Meteorology Lecture 1

1. Meteorology Lecture 1 Weather and Climate Review

2. What drives our weather? • The sun • Insolation – solar energy reaching the Earth • Remember the sun’s output can vary, which impacts weather on Earth • e.g. The Little Ice Age

3. Folklore: Sirius – The Dog Star • Thought to produce heat at the end of summer • Worshipped by numerous civilizations • The “Dog Days of Summer” Sirius Sun

4. What about the Moon? • Does it warm the Earth? • Why does it glow? • Albedo – % of insolation an object reflects • High – light surfaces • Low – dark surfaces

5. Solar Radiation and Earth’s Surface

6. Why do we have seasons?

7. Sun conditions at the Solstices and Equinoxes

9. Solar declination: latitudinal change ofsubsolar points

10. Energy Pathways Figure 4.1

11. Heat Transfer • Heat – energy produced by the motion of molecules and atoms in a substance • 4 ways to transfer heat: 1. Radiation – electromagnetic waves (sunlight) 2. Conduction – energy moved from high to low 3. Convection – vertical movement of energy 4. Advection – horizontal movement of energy

12. Earth’s Modern Atmosphere • The atmosphere is absolutely essential for life on Earth • Earth’s atmosphere exists in a series of spheres or layers that grade into one another   • Layers: Composition, temperature, and function 

14. Protective Atmosphere Figure 3.6

15. Energy Balance in the Troposphere   • Greenhouse Effect – where gases (carbon dioxide, water vapor, methane, nitrous oxide, and CFCs) absorb insolation and reradiate it back to Earth in longer wavelengths thereby warming the lower troposphere • The Greenhouse Effect and Atmospheric Warming • Atmosphere absorbs heat energy • Atmosphere delays transfer of heat from Earth into space

16. Local Factors Influencing Air Temperature • Urban Effect • Urban Heat Island • Darker surfaces – less reflection • Less forest cover • Less water on surface • Heat from human energy use

17. The Urban Environment Figure 4.21

18. Urban Heat Island Figure 4.22

19. Global NET R • Surfaces lose heat in one of 3 ways: • Latent heat of evaporation – energy released as water changes state; can’t feel it • Sensible heat – heat you can feel and measure; convection and conduction • Ground heating and cooling – energy stored during warm periods and released during cool periods

20. Radiation Budgets El Mirage, CA Pitt Meadows, BC Figure 4.20

21. Principal Temperature Controls • Latitude • Altitude • Cloud Cover • Land-Water Heating Differences

22. Latitude and Temperature • Latitude   • Affects insolation • Sun angles • Daylength Figure 5.4

23. Altitude • Altitude   • High altitude has greater daily range • High altitude has lower annual average Figure 5.5

24. Cloud Cover

25. Land–Water Heating Differences  • Evaporation (= latent heat) • Transparency (= penetration of insolation) • Specific heat (differs among objects) • Movement (= vertical mixing) • Ocean currents and sea surface temperatures(= spread of energy spatially) All this leads to this important concept:Marine vs. continental effects

26. Land–Water Heating Differences   Figure 5.7

27. Global Temperature Ranges Figure 5.17

28. Atmospheric Pressure Systems High-pressure system -also called anticyclone -circulating body of air -descending air -clockwise circulation in northern hemisphere Low-pressure system -also called cyclone -circulating body of air -rising air -counterclockwise circ. in northern hemisphere

29. Atmospheric Pressure Map Isobars – lines of equal air pressure on a map

30. Wind Direction Winds are named according to the direction FROM which they are blowing

31. Direction of Air Flow • Unequal heating of land surfaces • Pressure gradient force – air flows from high to low • Coriolis force – deflection or change in direction caused by Earth’s rotation • Frictional forces – places a drag on that air flow

32. Pressure Gradient Force High pressure to low pressure, perpendicular to isobars Fluctuations in the Pressure Gradient

33. Coriolis Force • Due to Earth’s rotation • Pulls wind to right in northern hemisphere • Pulls wind to left in southern hemisphere • Strongest at poles • None at equator Coriolis Force

34. Frictional Forces • Near surface, friction (f) works against pressure gradient force (pgf), so resulting wind direction is between pressure gradient force and coriolis force (cf) WIND pgf cf – northern hemisphere f

35. Three Forces Combined

36. Rossby Waves Figure 6.17

37. The Polar Front and Jet Streams • Strong boundaries often occur between warm and cold air. In the mid-latitudes, the polar front marks this thermal discontinuity at the surface.

38. Relative Humidity • Relative humidity is the indication of how close the air is to saturation and when condensation will begin • Dew-point temperature not really a temperature, but a measure of moisture content • When air temperature tries to decrease below the dew point, surplus water vapor is removed from the air by condensation

39. Cooling Warming Relative Humidity Actualwater vapor Figure 7.8

41. Hydrologic Cycle