# Houghton Lecture - Joe Lacasce, Univ. of Oslo

Professor Joe Lacasce will give a 3 lecture course on Lagrangian methods as applied to mixing in the ocean and atmosphere followed by a lecture defending the use of linear models to understand ocean circulation.

## Lectures 1-3

Jan 15, 17 and 22 at noon in MIT 24-411 (with live broadcast to WHOI)

### A short course on Lagrangian methods and mixing

The use of freely-drifting surface buoys and subsurface floats is a cost effective means of sampling the ocean and has become more common in recent years. Studying drifter motion moreover improves our understanding of the behavior of other passive tracers, such as spilled oil or volcanic ash. But what does one do with such data? I will outline some of the principal issues in Lagrangian analysis. The lectures are meant to be a short course on the subject, but each lecture will be self-contained. Lecture 1 concerns diffusivities and the effect of mean flows on dispersion. Lecture 2 considers how PV conservation affects dispersion and examines Lagrangian spectra and stochastic models. In Lecture 3, we'll focus on pairs of particles (relative dispersion) and see how they can be used e.g. to infer kinetic energy spectra. Examples from the ocean and atmosphere will be presented along the way.

## Lecture 4

Jan 24 at noon, location t.b.d.

### In defense of using linear models to understand ocean circulation

Like the atmosphere, the ocean is fundamentally nonlinear and chaotic. So ocean "weather" is as unpredictable as the actual weather. Nevertheless, much of our understanding about how the ocean works comes from idealized *linear* models. The most familiar examples are perhaps Stommel's models of the Gulf Stream and the Deep Western Boundary Current. But related models have been used to explain current fluctuations in the Nordic Seas, boundary current separation off South Africa and the dependence of the Antarctic Circumpolar Current on wind forcing. I'll discuss several such examples, hopefully to persuade you that linear models are still worth studying.

## About the Spring 2013 Houghton Lecturer:

Professor Joe Lacasce is Section Chair in Meteorology and Oceanography, in the Department of Geophysics at the University of Oslo, Norway. He also holds an Adjunct Scientist position at WHOI. Particular interests include large scale dynamics in the atmosphere and ocean, turbulence, and Lagrangian statistics. Lacasce graduated from the MIT-WHOI Joint Program in 1996 where his doctoral thesis, Baroclinic Vortices over a Sloping Bottom, was advised by WHOI Scientist Ken Brink.

**Recent Publications**

Lacasce, J. H. (2012), Surface Quasigeostrophic Solutions and Baroclinic Modes with Exponential Stratification, Journal of Physical Oceanography, ISSN 0022-3670, 42(4), s 569-580, doi: 10.1175/JPO-D-11-0111.1

Lacasce, J. H. (2010), Relative displacement probability distribution functions from balloons and drifters, Journal of Marine Research, ISSN 0022-2402. 68(3-4), s 433- 457, doi: 10.1357/002224010794657155

Lacasce, J. H. (2008), Statistics from Lagrangian observations, Progress in Oceanography, ISSN 0079-6611, 77, s 1- 29, doi:10.1016/j.pocean.2008.02.002