 |
| Titel |
Turbulence measurements in an Alpine valley: The CividatEX Experiment case |
| VerfasserIn |
Marco Falocchi, Stefano Barontini, Dino Zardi, Roberto Ranzi |
| Konferenz |
EGU General Assembly 2015
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250111961
|
| Publikation (Nr.) |
 EGU/EGU2015-12115.pdf |
|
|
|
|
|
| Zusammenfassung |
| Results regarding the analysis of turbulence data, collected during Summer 2012, 2013 and
2014 in the framework of the CividatEX Experiment, are presented. The CividatEX
Experiment, kicked off in July 2012 and still ongoing, aims at quantifying the mass
and energy fluxes exchanged at the soil–atmosphere interface in an Alpine valley.
A micro–meteorological station, equipped with standard meteorological devices,
four TDR probes, soil heat–flux plate, soil thermometers and an eddy–covariance
system (sonic anemometer and gas analyser), was installed on the valley floor of
Valle Camonica at Cividate Camuno (274ma.s.l., Oglio river basin, Central Italian
Alps).
The experimental site is a gentle–sloping Technosol lawn, covered by common grass and
surrounded by a steep hill (E and S) and by an anthropized landscape (W and N). Such
complex terrain conditions affect the wind regime that, especially during fair weather
conditions, is mainly regulated by thermally–driven winds. At least three winds
were recognized, i.e. (1) the local wind Óra del Sebino (WSW, speed ranging from
2 to 4 ms-1), which rises the valley from Lake Iseo (Sebino) in the afternoon;
(2) a katabatic flow with small speed (from 0.5 to 1.5 ms-1) blowing down the
hillslope (directions ranging from E to SE) since the evening to the sunrise; and
(3) an up–slope cross–valley wind (W, from 0.5 to 1.5 ms-1) flowing in the late
morning.
The 15 and 30–minutes eddy–covariance fluxes of momentum (Ï), latent heat (λE) and
sensible heat (Hs) were estimated using the software EddyPro. The surface energy
imbalance was calculated as 1 - (λE + Hs)/(Rn - G), where Rn and G are
the net radiation and the ground heat flux respectively. For all the three data–sets
the imbalance assumes values ranging between 0.3 and 0.4. A dependence of its
magnitude from the atmospheric stability and from the blowing wind was observed. In
fact the imbalance reduces during unstable conditions, when the Óra occurs, and it
increases during the night when the wind speed is small and stable conditions are
approached.
The separation of the turbulent components from the low–frequency unsteadiness of the
mean–flow was investigated by means of three different approaches, that are the block
average, the linear detrending and a digital recursive–filtering technique. The obtained
dimensionless standard deviations of the wind velocities and of the temperature fluctuations
were analyzed in the framework of the Monin–Obukhov similarity theory by checking their
thickening on the similarity relationships. Due to the presence of meaningful unsteadiness
during the investigated time–windows, the block average and the linear detrending were less
effective than the recursive–filtering procedure at separating the turbulent fluctuations from
the mean–flow. |
|
|
|
|
|
|