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Boundary-Layer Meteorology

, Volume 101, Issue 2, pp 243–260 | Cite as

Shallow Drainage Flows

  • L. Mahrt
  • Dean Vickers
  • Reina Nakamura
  • M. R. Soler
  • Jielun Sun
  • Sean Burns
  • D.H. Lenschow
Article

Abstract

Two-dimensional sonic anemometers and slowresponse thermistors were deployedacross a shallow gully during CASES99. Weak gully flow of a few tenths of m s-1 anda depth of a few metres develops in the earlyevening on most nights with clear skies.Flow down the gully developed sometimes evenwhen the opposing ambient wind exceeded10 m s-1 at the top of the60–m tower. Cold air drainage fromlarger-scale slopes flows over the top ofthe colder gully flow. The gully flowand other drainage flows are generally eliminated in the middle of the night in conjunctionwith flow acceleration abovethe surface inversion layer and downwardmixing of warmer air and highermomentum. As the flow decelerates later inthe night, the gully flow may re-form.

The thin drainage flows decouple standard observational levels of3–10 m from the surface.Under such common conditions, eddy correlationflux measurements cannot be used toestimate surface fluxes nor even detect thethin gully and drainage flows. The gentlegully system in this field program is typical ofmuch of the Earth’s land surface.

Drainage flows Gravity winds Katabatic winds Nocturnal boundary layer Temperature minimum 

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Copyright information

© Kluwer Academic Publishers 2001

Authors and Affiliations

  • L. Mahrt
    • 1
  • Dean Vickers
    • 1
  • Reina Nakamura
    • 1
  • M. R. Soler
    • 2
  • Jielun Sun
    • 3
  • Sean Burns
    • 3
  • D.H. Lenschow
    • 3
  1. 1.College of Oceanic and Atmospheric SciencesOregon State UniversityCorvallisUSA
  2. 2.Astronomy and MeteorologyUniversity of BarcelonaBarcelonaSpain
  3. 3.National Center for Atmospheric ResearchBoulderUSA

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