Ocean Atmosphere Interaction in the Agulhas Current System

Speaker: 
Mathieu Rouault
Affiliation: 
Nansen Tutu Center for Environmental Research, University of Cape Town, South Africa
Seminar Date: 
8. October 2013 - 11:15 - 12:00
Location: 
Lecture room, Ground Floor, NERSC

Oceans gain heat at the Equator and in upwelling areas and lose it in western boundary currents such as the Gulf Stream, the Kuroshio or the Agulhas Current. This loss of energy is due to a sea surface temperature contrast between western boundary currents and their surroundings, leading to a high evaporation rate and substantial turbulent latent and sensible heat fluxes. In that respect, the Agulhas Current system has an important role to play in global climate on top of its role on the exchange of heat and salt between the Indian and Atlantic Oceans. Measurements in the Agulhas Current have shown substantial transfers of water vapour in the marine boundary layer, increased wind speed above its core, a deepening of the marine boundary layer due to intense mixing, and unstable surface atmospheric stability created by the advection of colder and drier air above the current.

The Agulhas current has an influence on the diurnal cycle of rainfall in South Africa; evolution of severe storm over the coast and it is a source region of moisture for Southern Africa. It has also an impact on marine ecosystem by creating dynamic upwelling along the coast and transporting nutrient plankton and larvae. It is possible that the Agulhas Current had an important role to play in the survival of the first Homo Sapiens that were found along the coast of South Africa 140 000 years ago. In recent years the Agulhas Current system has warmed by up to 1.5 °C since the 1980 due to an intensification of the Agulhas Current system in response to an increase in wind stress curl at relevant latitudes in the Indian Ocean. Major challenges exist in modelling the influence of the Agulhas Current on weather and climate.