The Bjerknes Centre is a collaboration on climate research, between the University of Bergen, NORCE, the Institute of Marine Research, Nansen Environmental and Remote Sensing Centre.

Seminar talk: Atmospheric origins of variability in the South Atlantic meridional overturning circulation

Timothy Smith from The University of Texas at Austin will give a seminar talk on August 26.

Timothy Smith
Timothy Smith


Short biography:

I am a Ph.D. candidate working with Patrick Heimbach at the Oden Institute for Computational Engineering and Sciences at the University of Texas. I am broadly interested in developing and implementing computational tools to (1) better understand oceanographic processes relevant to the climate system and (2) quantify uncertainties in ocean models. Currently, I am focused on attributing variability in the Atlantic Meridional Overturning Circulation to its geographical origins using a 20 year ocean state estimate produced by the ECCO consortium.



Insights from the RAPID–MOCHA observation network in the North Atlantic have motivated a recent focus on the South Atlantic, where water masses are exchanged with the neighboring Indian and Pacific ocean basins. Moreover, the South Atlantic meridional overturning circulation basin-wide array (SAMBA) was recently launched to monitor variability in the South Atlantic MOC (SAMOC) at 34.5◦S. In this study, we are interested in understanding the processes which generate volume transport variability that would be observed at this latitude band. To perform this attribution, we compute sensitivities of the SAMOC at 34◦S to atmospheric state variables using the adjoint of a global ocean model which is fit to a vast number of ocean observations over the past 20 years. These sensitivities elucidate the oceanic mechanisms which carry atmospheric forcing perturbations to the SAMOC, and isolate the impact from each variable (e.g. wind stress, precipitation). We convolve historical forcing variability from ERA-Interim with these sensitivities in order to attribute seasonal to interannual SAMOC variability to each atmospheric component. The seasonal cycle of the SAMOC is therefore shown to be largely driven by local zonal wind forcing. Interannual variability, however, is shown to have originated from remote locations across the globe, including a nontrivial component originating from the tropical Pacific. We conclude with preliminary results which employ both modeling results and an analysis of modern altimetry observations to show how El Niño Southern Oscillation wind variability might influence the South Atlantic.


Arranged date for the seminar talk: Aug 26, 2019