Stationarity of Turbulence in Light Winds during the Maritime Continent Thunderstorm Experiment |
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Authors: | Eric W Schulz B G Sanderson |
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Institution: | (1) School of Mathematics, The University of New South Wales, Australia |
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Abstract: | Non-stationary turbulence can invalidate eddy flux calculations. Two-hour longrecords of wind velocity, temperature and humidity are classified as stationaryor non-stationary based on the behaviour of the flux as a function of Reynoldsaveraging period; a number of indicators of stationarity are investigated. Thetwo-hour Maritime Continent Thunderstorm Experiment wind datasets are notcompletely stationary, as indicated by the lack of a spectral gap, but can beclassified as approximately stationary, when the mean wind speed is greaterthan 3.8 m s-1, or the standard deviation of true wind direction is 10°, or the ratio of horizontal wind variance to wind speed is <0.25. In the stationary case the calculated friction velocity exhibits a 7% decrease on average when the Reynolds averaging period is doubled, while data classified as non-stationaryexhibit an increase of 32%. There is little non-stationary behaviour in the kinematicheat fluxes, and is independent of the non-stationarity of the friction velocity. Thekinematic heat fluxes show small decreases (around 3%) when the Reynolds averagingperiod is doubled. |
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Keywords: | Eddy covariance Stationarity Turbulence flux |
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