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| Titel |
Estimating Turbulence in Mountainous Regions from Airborne In Situ and Remotely-Sensed Data |
| VerfasserIn |
Lukas Strauss, Stefano Serafin, Vanda Grubišić |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250080214
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| Zusammenfassung |
| Turbulence in atmospheric flow over and around orographic obstacles has been at the focus of
numerous studies in the past. Reasons for this range from primary interest in the
turbulence-generating processes (gravity-wave breaking, downslope windstorms etc.) to,
more recently, issues regarding flight safety.
Our work focuses on the observational analysis of turbulence during events of boundary-layer
separation and rotor formation. The study is based on observations from two recent field
campaigns over the Medicine Bow Mountains in SE Wyoming (NASA06) and the Sierra
Nevada in Southern California (T-REX). During these campaigns, the University of Wyoming
King Air (UWKA) research aircraft flew straight-and-level legs aligned with the mean
wind direction to document the variation of flow and turbulence over the mountain
ridges. Aircraft in situ data of wind, pressure and temperature were recorded at a
frequency of 25 Hz. The Wyoming Cloud Radar (WCR), carried aboard UWKA,
measured Doppler vertical wind velocities at multiple levels at a frequency of 30
Hz.
The objective of this work is to quantify turbulence intensity during the observed
boundary-layer separation and rotor formation events. To this end, estimates of the variance
of vertical wind speed and the eddy-dissipation rate are computed from airborne in situ as
well as remotely-sensed data. The comparison of two wave events during the NASA06
campaign reveals similar turbulence intensities with maximum eddy-dissipation rates in the
range 0.25-0.30 m2 s-3. The dynamic origin of turbulence, however, appears to be
different. For 26 January 2006, results are indicative of a breaking gravity wave
aloft leading to wave-induced boundary-layer separation and rotor formation, with
maximum turbulence levels located in the rotor interior. In contrast, on 5 February 2006,
the lee wave pattern aloft remained laminar while the boundary-layer flow was
heavily perturbed. The spatial distribution of turbulence in the flow suggests that
turbulence originated from bluff-body separation of the boundary layer at the mountain
peak.
Preliminary results from the T-REX field campaign provide a similar picture. Regions of
strong turbulence from wave-induced boundary-layer separation and rotor formation exist in
the lee of the Sierra Nevada. Besides, highly turbulent flow patches can be found right behind
smaller but steep crests of the main ridge of the Sierra Nevada.
The type of analysis employed in this study is expected to be valuable in general for detection
of strong turbulence in mountainous terrain and for quantification of its intensity. |
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