EG1204: Earth Systems: an introduction

1. EG1204: Earth Systems: an introduction Meteorology and Climate Dr Mark Cresswell Structure of the atmosphere & oceans

2. Topics we will cover • Introduction to lecture series & basic Astronomy • Composition of the atmosphere • Vertical structure of the atmosphere • Relationships between pressure, temperature and height • Introduction to the oceans • Structure of the oceans • Characteristics of oceans and circulation

3. 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.

4. Suggested References #2 Scientific Journals: • Quarterly Journal of the Royal Meteorological Society • Monthly Weather Review • Meteorological Applications • Journal of Climatology

5. 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/

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. 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

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

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

11. Composition of the atmosphere

13. 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

14. 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)

15. 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

16. 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

17. 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

19. Relationship between temperature and height

21. Introduction to the Oceans • The oceans occupy 71% of the earth’s surface • Over 60% of global ocean surface is in the southern hemisphere • Three quarters of the ocean area is between 3,000 and 6,000 metres deep

22. Structure of the Oceans • The thermocline is a layer characterised by decreasing temperature and increasing density with depth • The thermocline is stratified and inhibits vertical mixing

23. Structure of the Oceans • Below the thermocline layer is the deep layer of cold, dense water • Deep layer motion is mostly driven by density variations due to salinity change