The atmosphere-ocean heat engine is simply illustrated in the classic 'annulus experiment'
(click for video). Here
seen from above, the fluid is contained between cold 'polar' wall and warm 'tropical' wall, on a rotating
platform. The experiment is readily carried out with a salad bowl and soup-can of ice on a pawn-shop record player. Rather than
simply convecting as in a Hadley cell, the fluid develops two jet streams that carry heat meridionally, interlacing with long
waves
about isolated eddies that march eastward round the annulus. The waves are generic cousins of the Rossby waves seen elsewhere on
this page.
OPTICAL ALTIMETRY: IMAGING THE PRESSURE, VELOCITY AND VORTICITY IN A
ROTATING FLUID
A complete software package for analysis of AIV (color
altimetric images) is now available from Yakov Afanasyev, at the
Physics Department of Memorial University, St. Johns Newfoundland,
Canada. Once the
system is assembled (involving a color transparency and a light source
and camera mounted above the rotating table, or with mirror to double
the optical path, mounted at the height of the fluid), this software
makes efficient calculations of surface height field, geostrophic and
ageostrophic pressure and velocity, and vorticity and potential
vorticity. For examples see the recent JFM and JGR and Experiments
in Fluids reprints of
Afanasyev, Rhines and Lindahl under Recent Papers on our library page, here.
Contact
yakov@physics. mun.ca, and on the web www.physics.mun.ca/~yakov/
GFD lab altimetric images above of turbulent flow driven by
buoyant central
source, color-coded
by slope (I. Afanasyev); Click to enlarge. This is a polar beta-plane (in the
barotropic sense), with the
North Pole at the center. You are seeing the topography
of the water surface, with features ranging from a few microns, to a mm. in
height.
A "beta
plume" (above)
radiates westward from a buoyant source
of fluid that spills overtop of a dense lower layer. The anticyclonic vortex/rim
current that forms is unstable, spawing intense mesoscale eddies.
For animation (10Mb) click here.
above, vertical vorticity in cylinder wake, left: 'eastward' translation of
cylinder; right, 'westward' translation of cylinder; black: cyclonic, white: anticyclonic.
Image above is a field of periodically-forced Rossby waves; click to download
animation, 1 Mb Quicktime format.
The grey-shading shows the pressure
field (the elevation of the water surface), which is also the
stream-function for the geostrophic flow. The two views show
the surface topography with and without particle paths superimposed.
The flow is quasi-steady. 1
m. diameter cylinder with
paraboloidal free surface, rotating at 2.3 radians/sec. Driven by an
eastward (i.e., counter-clockwise) solid-body rotation of the fluid,
which is maintained by ramping down the table rotation rate.
The most energetic flow
features are the spiral jet/wake structure at the mountian. The
'tip-jet' at Cape Farewell Greenland may be an analogous feature from
the subpolar Atlantic. A 'Lighthill block' extends eastward around
circular latitude lines, upstream
of the mountain. Note the
ruddy moon-scape in this blocked region, which is a field of small
evaporative convection cells
('clouds' rotating cyclonically) east of the mountain, surrounded by
weak convective rolls in the region of shear. The amplitude of these tiny cells
is about 1 micron (1 micrometer) of surface elevation.
The image directly above these two is created by oscillating the table rotation
rate periodically, under computer control. The spherical cap mountain thus acts as
a wave source. At finite amplitude it is generating a spectrum of frequencies,
as time-dependent lee waves.
Note in the video (click) how Rossby waves appear to its east, yet inertial waves
appear to its west, during the westward flowing part of the cycle, when no
standing Rossby waves are possible. The still image above shows a long-crested
long Rossby waves sprialing into the North Pole, while short Rossby waves appear
to the east of the mountain (at 7 o'clock).
Lectures in GFD. This will be a
collected set of lectures from my teaching over the years. There will be
many laboratory images and videos from our GFD lab, and graphics from
observations and models. The lectures will be refined over time.
frontal instability of cold-water dome trapped above a mountain
The GFD lab moved in March 2000 to a new 1300 sq. ft facility in the newly
completed 
undular
bore
Chlorophyll during late spring bloom round Tasmania
(27xi1981), 1 km resolution (Courtesy of CZCS/SeaWiFS projects)
