Home | Meeting Announcement | Meeting Agenda | Call for Papers | Meeting Registration | Hotel Information | Travel Information | Attendees | Abstracts
2002 LAPCOD Meeting
Previous Abstract | Back to Abstracts Page | Next Abstract
Warm water motion in the tropical Atlantic from analysis of surface drifter trajectories
Semyon Grodsky, Jim Carton
University of Maryland
senya@atmos.umd.edu(Abstract received 09/24/2002 for session A)
ABSTRACT
Subtropical cells connect subduction zones of the eastern subtropics of both hemispheres to the equatorial current systems via equatorward flow in the thermocline. Some of this thermocline water is converted back into warm near-surface water in the eastern equatorial cold tongue from whence it is then exported poleward. Here we examine the export pathways from the cold tongue in the Atlantic based on recently available near-surface drifter data. We find that, similar to its Pacific counterpart, water upwelled in the Atlantic cold tongue follows multiple pathways back into the subtropics, but not directly to the subduction zones. Thus the subtropical cells are open to extensive influence from, and exchange with, the subtropical and midlatitude ocean.
The talk is organized in the following way. First we identify the spatial structure and timing of the entrainment of cool subthermocline water in the equatorial Atlantic mixed layer. Then we consider the drifter trajectories crossing through the cold tongue during the cold tongue season. It will turn out that the pathways taken by the drifters are determined by where they originate within the cold tongue. Finally we explore the sensitivity of pathways to point of origin using the gridded velocity analysis.
This study is based on five data sets: 15m-drogued drifter velocity and position, ocean mixed layer depth, and a gridded velocity analysis, itself resulting from drifter data, climatological surface velocity from historical ship drifts, altimeter sea level, and scatterometer winds.
Our analysis uses 55 drifter trajectories within the 15°S - 30°N band, obtained from the WOCE/TOGA archive at the NOAA/AOML, that pass within the rectangular domain 4°S-2°N and 30°W-0°E during the cold tongue seasons of boreal summer and fall (June-November) when SSTs are low and entrainment is strong. Becauseof limitations on the number and coverage of surface drifters, we supplement our velocity discussion using a multivariate optimal interpolation analysis of climatological seasonal near-surface currents on a 3x2 grid following. The analysis combines Eulerian velocities obtained from the drifter tracks with near-surface pressure variations based on TOPEX/POSEIDON altimetry and monthly scatterometer winds, which together provide information on the geostrophic and ageostrophic components of current.
Previous Abstract | Back to Abstracts Page | Next Abstract
2002 LAPCOD Meeting, Key Largo, Florida, December 12-16, 2000