Low-frequency eddy modulations in the Hawaiian Lee Countercurrent : observations and connection to the Pacific Decadal Oscillation
MetadataShow full item record
Interannual-to-decadal time scale eddy variability in the Hawaiian Lee Countercurrent (HLCC) band is investigated using the available sea surface height, sea surface temperature, and surface wind stress data sets. In the HLCC band of 17°N–21.7°N and 170E°–160°W, the prevailing interannual eddy kinetic energy (EKE) signals show enhanced eddy activities in 1993–1998 and 2002–2006, and subpar eddy activities in 1999–2001 and 2007–2009. These interannual EKE signals exhibit little connection to the zonal HLCC velocity changes generated by the dipolar wind stress curl forcing in the immediate lee of the island of Hawaii. Instead, they are highly correlated to the time series of the Pacific Decadal Oscillation (PDO) index. Through a budget analysis for the meridional temperature gradient along the HLCC, we find that during the positive phase of the PDO index, the surface heat flux forcing induces cold (warm) sea surface temperature (SST) anomalies to the north (south) of the HLCC, intensifying the vertical shear between the surface, eastward-flowing HLCC and the subsurface, westward-flowing North Equatorial Current (NEC). This increased vertical shear enhances the baroclinic instability of the HLCC-NEC system and leads to a higher regional EKE level. The opposite processes occur when the PDO switches to a negative phase with the resulting lowered EKE level along the HLCC band. Compared to the surface heat flux forcing, the Ekman flux convergence forcing is found to play a minor role in modifying the meridional SST changes along the HLCC band.
Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): C12009, doi:10.1029/2011JC007286.
Showing items related by title, author, creator and subject.
Moored current meter data from the Atlantic north equatorial countercurrent near 6°N 28°W (September, 1983-March, 1984) : vol. XXXVI Levy, Ellen; Richardson, Philip L. (Woods Hole Oceanographic Institution, 1984-09)This report presents current and wind data from the second of three surface mooring deployments in the Atlantic North Equatorial Countercurrent near 6°N and 28°W. A Vector Averaging Wind Recorder (VAWR) measured wind ...
Menezes, Viviane V.; Phillips, Helen E.; Vianna, Marcio L.; Bindoff, Nathaniel (John Wiley & Sons, 2016-05-26)In the present work, we investigate the interannual variability of the South Indian Countercurrent (SICC), a major and still understudied current of the Indian Ocean circulation. To characterize the interannual variability ...
Local and equatorial forcing of seasonal variations of the North Equatorial Countercurrent in the Atlantic Ocean Yang, Jiayan; Joyce, Terrence M. (American Meteorological Society, 2006-02)The seasonal variation of the North Equatorial Countercurrent (NECC) in the tropical Atlantic Ocean is investigated by using a linear, one-layer reduced-gravity ocean model and by analyzing sea surface height (SSH) data ...