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Agricultural Science
Climatology
Semester 2, 2007
Richard Thompson
http://www.physics.usyd.edu.au/Ag/agschome.htm
Course Coordinator: Mike Wheatland
LECTURE FIVE
“Our Atmosphere”
Chapter 3
Our Atmosphere
Composition of the Atmosphere
Atmospheric Pressure at Sea Level
• Standard atmospheric pressure is defined as
101,325 Pascals (1 atm) which is actually a
typical sea level pressure for mid latitude
regions on Earth
• Pressure is force per unit area. A Pascal is a
Force of 1 Newton/square metre. A mass of 1 kg
has a weight of 9.8 newtons
• Approximately, a mass of 1 kg spread over 1cm2
exerts a pressure equal to that of the
atmosphere
Units of Atmospheric Pressure
• 1atm = 101325 Pa
• 1atm = 101.325 kPa
• 1atm = 1013.25 millibars (mbar or mb) or
hectopascals (hPa) [hec is a unit for 100
which is rarely used elsewhere]
• 1atm = 760.001 mm-Hg at 0 degrees
Celsius
Aneroid Barometers
Source: www.stuffintheair.com
Mercury Barometer
Australian Bureau
of Meterology
Methods of Heat Transfer Through
Atmosphere
• Radiation – can even occur in a vacuum
• Conduction – direct contact needed;
atomic collisions enable heat transfer
• Convection and winds – transfer by bulk
motion of air or liquid mass
Strata in the Atmosphere
From Surface Going Upwards
• Troposphere (0-10km) – 80% mass of
atmosphere; all water vapour & aerosols;
tropopause caps weather, turbulence
• Stratosphere (10-50km) – protective
ozone layer; rising temperature; bounded
by stratopause
Strata in the Atmosphere (2)
Higher Still
• Mesosphere (50-80km) – thin, cold
• Ionosphere (80-600km) – ionised, heated
by UV, reflects radio waves
Temperature
Profile in
Earth’s
Atmosphere
source: UCAR
Structure of the Atmosphere (1)
Structure of the Atmosphere (2)
Ionosphere (1)
Ionosphere (2)
• A region of charged particles between around
50km to 600km above the earth’s surface
• Formed by energetic radiation from the sun
stripping electrons from the atoms of the
atmosphere (ionisation)
• Consists of several layers (D, E, F1, F2), the
character of which changes during the day and
after activity generated by the sun (space
weather)
• Important for a number of reasons, especially for
HF communication which are cheap and flexible.
Map of the Ionosphere
University of Berne
Radio Communication via the
Ionosphere
Space Weather Effects
Source: Bell Laboratories
Space Weather Effects
NASA/ESA
Mesosphere
• Between 50 and 80km above surface
• Above aircraft flight altitudes but below typical
orbits of satellites (meaning that the region is
less well understood than the others)
• Temperature decreases with increasing altitude
falling as low as 200K at the top of the layer
(depending on latitude and season)
• Meteors generally burn up in this layer
• Location of noctilucent clouds
Stratosphere
• Located at 10 to 50km above surface
• Location of the ozone layer (15-30km altitude)
which is formed by ionisation by UV radiation
from the sun
• Ozone layer protects life on Earth by absorbing
UV radiation
• Temperature is essentially constant in the lower
part of the stratosphere and there is little mixing
of air.
Troposphere (1)
• Located from 0 to 10km above the surface
• Layer in which most ‘weather’ takes place
• Contains 80% of total atmosphere and virtually
all of the water vapour
• Zone is often capped by a temperature inversion
layer (warm air over a colder layer) which makes
layer self-contained
• This is called the tropopause and its altitude is
not constant, either in location or time
• Typically around 16km at equator and 8km at
poles
Troposphere (2)
• Uneven heating in the troposphere (e.g.
between equator and poles) cause
atmospheric convection currents which
move air and moisture around globe
• It is these circulation patterns than gives
rise to climate zones (e.g. monsoon
regions; desert zones etc).
Weather patterns & circulation in
Troposphere
• Attenuation of solar radiation – reflected, absorbed,
scattered, transmitted.
• Uneven heating causes convection currents (Equator to
poles).
• High & low pressure areas also cause currents.
• Rotation of Earth deflects air (Coriolis force).
• Local turbulence disrupts patterns.
• Convection transports heat vertically; horizontal heat
transfer is called advection (advection fog caused by
warm sea air moving over cold land)
(pages 47, 160)
Atmospheric Circulation Patterns
Global Climate Zones
Australian Rainfall
Climate Zones of Australia
Australian Climate Zones