Search

The influence of mesoscale eddies on the flow field and the water masses, especially the oxygen distribution of the eastern tropical South Pacific, is investigated from a mooring, float, and satellite data set. Two anticyclonic (ACE1/2), one mode-water (MWE), and one cyclonic eddy (CE) are identified and followed in detail with satellite data on their westward transition with velocities of 3.2 to 6.0 cm s-1 from their generation region, the shelf of the Peruvian and Chilean upwelling regime, across the Stratus Ocean Reference Station (ORS; ~ 20 ° S, 85 ° W) to their decaying region far west in the oligotrophic open ocean. The ORS is located in the transition zone between the oxygen minimum zone and the well oxygenated South Pacific subtropical gyre. Velocity, hydrographic, and oxygen measurements at the mooring show the impact of eddies on the weak flow region of the eastern tropical South Pacific. Strong anomalies are related to the passage of eddies and are not associated with a seasonal signal in the open ocean. The mass transport of the four observed eddies across 85 °W is between 1.1 and 1.8 Sv. The eddy type-dependent available heat, salt, and oxygen anomalies are 8:1 ×1018 J (ACE2), 1:0 ×1018 J (MWE), and -8.9 ×1018 J (CE) for heat; 25.2 ×1010 kg (ACE2), -3.1 ×1010 kg (MWE), and -41.5 ×1010 kg (CE) for salt; and -3.6 ×1016 μmol (ACE2), -3.5 ×1016 μmol (MWE), and -6.5 ×1016 μmol (CE) for oxygen showing a strong imbalance between anticyclones and cyclones for salt transports probably due to seasonal variability in water mass properties in the formation region of the eddies. Heat, salt, and oxygen fluxes out of the coastal region across the ORS region in the oligotrophic open South Pacific are estimated based on these eddy anomalies and on eddy statistics (gained out of 23 years of satellite data). Furthermore, four profiling floats were trapped in the ACE2 during its westward propagation between the formation region and the open ocean, which allows for conclusions on lateral mixing of water mass properties with time between the core of the eddy and the surrounding water. The strongest lateral mixing was found between the seasonal thermocline and the eddy core during the first half of the eddy lifetime. [ABSTRACT FROM AUTHOR]

This paper describes the occurrence of diurnal restratification events found in the southeast trade wind regime off northern Chile. This is a region where persistent marine stratus clouds are found and where there is a less than complete understanding of the dynamics that govern the maintenance of the sea surface temperature. A surface mooring deployed in the region provides surface meteorological, air-sea flux, and upper-ocean temperature, salinity, and velocity data. In the presence of steady southeast trade winds and strong evaporation, a warm, salty surface mixed layer is found in the upper ocean. During the year, these trade winds, at times, drop dramatically and surface heating leads to the formation of shallow, warm diurnal mixed layers over one to several days. At the end of such a low wind period, mean sea surface temperature is warmer. Though magnitudes of the individual diurnal warming events are consistent with local forcing, as judged by running a one-dimensional model, the net warming at the end of a low wind event is more difficult to predict. This is found to stem from differences between the observed and predicted near-inertial shear and the depths over which the warmed water is distributed. As a result, the evolution of SST has a dependency on these diurnal restratification events and on near-surface processes that govern the depth over which the heat gained during such events is distributed. [ABSTRACT FROM AUTHOR]

The Hasselmann feedback model was applied to hindcast western Pacific warm pool sea surface temperatures (SST) with heat flux observations obtained near 28S, 1568E from October 1992 to February 1993 during the Tropical Ocean Global Atmosphere Coupled Ocean--Atmosphere Response Experiment (TOGA COARE). The model versus observed SST correlations were greater than 0.85. Two important feedback (or damping) timescales emerged, with e-folding times of l 21 5 0.2 days and 8 days, fitting to the diurnal and subdiurnal variations, respectively. Distinct mixed layer depth scales were also found for the respective timescales. A time-varying depth parameter with a median of ˜5 m was derived for the shorter timescale and varied with the observed daily minimum mixed layer depth. A constant ˜16 m was optimal for the longer timescale, which is similar to the time-averaged observed mixed layer depth of 14.8 m and the Monin--Obukhov scale of ˜17 m. This bears on the choice of mixed layer parameters for climate model simulations of warm pool conditions observed in TOGA COARE. The low-frequency time- and depth-scale parameters give a negative feedback of about 95 W m 22 8C 21 , which is significantly greater than previous studies have indicated. This restoring influence was treated separately from fluxes across the air--sea interface such as latent, radiative, and sensible heat loss or cloud shading, and is thus attributed to oceanic mixed layer processes. The frequency band where the damping or feedback becomes important is defined by v l, which is found to coincide with the diurnal cycle and the ˜50-day Madden--Julian oscillations for the respective l 21 timescales. This indicates a possible dynamic con-nection between the surface heat forcing and mixed layer dissipation timescales, which the authors suggest might be accounted for if the dissipation is parameterized as being proportional to the amplitude of SST variations. [ABSTRACT FROM AUTHOR]