My overall research
objective is to better understand the dynamical processes that govern the
behavior of the stratified and rotating fluid that comprise the Earth's
oceans, so as to improve upon existing capacity to predict evolution of
complex geophysical fluid dynamical processes. In pursuing this goal I have
come to rely upon an approach combining theoretical, experimental and
numerical techniques. This is an exciting area of research, as it gives us insight
into fundamental oceanic and atmospheric physics, and also has relevance to
our interaction with the environment.
Current projects:
Picture above shows evolution of thermally induced turbulence on a
polar beta-plane, as seen from above the North pole (the center). Color shows the
surface elevation field. The bottom is heated along a radius, and the convective turbulence generates zonal circulation
in turbulent beta-plumes, which involve Rossby-wave signalling westward from
the energy source. Visualized with optical altimetry which displays surface
height variations of a few microns (millionths of a meter). Physics Today inside back cover, October 2011.
Ocean/atmosphere experiments on a rotating table use the parabolic water surface
to simulate the polar cap of the planet.
I am creating a library of videos which can be used for demonstrations in oceanography or geophysical fluid dynamics. Check them out at Youtube:
OPTICAL ALTIMETRY: IMAGING THE PRESSURE, VELOCITY AND
VORTICITY IN A ROTATING FLUID
NEWS! A complete
software package for analysis of AIV (color altimetric images) is now
available. Once the system is assembled (involving a color transparency and a
light source and camera mounted above the rotating table, or with
mirror mounted halfway above the fluid in the laboratories with low
ceiling), this software makes efficient calculations of surface height field,
geostrophic and ageostrophic pressure and velocity, and vorticity and
potential vorticity. Contact yakov@physics.mun.ca
I
am back from sabbatical where I was working with Peter Rhines at the
University of Washington . Here are a few movies and pictures of our recent
results:
"Designer planets" Atmosphere (ocean) in a soap bubble:
The iris of this eye is an
experimental image of a large soap bubble (diameter 30 cm). The soap bubble
when placed on a rapidly rotating platform can model a planetary
atmosphere or an ocean. Convective motions within the bubble create color
pattern due to interference of light.
For 10mb wmv movie (with
sound) of rotating soap bubbles click here.
Experimental image of a
phenomenon which occurs often in oceans and atmosphere. This phenomenon is
called baroclinic instability. The image is obained by a new
method of color altimetry developed recently in collaboration with the University of Washington.
For 2mb wmv movie of a rotating flow over a mountain illustrating
Rossby and inertia waves click here.
Wakes
behind towed and self propelled bodies in 2D and 3D
Theoretical, numerical and laboratory investigation of wakes behind moving
forcing of different configurations. Applications include flying insects and
birds, swimming microorganisms and fish, wakes behind submarines and bluff bodies.
Flight in a viscous
fluid.
Experimental image of a flow modelling the vortical wake behind a
hydrodynamic model of a small insect. This image won 1st prize at the
recent Art of Physics competition of Canadian Association of Physicists.
This picture shows the wake behind a “virtual” insect flying in
fluid. The model of the insect is translated in water horizontally. It has a
permanent magnet in its rear end which provides a magnetic field in the
direction of motion. At the same time the electric current flows between two
electrodes in a perpendicular direction in the horizontal plane. The
resulting Lorentz force on the fluid is perpendicular to both the current and
the magnetic field and acts in the vertical direction. This force, if applied
impulsively during some time intervals, simulates the lift force applied by the
flapping wings of an insect during downstrokes. This force transfers momentum
downwards while the reaction to this force supports the insect in the air.
Momentum transfers in the form of vortex rings. These “rings”
look like a Greek letter W and are connected to each other. The
insect is small and the viscosity of the fluid is important. As a result the
vortex tubes diffuse in the fluid.
Topographic
flows, mixing and transport in fjords
Recent interests have included
numerical modeling of unstable internal gravity waves, using a fully
three-dimensional ``state-of-the-art'' numerical model on various Cray vector
supercomputers. The most interesting and dynamically significant effect of
internal wave propagation in a stratified fluid arises when the wave achieves
such amplitude that it becomes subject to a local convective instability.
This is commonly referred as ``wave breaking'' and it is thought to be
associated with the transfer of momentum from the wave field to the main
flow. The oceanographic examples include flows in coastal inlets subject to
gradually changing tidal currents (e.g. Newman Sound, NF; Knight Inlet, BC).
Such fjords are typical features of the Newfoundland coast and many of them
are used for aquaculture. Thus the study of mixing and forcing of circulation
is also of great importance for biological applications. A significant new
study devoted to understanding this interesting oceanic nearshore process is
currently under way and will be continued. A field study will be considered
at a later stage of the project.
Mixing
and transport by vortices in a rotating stratified fluid
Vortex structures such as monopoles,
dipoles as well as more complex structures are fundamental elements of
geophysical turbulence. Because they can effectively transport momentum,
heat, salt and biochemical products, they play an essential role in ocean
dynamics, determining the instantaneous fields of velocity, temperature and
salinity, i.e. so-called internal oceanic weather. A very efficient tool for
the investigation of vortices clearly consists of laboratory experimentation.
The following specific projects are under way: vortex formation in coastal flows;
stability of barotropic vortices in a rotating stratified fluid; dynamics and
interactions of vortex structures on a ``beta-plane''. The experimental part
of these projects includes setup of PIV (Particle Image Velocimetry) system
for the computerized measurements of flow fields. In the framework of this
research stream I also plan to initiate a project in collaboration with
colleagues from the P.P.Shirshov Institute on thermal variability of the
waters of the Newfoundland shelf using satellite SST data.
Details of graduate studies in Physics and Physical Oceanography at
Memorial University can be found here
Previous:
Krista Galway
(NSERC summer student 2004,co-supervised with Daniel Bourgault) Bariclinic
instability in the Gaspe Current (Gulf of St. Lawrence): Laboratory
experiments
Marina Blokhina
(M.Sc. 2003) Mesoscale Variability in the Black Sea: Satellite Observations
and Laboratory Experiments
Shawn
Chatman (physics honors student 2001) Analysis of velocity field from
satellite images of the ocean
Kylie Gould (physics honors student 2001) Spontaneous emission of
inertia-gravity waves by interacting vortices
<>Two-dimensional
turbulence can be modified significantly when the Coriolis parameter varies
with latitude such as that on the rotating Earth. The vortices that comprise
the turbulent flow are found to distribute themselves in such a way that they
form zonal jets. Such zonal jets have been observed in many geophysical
systems and are a common feature in the atmospheres of Jupiter, Saturn and
the Earth. This picture shows vorticity (color) and velocity (arrows)
fields measured during a laboratory experiment on quasi-two-dimensional
turbulence on a polar beta-plane. A well-defined polar vortex can be clearly
seen in the center of the picture surrounded by an intense cyclonic jet that
is subject to Rossby waves.
Afanasyev, Y. D. and Wells, J., "Quasi-two-dimensional turbulence on the
polar beta-plane: laboratory experiments", Geophys. Astrophys. Fluid
Dynamics, 99 (1), 1-17 (2005).
<> This
picture shows the baroclinic instability of a coastal gravity current
visualized by dye. Our experiments were carried out using a scaled model of
the Black Sea mounted on a rotating table
to simulate the effects of the Earth’s rotation. The tank was filled
with saline water while the source of fresh dyed water was located in the
lower right hand corner of the model. The source allowed us to simulate the
supply of fresh water by rivers in the western part of the Black
Sea. The fresh water is then transported in cyclonic direction
around the sea forming the so-called Rim Current. The current becomes
unstable due to the baroclinic instability and forms meanders and vortices.
Arrow in the picture indicates the pairing of two vortices.
<>(Blokhina, M. D. and Y. D. Afanasyev: Baroclinic instability and
transient features of mesoscale surface circulation in the Black
Sea: laboratory experiment, J. Geophys. Res. Oceans, 2003,
108 (C10), 3322, doi:10.1029/3003JC001979).
Fall 2011: Physics 6363 - - Laboratory Experiment in
Geophysical Fluid Dynamics. The objective of this course is to give the
student the theoretical basis of the laboratory experimentation in Geophysical Fluid Dynamics
through lectures as well as practical skills. This will include the
development and implementation of your own fluid dynamics experiment to study
a problem that interests you, the results of which will be reported in a paper and video
which you will create. Prerequisite(s): P4205 or AMAT 4180 Lectures:
Three hours per week.
Fall 2007, 2009:1051 -
General Physics II: Oscillations, Waves, Electromagnetism.
is a calculus based introduction to oscillations, wave motion, physical
optics and electromagnetism.
Prerequisites: Physics 1050 or 1020 (with a minimum grade of 65%) and
Mathematics 1001. Mathematics 1001 may be taken concurrently.
Laboratories: Normally six laboratory sessions per semester, with each
session lasting a maximum of three hours.
covers kinematics and dynamics of a particle. Moving reference
systems. Celestial mechanics. Systems of particles.
Prerequisites: Physics 2820 and Applied Mathematics/Pure Mathematics 3260. Applied
Mathematics/Pure Mathematics 3260 may be taken concurrently.
Lectures: Three hours per week.
Winter 2001: 3230 - Classical Mechanics II.
Rigid body motion. Lagrange's equations. Hamilton's equations. Vibrations.
Special theory of relativity. Prerequisite(s): Physics 3220, Physics 3810 (or
AM/PM 3202) and AM/PM 3260. Lectures: Three hours per week.
Winter 2002: 2056 - General Physics VI: Modern
Physics. Special relativity, quanta of light, atomic structure and
spectral lines, quantum structure of atoms and molecules, nuclei and
elementary particles. Prerequisite(s): Mathematics 1001, Physics 1050 (or
1020 and 1021), and Physics 1054. Math 1001 and Physics 1054 may be taken
concurrently. Lectures: Three hours per week. Laboratory: Three hours per
week.
Winter 2002: 3300 - - Introduction to Physical
Oceanography. The course deals with the physics of processes in the
ocean, but provides an integrated view of the whole field of oceanography.
The importance of physical processes to other aspects of oceanography is
treated. Prerequisite(s): Physics 2053 and Mathematics 2000. Lectures: Three
hours per week.
Winter 2003: 4205 - - Introduction to Fluid
Dynamics (same as AM 4180). Basic observations, mass conservation,
vorticity, stress, hydrostatics, rate of strain, momentum conservation
(Navier-Stokes equation), simple viscous and inviscid flows, Reynolds number,
boundary layers, Bernoulli's and Kelvin's theorems, potential flows, water
waves, thermodynamics.. Prerequisite(s): Physics 3230 and either Physics 3821
or AM 4160.. Lectures: Three hours per week.
Fall 2003, 2004: 3821 - - Mathematical Physics
III. Further topics on the partial differential equations of
mathematical physics and boundary value problems.
Prerequisite(s): Physics 3820.
Lectures: Three hours per week.
Fall 2003: 6323 - - Stability Theory. Kelvin-Helmholtz
and Rayleigh-Taylor instabilities, centrifugal instability, stability on f-
and beta- planes. Effects of viscosity: Orr-Sommerfeld equation. Thermal
instability, stability of stratified fluids, baroclinic instability,
transition to turbulence.
Winter 2013, 2012: P4300 (and parallel graduate course P6310)
- -Advanced Physical Oceanography. Fundamental properties of
seawater and techniques of oceanographic measurement. The dynamical equations
of oceanography are derived and solutions explored by comparison with oceanic
observations. Properties of waves in rotating and non- rotating fluids.
Linear and non-linear wave theory are developed.
Prerequisites: Physics 3300 and 3820, or Engineering 7033, or the permission
of the instructor.
Lectures: Three hours per week.
Fall 2005: 6321 - -Coastal
Oceanography. Coastal
circulation: observations and theory; coastal trapped waves; wind-forced
response; uniform density models; effect of density stratification
Prerequisites: permission of the instructor.
Lectures: Three hours per week.
P2053 - Vortex streets
This is a new lab experiment in Physics 2053. This laboratory experiment is
designed to study regular arrays of vortices occurring behind an object in a
stream of fluid. This phenomenon is observed in industrial flows, flows in
the ocean and in the atmosphere. We consider the flow behind a circular
cylinder. In the second part of the experiment the effect of the body on the
fluid is imitated by using an appropriate force field when there is no real
body present in the fluid. The force field (virtual body) is created by a
permanent magnet located above the surface of water in combination with
electric current applied in the horizontal direction.
This
site is maintained by: Yakov Afanasyev.
Last updated: November, 2011.
