| Strong air-sea-land interactions and an abundance of nearby human populations make tropical Atlantic climate an interesting and important, yet challenging, topic of research. This dissertation discusses three aspects of tropical Atlantic climate: the exceedingly strong seasonal cycles of temperature and salinity in the near-surface mixed layer, and a key aspect of the strongest source of intraseasonal variability, tropical instability waves.; The seasonal cycle of mixed layer temperature is examined using observations to determine the key terms in the heat budget, focusing on a set of eight locations where ocean moorings provide enhanced data. I find that energy exchange with the atmosphere (latent heat loss and solar radiation absorption) is responsible for seasonal sea surface temperature variability in the northwest basin (8°N–15°N along 38°W). Along the equator (10°W–35°W) contributions from latent heat loss are diminished, while oceanic effects (horizontal temperature advection and vertical entrainment) contribute significantly. The balance in the southeast (6°S–10°S along 10°W) is similar to that in the northwest, with surface energy fluxes playing an important role.; The second problem I address is the corresponding salinity balance. Salinity satisfies a conservation equation like temperature, with sources and sinks consisting of evaporation and precipitation. I find that these surface terms, as well as vertical entrainment and mean horizontal salt advection, contribute significantly to seasonal mixed layer salinity variability throughout the basin.; The third topic I address is the breaking of tropical instability waves and the kinematics and dynamics of the resulting anticyclonic (clockwise rotating) vortices. Most prominent during boreal summer, these vortices form a few degrees north of the equator. They are characterized by 400 km spatial scales and are among the most nonlinear features of the deep ocean circulation, with Rossby Numbers (the ratio of advective to Coriolis terms) of ∼½. After characterizing these features I use an extremely high resolution numerical simulation provided by the University of Miami to examine the vertical structure and vorticity dynamics of the vortices, showing, among other things, their acquisition of low potential vorticity southern hemisphere water, which is carried into the northwestward flowing North Brazil Current. |
