Idealized Modeling Of Seasonal Variation In The Alaska Coastal Current
dc.contributor.author  Williams, William James  
dc.date.accessioned  20180614T01:29:10Z  
dc.date.available  20180614T01:29:10Z  
dc.date.issued  2003  
dc.identifier.uri  http://hdl.handle.net/11122/8670  
dc.description  Thesis (Ph.D.) University of Alaska Fairbanks, 2003  
dc.description.abstract  Analytical and idealizednumerical models were used to understand the physical processes that govern the seasonal variation and fate of the freshwater in the Alaska Coastal Current (ACC). The ACC is forced by freshwater inflow and by mean easterly winds that cause downwelling over the shelf. Twodimensional modeling using a linesource buoyant inflow gives the coastal current depth <math> <f> H=<fr><nu>3<sup>2/3</sup></nu><de>2</de></fr><fen lp="par"><fr><nu> f<sup>2</sup>Q<sup>2</sup></nu><de>g<sup>'</sup></de></fr> <rp post="par"></fen>t<sup>2/3</sup></f> </math> and coastal current width <math> <f> Y<inf>2D</inf>=3<sup>1/3</sup><fen lp="par"><fr><nu>g<sup>' </sup>Q</nu><de>f<sup>2</sup></de></fr><rp post="par"></fen><sup> 1/3</sup>t<sup>1/3</sup></f> </math>, where f is the Coriolis frequency, g ' is reduced gravity, Q is inflow rate and t is time since inflow began. Addition of downwelling windstress causes a steep coastal current front that intersects the bottom and is either convecting, stable and steady, or stable and oscillatory depending on <math> <f> <fr><nu>D</nu><de><g>d</g><inf>*</inf></de></fr></f> </math> and <math> <f> <fr><nu>b<inf>y</inf></nu><de>f<sup>2</sup></de></fr></f> </math>, where D is bottom depth, delta* is an Ekman depth and by is the crossshelf buoyancy gradient. Threedimensional modeling of a halfline source initially develops twodimensionally but becomes threedimensional from a balance between coastal influx of buoyancy and its downstream transport. This balance results in a coastal current depth limit <math> <f> H<inf><rf>max</rf></inf>=<fen lp="par"><fr><nu>2Qf</nu><de>g<sup> '</sup></de></fr><rp post="par"></fen><sup>1/2</sup>x<sup> 1/2</sup></f> </math>, where x is alongshelf distance. This limit is unchanged under downwelling windstress and is reached on time scales of less than 1 month for the ACC. The halfline source coastal current width develops as <math> <f> Y<inf>2D</inf></f> </math> away from the beginning of the line source. Imposition of a downwelling windstress tau results in an approximate balance among windstress and along and crossshelf momentum advection so that the current width is reduced to <math> <f> Y<inf>wind</inf>≈L<inf>D</inf><fen lp="par"><fr><nu>Qf</nu> <de><g>t</g>/<g>r</g><inf>0</inf></de></fr><rp post="par"></fen><sup> 1/2</sup></f> </math>, where LD is the Rossby radius of deformation. Waves and eddying motions eventually grow in the halfline source coastal current with wavelengths proportional to the coastal current width and with a downstream phase speed slower than the maximum current speed. These features cause an offshore flux of buoyant water, a broader coastal current and accumulation of buoyancy on the shelf. Increasing downwelling wind stress reduces the effects of the instabilities. Although buoyancy accumulates on the shelf during most model runs, there is little accumulation under maximum winter downwelling windstress. This suggests that freshwater accumulates on the shelf from spring through fall, but is then transported downstream during winter.  
dc.subject  Physical oceanography  
dc.subject  Geophysics  
dc.title  Idealized Modeling Of Seasonal Variation In The Alaska Coastal Current  
dc.type  Thesis  
dc.type.degree  phd  
dc.identifier.department  Program in Marine Science and Limnology  
dc.contributor.chair  Weingartner, Thomas  
refterms.dateFOA  20200305T16:02:05Z 
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