Mixing and the down fall of a warm ENSO event?
Was the profoundly rapid shutdown of the 1997-98 ENSO event
( 125 West, 0N and
140 West, 0N ) due to
an abrupt mixing event that came about because (A) of a highly nonlinear
relationship between the efficiency of entrainment, the strength of the
wind and the slope and shear of the equatorial undercurrent (with the
latter two changing realively slowly compared to the turbulent mixing)?
While "A" has been demonstrated in the laboratory for the non-rotating
case of a tilted jet in a stratified shear, it has not been examined
in a geophysical setting. This might be a fun project, that would
involve Prof. Bob Breidenthal from Aeronautics and Astronautics.
Contribution from John Micket (May 2001)
Why is the
amplitude of the seasonal cycle in SST
the midlatitude oceans 2-3 times
greater in the northern hemisphere than in the southern
In class, we hypothesized that the answer involved land: there is
much more in the northern hemisphere than in the southern hemisphere. We
discussed three effects: seasonality in mixed layer depth (due to seaonality
in storminess), the differential heat capacity of land and upper ocean (in
the face of advection by the ubiquitous westerlies), and seaonality in the
ocean heat transport. Which of these three effects are important?
Does the answer give you any insight on the processes that are likely
to be most important for climate variability ?
The width of
the equatorial cold tongues:
Equatorial upwelling is thought to be confined to well within
100 km from the equator. The equatorial cold tongue is much
wider than this (extending about 500 km from the equator).
What sets the width of the cold tongue to the north and south of
the equator? Is it wind stress curl? Is it ocean instabilities?
Why is there no cold tongue in the Indian Ocean?
On the face of it, one could argue that there are no
mean Trade Winds to set up an east-west tilt. More specifically,
there is no cold tongue because of the synergy of two facts:
the amplitude of the annual cycle in the Trade Wind is larger than
the climatological mean Trade Wind amplitude, and
the seasonal cycle of winds is too short of a period
compared to the ocean adjustment time.
Another possiblity: the mean Indoneasian Throughflow keeps the
mean themocline too deep along the equator to creat a cold
tongue. Which of these factors is more important? What would
it take to get an Indian Ocean cold tongue (and, thus, an ENSO-like
mode in the Indian Ocean)?
the cold tongue in the equatorial Pacific found in the July-October season?
what sets the phasing of the annual cylce in the tropical