Part 1

• Physical geography


  Understanding interactions of processes involving the Earth's climate system, oceans, landforms, animals, plants and people. This understanding requires linking the physical systems together and relating human actions to the physical environment.
• All planning in terms of sustainable development will need to be based on predictions of future conditions - study of weather and climate is integral to this prediction
• Weather


  Sum total of the conditions of the atmosphere (with regard to temperature, atmospheric pressure, wind, rainfall and other elements) at a given place at a given time
• Climate


  Average condition of the atmosphere / integration of weather conditions for a given period of time within a given area
• Climate is what you expect – weather is what you get
• Observing climate


  • Ground-based automatic weather stations (AWS)
  • Radiosondes
  • Weather radar
  • Satellite-based remote sensing

  
• Automatic Weather Stations

  Ground-based, measure/collect the four fundamental microclimate variables, range from simple to complex systems, representational of the microclimate (2km radius)

  
• Radiosondes


  Weather balloons, measure/collect high frequency samples of the atmosphere, also include GPS tracking – wind speed and direction, representational of the total lower atmosphere profile

  
• Weather radar


  Use radiowaves to collect data, useful in collecting rainfall/storm data, lots of developments, can gather data over large areas with good resolution

  
• Satellite-based remote sensing


  Polar-orbiting and geostationary satellites, generally radiation specific variables, active sensors can measure other variables e.g. rainfall

  
• No single system is the best. Need to use each in combination. For climate data: ground-based AWS network is the best. For meteorological data/forecasting/nowcasting: use the other systems too.
• Numerical Weather Prediction (NWP)


  The use of computer models to predict the future state of the atmosphere given observations and equations that describe relevant physical processes

  
• Stages of the Forecasting Process

  1. Data Collection

  2. Quality Control

  3. Data Assimilation

  4. Model Integration

  5. Post Processing of Model Forecasts

  6. Human Interpretation

  7. Product and graphics generation
• Primitive Equations


  Derived from the conservation laws of momentum, mass, energy, and moisture. Used to forecast variables like wind, temperature, and moisture.
• Models must include smaller scale processes/features that cannot be resolved, this is done through parameterization - including the effects of physical processes indirectly when we can't include the processes directly.
• Post Processing


  Statistical processing of models to remove biases and improve quality of predictions, known as Model Output Statistics (MOS)
• Types of models


  • Empirical/Statistical models
  • Theoretical/Dynamical models
• Elements of Weather


  • Atmospheric pressure
  • Air Temperature
  • Atmospheric Humidity
  • Precipitation (rain, snow)
  • Cloud Type (cloud microphysics)
  • Motion (Wind)

  
• Geostrophic winds


  Horizontal wind produced by the balance of the Coriolis force and the horizontal pressure-gradient force, upper level air flow and is parallel to the isobars

  
• Gradient winds


  Horizontal wind produced by balance of Coriolis, centrifugal and horizontal pressure gradient forces with cyclonic or anticyclonic curvature
• SU3: Learning Outcomes


  • Know the typical synoptic patterns observed over southern Africa
  • Interpret a synoptic chart, numerical weather analysis of surface and 500hPa pressure, satellite images and radiosonde sounding to deduce the implications for rainfall and temperature over southern Africa

  
• Geostrophic flow


  Horizontal wind produced by the balance of the Coriolis force and the horizontal pressure-gradient force
• Coriolis force


  Proportional to wind speed
• Stronger PGF


  Causes flow to become ageostrophic & deflected across isobars at an angle in the direction which the PGF acts
• Frictional effect


  Diminishes with height
• Ekman Spiral


  Projection of wind vectors onto the horizontal
• Ekman Layer


  Friction layer
• Gradient wind


  Horizontal wind produced by balance of Coriolis, centrifugal and horizontal pressure gradient forces with cyclonic or anticyclonic curvature
• In gradient flow balance the Pressure-gradient force = the Coriolis + centrifugal forces
• Cyclostrophic wind


  Horizontal circular air motion in which the centrifugal force balances the pressure-gradient force
• In cyclostrophic balance the Pressure-gradient force = centrifugal force
• Convergent air


  Air that moves into an area from more than once direction
• Divergent air


  Air that moves out a region in more than one direction
• Above an area of surface convergence we have an area of divergence in the upper air
• Cyclones


  • Air motion around a low pressure centre
• Anticyclones


  • Air motion around a high pressure centre
• Wind systems


  • Geostrophic winds
  • General surface atmospheric circulation (primary & secondary)
  • Circulation of the upper Atmosphere
  • Tertiary and local winds
  • Ocean-atmospheric circulation
• Wind flow in the upper atmosphere is geostrophic and dominated by ZONAL flow – westerly in its configuration
• Rossby and Kelvin waves


  Periodic deviations from the zonal (west-to-east) flow
• Jet Streams


  Zones of concentrated flow in the upper atmosphere