This document summarizes information about hurricanes, weather, climate, and atmospheric conditions. It discusses Hurricane Bertha in 1996 that caused damage in the Caribbean and eastern US. It then provides an overview of typical weather phenomena and how extreme events occasionally emerge. It describes how weather is recorded and climate is characterized. It explains that the troposphere is the lowest layer of the atmosphere. It discusses objectives to understand the lower atmosphere and how weather affects climate. It outlines factors that influence air temperature like solar radiation, water vapor, cloud cover, surface type, elevation, and air movement.

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

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

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

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

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

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

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)

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

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

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

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

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

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

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

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’

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