Recorded presentation7.1
Oceanic Eddies in the VOCALS Region of the Southeast Pacific Ocean
Dudley Chelton, College of Oceanic and Atmospheric Sciences (Oregon State Univ.), Corvallis, OR
The southeast Pacific (SEP) ocean off the coasts of Peru and northern Chile is a region of strong coupling between the ocean, the atmosphere and the land. The sea-surface temperature (SST) is cold over a broad region of the SEP. In combination with warm, dry air aloft, this cold SST results in the largest and most persistent subtropical stratocumulus deck in the world. This extensive cloud deck has a major impact on the Earth's radiation budget; the enhanced albedo from the clouds results in a positive feedback that helps maintain the cool SST. Coupled ocean-atmosphere models exhibit strong biases in SST and rainfall in this region. The VAMOS (Variability of the American Monsoon Systems) Ocean-Cloud-Atmosphere-Land Study (VOCALS) is an international CLIVAR program to develop and promote scientific activities leading to improved understanding and prediction of the SEP coupled ocean-atmosphere land system. A broader goal of VOCALS is to improve model simulations of the climate variability throughout the tropics and the subtropics.
The climate in the VOCALS region involves poorly understood interactions between clouds, aerosols, marine atmospheric boundary layer (MABL) processes, upper-ocean dynamics and thermodynamics, coastal currents and upwelling, large-scale subsidence, and regional diurnal circulations. The cold water in this region is partly attributable to the presence of the Andes Cordillera, which increases the static stability of the lower troposphere that enhances low cloud cover. The Andes also act as a barrier to zonal flow that results in the formation of a strong near-coastal wind jet in the MABL that blows parallel to the coast in an upwelling-favorable equatorward direction. It is believed that cold-core cyclonic mesoscale ocean eddies play a critical role in the heat budget of the broader VOCALS region through the offshore transport of cold, upwelled water that originates at the coast. Because the cold source water is also high in nutrient content, these oceanic eddies may also impact the ocean-atmosphere flux of dimethylsulfide (DMS), which photo-oxidizes in the atmosphere to become sulfate aerosols that provide cloud condensation nuclei that may play a role in the maintenance of the stratocumulus cloud deck.
The characteristics of eddies in the VOCALS region will be summarized in this presentation based on 10 years of simultaneous observations of sea-surface height (SSH) by the TOPEX and ERS-1/2 altimeters and 10 years of output from the Parallel Ocean Program (POP) model run at the Los Alamos National Laboratory. The analysis includes a comparison of the frequencies of occurrence, amplitudes, diameters, trajectories and lifetimes of cyclonic and anticyclonic eddies deduced using an automated eddy tracking procedure. The tracked eddies will also be compared with satellite measurements of SST and ocean chlorophyll to investigate whether the eddies are sufficiently nonlinear to advect these water properties from the coastal waters into the interior Pacific.
Session 7, Remote sensing applied to air-sea interaction
Tuesday, 21 August 2007, 1:30 PM-3:00 PM, Broadway-Weidler-Halsey
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