On the turbulent Prandtl number in the stable atmospheric boundary layer |
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| Authors: | Andrey A Grachev Edgar L Andreas Christopher W Fairall Peter S Guest P Ola G Persson |
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| Institution: | (1) Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA;(2) NOAA Earth System Research Laboratory, Boulder, CO, USA;(3) NorthWest Research Associates, Inc. (Bellevue Division), Lebanon, NH, USA;(4) Naval Postgraduate School, Monterey, CA, USA |
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| Abstract: | This study focuses on the behaviour of the turbulent Prandtl number, Pr
t
, in the stable atmospheric boundary layer (SBL) based on measurements made during the Surface Heat Budget of the Arctic Ocean
experiment (SHEBA). It is found that Pr
t
increases with increasing stability if Pr
t
is plotted vs. gradient Richardson number, Ri; but at the same time, Pr
t
decreases with increasing stability if Pr
t
is plotted vs. flux Richardson number, Rf, or vs. ζ = z/L. This paradoxical behaviour of the turbulent Prandtl number in the SBL derives from the fact that plots of Pr
t
vs. Ri (as well as vs. Rf and ζ) for individual 1-h observations and conventional bin-averaged values of the individual quantities
have built-in correlation (or self-correlation) because of the shared variables. For independent estimates of how Pr
t
behaves in very stable stratification, Pr
t
is plotted against the bulk Richardson number; such plots have no built-in correlation. These plots based on the SHEBA data
show that, on the average, Pr
t
decreases with increasing stability and Pr
t
< 1 in the very stable case. For specific heights and stabilities, though, the turbulent Prandtl number has more complicated
behaviour in the SBL. |
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| Keywords: | Richardson number SHEBA Stable boundary layer Turbulent Prandtl number |
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