On the characteristics of eddies in the stable atmospheric boundary layer

Abstract

A discussion of the cross-spectral properties of eddies in the lowest 40m of the nocturnal boundary layer is presented. The study involves the analysis of meteorological data collected by the British Antarctic Survey at Halley Station, Antarctica, during the austral winter of 1986. Cross-spectral analysis is used to determine whether the nature of the observed eddies is primarily turbulent or whether their structure is characteristic of ,qoherent internal gravity waves. It is found that the crossspectral phases indicate the presence of turbulent eddies only when the local gradient Richardson number (Ri) is less than the critical value of l/4. Trapped modes were only observed when an offshore wind prevailed, indicating that topographic effects are responsible for their generation. The relative phases of velocity and temperature were often observed to change with height. This can be explained by examining the underlying meteorological conditions. On several occasions, regions of counter-gradient fluxes were detected. A physical explanation of this phenomenon is proposed.

Characterisation of the Nocturnal Boundary Layer at a Site in Northern Spain

“…Later (not shown), phases of 90 degrees can be found between temperature and vertical velocity w, indicating that this event might be followed by significant wave activity (Rees 1991). The presence of the LLJ at the higher levels also acts as a generator of upper level turbulence and contributes to the increase of spectral energy at these heights.…”

A Climatological Study of Internal Gravity Waves in the Atmospheric Boundary Layer Overlying the Brunt Ice Shelf, Antarctica

“…2, can be used to calculate the cross-spectral phase and coherence over the frequencies of interest. Following Rees (1991), it can be demonstrated that horizontally propagating IGWs, Kelvin-Helmholtz (K-H) instabilities, and turbulence have different cross-spectral phase ''signatures.'' We denote the cross-spectral phase between instruments a and b as Ph(ab).…”

Long solitary internal waves in stable stratifications

“…Thus the site serves as an "ideal" natural laboratory for the study of the stable atmospheric boundary layer and any wave-like structures it may support. The British Antarctic Survey have compiled a database of meteorological measurements from Halley IV station during their STABLE project for the purpose of developing a climatology of gravity wave activity in the boundary layer (King and Anderson, 1988;Rees, 1991;Rees et al, 2000). The solitary large amplitude disturbances reported here are typical examples of several observations in the data set.…”