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Chapter 2 Weather Su09
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Chapter 2 Weather Su09


GEOG 100 Lecture Gerbman/Getis weather

GEOG 100 Lecture Gerbman/Getis weather

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  • 1. Physical Geography Weather and Climate
  • 2. Hurricane Bertha
    • Second Hurricane of 1996
    • Swept through St Thomas, Virgin Islands; Puerto Rico; Bahamas
    • High winds toppled trees; damaged houses; six people killed
    • Plowed into coastal North Carolina
    • A million people evacuated – no one in U.S. killed
    • 105 MPH winds
    • Seas 8 feet above high tide
    • Heavy rain; beach erosion
  • 3.  
  • 4. Weather
    • Power of Hurricanes is concentrated in a narrow path
    • They do great damage
    • Tropical storms such as these are one extreme type of weather phenomenon
    • We will look at normal, patterned phenomena from which extreme weather events occasionally emerge
  • 5. Weather and Climate
    • Current conditions are recorded for a limited region
      • Temperature
      • Wind
      • Precipitation
    • Weather ‘inventory’ is established
    • Trends in the data establish typical or characteristic conditions
    • Characteristic conditions describe the climate of a region
  • 6. Troposphere
    • We are concerned with conditions that affect the earth’s surface
    • The troposphere is the part of the atmosphere closest to the surface of the earth extending up about 10 kilometers (6 or 7 miles)
    • Contains virtually all of the air, clouds and precipitation of the earth
  • 7. Objective
    • Understand the characteristics of the lower atmosphere
    • Attempt to understand how weather affects climate
    • Climate is key to understanding, in a broad way, the distribution of the world population
    • We will focus in class on elements that constitute the weather
    • READ and STUDY the section on Climate Regions (pages 111 through 123)
  • 8. Air Temperature
    • Solar energy, energy from the sun, is transformed into heat at the earth’s surface and, to a lesser degree, in the atmosphere
    • The amount of solar energy received varies across the globe
    • Insolation (not to be confused with insulation) – the amount of solar radiation received at a given place
      • Intensity of radiation
      • Duration of radiation
      • Angle of the sun
      • Hours of sunlight
  • 9. Five Modifying Variables
    • Amount of water vapor in the air
    • Degree of cloud cover
    • Nature of the surface of the earth
      • Land
      • Water
    • Elevation above sea level
    • Degree and direction of air movement
  • 10. Earth Inclination
    • Earth’s axis of rotation is tilted about 23.5 ° from perpendicular to the orbital plane
    • Every 24 hours the earth makes one revolution around it’s axis of rotation
    • 365 days to circle the sun
    • Tilt of the earth causes the amount of solar energy received at a latitude to vary during the year
  • 11.  
  • 12.  
  • 13.  
  • 14. Solar Intensity
    • Highest incidence (intensity) of sun’s radiation located where sun is closest to vertical overhead
    • When earth is tilted with north towards the sun
      • Vertical rays are felt as far north as 23.5 ° (Tropic of Cancer) – June 21
      • Days are longer – more solar radiation hours
    • Solar intensity becomes less as angle to the sun increases
  • 15. Imagine sun’s ray is a flashlight beam
  • 16.
    • Solar radiation received at the poles is low even though 24 hour days in summer
      • Solar energy spread over a large area due to low sun angle
    • Solar radiation received is greatest between the Tropic of Cancer and the Tropic of Capricorn (23.5 ° N & S Respectively)
      • Sun is near vertical all year
    • Highest solar radiation received at equator
  • 17. Reflection and Reradiation
    • Much of potentially receivable radiation is reflected back into space or diffused by the troposphere
    • Clouds are reflective
    • Light colored surfaces, like snow, reflect large amounts of solar energy
    • The remainder is absorbed by the earth during sunlight hours
  • 18.  
  • 19. Reradiation
    • Energy is also lost through reradiation
    • On a clear night, solar energy in the form of heat is released from the earth into the air
    • Convection carries the warm air aloft where the air cools and reradiates the heat back into space
    • Clouds act as a sort of blanket that traps the heated air
  • 20. Solar Radiation Absorption
    • Some surface materials store solar energy more effectively than others
    • Water is transparent and stores solar energy deep within its surface
    • Currents distribute the heat effectively
    • Land surfaces are opaque, store solar energy near the surface – no currents to distribute the heat
  • 21.
    • Land surfaces reradiate more quickly (all the energy is at the surface)
    • Air is heated by the process of reradiation from the earth and not directly by energy from the sun
    • Hot and cold extremes occur over land because the land heats and cools more rapidly than water
  • 22.
    • Large bodies of water moderate temperatures
    • Note that coastal areas are cooler in the summer and warmer in the winter than inland areas at the same latitude
  • 23.  
  • 24. Air Temperature Continued
    • Adiabatic Lapse Rate
      • Air cools at a rate of 6.4 °C per 1000 meters (3.5°F per 1000 ft) increase in elevation
        • Atmosphere is thinner
        • Gasses less dense
        • Energy distributed in larger volume
      • Temperature Inversion
        • Rapid reradiation causes air temperatures above the surface to be higher than at the surface itself
        • Because the upper air is warmer, lower air cannot rise above the inversion layer – traps emissions - smog
  • 25.  
  • 26. The Donora Tragedy
    • Donora, Pennsylvania; Late October, 1948
    • Stagnant, moisture-filled air trapped in the valley by temperature inversion
    • Smoke and fumes from town’s zinc works filled the air
    • Sulfur dioxide becomes deadly sulfur trioxide in air
    • For 5 days smog concentration increased
    • Widespread respiratory problems; 20 dead; hundreds hospitalized
  • 27.  
  • 28. Air Pressure and Winds
    • How do differences in air pressure from place to place affect weather conditions?
    • To answer this question we first need to understand why differences in air pressure occur
  • 29. Air Pressure
    • Air is a gaseous substance comprised of several gasses
      • Nitrogen
      • Oxygen
      • Carbon Dioxide
      • Numerous other gasses in lesser quantities
    • Imagine a column of air that is one square inch at the earth’s surface and that you could weigh the column of air above it.
  • 30.
    • The column would weigh approximately 14.7 pounds (6.67 kilograms) – Standard Air Pressure
    • If you repeated the above at a higher altitude, the column would be shorter and therefore would weigh less.
    • Air is heavier and air pressure is higher closer to the surface of the earth
    • Air pressure is normally reported corrected to sea level.
    • By comparing the local air pressure to the sea level air pressure you can determine altitude. Altimeter
  • 31.
    • Physical Law
      • Cold air is heavier than warm air
      • Hot air balloons rise and float in the wind
    • Cold morning – relatively heavy air
    • Warm afternoon – relatively light air
    • Barometers record changes in air pressure
    • Air pressure changes at a given location as the surface warms and cools
    • Barometers record a drop in atmospheric pressure when air heats and a rise when the air cools
  • 32.
    • Air is a fluid and behaves in many ways like a liquid in a tank
    • Imagine warm air as an oil (light fluid) and cool air as water (heavier fluid)
    • Place the water and oil in a tank
    • The light oil (warm air) floats on the top
    • The heavy water (cool air) sinks to the bottom
    • Both liquids will come to equilibrium in flat layers
  • 33.
    • This horizontal movement and eventual equilibrium represents air movement
    • Air attempts to achieve equilibrium by evening out pressure imbalances that result from uneven heating of the surface
    • Air races from heavy (cold) air locations to Light (warm) air locations – from high pressure to low pressure
    • The greater the pressure difference the greater the wind
  • 34. Pressure Gradient Force
    • Differences in earth’s surface
      • Desert
      • Snow cap
      • Forest
      • Cities, etc
    • Create zones or regions of high or low pressure
    • Can cover entire continents or very large regions
      • Small variation will occur within a region or zone
  • 35. Pressure Gradient
    • Adjacent areas or zones at different air pressure
    • Causes air to blow from high pressure (cool) area to low pressure (warm) area
    • In order to achieve equilibrium the dense cool air moves into the less dense warm are and displaces the warmer air – cool air travels along the surface, warm air travels aloft
  • 36.
    • The greater the difference in pressure, the stronger the wind
    • The closer the zones are to one another the greater the wind velocity (sharper or steeper pressure gradient
    • This circulation pattern is called convection (the same phenomena we encountered with magma when we discussed continental plate movement)
  • 37.  
  • 38. Breezes
    • Breezes are the predominate wind patterns
    • Land Sea Breezes are caused by the different rates of heating and cooling characteristics of water and land
    • Mountain and Valley breezes are caused by the difference in elevation (air pressure) as air warms and cools
  • 39.  
  • 40. Coriolis Effect
    • Caused by the rotation of the earth
    • In the Northern Hemisphere wind will curve right – opposite in Southern Hemisphere
    • Equator is traveling faster than the poles
    • If the earth were not rotating, winds would travel in a straight line
    • The result of the coriolis effect and pressure gradients is that wind forms spirals rather than straight line patterns
  • 41.  
  • 42. The Frictional Effect
    • The earth’s surface cause a friction drag on wind
    • Affects wind velocity up to about a mile above the surface
    • Wind speed and direction is changed
    • Frictional Effect cause wind to follow an intermediate path – not just pressure gradient and coriolis
      • Around mountains
      • Through deep valleys
      • Forests
      • Plains, etc
  • 43. Global Air Circulation Patterns
    • Equatorial Zone – Low Pressure region
    • Poles are high pressure zone
    • Air rises in the equator low pressure are and generally flows north or south towards the poles as it cools
    • Cool air drops causing surface zones of high pressure
    • Sub Tropical high pressure zones occur at around 30 ° N & S
  • 44. Northern Hemisphere wind belts
    • Cooled air reaches the surface
    • Spreads N & S
    • Coriolis effect modifies wind direction
    • Creates belts of wind – named for the direction the wind comes from
      • Northeast trades - tropics
      • Westerlies – mid latitudes – most of U.S.
    • Pattern repeats near the poles
      • Polar easterlies
        • Connects polar low to the polar high
  • 45.  
  • 46. Global Air Circulation Continued
    • Belts or cells of air circulation move north or south as the earth moves around the sun and the sun angle over the equator changes
    • Strongest flows of air occur in the North and South Hemisphere at about 30,000 to 40,000 feet called Jet Streams
    • Jet Streams are aloft winds that travel west to east in both the Northern and Southern Hemisphere
      • Wind speeds 100 – 200 MPH (160 – 320 KPH)
  • 47.
    • Jet streams undulate north and south as they circle the earth
    • Three to six undulations that constantly change
    • Control the flow of air masses on the earth’s surface.
    • Jet streams move north or south seasonally because of the sun angle
    • In the northern hemisphere a jet stream undulation that comes south brings cold polar air south
  • 48.
    • The undulating jet stream causes circular depressions along its edges
    • Common to see spiral shaped fronts approach the U.S west coast – watch tonight’s weather forecast!
  • 49. Ocean Currents
    • Surface ocean currents correspond to global wind direction patterns
    • However, just as differences in air pressure cause wind movement, so do differences in water density cause water movement
    • Salt water is heavier than fresh water
    • Water density increases with higher salinity
    • As salt water evaporates, salinity increases
  • 50. Ocean Currents
    • High density water (high salinity, high evaporation) exists in areas of high pressure
      • Descending dry air warms on the water surface and picks up moisture
    • Low density water (low salinity, low evaporation) exists in areas of low pressure (high rainfall)
    • Differences in water density and the coriolis effect cause water to move in wide paths from one part of the ocean to another
  • 51. Ocean Currents
    • Major difference in water movement
      • Continents redirect water flow
      • Air moves across continents
    • Shape of the oceans has a large affect on ocean flows
    • North Pacific strikes North America and diverts north and south – Pineapple Express
    • North Atlantic flows north of Great Britain along the north of the Eurasian continent – North Atlantic Drift - milder northern climate
  • 52.  
  • 53. Ocean Currents
    • Ocean currents also affect precipitation on adjacent land
    • Cool ocean temperatures cause cool air above
      • Little convection occurs
      • Denies moisture to adjacent land
      • Coastal deserts
  • 54. Ocean Currents
    • Warm ocean temperatures cause moist air above – Coast of India
      • Brings moisture to adjacent land
      • Especially with prevailing landward winds
    • Now we can answer the question we started with “How do differences in air pressure from place to place affect weather conditions?”
  • 55. Moisture in the Atmosphere
    • All air contains water vapor (what we feel as humidity)
      • Relative Humidity is the measure of how much water vapor is contained in the air at the ambient temperature compared to the maximum amount the air could hold expressed as a percentage.
      • For a given amount of water vapor in a volume of air, relative humidity goes up as the air cools (has less holding capacity) and goes down as the temperature goes up (higher holding capacity)
  • 56. Relative Humidity
    • Therefore 60 % Relative Humidity on a hot day means the air is very humid and uncomfortable
    • However, on a cold day, in absolute terms, the air contains much less water vapor
    • This is why your home seems so dry in the winter when you run the furnace – because it is! The outside humidity may be 75 or 80% at 40° but will only be 45 to 50% inside in the warm 72° - Drink more fluids in the winter!!!
  • 57.
    • Dew on the ground in the morning means that the air temperature dropped below the point at which condensation occurs
    • Dew Point
      • The critical temperature at which condensation occurs
  • 58.  
  • 59. Water & Stored Energy
    • Energy state
      • Ice
      • Water
      • Vapor
    • Ice to Water ; Water to Vapor
      • Add and store energy – Latent Heat
    • Vapor to Water ; Water to Ice
      • Release energy – Sensible heat
    • Nature uses to move energy
  • 60. Moisture in the Atmosphere
    • Precipitation is any form of water particle that falls from the atmosphere that reaches the earth’s surface
      • Rain
      • Sleet
      • Hail
      • Snow
  • 61.
    • Warm, moisture lade air rise and cools
    • As the air cools it becomes supersaturated (has more water vapor than it can hold)
    • The water vapor condenses (changes for gas to liquid) onto particles in the air just like on a cold glass
      • Dust
      • Pollen
      • Smoke
      • Salt crystals
  • 62.
    • Particles too light to fall at first
    • May freeze
    • Droplets coalesce into larger and larger drops until clouds are formed
    • When they coalesce enough and get heavy enough they fall
    • If the droplets are frozen, snow is formed
    • If the air at the surface is below freezing, snow will accumulate. Otherwise the particles thaw into rain as they fall
  • 63.  
  • 64.
    • Sometimes the falling frozen crystals will partially melt and coalesce with other partially melted crystals that are blown back up by rising air masses
    • Forms super heavy ice particles that fall as hail
    • Hail stones can become very large measuring as much as 2 inches or more in diameter
  • 65. Types of Precipitation
    • Convectional
    • Orographic
    • Cyclonic or Frontal
  • 66. Convectional
    • Results from rising, heated, moisture laden air
    • Rising air cools
    • Air temperature drops below the dew point
    • Water vapor coalesce into rain droplets
  • 67.  
  • 68. Orographic
    • Warm air travels horizontally
    • Encounters land mass that forces the air up
    • Air cools
    • Dew Point crossed
    • Rain occurs
    • Routinely happens here on the Olympics and Cascade Mountains
    • Seattle in ‘Rain Shadow’
  • 69.  
  • 70. Cyclonic and Frontal Precipitation
    • When you have listened to this lecture at least once, you will be able to open the Video folder and watch the 4 required videos.
    • Cyclonic and Frontal Weather
      • Weather & Climate – Weather Fronts (6’-31”)
    • Sever Weather Videos
      • Anatomy of a Hurricane (5’-30”)
      • Hurricane Andrew (7’-30”)
      • Inside the Tornado (4’-20”)
  • 71. Coming Up Next Week Landforms Chapter 3