Anomalous Upwelling in Nan Wan: July 2008

Abstract

Tidally induced, sudden temperature drops in Nan Wan, particularly pronounced during the spring tide, of ten bear eco logical consequences. We use an Ocean Nowcast/Forecast System (ONFS) at the US Naval Research Laboratory (NRL) to examine a widely publicized cold-water intrusion event in July 2008, and com pare it with what we perceived as a normal intrusion event in June 2007. For a normal cold-water intrusion, cold anomalies eventually propagate away in forms similar to internal Kelvin waves. For early July of 2008, the NRL ONFS suggested an anomalous, subtidal and essentially east ward cur rent near Nan Wan. The subtidal current, super imposed on the ebb cur rent, blocks the prop a gation of cold anomalies in the direction of in ternal Kelvin waves, inducing anomalous and in efficient cold-water dispersal. The NRL ONFS also suggested the anomalous subtidal current as a post-typhoon response to the passage of Typhoon Fengshen.

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