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Lecture Outlines Natural Disasters, 7 th edition

Lecture Outlines Natural Disasters, 7 th edition. Patrick L. Abbott. Weather Principles and Tornadoes Natural Disasters, 7 th edition, Chapter 11. Weather Versus Climate. Weather : short-term processes Tornadoes, heat waves, hurricanes, floods Climate : long-term processes

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Lecture Outlines Natural Disasters, 7 th edition

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  1. Lecture OutlinesNatural Disasters, 7th edition Patrick L. Abbott

  2. Weather Principles and TornadoesNatural Disasters, 7th edition, Chapter 11

  3. Weather Versus Climate • Weather: short-term processes • Tornadoes, heat waves, hurricanes, floods • Climate: long-term processes • Ice ages, droughts, atmosphere changes, ocean circulation shifts

  4. Processes and Disasters Fueled by Sun • Sun powers hydrologic cycle and (with gravity) drives agents of erosion • Sun heats Earthunequally • Equatorial regions receive about2.4 timesmore solar energy than polar regions • Earth’s spin and gravity set upcirculation patternsin ocean and atmosphere to even out heat distribution • Circulation patterns determine weather and climate

  5. Solar Radiation Received by Earth • Relative amounts reflected, used in hydrologic cycle and converted to heat are different at different latitudes • Equatorial belt(38oN to 38oS) faces Sun directly, so massive amounts of solar radiation areabsorbed • Polar regionsreceive solar radiation at low angle, so much isreflected  net cooling • Excess heatat equator istransferredthrough mid-latitudes to polar regions Insert new Figure 11.2 here Figure 11.2

  6. Solar Radiation Received by Earth • Climatic feedback cycle in polar regions: • Receive less solar radiation  colder • More snow and ice forms  higher albedo (reflectivity) • More solar radiation reflected, less absorbed • High albedos lower Earth’s surface temperature

  7. Solar Radiation Received by Earth • Greenhouse effect raises Earth’s surface temperature • Solar radiation reaches Earth at short wavelengths • Absorbed solar radiation raises Earth’s surface temperature • Excess heat is re-radiated at long wavelengths and absorbed by greenhouse gases (water vapor, CO2, methane) in atmosphere, then radiated back down to Earth’s surface  warms Earth’s climate • About 95% of long wavelength re-radiated heat is trapped • Examine greenhouse effect on Earth in Chapter 12: • Runaway greenhouse effect in early Earth history • Human-increased greenhouse effect of 20th, 21st centuries

  8. Side Note: Temperature Scales Fahrenheit, centigrade, Kelvin • Fahrenheit sets freezing point of water at 32oF, boiling point at 212oF (most common in United States) • Centigrade (or Celsius) sets freezing point of water at 0oC and boiling point at 100oC (everywhere else) • Conversion: oF = 9/5 oC + 32 oC = 5/9 (oF – 32) • Kelvin: absolute zero (0K) = no heat energy (-460oF, -273oC) • Conversion: K = oC + 273

  9. Water and Heat • Required amount of heat to raise temperature of water (specific heat) is high • Convection: transmission of heat in flowing water or air • Conduction: direct transmission of heat through contact • Beach example: temperature of high heat capacity water changes little from day to night, but hot beach sand (with low heat capacity) becomes cool at night Insert table 11.1

  10. Water and Heat • Water vapor in atmosphere: between 0 and 4% by volume • Humidity • Saturation humidity: maximum amount of water an air mass can hold (increases with increasing temperature) • Relative humidity: ratio of absolute humidity to saturation humidity • If temperature of air mass is lowered without changing absolute humidity, will reach 100% relative humidity because at each lower temperature, a lower saturation humidity applies • When relative humidity reaches 100%, excess water vapor condenses to liquid water  temperature = dew point

  11. Water and Heat • Waterabsorbs, stores and releaseshuge amounts of energy changing phases between liquid, solid and gas • Ice melting to water absorbs 80 calories of heat per gram of water (cal/g):latent heat • Liquid  vapor absorbs 600 cal/g:latent heat of vaporization • Ice  vapor absorbs 680 cal/g: latent heat of sublimation • Liquid  ice releases 80 cal/g:latent heat of fusion • Vapor  liquid releases 600 cal/g:latent heat of condensation • Vapor  ice releases 680 cal/g: latent heat of deposition Figure 11.5

  12. Vertical Movement of Air • Air: easily compressed, denser and denser closer to Earth’s surface • Flows from higher to lower pressure, upward in atmosphere, if can overcome pull of gravity  add heat • As heated air rises, it is under lower pressure so expands • Expansion causes adiabatic cooling (temperature decrease without loss of heat energy) • Descending air is compressed and undergoes adiabatic warming (temperature increase without gain in heat energy)

  13. Vertical Movement of Air • Air undergoes about 10oC adiabatic cooling per km of rise, 10oC adiabatic warming per km of descent (dry adiabatic lapse rate) • As air cools, can hold less and less water vapor relative humidity increases • When relative humidity = 100% (altitude = lifting condensation level),water vapor condenses and latent heat is released, which slows rate of upward cooling to about5oCper km of rise (moist adiabatic lapse rate)

  14. Vertical Movement of Air Differential Heating of Land and Water • Low heat capacity of rock  land heats up and cools down quickly • Winter: • Land cools down quickly, so cool air sinks toward ground  high-pressure region • Ocean retains warmth, so warm, moist air rises • Cold, dry air from land flows out over ocean • Summer: • Land heats up quickly, so hot, dry air rises  low pressure • Ocean warms more slowly, so cool, moist air sinks over ocean • Cool, moist air over ocean is drawn into land, warms over land and rises to cool, condense and form rain  summer monsoons

  15. Vertical Movement of Air Figure 11.5

  16. Layering of the Lower Atmosphere Troposphere: • Lowest layer of atmosphere • 8 km at poles and 18 km at equator • Warmer at base, colder above  instability as warm air rises and cold air sinks, constant mixing leads to weather Tropopause: • Top of troposphere Stratosphere: • Stable configuration of warmer air above colder air Insert revised figure 11.7 here Figure 11.6

  17. General Circulation of Atmosphere Atmosphere transports heat: low latitudes to high latitudes Insert revised figure 11.8 here Figure 11.7

  18. General Circulation of Atmosphere Low Latitudes • Solar radiation at equator powers circulation ofHadley cells • Warm equatorial air rises at Intertropical Convergence Zone (ITCZ), then cools and drops condensed moisture in tropics • Cooled air spreads and sinks at 30oN and 30oS, warming adiabatically Figure 11.9

  19. General Circulation of Atmosphere Middle and High Latitudes • Hadley cells create bands of high pressure air at 30oN and 30oS • Air flows away from high pressure zones • Cold air flows over land from poles to collide atpolar frontaround 60oN and 60oS • Hadley, Ferrel and polar cells  convergence at ITCZ (rain) and polar front (regional air masses) • Global wind pattern modified by continental masses, mountain ranges, seasons, Coriolis effect

  20. General Circulation of Atmosphere Air Masses • North America: • Cold polar air masses, warm tropical air masses • Dry air masses form over land, wet air masses form over ocean • Dominant air-mass movement direction is west to east • Pacific Ocean air masses have more impact than Atlantic Ocean Figure 11.10

  21. General Circulation of Atmosphere Fronts • Sloping surface separating air masses with different temperature and moisture content, can trigger severe weather, violent storms • Cold front: cold air mass moves in and under warm air mass, lifting it up (tall clouds, thunderstorms) • Warm front: warm air flows up and over cold air mass (widespread clouds) Figure 11.11

  22. General Circulation of Atmosphere Jet Streams • Relatively narrow bands of high-velocity (around 200 km/hr) winds flowing from west to east at high altitudes • Pressure decreases more slowly moving upward through warm air than through cold air  warm air aloft has lower pressure than cold air  warm air flows toward cold air (toward poles) • Spin of Earth turns poleward air flows to high-speed jet stream winds from the west (Coriolis effect) • Subtropical jet: about 30oN • Polar jet: more powerful, about 60oN, changing path Figure 11.14

  23. General Circulation of Atmosphere Rotating Air Bodies • Northern hemisphere: • Rising warm air creates low pressure area  air flows toward low pressure, in counterclockwise direction • Sinking cold air creates high pressure area  air flows away from high pressure, in clockwise direction Figure 11.17

  24. General Circulation of Atmosphere Rotating Air Bodies • Northern hemisphere: • Meanders in jet stream may help to create rotating air bodies • Trough of lower pressure (concavenorthward bend) • Forms core ofcyclone(counterclockwise flow) • Ridgeof higher pressure (convexnorthward bend) • Forms core ofanticyclone(clockwise flow) Figure 11.18

  25. General Circulation of Atmosphere Observed Circulation of the Atmosphere • Significant variation of air pressure and wind patterns by hemisphere and season • Seasonal changes not so great in Southern Hemisphere with mostly water surface • Northern Hemisphere wind and heat flow directions change with seasons • Winter has strong high-pressure air masses of cold air over continents • Summer has thermal lows over continents, Pacific and Bermuda highs

  26. Coriolis Effect • Velocity of rotation varies by latitude: • 465 m/sec at equator, 0 m/sec at poles • Bodies moving to different latitudes follow curved paths • Northern hemisphere: veer to right-hand side • Southern hemisphere: veer to left-hand side • Magnitude increases with increasing speed of moving body and with increasing latitude (zero at equator) Insert revised figure 11.15 here Figure 11.14

  27. Coriolis Effect • Determines paths of ocean currents, large wind systems, hurricanes (not water draining in sinks or toilets) Merry-go-round analogy: • Looking down on counter-clockwise spinning merry-go-round is analogous to rotation of Earth’s northern hemisphere viewed from North Pole • Outside edge of merry-go-round (equator) spins much faster than center of merry-go-round (North Pole) • Person at center tosses ball at person on edge: person on edge has rotated away and ball curves to right • Opposite spin and direction for southern hemisphere

  28. General Circulation of the Oceans • Surface and near-surface ocean waters absorb and store huge amounts of solar energy • Some solar heat transferred deeper by tides and winds • Surface- and deep-oceancirculationtransfers heat throughout oceans,affects global climate

  29. General Circulation of the Oceans Surface Circulation • Surface circulation mostly driven by winds • Movement of top layer of water drags on lower layer, etc., moving water to depth of about 100 m • Wind-driven flow directions are modified by Coriolis effect and deflection off continents • Carries heat from low latitudes toward poles

  30. General Circulation of the Oceans Surface Circulation • North Atlantic Ocean: • Warm surface water blown westward from Africa into Caribbean Sea and Gulf of Mexico • Westward path blocked by continents, forced northward along eastern side of North America, east to Europe (warms Europe) Figure 11.20

  31. General Circulation of the Oceans Deep-Ocean Circulation • Oceans: layered bodies of water with progressively denser layers going deeper • Water density is increased by: • Lower temperature • Increased dissolved salt content • Deep-ocean water flow isthermohaline(from heat, salt) flow:overturning circulation

  32. General Circulation of the Oceans • Ocean water hashigher density at • High latitudes(lower temperature) • Arctic and Antarctic(fresh water frozen in sea ice, remaining water made saltier) • Warm climates(fresh water evaporated, remaining water made saltier) • Densest ocean water forms in northern Atlantic Ocean and Southern Ocean

  33. Severe Weather • Causes about 75% of yearly deaths and damages from natural disasters • More people killed usually by severe weather than by earthquakes, volcanoes, mass movements combined • From 1980 to 2005, U.S. had 67 weather-related disasters causing more than $1 billion (each) in damages • Total more than $556 billion

  34. Midlatitude Cyclones • Northern Hemisphere cyclone: counterclockwise air mass rotating around low-pressure core • Large scale: trough in jet stream juxtaposes northern cold front and southern warm front  line of thunderstorms • Northeastern U.S.: low-pressure system moving up Atlantic coast draws northern cold air, moisture from east  nor’easter • Medium scale: individual thunderstorms • Small scale: tornado Figure 11.22

  35. Midlatitude Cyclones The Eastern U.S. “Storm of the Century” of 1993 • Immense cyclone covered area from Cuba to Canada between March 12 to 15 • Killed 270 people, more than $8 billion in damages • Large trough in jet stream caused collision of three air masses over Florida: • Low-pressure, warm, moist air from Gulf of Mexico • Fast-moving frigid arctic airmass from north • Rainy,snowy east-moving airmass from Pacific • Rode jet stream north up coast

  36. In Greater Depth: Doppler Radar • Measures relative velocity between two objects • Radar guns for police • Velocities in sports • Describing weather systems • Radar detects precipitation using reflection of microwaves • Reflectivity increases as precipitation increases • Allows life-saving advance warnings Figure 11.24

  37. Midlatitude Cyclones Blizzards • Strong cyclone with winds at least 60 km/hr and below freezing temperatures, blowing/falling snow • Cyclone may travel slowly though winds are fast Northeastern United States, 6-8 January 1996 • Canadian blizzard dropped record snowfalls in Ohio, Pennsylvania, West Virginia, New Jersey • Wind speeds exceeding80 km/hr • Killed 154 people • Followed immediately bywarm weather and heavy rains  destructive flooding

  38. Midlatitude Cyclones Ice Storms • Precipitation falls as snow flakes or ice particles • May pass downward through air warm enough to cause melting to rain • If rain then enters below-freezing layer near ground, refreezes into sleet • If rain is not in below-freezing layer long enough to refreeze, becomes supercooled, and then refreezes as soon as comes into contact with ground or solid object, forming coating of ice

  39. Midlatitude Cyclones Insert new 11.27 here Figure 11.27 Canadian Ice Storm, 5-9 January 1998 • 80 hours of freezing rain • 25 people died of hypothermia, $7 billion in damage • Power system collapsed under immense damage, had to be rebuilt

  40. How a Thunderstorm Works • Air temperature normally decreases upward from surface at about 6oC/km: lapse rate • If lapse rate is greater than 6-10oC/km, atmosphere is unstable • Rising warm, moist air may begincondensation, releasing latent heat and providingenergyfor severe weather, building cloud top higher

  41. How a Thunderstorm Works Insert revised figure 11.30 here Figure 11.30

  42. How a Thunderstorm Works • Early stage: requirescontinuous supplyof rising, warm, moist air to keep updraft and cloud mass growing • Mature stage: • Upper-levelprecipitationbegins when ice crystals and water drops become too heavy for updrafts to support • Falling rain causesdowndrafts, pulling in cooler, dryer air • Updrafts and downdrafts blow side by side, creating gusty winds, heavy rain, thunder and lightning, hail • Dissipating stage: downdrafts drag in so much cool, dry air that updrafts necessary to fuel thunderstorm are cut off

  43. How a Thunderstorm Works Downbursts: An Airplane’s Enemy • Violent downdrafts of cold air with rain and hail during mature stage of thunderstorm • Especially dangerous to airplanes, pushing plane into ground before pilot can react • Airplanes also threatened byhorizontal wind shear– wind shift from head winds (necessary to maintain lift) to tail winds

  44. Thunderstorms in North America Air Mass Thunderstorms: Most common type , result from convection Common in low latitudes all year Common in mid-latitudes in summer, especially late afternoon Severe Thunderstorms: Mid-latitude frontal collisions Insert revised figure 11.32 here Figure 11.32

  45. Thunderstorms in North America • Warm, moist air necessary for thunderstorm formation comes from Gulf of Mexico  more thunderstorms in central and southern U.S., particularly Florida Insert revised figure 11.33 here Figure 11.33

  46. Thunderstorms in North America Heavy Rains and Flash Floods Thunderstorms can be major supplier of water to area Central Texas • Warm, moist air from Gulf of Mexico meets warm, dry air from west, forming dry line (thunderstorm trigger) • Air flow turned upward at escarpment of Balcones fault zone – eroded fault scarp 30 to 150 m high, 545 km long • Torrential thunderstorm downpours

  47. Thunderstorms in North America Hail • Layered ice balls dropped from storms with: • Buoyant hot airrising from heated ground • Upper-level cold aircreating large temperature contrasts • Strong updraftskeeping hailstones aloft while adding layers • Most common in late spring and summer, along jet stream in colder midcontinent Insert revised figure 11.36 here Figure 11.36

  48. Thunderstorms in North America Lightning • Leading cause of forest fires, major cause of weather-related deaths • Lightning distribution same as thunderstorm distribution Insert revised figure 11.39 here Figure 11.39

  49. Thunderstorms in North America How Lightning Works • Flow of electric current: top of clouds’ excess positive charge seeks balance with bottom of clouds’ excess negative charge • Speeds up to 6,000 miles/second, in several strokes within few seconds Figure 11.41

  50. Thunderstorms in North America How Lightning Works • Charge imbalance from freezing and shattering of super-cooled water drops – charge separations distributed by updrafts and downdrafts during early cloud buildup • Negative charge at bottom of cloud induces buildup of positive charge in ground below • Discharge begins within cloud, initiates downward stream of electrons  stepped leader • As stepped leader nears ground, ground electric field increases greatly, sending streamers of positive sparks upward, connecting with stepped leader about 50 m above ground

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