The Onset of the Very Stable Boundary Layer

B.J.H. van de Wiel, A.F. Moene, H.J.J. Jonker, P. Baas, S. Basu, J. Sun, A.A.M. Holtslag

Research output: Chapter in Book/Report/Conference proceedingConference paper

Abstract

Here, the mechanism behind the collapse of turbulence in the evening is investigated as a precursor to the onset of the very stable boundary layer. A cooled, pressure-driven flow is investigated by means of a local similarity model. Simulations reveal a temporary collapse of turbulence whenever the surface heat extraction, expressed in its non-dimensional form h/L, exceeds a critical value. As any temporary reduction of turbulent friction is followed by flow acceleration, the long-term state is unconditionally turbulent. In contrast, the temporary cessation of turbulence, which may actually last for several hours in the nocturnal boundary layer, can be understood from the fact that the time scale for boundary layer diffusion is much smaller than the time-scale for flow acceleration. This limits the available momentum that can be used for downward heat transport. In case the surface heat extraction exceeds the so-called maximum sustainable heat flux (MSHF), the near-surface inversion rapidly increases. Turbulent activity is largely suppressed by the intense density stratification which supports the emergence of a different, calmer boundary layer regime. Finally, results are translated into a practical model to predict the minimum wind speed for sustained turbulence in the atmosphere. It is shown that under clear sky conditions 5 m/s is the typical geostrophic wind limit for Cabauw, below which continuous turbulence cannot be sustained. Below this threshold therefore the emergence of the very stable nocturnal boundary regime is foreseen.
Original languageEnglish
Title of host publication20th Symposium on Boundary Layers and Turbulence/18th Conference on Air-Sea Interaction, American Meteorological Society (9-13 July 2012, Boston, MA)
Place of PublicationBoston
PublisherAmerican Meteorological Society
Pages2.4
Publication statusPublished - 2012
Event20th Symposium on Boundary Layers and Turbulence/18th Conference on Air-Sea Interaction - Boston, United States
Duration: 9 Jul 201213 Jul 2012

Conference

Conference20th Symposium on Boundary Layers and Turbulence/18th Conference on Air-Sea Interaction
CountryUnited States
CityBoston
Period9/07/1213/07/12

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    van de Wiel, B. J. H., Moene, A. F., Jonker, H. J. J., Baas, P., Basu, S., Sun, J., & Holtslag, A. A. M. (2012). The Onset of the Very Stable Boundary Layer. In 20th Symposium on Boundary Layers and Turbulence/18th Conference on Air-Sea Interaction, American Meteorological Society (9-13 July 2012, Boston, MA) (pp. 2.4). American Meteorological Society. https://ams.confex.com/ams/20BLT18AirSea/webprogram/Paper208966.html