Paola Cessi

Paola Cessi, Professor, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA, USA

Left: Time- and longitudinally averaged wind stress as a function of latitude. Right: Contours of oceanic mass trans-port (in Sverdrups, black lines) and contours of sea surface temperatures (in Centigrade, colors). Th e transport of sea surface temperatures by the oceanic currents creates a thermal front beneath the westerlies’ maximum, which contributes to the local intensity of the surface winds.

My research focuses on the large-scale circulation of the ocean and its role in Earth’s climate. My approach is to formulate and analyze idealized fluid dynamical models of the ocean-atmosphere system that isolate specific processes. For example, I constructed a minimal description of the large-scale interaction between the upper ocean wind-driven circulation and the mid-latitude atmospheric flows, based on the conservation principles of heat and momentum, to show how the oceanic heat transport can influence the wind. The figure exemplifies one such model. The “theoretician’s view” of the oceanic currents offered by these simplified descriptions lacks the realism of nature and the complexity of large numerical simulations. However, I find it very satisfying to obtain mathematical solutions either by hand or by small numerical integrations becauseboth methods allow the complete exploration of the external parameters controlling the solution. For me this view is necessary to achieve the full understanding of the physical mechanisms involved.

Indeed, the possibility of conceiving and solving mathematical models of physical processes, and evaluating theoretical explanations against observations, is what initially attracted me to physical oceanography. As a physics undergraduate during the early eighties in Bologna (Italy), I was not interested in becoming a small part of a big high-energy physics experiment that would test someone else’s theory. Instead, I was attracted to a field where the constant improvements in observations allows opportunistic theories to sprout, be modified, or be revived every few years. Thus, I can keep my interests perked up by changing the topic of research every two or three years. Fortunately, oceanography is a relatively young science, and it is easy to find many fundamental problems that are still unsolved. At the moment, I am intrigued by the processes that transfer the surface temperature differences imposed by differential insolation to the deep ocean. The hope is that a comprehensive theory accounting for the deep structure of temperature and salinity in the ocean will clarify the dynamics of the thermohaline circulation, providing clues to the fate of the oceanic component of the poleward heat transport under changing climate scenarios. My current goal is to contribute to the unraveling of this problem.