Posted by Alan Leonardi on December 18, 2001 at 09:07:35:
In Reply to: NHRC poster posted by Steve Morey on December 03, 2001 at 10:40:37:
To answer your question, the NHRC is a robust feature of the long term mean. Individual snapshots of the flow along the islands reveal that the eddies in the region dominate the flow structure. As a result, the given flow along the islands can be both northwestward and southeastward. However, annual means reveal that the overall nature of the flow is along the island chain to the northwest. Additionally, studies of the eddy radii suggest that the flow is not consistent with eddy induced flow, but rather with that of a viscous (Munk type) western boundary layer. The width of the current concurs with this fact.
As for the current vriability, I refer you, firstly, to the comment and follow up of Raghu Murtgudde. However, in addition, I have these few remarks. In a recent study Leonardi et al. (JPO, in press) examined the nature of large scale wind forcing and Rossby wave dynamics upstream of the Hawaiian Islands. What we find is that on interannual timescales, the largest source of variability along the latitude band of the islands (20 North) is due to large scale changes in Ekman pumping. These give rise to westward propagating wind forced Rossby waves with phase speeds roughly twice that expected from linear theory (and from freely propagating coastally generated Rossby waves). The study did not extend to examine the net effects on the Hawaiian Islands and any transport changes, but one could extend, at least on a conceptual level, the results to possible manifestations of interannual variability in Hawaiian region, an in particular in the NHRC. A few questions that could be addressed are: (1) what is the overall affect of these Rossby waves on the flow and interannual variability in the Hawaiian region, (2) Does the variability, if any, result in enhanced transport north of the ridge? Enhanced/reduced flow through gaps/channels? and (3) what is the overall affect, if any, on regional nutrient transport/fluxes, and as a result, on fisheries?
These are all interesting question. If anyone out there has any suggestions, I would be more than willing to discuss them with you.