- El Nino is an oceanographic
phenomenon first observed in the eastern Pacific near Peru.
It occurs periodically with an irregular period of about 4--7 years, and
consists of anomalous warming of the waters near Peru and cooling near the
Philippines. It involves major changes in both the atmospheric and oceanic
circulation over the Equatorial Pacific, and is a clear example of
large-scale air--sea coupling and short term climatic variation. The first
observations noted an unusual warming of the waters off Peru (which came
usually around Christmas, hence the name, which means ``Christ child'').
The warming diminishes the usual upwelling of cold and nutrient-rich waters
to the surface, so it leads to a disastrous decrease in anchovies and other
fish production with large economic consequences.
- A radar altimeter measures the
distance from the satellite to the surface of the ocean, and if the
position of the satellite in space is known, this measurement allows the
ocean surface deviations from the level corresponding to no motion to be
inferred on time scales of a few days to years. The time scale of
significant large scale variation of wind forcing is a few days and is
called synoptic time scale.
- Gravity waves are waves that propagate at the air--sea
interface under the action of gravity. Note that the displacement of the
heavy fluid represents available potential energy and the resulting
equations are somewhat similar to those governing waves on a string.
Sea: Greenland--Iceland--Norwegian Sea.