Download Rainfall for Canary Island from 1947 – 1992

Name ___________________________
Date _________ Period 1 2 3 4 5 6
El Niño!
Sometimes, the Pacific Ocean near America warms.
Normal ocean currents and winds change. The oceans
to the north-east of Australia cool. El Niño is here!
The Pacific Ocean's Circulation Features
The Pacific Ocean is a huge mass of water, which
controls many climate features in its region. Its
equatorial expanse, far larger than the Indian or
Atlantic Oceans, is critical to the development of the
Southern Oscillation and El Niño. In most years the
Humboldt current brings relatively cold water
northward along the west coast of South America, an
effect increased by upwelling of cold water along the
Peruvian coast. The cold water then flows westward
along the equator and is heated by the tropical sun.
These normal conditions make the western Pacific
about 3°C to 8°C warmer than the eastern Pacific.
However, in El Niño years the central or eastern
Pacific may become as warm as the western Pacific.
is positive, it means that there was no El Niño
event in that year.
The Southern Oscillation Index (SOI) is determined by the difference in barometric pressure
between Tahiti and Darwin. Pressure fluctuates
between the two locations, but in El Niño years
(SOI is negative), the pressure is higher in Darwin
than in Tahiti. See the SOI graph below for the
current values.
The Walker Circulation
The Walker circulation is named after Sir Gilbert
Walker, a Director-General of British observatories in
India who, early this century, identified a number of
relationships between seasonal climate variations in
Asia and the Pacific region.
Climate Clues to El Niño
The easterly trade winds are part of the low-level
component of the Walker circulation. Typically, the
trades bring warm moist air towards the Indonesian
region. Here, moving over normally very warm seas,
moist air rises to high levels of the atmosphere. The
air then travels eastward before sinking over the
eastern Pacific Ocean. The rising air is associated
with a region of low air pressure, towering
cumulonimbus clouds and rain. High pressure & dry
conditions accompany the sinking air.
The Southern Oscillation Index (SOI)
The "SOI", or Southern Oscillation Index, is a
measure that scientists use to establish whether El
Niño is present and how strong it is. A negative SOI
value indicates an El Niño. The lower the value of the
SOI, the stronger the El Niño event. If the SOI value
Meteorologists watch for changes to the
atmosphere and ocean circulation, which help
them detect an El Niño, or forecast its lifetime.
Indicators are:
 The Walker circulation and trade winds weaken.
During more intense El Niño episodes, westerly
winds are observed over parts of the equatorial
western and central Pacific.
 The area of warm water usually over the western
tropical Pacific cools and the warmest water is
displaced eastward to the central Pacific.
 The normally cold waters on the South American
coast warm by 2°C to 8°C.
 The Southern Oscillation Index remains negative.
 Enhanced cloudiness develops over the central
equatorial Pacific.
Name ___________________________
Date _________ Period 1 2 3 4 5 6
Changes in the Weather
El Niño's Opposite Phase
The following table presents information on El Niño
and rainfall for the years from 1947 to 1992. The
rainfall column of the table gives the total annual
rainfall for Canary Island in northern Victoria.
When the Southern Oscillation Index sustains
high positive values, the Walker circulation
intensifies, and the eastern Pacific cools. These
changes often bring widespread rain and flooding
to Australia - this phase is sometimes called antiEl Niño (or La Niña). Australia's strongest recent
examples were in 1973-74 (Brisbane's worst
flooding this century in January 1974) and in
1988-89 (vast areas of inland Australia had record
rainfall in March 1989).
Rainfall for Canary Island from 1947 – 1992
Year
SOI
Rainfall
Year
SOI
Rainfall
1947
2.3
382
1948
-1.2
286
1970
3.9
406
1971
11.0
1949
-1.1
535
331
1972
-7.4
268
1950
1951
15.4
493
1973
7.3
812
-0.7
380
1974
9.9
598
1952
-2.3
438
1975
13.6
441
1953
-6.8
360
1976
1.1
269
1954
4.1
381
1977
-9.9
231
1955
10.6
594
1978
-1.7
471
1956
10.7
635
1979
-1.9
369
1957
-3.9
289
1980
-3.1
328
1958
-3.2
481
1981
1.8
400
1959
0.0
283
1982
-13.1
123
1960
3.8
568
1983
-8.3
527
1961
0.8
381
1984
-0.1
336
1962
5.4
383
1985
0.9
395
1963
-2.0
431
1986
-2.4
379
1964
6.3
465
1987
-13.1
366
1965
-8.4
335
1988
7.8
445
1966
-4.2
400
1899
6.8
488
1967
3.2
156
1990
-2.2
278
1968
3.0
430
1991
-8.8
321
1969
-5.4
443
1992
-10.4
544
Questions:
1. In how many years was the SOI less than -10?
2. Write down the rainfall for each year that the
SOI was less than -10.
3. Calculate the avg rainfall for all the years in
which the SOl was less than -10. This is the
avg rainfall in years when El Niño was present.
4. How many years was the SOI greater than 10?Write down the rainfall for each year that the SOI was
greater than 10.
5. Calculate the average rainfall for all these years in which the SOI was greater than 10.
6. From your answers to questions 3 and 5, what do you notice about the impact of El Niño on rainfall at
Canary Island in northern Victoria?
7. Describe the weather in the eastern Pacific during El Niño. How about the western Pacific?
8. How about both sides of the Pacific during La Niña?
9. According to the SOI graph when did we have our strongest El Niño effect in the last five years?