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

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

Suggested References #1 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. Text Books:

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

Suggested References #3 KNMI climate explorer: – Royal Meteorological Society: – The Met. Office: – NOAA-ENSO: – Internet:

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

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

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

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

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

Composition of the atmosphere

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

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)

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

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 hPa We can sense sudden changes in pressure when our ears ‘pop’ such as that experienced in old aircraft

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

Relationship between temperature and height

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

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

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