Atmospheric and Climate Sciences, 2012, 2, 562-567
http://dx.doi.org/10.4236/acs.2012.24051 Published Online October 2012 (http://www.SciRP.org/journal/acs)
The Impact of Climate Modes on Summer Temperature
and Precipitation of Darwin, Australia, 1870-2011
Cameron Hunter, Jacqueline Binyamin*
University of Winnipeg, Department of Geography, Winnipeg, Canada
Received August 23, 2012; revised September 25, 2012; accepted October 5, 2012
ABSTRACT
Monthly mean summer (DJF) temperature and precipitation from Global Historical Climate Network (GHCN-V3) for
the period of 1870-2011, are analyzed to assess the role of teleconnections on climate of Darwin, Australia. Indices of
El Niño-Southern Oscillation (ENSO), Antarctic Oscillation (AAO), Pacific Decadal Oscillation (PDO), North Atlantic
Oscillation (NAO), Arctic Oscillation (AO), and Pacific North American Oscillation (PNA) are extracted from monthly
means and compared with climatic data of Darwin. Most of these climate modes are shown to have a strong influence
on the monthly mean summer temperature and precipitation. ENSO is shown to have a positive relationship with the
amount of precipitation received and a negative relationship with the temperature. Where an El Niño event produces
warmer drier conditions and a La Niña event produces colder wetter conditions. The AAO is shown to cause cold and
dry condition s during the positive phase and warm and wet conditions during the neg ative phase. The PDO is shown to
cause El Niño like co ndition during the p ositive phase causing warmer, drier weather, and La Niña like conditio ns dur-
ing the negative phase causing cooler, wetter weather. Through the analysis it is also shown that the NAO, AO, and
PNA have little effect on the temperature and precipitation patterns of Darwin.
Keywords: Climate Modes; Teleconnections; Climate of Darwin; Climate Change; Climate Variability; ENSO; AAO;
PDO
1. Introduction
Darwin, Australia latitude 12.4˚ south, longitude 130.9˚
east is located on Australia’s northwestern coast. Month-
ly average temperature and total precipitation data for
Darwin International Airport, which is approximately 3
km from the Indian Ocean and is 30 m above sea level
are obtained from Global Historical Climate Network
(GHCN-V3) for the period of 1870-2011.
Darwin receives an average of 1693 mm of precipita-
tion yearly, with the distribution of precipitation being
very seasonal. Most of Darwin’s yearly total precipita-
tion is received in the summer months (DJF), while Dar-
win receives nearly no precipitation in the winter months
(JJA). Darwin’s average annual temperature is 27.6˚C
and due to its proximity to the ocean does not fluctuate
much throughout the year. The temperature ranges from
approximately 29˚C in summer to a low of 25.5˚C in
winter. The proximity to the ocean mediated Darwin’s
temperature, cooling the air during the summer months
and warming the air during the winter months. This mod-
erating effect causes Darwin’s small temperature range.
This paper investigates the effect of six teleconnec-
tions on summer temperature and precipitation of Darwin.
These teleconnections include El Niño-Southern Oscilla-
tion (ENSO), Antarctic Oscillation (AAO), Pacific De
cadal Oscillation (PDO), North Atlantic Oscillation
(NAO), Arctic Oscillation (AO), and Pacific North
American Oscillation (PNA). Our study is important be-
cause little work has been done on the effect that climate
modes have on Darwin’s temperature and precipitation.
The ENSO is categorized by sea surface temperature
and atmospheric pressure anomalies, and measured using
the Southern Oscillation Index (SOI) which is the pres-
sure difference between Tahiti, and Darwin. ENSO has
the strongest effect on the climate of the South Pacific,
causing below average rainfall amounts during El Niño
and above average rainfall amounts during La Niña for
Darwin [1,2]. Several studies have explored the precipi-
tation variability over Darwin and across the Australian
continent [3-5]. While others have explored ENSO’s
effect on the Australian continent [1,2,6-9].
The AAO is measured using the Antarctic Oscillation
Index (AOI) which is the difference between the surface
pressures at 40˚S and 65˚S [10]. The two phases of AAO,
the positive phase and the negative phase, are classified
by the strength of the subtropical high and the subpolar
*Corresponding a uthor.
C
opyright © 2012 SciRes. ACS

C. HUNTER, J. BINYAMIN 563
low. The positive phase shows a strengthening of the
subtropical high and a deepening of the subpolar low,
creating a greater than normal pressure difference be-
tween the two [11]. While the negative phase shows a
weakening of th e subtropical high and subpolar low, cre-
ating a weak pressure gradient [10]. The AAO has a
strong effect on the location of the southern hemisphere
midlatitudejet stream and through this affects the tem-
perature and precipitation patterns throughout southern
hemisph ere [4,10].
The PDO is a long-lived El Niño-like pattern of Pa-
cific climate variability. Its events can persist for 20 - 30
years and have a strong effect on the climate of North
America. Fluctuating sea surface temperatures (SSTs) in
the central North Pacific and along the west coast of
North America distinguishes the positive and negative
phases of this climate mode. When the PDO is in its
warm or positive phase, SSTs in the western coast of
North America are relatively warm and central North
Pacific SSTs are cooler and vice versa in the cool or
negative phase causing a change in the temperature and
precipitation patterns in these areas [12,13 ].
The NAO is the result of pressure differences between
the Azores high and the Icelandic low [14,15]. NAO af-
fects the northern hemisphere winter climates of eastern
North America and Europe, and as well affects the posi-
tion of the Atlantic storm track.
The AO is identified by the pressure difference be-
tween the polar high and the atmospheric low south of
the pole [16]. The strong pressure gradient causes the
circumpolar vortex to strengthen keeping the cold polar
air north [17,18]. The strengthening of the circumpolar
vortex causes mild weather throughout Europe and cold
weather in Greenland and Newfoundland during the nor-
thern hemisphere winter. The weak polar vortex brings
cold weather to Europe and the United States and warm
weather to Greenland and Newfoundland during the nor-
thern hemisphere win t e r.
The PNA affects the climate of the northern hemi-
sphere. It deals with the 700 mb heights for the locations,
Hawaii, the Aleutian Islands, southeastern United States
and the Intermountain region of North America. The
positive phase of the PNA shows higher than average
heights over Hawaii and the Intermountain region of
North American, while below average heights are re-
corded over the Aleutian Islands and the southeastern
United States. The negative phase shows a reversal of the
heights of these areas [19]. These height anomalies affect
the position of the East Asian jet stream and in the posi-
tive phase produce above average temperature in the
western United States and Canada and below average
temperatures across the southern United States. PNA also
affects the precipitation patterns of North America with
the positive phase causing above average precipitantion
on the Gulf of Alaska and below average precipitation
for the Midwestern United States [19,20].
Section 2 describes temperature and precipitation resu-
lts; and Section 3; summary and conclusions.
2. Results and Discussion
2.1. Temperature
Most of the Australian continent has experienced a war-
ming trend in the past century, except for a region of
cooling in the northwest [5]. Risbey [5] links this region
of cooling to the increased amount of precipitation re-
ceived in this area in the past century, and a greater per-
mcentage of cloudy days blocking incoming solar radia-
tion. Figure 1 shows that the temperature of Darwin has
cooled approximately by 1.5˚C over the past 129 years.
While there is a large amount of year-to-year variation in
the annual average temperature, there is clearly a strong
cooling trend in the temperature. As Darwin is located
along the northwest coast of Australia and as it is shown
in Section 2.2., has seen an increase in the total precip ita-
tion received, this blocking of solar radiation by cloud
cover could be one of the causes of the cooling tempera-
ture trend. Crowley [21] suggested that this cooling could
be due to the northern hemisphere exporting cold water
into the southern hemisphere. A seesaw effect is ob-
nserved where warming in the northern hemisphere
causes cold water from deep North Atlantic to circulate
and surface in the southern hemisphere thereby cooling
despite high CO2 levels [21].
Figure 2 shows again the trend of decreasing tem-
peratures in Darwin, but it also reveals a period of colder
than normal temperature. The period of 1942 to 2011 is
shown to be on average 0.5˚C cooler than would be ex-
pected by the trend. This period of cooling may be at-
tributed to increased amounts of aerosols in the earth’s
atmosphere specifically sulfate aerosols created by vol-
canic activity, as well as anthropogenic activity. These
Figure 1. Average annual temperature (˚C) for Darwin,
1882-2011. Data are incomplete for some years and there-
fore are omitted.

C. HUNTER, J. BINYAMIN
564
Figure 2. 30-year temperature (˚C) averages for Darwin, for
the period 1882-2011.
aerosols reflect incoming solar radiation and reduce the
amount of radiation reaching the surface, as well as act-
ing as cloud condensation nuclei and increasing the cloud
cover. Through th ese processes, sulfate aerosols d ecrease
the temperature of the surface and lower atmosphere.
We believe that sulfate aerosols are one of the possible
causes of this anomalous cold period from 1942-2011.
The ENSO, AAO and the PDO show the strongest
correlation with Darwin’s temperature. ENSO shows a
strong negative correlation with the summer temperature
at Darwin. The correlation coefficient of –0.36 means
strong negative values of the SOI will produce above
average temperatures. Large negative SOI values repre-
sent strong El Niño events, these events seem to produce
warm temperature anomalies, while positive SOI values
represent La Niña event and produce cold anomalies at
Darwin. Figure 3 shows this relationship between El
Niño/La Niña events and the summer temperature in
Darwin. The same relationship between temperature and
SOI has also been recognized previously by Power et al.
[6] and Suppiah [2]. This temperature trend could be due
to the pressure systems above Darwin in summer during
El Niño and La Niña events. During El Niño events a
high-pressure system persists above Darwin , with air sin-
king and diverging at the surface. Therefore there is no
uplift over Darwin and thus no clouds to reflect incoming
solar radiation. During La Niña events the opposite oc-
curs and a low-pressure system over Darwin causes con-
verging air and uplift. Greater amounts of cloud over can
be expected to reflect solar radiation increasing the local
albedo and so less radiation is received at the surface and
lower temperatures are experienced.
AAO also s eems to h ave a s trong eff ect on the av erag e
summer temperature of Darwin with a correlation coeffi-
cient of –0.42. Figure 4 shows strong positive AAO
events produces colder temperatures while negative
events produces warmer temperatures. The shift of the
southern hemisphere midlatitude jet stream by the change
in the pressure gradient between the polar and the sub-
tropical pressure centers produces bands of varying tem-
perature and rainfall differences in the southern hemi-
sphere, with a latitudinal band of cool temperatures fal-
ling on Australia during the positive phase and a latitu-
dinal band of warmer temperatures during the negative
phase [4].
PDO also shows a strong correlation with the average
summer temperature of Darwin shown in Figure 5. The
strong positive correlation coefficient of 0.37 shows
PDO’s strong effect on the summer temperatures of Dar-
win. The positive correlation means positive PDO even ts
produce warm temperature anomalies while negative
PDO events produce cold temperature anomalies. As we ll
as affecting the atmosphere and oceans in the northern
Pacific, the PDO also produces ENSO like conditions in
the South Pacific. The PDO produces El Niño like condi-
tions during the positive phase of the PDO, and La Niña
like conditions during the negative phase of PDO [12].
The analogous ENSO conditions produced by the PDO
explain the strong effect the PDO has on Darwin’s tem-
perature.
Figure 3. Correlation between average summer (DJF)
Southern Oscillation index (SOI) and average summer te m-
perature (˚C) for Darwin, 1882-2010. SOI data are from:
http://www.cru.uea.ac.uk/cru/data/soi/soi.dat.
Figure 4. Correlation between average summer (DJF) Ant-
arctic Oscillation (AAO) index and average summer tem-
perature (˚C) for Darwin, 1980-2010. AAO Index data are
from:
http://www.cpc.ncep.noaa.gov/products/precip/CWlink/dail
y_ao_index/aao/monthly.aao.index.b79.current.ascii.table.

C. HUNTER, J. BINYAMIN 565
Figure 5. Correlation between summer (DJF) Pacific De-
cadal Oscillation (PDO) index and the average summer
temperature (˚C) for Darwin, 1902-2010. PDO Index data
are from: http://jisao.washington. edu/pdo/PDO.latest.
The NAO, AO, and PNA are shown to have little ef-
fect on the temperature of Darwin. As these three tele-
connections affect the atmospheric and oceanic circula-
tion in the northern hemisphere, their effect on Darwin if
they have any, is too small to be discovered. If there is
any effect on the climate of Darwin, it is likely masked
by other interactions due to the large distance separating
Darwin from the centers of action of these oscillation
systems.
2.2. Precipitation
Darwin has experienced an increase in the yearly total
precipitation received in the last 142 years (Figure 6).
On average Darwin received 650 mm more precipitation
in a year now than in 1870. The trend in precipitation at
Darwin follows the trend of precipitation across all of
Australia, with the coastal wet regions receiving more
precipitation and the interior dry regi ons receiving le ss [5].
As with temperature the ENSO, AAO, and PDO all are
shown to have strong effects on the yearly summer pre-
cipitation totals. Again AO, NAO and PNA have little
effect on Darwin’s precipitation. The correlation coeffi-
cient between summer averages of SOI and total summer
precipitation for Darwin is 0.21 (Figure 7). The strong
positive correlation means that La Niña events, (positive
SOI values) causes greater than normal precipitation and
El Niño events (negative SOI values) produces less pre-
cipitation than normal. These precipitation anomalies are
due to the persistent high and low pressures above Dar-
win during La Niña and El Niño. During El Niño the
anomalous high-pressure over Darwin causes divergence
and sinking air, as there are few processes of up lift in
this area, therefore, less precipitation is received. La Niña
events have the opposite effect, anomalous low-pressure
over Darwin produces lots of uplift and thus lots of pre-
cipitation in the area [4,6,11]. Many strong El Niño/La
Niña events have caused large precipitation anomalies in
Darwin. Both the summers o f 1982-1983, and 1997-1998
were strong El Niño events with summer average SOI
values of –3.06 and –2.16 respectively; these years re-
ceived 576 mm, and 532 mm less than normal precipita-
tion. The strong La Niña event in the summers of 1998-
1999 had an av erag e SOI v alue of 1.16 , whic h re - cord ed
148 mm of precipitation more than normal (Figure 6).
The AAO has the strongest effect on the summer pre-
cipitation totals for Darwin. Figure 8 clearly shows the
positive relationship between the AAO index and the
total summer’s precipitation values with a correlation
coefficient of 0 .4. The positive cor relation between AAO
index and summer p recipitation means the positiv e phase
of AAO will cause greater than normal precipitation val-
ues in Darwin, and the negative ph ase of AAO will cau se
less than normal precipitation values. The movement of
the southern hemisphere midlatitude jet stream south in
the positive phase produ ces a dry band b etween 30˚S and
50˚S and a wetter band between 20˚C and 30˚S [4]. Dar-
win (latitude 12.4˚S) is located nearest to the later band
and obviously receives some residual effect of the wet
band. While the negative ph ase of AAO cause a dry band
between 20˚S and 30˚S and this must cause less precipi-
tation in Darwin.
The PDO also shows a strong influence on the pre-
cipitation of Darwin. As stated above the PDO creates El
Niño/La Niña conditions in the southern Pacific, as it
affects the Northern Pacific [12]. The correlation coeffi-
cient of –0.21 shows that dry El Niño type conditions are
produced by the positiv e phase of PDO and wet La Niña
like conditions are produced during by the negative
phase of PDO (Figure 9). The figure also shows the
negative relationship between PDO and summer precipi-
tation values.
3. Summary and Conclusions
Darwin has undergone a cooling of 1.5˚C of its average
Figure 6. Total annual precipitation (mm) received in Dar-
win, 1870-2011.

C. HUNTER, J. BINYAMIN
566
Figure 7. Correlation between the Southern Oscillation
Index (SOI), and the total summer (DJF) precipitation for
Darwin, 1871-2010. SOI data are from:
http://www.cru.uea.ac.uk/cru/data/soi/soi.dat.
Figure 8. Correlation between Antarctic Oscillation (AAO)
Index and the total summer (DJF) precipitation for Darwin,
1980-2011. AAO Index data are from:
http://www.cpc.ncep.noaa.gov/products/precip/CWlink/dail
y_ao_index/aao/monthly.aao.index.b79.current.ascii.table.
Figure 9. Correlation between the Pacific Decadal Oscilla-
tion (PDO) Index and the total summer (DJF) precipitation
for Darwin, 1902-2011. PDO Index data are from:
http://jisao.washington.edu/pdo/PDO.latest.
annual temperature dur ing the period of 1882-2011 . This
cooling can be attributed to increased precipitation in the
northwestern regions of Australia causing these areas to
receive less solar radiation due to blocking of solar radia-
tion by cloud cover. Another explanation of this cooling
could be due to cold water from deep north Atlantic sur-
facing in the southern hemisphere and cooling the south-
ern oceans. The atypical cool period from 1942-2011
could possibly be due to increased sulfate aerosols in th e
atmosphere, which reflect solar radiation. Sulfate aero-
sols also act as cloud condensation nuclei, increasing the
cloud cover and reducing the amount of radiation reach-
ing the surface leading to cooling of the surface and the
lower atmosphere.
The ENSO, AAO and PDO have all been shown to
have a large effect on Darwin’s average summer tem-
perature. The ENSO is shown to produce warmer condi-
tions at Darwin during El Niño events and cooler condi
tions during La Niña events. The AAO produces cold
weather during the positive phase and warm weather
during the negative phase. Unlike AAO the PDO’ posit-
ive phase is shown to produce warm weather and the ne-
gative phase is shown to produce cooler weather at Dar-
win.
Precipitation in Darwin increased during the 1870-
2011 period by an amount of 650 mm. Also, ENSO, AAO
and PDO are all observed to have a large effect on the
summer precipitation in Darwin. El Niño events produce
much dryer summers and La Niña events produce wetter
summers. The low-pressure present during La Niña
events causes convergence and precipitation over Darwin,
while the high pressure present during El Niño events
causes divergence and clear skies. The AAO is shown to
cause drier summer weather during the negative phase
and wetter summer weather during the positive phase.
Finally the PDO causes Darwin to experience dry sum-
mer weather during the positive phase and wet summer
weather during the negative phase.
Climate modes are shown to have a large effect on the
Darwin’s summer temperature and precipitation and have
significantly changed its yearly average temperature and
total precipitation in the past 1 40 years. A greater change
in the Earth’s climate will likely have an effect on the
frequency and strength of the climate modes discussed
and will thus greatly alter Darwin’s climate as well as the
climate of other locations. Future research is needed to
understand the relationship between climate change and
variability and the climate modes in order to be able to
forecast the effect of climate change on other locations.
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