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Observed and modelled characteristics of the marine atmospheric boundary layer over the Northeast Pacific Ocean : a cold air outbreak case study

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Title: Observed and modelled characteristics of the marine atmospheric boundary layer over the Northeast Pacific Ocean : a cold air outbreak case study
Author: Unrau, Greg
Degree Master of Science - MSc
Program Oceanography
Copyright Date: 1996
Abstract: The Marine Atmospheric Boundary Layer was investigated during a cold air outbreak (CAO) over the Northeast Pacific ocean. The horizontal structure and downwind modification of the lower boundary layer were studied. Considerable moisture is supplied to the atmosphere through the turbulent flux of latent heat. The bulk flux of latent heat increases downwind while the bulk flux of sensible heat decreases. The highest recorded total surface heat flux is 365 Wm⁻² based on eddy correlation statistics. Turbulence kinetic energy increases downwind and velocity variances were found to be more sensitive to stability than others have observed (Panofsky et al, 1977). A spectral analysis suggests the presence of roll circulations in the horizontal wind components (u, v) and specific humidity q at scales ranging from 5 to 25 km, as well as an increasing roll aspect ratio downstream. Boundary layer height increases downwind but height isolines are oriented more perpendicular to the sea surface temperature gradient than to the mean wind direction. A quasi-two-dimensional K-theory similarity model (Brown, 1972, 1974a, 1974b) was applied to a 40 x 40 horizontal grid and was used to estimate surface air velocities, stability and surface sensible heat flux. It incorporates the effects of stratification and baroclinicity and unlike other boundary layer models, explicitly parameterizes large eddy circulations. Model derived near surface air velocities, friction velocities and the flux of sensible heat emulate observed fields reasonably well. Modelled velocities are larger than observed values but not significantly in well determined regions of the model domain. In regions where modelled and observed air velocities agreed poorly, data paucity and nonstationarity effects are the proposed causes.
URI: http://hdl.handle.net/2429/6118
Series/Report no. UBC Retrospective Theses Digitization Project [http://www.library.ubc.ca/archives/retro_theses/]

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