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
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.
Suggested References #2
Scientific Journals:
• Quarterly Journal of the Royal
Meteorological Society
• Monthly Weather Review
• Meteorological Applications
• Journal of Climatology
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/
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 (23.9345 hours!) - this period is known as a day
Typical Diurnal Air Temperature
25
Temperature (Celcius)
20
15
10
5
0
00:00
06:00
12:00
18:00
00:00
06:00
12:00
Synoptic Hour
18:00
00:00
06:00
12:00
18:00
00:00
Basic Astronomy
• The Earth completes a single revolution around the Sun in
approx 365 days (365.256 days) - period is known as a year
Average Daily Maximum Temperature (London)
mean daily maximum temperature (celsius)
25
20
15
10
5
0
January
February
March
April
May
June
July
Month
August
September
October
November December
Basic Astronomy
• Axis about which the earth rotates tilts
Spring
Summer
Winter
Autumn
Composition of the atmosphere
GAS
PERCENT*
Nitrogen
78.08
Oxygen
20.95
Argon
0.93
Neon
0.0018
Helium
0.0005
Hydrogen
0.00006
Xenon
0.000009
* = Percent by volume dry air
** = Percent by volume
GAS & PARTICLES PERCENT**
ppm
Water vapour
0 to 4
Carbon dioxide
0.036
365
Methane
0.00017
1.7
Nitrous oxide
0.00003
0.3
Ozone
0.000004
0.04
Particles
0.000001 0.01-0.15
Chloroflourocarbons 0.00000002
0.0002
From Ahrens C. D, 2000
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 1013.25 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