Intermittency and the Exchange of Scalars in the Nocturnal Surface Layer |
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| Authors: | Otávio C Acevedo Osvaldo L L Moraes Gervásio A Degrazia Luiz E Medeiros |
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| Institution: | (1) Departamento de Física, Universidade Federal de Santa Maria, Santa Maria, RS, 97105-900, Brazil |
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| Abstract: | The determination of nocturnal surface fluxes in low wind conditions is a major problem for micrometeorological studies. The
eddy correlation technique, extensively used in field measurements, becomes inappropriate if not enough turbulent activity
exists. At the same time, the phenomenon of turbulence intermittency is responsible for the existence of localized events
of short duration within which a large fraction of the total nighttime scalar exchange occurs. The scalar flux within a certain
intermittent event varies considerably depending on the window used for the flux calculation. In many cases, events with very
different time durations occur in the same night, and therefore, the proper determination of the surface flux would require
averaging within data windows of different sizes for each event. In this work, the surface exchanges of temperature, moisture
and carbon dioxide are analysed at a micrometeorological tower at southern Brazil. Intermittent turbulence is a common occurrence
at the location. The analysis shows that the fluxes vary with turbulence intensity and the estimation technique. A variable-window
size method for flux estimation is suggested and shown to cause an increase in the magnitude of the nocturnal surface fluxes |
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| Keywords: | Intermittency Nocturnal Fluxes Stable boundary layer |
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