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| Titel |
Studying the height of atmospheric stable boundary layer from turbulence moments at different heights |
| VerfasserIn |
Francesco Tampieri, Samuel Viana, Carlos Yagüe |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250049968
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| Zusammenfassung |
| SABLES98 data constitutes a quite comprehensive description of atmospheric stable
boundary layer. Measurements taken at three different heights (5.8, 13.5 and 32 m a.g.l.) with
sonic anemometers and mean wind and temperature at many heights up to 100 m cover
a period from 10 to 28 September 1998. In this work we have used data form 7
consecutive nights forming the so called S-period characterised by weak to strong
stability.
MultiResolution Flux Decomposition (MRFD), which a multiscale technique, has been
applied to sonic data to evaluate the heat and momentum fluxes as well as temperature and
velocity variances. MRFD allows to know what timescales contribute more to the
covariance/variance of the temporal series and it has been used to locate the gap between
turbulence and larges scales, avoiding the ’contamination’ from higher scale motions on the
evaluation of turbulent fluxes or variances evaluated from eddy correlation technique with a
fixed time window.
The analysis presented here focuses on boundary layers that are expected to be directly
influenced by surface fluxes: namely, cases characterised by a decrease of turbulence second
order moments with height. (In detail, we took into consideration vertical fluxes of
momentum and sensible heat, and variances of vertical velocity and temperature
fluctuations.)
The vertical profiles of momentum and heat fluxes proposed by Nieuwstadt (1984) and
Zilitinkevich and Esau (2007) suggest possible dependences of the fluxes on the
height. Both theories give also expressions for the stable boundary layer height.
The functional forms have been fitted on the data, giving best-fit estimates of the
surface fluxes (which are expected to be larger that those measured at the lowest level
available in the tower) and of the boundary layer height, huw and hwt (the first one if
the fit is made on momentum flux measurements, the second one if heat flux is
considered). Also, Zilitinkevich and Esau (2007) formulas have been directly applied
to the measured fluxes at the lowest level, giving another estimate of the height,
hZE.
huw and hwt are different each other, and are different if Zilitinkevich and Esau (2007)
Gaussian shape or Nieuwstadt (1984) power law shape are chosen. However, the values are
broadly consistent. Remarkably, these values appear to be not strongly affected by the values
of the surface fluxes, in the ranges covered by the data set.
hZE is by its definition mainly a function of the surface fluxes (especially in conditions of
strong stability), although its representative value is not too far from that derived by the fitting
procedure.
If the fit is assumed to give an estimate of the stable boundary layer height,
the main result of this study is that this height cannot be expressed as a function
of the surface fluxes only, at variance with the theoretical formulations discussed
here. |
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