Walker Circulation
Mean Tropical Overturning Circulations
(Figure obtained from Introduction to Tropical Meteorology, 2nd Edition, © 2011 COMET.)
Base State Pacific Zonal Circulation
(Figure obtained from Introduction to Tropical Meteorology, 2nd Edition, © 2011 COMET.)
Base State Global Walker Circulation
(Figure obtained from Introduction to Tropical Meteorology, 2nd Edition, © 2011 COMET.)
Oceanic Transport
Consider a 2-D fluid bounded by land masses to the west and east with temperatures decreasing with
increased depth. Easterly winds at the surface of that fluid will attempt to carry the fluid westward. At
the eastern edge of the fluid, it is replaced by cooler fluid from below. At the western edge, the fluid is
forced downward.
z
warming
cooling
W
In reality, oceanic transport is far more complicated than in the simplistic diagram above. In particular,
Ekman transport results in a ~45° rightward deflection (NH) of the oceanic transport vector, resulting in
modest equatorial upwelling under easterly wind conditions. This becomes important when
considering El Nino conditions.
Mean Daily Precipitation: Jan-Mar
Enhanced
precipitation
found to the
west, especially
with Pacific
circulation and
over South
America.
Figures obtained using the freely-available NCEP-DOE Reanalysis II dataset.
Mean Daily Precipitation: Jul-Sep
Northward shift
of enhanced
precipitation
occurs but still
favors the
western
branches of the
three major
zonal
circulations.
Other heatinginduced
features also
contribute to
precipitation
patterns, as we
will discuss
later.
Figures obtained using the freely-available NCEP-DOE Reanalysis II dataset.
Linear Approximation: Walker Circulation
(Figure obtained from Introduction to Tropical Meteorology, 2nd Edition, © 2011 COMET.)
Linear Approximation: Walker Circulation
(u,v) - vectors
w - contours
(u,v) - vectors
p - contours
Meridionallyintegrated flow
(Figure obtained from Gill (1980), © 1980 Royal Meteorological Society/Wiley Interscience.)
Linear Approximation: Hadley Circulation
zonal velocity
streamfunction
pressure perturbation
(Figure obtained from Gill (1980), © 1980 Royal Meteorological Society/Wiley Interscience.)