EG4508: Issues in environmental science

1. EG4508: Issues in environmental science Meteorology and Climate Dr Mark Cresswell The Atmosphere 1

2. Suggested References #1 Text Books: • Ahrens, C. Donald. (2000) Meteorology today : an introduction to weather, climate, and the environment. • Harvey, Danny. (2000) Climate and global environmental change • Burroughs, William James. (2001) Climate change : a multidisciplinary approach. • Climate change 2001 : The scientific basis / edited by J.T. Houghton • McGuffie K and Henderson-Sellers A. (1997). A climate modelling primer. Published by John Wiley, England.

3. Suggested References #2 Scientific Journals: • Quarterly Journal of the Royal Meteorological Society • Monthly Weather Review • Meteorological Applications • Journal of Climatology SEE UKSCIENCE METEOROLOGY PAGES FOR MORE INFO

4. Suggested References #3 Internet: • KNMI climate explorer: • http://climexp.knmi.nl • Royal Meteorological Society: • http://www.royal-met-soc.org.uk/ • The Met. Office: • http://www.meto.gov.uk/ • NOAA-ENSO: • http://nsipp.gsfc.nasa.gov/enso/

5. WWW.UKSCIENCE.ORG  EGS UNITS  EG4508 LINK

6. General Points • The atmosphere behaves like a fluid • The atmosphere is a mixture of different gases, aerosols and particles • The atmosphere remains around the earth as an envelope because of gravity • Much of the observed motion in the atmosphere results from solar radiation

7. Basic Astronomy • For most of the Earth, energy varies on daily (diurnal) and seasonal (annual) time-scales. • Changes from daytime to night and progression through the four seasons depends on the configuration of the Earth-Sun orbit

8. Quantity of solar radiation may vary as a result of solar activity

9. Solar wind increases in magnitude at times of high sunspot activity

10. Basic Astronomy • The Earth completes a single rotation about its axis in approx 24 hours (23.9345 hours!) - this period is known as a day

11. Basic Astronomy • The Earth completes a single revolution around the Sun in approx 365 days (365.256 days) - period is known as a year

12. Basic Astronomy • Energy received at different points on the earth’s surface is not constant • As we move from the equator to the poles the quantity of energy decreases • This is due to Earth curvature • The same amount of energy is spread over a greater area and has to pass through a thicker layer of the atmosphere

14. Basic Astronomy • Axis about which the earth rotates tilts Spring Summer Winter Autumn

15. Basic Astronomy SUMMER (N. Hemisphere) WINTER (N. Hemisphere)

16. Basic Astronomy • The Earth does not spin perfectly about its axis - but tilts to trace a cone in space - caused by the combined Sun and Moon’s gravitational pull and is called precession • This tilt angle varies - between about 22º and 25º - it is currently 23.5º

17. Basic Astronomy • In addition to tilt - the elliptical orbit the Earth takes around the Sun varies also • Mean distance between the Earth and the Sun is 1AU (1.496 x 108 km). Minimum distance is 0.983AU and the maximum distance is 1.017AU

18. Basic Astronomy • In addition, the Earth’s path along its ellipse will vary slightly due to differential gravitation pull. This is known as the eccentricity of the orbit.

19. Basic Astronomy • The combination of factors such as orbital eccentricity, precession, tilt angle, distance from the Sun etc greatly affect our climate by varying the quantity of solar energy received • Collective term is Orbital Forcing • May have influenced the magnitude and period of past ice ages

20. Basic Astronomy • The gravitational pull of the moon affects our tides and also moderates energy levels in the oceans • Ocean dynamics greatly influences our Earth’s climate system

21. Composition of the atmosphere

23. Vertical structure of the atmosphere • Weight is the mass of an object multiplied by the acceleration of gravity Weight = mass x gravity • An object’s mass is the quantity of matter in the object

24. Vertical structure of the atmosphere • The density of air is determined by the mass of molecules and the amount of space between them Density = mass/volume • Density tells us how much matter is in a given space (or volume)

25. Vertical structure of the atmosphere • Each time an air molecule bounces against an object it gives a tiny push • This small pushing force divided by the area on which it pushes is called pressure Pressure = force/area

26. Vertical structure of the atmosphere • In meteorology we discuss air pressure in units of hectopascals (hPa) (previously called millibars mb) • The average atmospheric pressure at the Earth surface is 1013.25 hPa • We can sense sudden changes in pressure when our ears ‘pop’ such as that experienced in old aircraft

27. Relationship between pressure and height • As we climb in elevation (up a mountain or in a hot air balloon) fewer air molecules are above us: atmospheric pressure always decreases with increasing height

29. Energy: basic laws and theory • Energy is the ability or capacity to do work on some form of matter • Energy is transformed when it interacts with matter - e.g. potential energy is transformed into kinetic energy when a brick falls to the ground • Matter can neither be created nor destroyed - only change form

30. Energy: basic laws and theory • The energy stored in an object determines how much work it can do (e.g. water in a dam). This is potential energy PE = mgh PE = potential energy m = mass of the object g = acceleration of gravity h = object’s height above the ground

31. Energy: basic laws and theory • A volume of air aloft has more potential energy than the same volume of air above the surface • The air aloft has the potential to sink and warm through a greater depth of the atmosphere • Any moving object possesses energy of motion or kinetic energy

32. Energy: basic laws and theory • The kinetic energy of an object is equal to half its mass multiplied by its velocity squared: KE = ½ mv2 • The faster something moves, the greater its kinetic energy. A strong wind has more kinetic energy than a light breeze

33. Energy: basic laws and theory • Temperature is a measure of the average speed of the atoms and molecules, where higher temperatures correspond to faster average speeds • If a volume of air within a balloon were heated the molecules would move faster and slightly further apart - making the air less dense • Cooling air slows molecules down and so they crowd together becoming more dense

34. Energy: basic laws and theory • Heat is energy in the process of being transferred from one object to another because of the temperature difference between them

35. Temperature scales • Hypothetically, the lowest temperature attainable is absolute zero • Absolute zero is -273.15 ºC • Absolute zero has a value of 0 on a temperature scale called the Kelvin scale - after Lord Kelvin (1824-1907) • The Kelvin scale has no negative numbers

36. Temperature scales • The Celsius scale was introduced in the 18th century. The value of 0 is assigned to the freezing point of water and the value 100 when water boils at sea-level • An increasing temperature of 1 ºC equals an increase of 1.8 ºF

37. Specific heat and latent heat • Liquids such as water require a relatively large amount of heat energy to bring about just a small temperature change • The heat capacity of a substance is the ratio of the amount of heat energy absorbed by that substance to its corresponding temperature rise

38. Specific heat and latent heat • The heat capacity of a substance per unit mass is called specific heat • Specific heat is the amount of heat needed to raise the temperature of one gram (g) of a substance by one degree Celsius • 1g of liquid water on a stove would need 1 calorie (cal) to raise its temperature by 1 ºC

39. Specific heat and latent heat • When water changes its state (solid to liquid, liquid to gas etc) heat energy will be exchanged • The heat energy required to change a substance from one state to another is called latent heat • Evaporation is a cooling process • Condensation is a warming process

40. Energy transfer in the atmosphere • Conduction: transfer of heat from molecule to molecule (hot spoon) • Convection: transfer of heat by the mass movement of a fluid (such as water and air) • Radiation: Movement of energy as waves - the electromagnetic spectrum

41. Electromagnetic spectrum with enhanced detail for visible region of the spectrum Note the large range of wavelengths encompassed in the spectrum - it is over twenty orders of magnitude!

43. EMR and the Sun-atmosphere system • About 50% of incoming solar radiation is lost by the atmosphere: scattered (30%) and absorbed (20%) • Scattering involves the absorption and re-emission of energy by particles • Absorption (unlike scattering) involves energy exchange

44. EMR and the Sun-atmosphere system • Wavelengths less than and greater than 0.8µm (800nm) are often referred to as shortwave and longwave radiation respectively • The shortwave solar radiation consists of ultraviolet and visible • The terrestrial longwave component is known as infrared

45. EMR and the Sun-atmosphere system • Just under 50% of the radiation reaching the Earth’s surface is in the visible range • Components of visible light are referred to as colours • Each colour behaves differently and white light can be separated out by use of a prism

46. EMR and the Sun-atmosphere system • The human eye cannot see infrared radiation • Infrared radiation is absorbed by water vapour and carbon dioxide in the troposphere • The atmosphere’s relative transparency to incoming solar (SW) radiation, and ability to absorb/re-emit outgoing infrared (LW) radiation is the natural greenhouse effect

47. The Earth’s energy balance • Incoming solar (shortwave) energy should be balanced by outgoing terrestrial (longwave) energy • Without a balance the Earth would heat up or cool down uncontrollably • Energy may take a tortuous path from Sun to ground and back to space.

48. Greenhouse effect • The natural greenhouse effect maintains a stable climate for life on earth • Outgoing radiation (longwave) is absorbed by molecules such as water vapour and carbon dioxide • Energy is then re-emitted in all directions - forming a blanket

49. Greenhouse Effect