V1003 Climate & Society
Homework 4
Due in Class: October 22, 2014
Part A:
In class we have been discussing ENSO; below is a graph and the corresponding table of
values of the SOI (southern oscillation index) from 1960-1990. SOI is one way used to
track ENSO activity. Note that the equation for SOI is:
SOI=(SLP at Tahiti- SLP at Darwin)/SD(SLP at Tahiti- SLP at Darwin)
Where SLP=sea level pressure and SD=standard deviation
a) Are El Nino years represented by a positive or negative SOI value?
b) Why is this? Explain how ENSO affects atmospheric pressure gradients
c) Based on this data, calculate the recurrence time of both El Nino and La Nina
events (i.e. use the peak value and look at the average of how many years are
between events). Please show your work.
SOI timeseries
25
20
15
10
SOI
5
0
1960
1962
1964
1966
1968
1970
1972
1974
1976
1978
1980
1982
-5
-10
-15
-20
-25
year
Year
SOI
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
Year
0.4
5
-6.7
9.7
-15
-0.1
2.5
2
-5.7
8.5
10
-11.5
14.3
6.8
18.6
SOI
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
-4.2
-13.6
1
-2.2
-2.6
5.3
-22.6
0.5
-0.5
-1.7
-1.3
-11.8
13
3.6
-1.6
1984
1986
1988
1990
Part B:
1) Imagine you are a fisherman in Peru and an El Niño is forecast to begin this fall
and into early next year (as it is!).
a) Should you expect a prosperous year; why or why not? (2 sentences or
less)
b) How would your outlook differ if it were an La Niña year and why? (2
sentences or less).
c) Draw a sketch of the Pacific Ocean as you expect it to be in December
2014, indicating the ocean temperature gradients (where it is warm/cold),
the Walker circulation, where convection/rain occurs and where it is dry,
the thermocline slope, sea surface height, trade winds (are they stronger or
weaker than normal?), and upwelling (same).
2) Imagine Aqua-World – a world with no land surface anywhere, but a planet the
same size and rotation rate as Earth.
a) Would there be trade winds? Why/why not?
b) Would there be equatorial upwelling? Why/why not?
c) Would there be Walker circulation? Why/why not?
d) Would there be an ENSO oscillation? Why/why not?
e) Sketch this world showing trade winds, upwelling, and where the rain fall
occurs.
1) Now imagine Wall-World, which is the same as Aqua-World except that it has
two large narrow landmasses (say, 100 km wide, see black bar on figure below),
east and west Waldonia, bracketing a large open expanse of ocean like the modern
Pacific Ocean except a lot larger.
a) Would there be trade winds? Why/why not?
b) Would there be upwelling? Why/why not? Where
c) Would there be Walker circulation? Why/why not?
d) Would there be an ENSO oscillation? Why/why not?
e) Sketch this world showing trade winds, upwelling, and where the rainfall
occurs.
WEST
EAST
2) Now imagine that you are the Climate Prediction Specialist for Walldonia.
a) The citizens of east Walldonia want to know if their rainfall will be
constant year to year or if it will vary. What do you tell them?
b) Now they want you to tell them whether the interannual (that is, year to
year) rainfall variability at east Walldonia will be longer or shorter period
that the 4 year average ENSO period on Earth. What do you tell them?
c) Imagine now that you could put TWO reporting stations anywhere on
Wall-world to measure and (automatically report back) any TWO of the
following climate properties (SST, pressure, winds, rainfall, sea level) at
any TWO stations. Where would you put the stations and why? What
TWO properties would they measure and why?
d) What would these stations tell you that would be helpful for climate
prediction in Walldonia?