Andrew F. Thompson's homepage

Andrew Thompson

DAMTP, University of Cambridge

A.F.Thompson@damtp.cam.ac.uk

Movie Gallery

Jet interaction with topography Zonal jets form in the presence of a large-scale potential vorticity (PV) gradient (see below). Topographical features can also influence PV gradients by changing the depth of a fluid. The following movie shows an interesting feedback mechanism leading to oscillatory jet behavior. Jets are initially steered by a series of sinusoidal bumps that have the same length scale as the jet spacing. Feedbacks between mean flow orientation and baroclinic instability (e.g. meridional flows are more efficient at generating eddy kinetic energy, EKE) allow the eddy/jet scale to grow until they swamp the local topographical PV signature. The planetary PV gradient then induces zonal jets, but energy decays because the EKE levels can not be sustained in this configuration. Eddy length scales decay and the sequence begins again. (Upper left panel) Time series of EKE (black) and zonal kinetic energy (blue); (lower left panel) time series of the jet spacing to topographic scale ratio; (right panel) upper layer PV.

ADELIE drifters

40 surface drifters were deployed off the tip of the Antarctic Peninsula in February 2007 as part of the ADELIE project. This movie shows the drifter trajectories overlaid on the local bathymetry, indicating the strong control of bathymetry in the region. The advance of the ice edge is given by the light blue line to the south of the drifters.

Jet formation in baroclinic turbulence

Two-layer baroclinic turbulence in a doubly-periodic domain with a large-scale potential vorticity (PV) gradient. The PV gradient encourages the formation of zonally elongated flows known as jets. In the region between the strong eastward jets, PV becomes homogenized. The upper panels show the total PV in the upper (left) and lower (right) layers. The strong eastward jets coincide with the sharp meridional jumps in PV. The lower panels show upper and lower PV with the large scale gradient removed.

Baroclinic f-plane turbulence

In the absence of a large-scale potential vorticity gradient, a baroclinically-unstable flow will form coherent axisymmetric vortices that either have warm cores (anti-cyclonic) or cold cores (cyclonic). This movies tracks the coherent vortices during the statistically equilibrated state of a two-layer quasi-geostrophic model. The system is forced by a fixed large-scale temperature gradient (or equivalently a vertical shear) that is balanced by dissipation by bottom friction. The upper panel shows a time series of eddy kinetic energy (red) and number of vortices (blue) above a threshold. The lower panel shows the position of the vortices, the color indicates temperature at the core and the size indicates the magnitude of vorticity.