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PX350 The Weather and the Environment

Lecturer: David Leadley

Weighting: 7.5 CATS

The diffusion, convection, chemical reactions and the interaction with living organisms, which take place in or at the boundaries of the atmosphere, determine the weather patterns we observe. The module looks at some of these processes. The module also treats the phenomenon of cloud-formation and the role of the earth's rotation in determining flow patterns in the atmosphere.

Aims:

To show how the troposphere 'works'. To show how, with only very simple ideas from mechanics and thermodynamics, one can explain most of what we call 'weather'.

Objectives:

By the end of the module you should:

  • be able to describe the structure and composition of the earth's atmosphere and how it developed.
  • appreciate how motion in the troposphere is driven by the (differential) heating of the earth by the sun.
  • understand how the troposphere transfers heat and matter by convection-generated flows and the effect on these flows of the earth's rotation
  • understand the mechanisms that lead to precipitation
  • be aware of the influence of human activity on the atmosphere and climate

The module is quite descriptive. You will need to develop your ability to be precise and accurate when writing about and describing phenomena, even when not referring to a quantitative theory.

Syllabus:

Description of the atmosphere
Composition: permanent and variable gases
Layer profile: troposphere, stratosphere (ozone layer), mesosphere and beyond
Atmospheric energy balance: surface temperature, albedo and greenhouse effect
Origin of the earth's atmosphere and the role of life in determining past and future climates
Vertical motion and role of water
Atmospheric stability: dry and saturated adiabatic lapse rates
Water vapour: relative humidity, evaporation and condensation
Cloud formation: condensation nuclei, growth by diffusion and accretion
Precipitation: warm rain, the three-stage process
Atmospheric electricity: lightning
Flow Patterns - wind and weather
Pressure gradients and their origins: sea breezes
Mechanics in a rotating frame: Coriolis force, geostrophic wind
Circulation on a global scale: prevailing winds, jet streams
Synoptic scale motion: air masses, fronts, cyclones and accompanying weather patterns
Mesoscale and microscale motion: planetary boundary layer.
Influence of the oceans: El Niño, Gulf Stream.

Commitment: 15 Lectures + examples sheets

The examples sheets are designed to take you through (usually) very simple arguments which explain a number of surprising and familiar phenomena from everyday experience, eg the size of raindrops, why smoke sometimes rises vertically and sometimes is advected downstream by the wind, why the wind direction rotates with height, the relative sizes of the gravitational, Coriolis and other horizontal forces.

This module has its own home page.

Assessment: 1.5 hour examination

Recommended Text: JFR McIlveen, Fundamentals of Weather and Climate, 2nd Ed., Oxford, 2010;
or 1st Ed., Fundamentals of Weather and Climate Chapman & Hall, 1992;
John M. Wallace and Peter V. Hobbs, Atmospheric science : an introductory survey (2nd ed), Academic Press, 2006.

Leads from: The module has no real prerequisites, but draws on some elementary concepts discussed in: PX148 Classical Mechanics and Relativity, PX264 Physics of Fluids