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 Physical Climatology: Field Methods

GEOG 5231/4231 - Fall 2001

Professor Konrad Steffen
CIRES Ekeley Building, S264
Tel o: 492 4524; h: 494 6276
e-mail koni@seaice.colorado.edu


Lab II

Objectives 

  • Calibration of temperature, humidity and wind sensors 
  • Evaluation of temperature, humidity and wind 
  • Evaluation of radiative fluxes 
  • Evaluation of conductive fluxes 

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    Relative Calibration of temperature, humidity and wind sensors
    a) Select one instrument as the reference (e.g. mean wind speed, sensor 1)
    b) Derive the mean difference between wind sensor 1,2,and 4 for the entire measuring period.
    c) Derive the mean wind difference between the wind sensors for certain wind speed levels (e.g. 0-2 m/s, 2-4  m/s, …). Compare the results from a) and b). 
    d) Propose a correction function for wind sensors 2,3 based on your analysis above.

    Tito for the relative calibration of humidity and temperature. 

    Ground heat flux
    Calculate the ground heat flux based on the heat flux plates and the thermister temperature profile. Use the soil temperature that was closest to the surface - but check first if there was some direct radiative heating.
     

    Plot the temperature and wind profile, eg, log(z) versus T and V.
    The following two plots are temperature and wind plotted against height in logarithmic scale.  T1 and T2 refer to “time 1” and “time 2,” respectively. Plot this graph for an afternoon and night period.

    Richardson number
    The Richardson Number is a convenient means of categorizing atmospheric stability (and the state of turbulence) in the lowest layers, expressed by the following equation:

          Ri = (g/Tbar)*[(DTbar/Dz)/(DUbar/Dz)2]

    where g = acceleration due to gravity, and Tbar = mean temperature in the layer Dz, and Ri is a dimensionless number.  Richardson’s Number relates the relative roles of buoyancy (numerator) to mechanical (denominator) forces (i.e., free to forced convection) in turbulent flow.  Thus in strong lapse (unstable) conditions, the free forces dominate and Ri is a negative number which increases with the size of the temperature gradient but is reduced by an increase in the wind speed gradient.  In an inversion (stable) condition, Ri is positive, and in neutral conditions, Ri approaches zero.

    Calculate the Richardson number for the follwong time periods: ~ 4 PM, ~10 PM, ~3 AM, and ~ 10 AM

    General reading: 
    Book: Boundary layer Climates (Oke, 1987): 

  • Appendix 2: Evaluation oif Energy and Mass Fluxes, p. 357-391.

    • Boundary Layer Meteorology (Stull, 1999):
  • Chapter 10: Measurements and simulation techniques (405-440)

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    Lab report II is due on November 8, 2001