Article

Boundary-Layer Meteorology

, Volume 147, Issue 2, pp 179-199

Open Access This content is freely available online to anyone, anywhere at any time.

Non-stationary Generation of Weak Turbulence for Very Stable and Weak-Wind Conditions

  • Larry MahrtAffiliated withCEOAS, Oregon State University Email author 
  • , Christoph ThomasAffiliated withCEOAS, Oregon State University
  • , Scott RichardsonAffiliated withDepartment of Meteorology, Pennsylvania State University
  • , Nelson SeamanAffiliated withDepartment of Meteorology, Pennsylvania State University
  • , David StaufferAffiliated withDepartment of Meteorology, Pennsylvania State University
  • , Matthias ZeemanAffiliated withInstitute of Meteorology and Climate Research (IMK-IFU), Karlsruhe Institute of Technology (KIT)

Abstract

Turbulence measurements for very stable conditions near the surface are contrasted among three sites: a high altitude basin during winter with grass or snow-covered grass, a broad valley with complex agricultural land use, and a more narrow valley that is influenced by a valley cold pool and cold air drainage. In contrast to previous studies, this investigation emphasizes the very weak turbulence with large bulk Richardson number occurring during extensive periods between brief mixing events. The relationship of the turbulence to the non-stationary wind and stratification is examined along with the impact of short-term flow accelerations, directional shear and downward diffusion of turbulence from higher levels. The failure of the turbulence for strong stratification to decrease with further increase of stratification is explored. Additional analyses are applied to weak-wind cases for the entire range of stratification, including weak stratification associated with cloudy conditions.

Keywords

Intermittent turbulence Nocturnal boundary layer Stable boundary layer Submeso Weak winds