Chapter 2 Weather Su09


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GEOG 100 Lecture Gerbman/Getis weather

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Chapter 2 Weather Su09

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