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EG4508: Issues in environmental science. Meteorology and Climate Dr Mark Cresswell The Atmosphere 1. Suggested References #1. Text Books:. Ahrens, C. Donald. (2000) Meteorology today : an introduction to weather, climate, and the environment.

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eg4508 issues in environmental science

EG4508: Issues in environmental science

Meteorology and Climate

Dr Mark Cresswell

The Atmosphere 1

suggested references 1
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
Suggested References #2

Scientific Journals:

  • Quarterly Journal of the Royal Meteorological Society
  • Monthly Weather Review
  • Meteorological Applications
  • Journal of Climatology


suggested references 3
Suggested References #3


  • KNMI climate explorer:
  • Royal Meteorological Society:
  • The Met. Office:
general points
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
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 astronomy1
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
basic astronomy2
Basic Astronomy
  • The Earth completes a single revolution around the Sun in approx 365 days (365.256 days) - period is known as a year
basic astronomy3
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
basic astronomy4
Basic Astronomy
  • Axis about which the earth rotates tilts





basic astronomy5
Basic Astronomy

SUMMER (N. Hemisphere) WINTER (N. Hemisphere)

basic astronomy6
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
basic astronomy7
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
basic astronomy8
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.
basic astronomy9
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
basic astronomy10
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
vertical structure 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 atmosphere1
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 atmosphere2
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 atmosphere3
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
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

energy basic laws and theory
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
energy basic laws and theory1
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

energy basic laws and theory2
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
energy basic laws and theory3
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
energy basic laws and theory4
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
energy basic laws and theory5
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
temperature scales
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
temperature scales1
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
specific heat and latent heat
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
specific heat and latent heat1
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
specific heat and latent heat2
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
energy transfer in the atmosphere
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

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!

emr and the sun atmosphere system
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
emr and the sun atmosphere system1
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
emr and the sun atmosphere system2
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
emr and the sun atmosphere system3
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
the earth s energy balance
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.
greenhouse effect
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