Regional Weather Patterns during Anomalous Air–Sea Fluxes at the Kuroshio Extension Observatory (KEO)*

Abstract

Abstract The weather patterns during periods of anomalous surface fluxes in the Kuroshio recirculation gyre of the western North Pacific are documented. Separate analyses are carried out for the cold season (October– March) when the net surface heat flux is controlled by the combination of the turbulent sensible and latent heat fluxes (Qturb), and for the warm season (May–August) when the net heating is dominated by the net radiative fluxes (Qrad). For analysis of high-frequency (daily to weekly) variations in the fluxes, direct measurements from the Kuroshio Extension Observatory (KEO) for the period June 2004–November 2005 are used to specify flux events. For analysis of interannual variations, these events are selected using NCEP–NCAR reanalysis estimates for Qturb in the cold season, and International Comprehensive Ocean–Atmosphere Data Set (ICOADS) data for cloud fraction, as a proxy for Qrad, in the warm season. During the cold season, episodic high-frequency flux events are associated with significant anomalies in the east–west sea level pressure gradients, and hence meridional winds and lower-tropospheric air temperature, reflecting the dominance of the atmospheric forcing of the flux variability. On the other hand, interannual variations in Qturb are associated with relatively weak atmospheric circulation anomalies, implying a relatively important role for the ocean. During the warm season, high-frequency fluctuations in the net surface fluxes occur due to a mix of anomalies in Qturb and Qrad. Enhanced cloudiness in the vicinity of KEO, and hence reduced Qrad, tends to occur in association with weak cyclonic disturbances of extratropical origin. A regional atmospheric circulation favoring these types of events also was found for warm seasons that were cloudier on the whole. Results suggest that the ocean’s influence on air–sea fluxes at KEO is manifested mostly on interannual time scales during the cold season.