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A note on sodar return signals in the stable atmospheric boundary layer

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Abstract:

A problem concerning the reliability of the determination of temperature structure parameter with the help of sodar is considered. The results of comparisons between remote and measurements of in the atmospheric boundary layer (ABL) are briefly reviewed. Some examples of a systematic overestimation of the value derived from sodar return in the stable ABL are given. Possible technical and physical causes of the discrepancies are discussed, including: (1) the contribution of a partial (Fresnel) reflection of sound from layers with a sharp temperature jump, (2) the anisotropy of small-scale turbulence, (3) the turbulence intermittency, (4) the contribution of quasi-wave air-density inhomogeneities, and (5) the contribution of wind speed fluctuations to backscattering. The cause (1) seems to be the main reason for the discrepancy.

German
Der vorliegende Beitrag diskutiert die Frage der zuverlässigen quantitativen Bestimmung des Temperatur-Struktur-Parameters (C 2 T ) auf der Basis von Sodar-Messungen. In der Literatur mitgeteilte Ergebnisse von Vergleichen zwischen in situ Messungen und Sodar-Daten werden zusammengefasst, sie zeigen in mehreren Fällen eine systematische Überschätzung von C 2 T aus Sodar-Daten in der stabil geschichteten atmosphärischen Grenzschicht. Die möglichen technischen und physikalischen Ursachen dieser Abweichungen werden diskutiert, hierzu zählen (1) Beiträge einer partiellen (Fresnel)-Reflexion des Schallsignals an Schichten mit markanten Temperatursprüngen, (2) die Anisotropie kleinskaliger turbulenter Wirbel, (3) inter-mittierende Turbulenz, (4) der Beitrag quasi-wellenförmiger Inhomogenitäten des Luftdichte-Feldes, sowie (5) der Beitrag von Windgeschwindigkeitsfluktuationen zum Schall-Rückstreusignal. Die Ursache (1) scheint der Hauptgrund für die Unterschiede zu sein.

Document Type: Research Article

DOI: https://doi.org/10.1127/0941-2948/2009/0387

Publication date: 2009-06-01

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