.18d 2012 Pearson Education, Inc. Tornado DevelopmentShrinking and Rope Stage Shrinking stage Supply of warm air is reduced and tornado begins to thin More dangerous because wind speeds increase as diameter decreases Rope stage Downdrafts cause tornado to move erratically and disappear 2012 Pearson Education, Inc. Tornado Classification Classified according to damage that they produce using Enhanced Fujita Scale (EF) Waterspouts Tornadoes that form over water Develop beneath fair weather cumulus clouds as a result of wind shear 2012 Pearson Education, Inc. Table 9.1 2012 Pearson Education, Inc. Figure 9.21 2012 Pearson Education, Inc. Hazardous Weather: Blizzards Severe winter storms with large amounts of falling or blowing snow, High winds Low visibilities for extended period of time Whiteout Extremely low visibility In United States: winds > 56 km (35 mi.) per hour, visibilities < 0.4 km (0.25 mi.) for at least 3 hours In Canada: winds > 40 km (25 mi.) per hour, visibilities < 1 km (1.6 mi.) for at least 4 hours Wind chill wind cools skin, evaporates moisture, reduces time it takes for frostbite to form 2012 Pearson Education, Inc. Causes of Blizzards Interaction between upper-level low pressure trough and surface low pressure Colorado and coastal storms derived from moist ocean air Alberta Clippers are drier with less snow and cold temperatures Noreasters on East Coast have hurricane force winds, heavy snows, intense precipitation, and high waves 2012 Pearson Education, Inc. Figure 9.22 2012 Pearson Education, Inc. Ice Storms Prolonged periods of freezing rain Upon contact with cold objects, rain immediately freezes to form a coating of ice Develop during winter on the north side of a stationary or warm front Three conditions for freezing rain 1.Ample source of moisture 2.Warm air over shallow layer of cold air 3.Objects on land close to or at freezing 2012 Pearson Education, Inc. Figure 9.24 2012 Pearson Education, Inc. Fog A cloud in contact with ground Form by air cooling to condensation or adding water to cooled air through evaporation Cooling At night heat radiates from land Warm air blows over cold water Humid air rises up a mountain side Evaporation Cold air flows over warm body of water Warm rain falls through cool air 2012 Pearson Education, Inc. Drought Extended period of low precipitation Produces a shortage of water for people, animals and plants Regional food shortages Affects more people than any other natural hazard Causes water and power shortages and agricultural problems 2012 Pearson Education, Inc. Figure 9.25 2012 Pearson Education, Inc. Mountain Windstorms Develop seasonally on the downwind side of mountain ranges or glacial ice fields Mountains block prevailing winds and can, under specific conditions, cause winds to move quickly down slopes Chinooks, east of Rocky Mountains Santa Ana, in Southern California Can cause roof and tree damage, blow cars off highways, contribute to large wildfires 2012 Pearson Education, Inc. Dust Storms Strong windstorms in which dust reduces visibility for significant amount of time Can be several hundred kilometers in diameter and carry 100 million tons of dust Safety hazard for travel Affect climate and human health Figure 9.26a 2012 Pearson Education, Inc. Sandstorms Desert phenomenon where sand transported in a cloud Rarely extends > 2m (6.5 ft.) above land Along with dust storms, occur mostly in midlatitude, semiarid, and arid regions 2012 Pearson Education, Inc. Heatwaves Prolonged periods of extreme heat that are both longer and hotter than normal Associated with long areas of high pressure, called ridges Wet conditions to the west of ridge Dry conditions to the east of ridge Accompany either severe humidity or extreme dryness Heat index Bodys perception of air temperature 2012 Pearson Education, Inc. Figure 9.27 2012 Pearson Education, Inc. Table 9.A 2012 Pearson Education, Inc. Human Interaction with Weather Land use Agriculture Contributes to dust storms Urban Heat Island Effect Causes urban area to be 12C (22F) warmer Global Warming Increases heat index and heatwaves Increases intensity of precipitation Increase risk of drought Increases intensities of hurricanes, typhoons, and other tropical cyclones 2012 Pearson Education, Inc. Links with Other Hazards Flooding Mass wasting Wildfires Global Climate Tropical and extratropical cyclones 2012 Pearson Education, Inc. Natural Service Functions Contribute to health of forests Wildfires clear old growth Windstorms topple dead trees Source of water Aesthetic value Clouds, snow, lightning Tourism Tornado chasing 2012 Pearson Education, Inc. Minimizing Severe Weather Hazards: Forecasting and Prediction Difficult to forecast weather events Doppler radar Detects clouds, rain, ice particles, etc Used to make short term predictions Watch Possibility of severe weather developing Warning Severe weather has been spotted, take action 2012 Pearson Education, Inc. Forecasting and Prediction, cont. Not able to predict tornado intensity Predicting amounts of snow and ice is difficult Nowcasting makes real time predictions Using radar, satellites, weather station data once storms have formed 2012 Pearson Education, Inc. Mitigation of Hazard Mitigation Long-term actions to prevent or minimize death, injuries, and damage are considered mitigation Mitigation techniques: Building new structures Wind proofing Ensuring utilities can continue to function in severe weather Warning systems Hazard insurance 2012 Pearson Education, Inc. Preparedness and Personal Adjustments Know your climate and when hazards are most likely Prepare your home for likely hazards Get information NOAA, National Weather Service, FEMA Wear proper clothing Protection from heat or cold Know the signs of hypothermia 2012 Pearson Education, Inc. End Atmosphere and Severe Weather Chapter 9