Media: Preferred medium is 2.3 Gbyte Exabyte tape
Notes: The archive datasets are available to the community together with
the Fortran 77 software needed to read the file and extract horizontal and
vertical (N-S and E-W) sections of the model variables. Users will need to
write their own programs to extract sections at other angles or which cover
only part of the model domain. Plotting programs in the 'C' language are
also available for use on SUN 4 computers.
Model Description
FRAM is a primitive equation numerical model of the Southern Ocean between
latitudes 24S and 79S. The code is based on that of Cox. The model starts
from rest with initial temperature of -2C and salinity 36.69 everywhere,
and relaxes to the Levitus annual mean temperature and salinity over 6
years. For the first 2 years 160 days, the relaxation timescale is 180
days for depths above 160 m and 540 days for the deeper levels. From then
until 6 years the timescale is 360 days throughout. This is equivalent to
the normal robust diagnostic scheme, except that the relaxation is so weak
that the eddy field can develop. Surface forcing (Hellerman annual mean
winds), is introduced after 2 years 6 months - increasing linearly from
zero to the mean values over 6 months. After 6 years seasonal winds are
introduced and surface forcing of temperature and salinity is operated by
relaxing the surface layer only to the annual mean Levitus values with a
time scale of one year. Towards the end of 9 years (day 3256), the
viscosity and diffusion change from harmonic to a mixture of harmonic and
biharmonic and the bottom friction changes from linear to quadratic. The
model runs on to the end of 16 years.
Model Behaviour
After one model day the stream function shows large amounts of energy
generated around topography. By day 10 the model has settled down and
produced a recognisable Circumpolar Current with steering south of New
Zealand, round Kerguelen and through the fracture zone of the mid-ocean
ridge of the South Pacific. The amplitude of the Circumpolar Current,
measured by the transport through Drake Passage, grows roughly linearly
with time. When the winds are added, the model responds in about 10 days
with a 23 Sv increase in transport. The transport, total kinetic energy of
the model and other diagnostic fields settle down between years 5 and 6,
indicating that the momentum budget of the model is near its asymptotic
state. The transport through Drake Passage is about 200 Sv. The main
regions of eddy formation are in the Agulhas Current and along the path of
the Circumpolar Current. The stream function after six years is
illustrated in Figure 1. Following the
introduction of seasonal forcing after 6 years, the transport through Drake
Passage has been oscillating between 195 and 200 Sv. There has been an
increase in eddy energy near the ACC and eddies produced by the Agulhas
Current (see the animation of temperature at 120m)
are continuing to radiate into the South Atlantic.
Eddies are also formed along the East Australia Current
(see the second animation of temperature at 120m).
Further details can be found in FRAM publications.
