SeaSpace (United States)

IN the equatorial Pacific Ocean, easterly trade winds and the Earth's rotation combine to drive surface currents away from the Equator, thereby causing cold nutrient-rich subsurface water to upwell. The front1 that forms between this upwelled water and warmer waters north of the Equator is sometimes visible as a spectacular "line in the sea"2 between 2° and 6° N. Westward-propagating cusp-shaped disturbances observed along this front3 have been attributed to the effect of dynamical instabilities in the system of zonal equatorial currents4–11but the connection between these phenomena remains unclear. Here we report extensive measurements from shipboard sensors, satellite and drifting buoys which reveal the three-dimensional structure of an anticyclonic eddy (or vortex) 500 km in diameter and centred at 4° N. We suggest that cusp-shaped disturbances of the front are caused by trains of large-amplitude vortices, which are driven by instability of the mean zonal shear. We show that these vortices not only play an important role in the meridional transport of heat, salt and momentum, but are also associated with regions of intense horizontal convergence along the front, where dramatic concentrations of marine life are observed.

Abstract Ordinary least-squares is used to estimate the accuracy of monthly averaged sea surface temperature products in the eastern near-equatorial Pacific. Daytime multichannel sea surface temperature (MCSST) data, nighttime MCSST data, Climate Analysis Center (CAC) in situ temperatures, and CAC blended temperatures are all compared to monthly averaged, equatorial, 1 m moored-buoy temperatures at 110°W, 124°W, and 140°W. In addition, reduced least-squares (RLS) is used to develop regression equations between the CAC in situ temperature and the MCSST data. Bootstrap methods are used to estimate the RLS regression statistics. new regression equations are used to convert the MCSST to equivalent in situ temperatures prior to combining the two datasets with a one over distance-squared gridding algorithm. Data used in this study are from the period January 1983 to December 1985. When data from the 1982/1983 El Niho are excluded from analysis, the MCSST data are not significantly different from the moored-buoy...