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Introduction To Weather Dynamics

Introduction To Weather Dynamics. What you will learn…. In this chapter, you will… Describe Earth’s energy budget Explain how energy is transferred between and among land, air and water Describe weather-related properties of the atmosphere such as pressure and humidity

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Introduction To Weather Dynamics

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  1. Introduction To Weather Dynamics

  2. What you will learn… • In this chapter, you will… • Describe Earth’s energy budget • Explain how energy is transferred between and among land, air and water • Describe weather-related properties of the atmosphere such as pressure and humidity • Explain how areas of high and low pressure move air and energy around the globe

  3. Meteorology The study of the Earth’s atmosphere and weather systems.

  4. Climate A widespread, long-lasting and recurring conditions of the atmosphere.

  5. Weather(page 10) The day to day changes in the atmosphere at a particular location on Earth.

  6. Components of Weather(see Table 1.1, page 11)

  7. Earth’s Energy Budget(page 13)

  8. Types of Energy Transfer - Conduction • Requires contact between atoms; more energetic atoms collide with more energetic atoms and energy is transferred

  9. Types of Energy Transfer - Convection • In a gas or liquid, atoms are free to move and as they warm, they will move away from the heat source and be replaced by cooler atoms

  10. Types of Energy Transfer - Radiation • Energy is transmitted as photons (electromagnetic radiation); does not require a medium

  11. Solar Radiation • Is composed primarily of: • Infrared • Visible • Ultraviolet Light • Solar constant is defined as the amount of radiant energy that hits one square meter of the Earth’s outer atmosphere every second (1362 J/s/m2) • Unit of energy  Joule (J) • See Figure 1.7, page 17 • Greenhouse Effect – the warming of Earth as a result of greenhouse gases (CO2, water), which trap some of the energy that would otherwise leave Earth

  12. Solar Radiation Arriving at Earth’s Surface (see Figure 1.4, page 14)

  13. Terrestrial Radiation • Earth would constantly increase in temperature if it did not radiate energy back to space. • It would take approximately 25 years for the oceans to boil if no energy was emitted back to space • Terrestrial Radiation is composed primarily of infrared photons (light) • Albedo – the reflectivity of a surface

  14. Energy Transfer & Water • Specific Heat Capacity – a property of a substance that determines the rate at which energy is absorbed or release • Water has a higher specific heat capacity than land and air • Heat Sink – any substance that can absorb and keep a “pool of energy without changing state • Water is a good heat sink  thus major weather factor!

  15. Has a large specific heat capacity in all three states Gas 2080 J/kg/°C Liquid 4186 J/kg/°C Solid 2050 J/kg/°C This means that water has the ability to absorb large amounts of energy with a small temperature change Has a large heat of vapourization (liquid to gas transition) Has a large heat of fusion (solid to liquid transition) This means that water will also absorb large amounts of energy as it changes state Energy Transfer & Water

  16. Energy Transfer & Water

  17. Humidity Humidity • Humidity – the amount of water vapor in the air • Warmer air can hold more water than cooler air • Air at -20°C can hold 0.78g of water per kg • Air at 0°C can hold 3.84g of water per kg • Air at 20°C can hold 15.0g of water per kg • Since it varies with temperature, we usually discuss relative humidity

  18. Relative Humidity Relative Humidity • Relative humidity is the measure of how saturated the air is • It is calculated by dividing the amount of water in the air by the amount of water that can be held by the air and is reported as a percentage • Dew Point – the temperature at which air is saturated with water vapor so that it condenses and falls as precipitation

  19. See Figure 1.9, page 20

  20. Water (Hydrological) Cycle Water Cycle

  21. Layers of the Atmosphere

  22. Layers of the Atmosphere • Atmospheric Pressure – the pressure exerted by air on its surroundings due to the weight of the air • Measured in kilopascals (kPa) • At sea level, the atmospheric pressure is 101.3 kPa (or 1 kg/cm3)

  23. Layers of the Atmosphere See Figure 1.8, page 19

  24. Layers of the Atmosphere Layers of the Atmosphere • Troposphere • All water vapour is present here • All weather occurs here • From surface to ~10km • Temperature ranges from -50°C to 50°C • Stratosphere • Ozone is present here • From 10km-50km • Temperature ranges -50°C to -30°C

  25. Layers of the Atmosphere • Mesosphere • Meteorites burn up here • Some ions are present here • From 50km to 90km • Temperature ranges from -30°C to -90°C • Thermosphere • Aurora present • Some ions are present here • From 90km to 180km (space) • Temperature ranges from -90°C to over 200°C

  26. Layers of the Atmosphere Ionosphere • Ionosphere -Light from the sun is powerful enough to ionize atoms (remove electrons) -This results in a layer of ions in the upper atmosphere that reflects radio waves

  27. The Causes of Weather Science 10

  28. Latitude Degrees north and south of the equator Range from 90°N (north pole) to 90°S (south pole) passing through 0° (equator) Lines are all equidistance apart

  29. Longitude Degrees east and west of the prime meridian Ranges from 180°E (international date line) to 180°W (international date line) through 0° (prime meridian) Lines are furthest apart at the equator and closest together at the poles

  30. Sun’s Rays The angle that the radiation from the Sun strikes the Earth is important to local climate conditions Approximately perpendicular at the equator See Figure 1.11, page 26

  31. Tilt of the Earth Earth’s poles are not oriented perpendicularly to the orbital axis This results in seasonal variation The angle is approximately 23.5° Note: seasons are not due to how close Earth is to Sun, i.e. Earth is 3% closer to Sun during winter months in NH (see Figure 1.13, page 27)

  32. Four Seasons Four main positions: Summer solstice (Jun 21) Autumnal equinox (Sep 23) Winter solstice (Dec 21) Vernal equinox (Mar 20)

  33. Circles and Zones Arctic Circle 24 hours of daylight during NH summer Antarctic Circle 24 hours of daylight during SH summer Tropic of Cancer Direct sunlight on Jun 21 Tropic of Capricorn Direct sunlight on Dec 21

  34. Air Masses Air will have different characteristics depending on where it forms Air Mass – a very large mass of air that has nearly uniform properties, i.e. temperature, humidity, pressure There are two main regions: Polar Tropical There are two main types: Maritime Continental

  35. See Figure 1.14, page 28

  36. Air Masses of North America See Table 1.2, page 28

  37. Worldwide Wind and Ocean Currents Science 10

  38. Global Warming and Cooling of Air Air is warmest at the equator and coolest at poles So air should rise at the equator and sink at the poles However, due to the size of the Earth, air from the equator cools before it reaches the poles and air from the poles will warm before it reaches the equator See Figures 1.16.1.17, page 30

  39. Actual Wind Currents Air from the equator will cool by about 30° latitude and sink Air from the pole will warm by about 60° latitude and rise Further, air descends at 30° and rises at 60°

  40. Coriolis Effect Due to the rotation of the Earth, any object that moves across the surface of the Earth will be pushed to the left or right The deflection direction is shown in the diagram

  41. Global Wind Patterns Main wind currents: Polar Easterlies (north and south) Prevailing Westerlies (north and south) Northeast Tradewinds (north only) Southeast Tradewinds (south only) See Figure 1.19, page 31 Note: ‘prevailing’ means to the usual direction from which the wind blows!

  42. Global Wind Systems See Table 1.3, page 31

  43. Jet Streams A narrow band of fast-moving wind Polar Easterlies collide with Prevailing Westerlies Warmer Prevailing Westerlies climb over the cooler Polar Easterlies and result in a fast moving stream of air at the edge of the troposphere Aided by Coriolis Effect Up to 300 kph Altitude 10 – 12 km

  44. Polar Jet Streams Major jet streams are polar jet streams Separate the polar easterlies from prevailing westerlies in NH and SH Occur between 40o to 60o N & 40o to 60o S Move west to east See Figure 1.20, page 32

  45. Subtropical Jet Streams Minor jet streams are subtropical jet streams Occur where tradewinds meet polar westerlies Occur between 20o to 30o N & 20o to 30o S Move west to east Storms form along jet streams & cause large-scale weather systems (i.e. their intensity Weather systems usually follow path of jet streams See Figure 1.20, page 32

  46. Ocean Currents Due to the uneven heating of the oceans, convection currents are established Cold currents carry cold air and warm currents carry warm air so continental weather is affected by the currents

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