Syamsuddm et al Effects of El Nino-Southern Oscillation on catches of Thunnus obesus in the eastern Indian Ocean 
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Figure 4 
Spatial patterns of the empirical orthogonal function modes in the eastern Indian Ocean off Java 
from September 1997 to December 2000: (A) first mode of sea-surface-height anomaly (SSHA), (B) 
second mode of SSHA, (C) first mode of sea-surface temperature (SST), (D) second mode of SST, (E) 
first mode of chlorophyll-a (chl-a) concentrations, and (F) second mode of chl-a concentrations. Scale 
units are in centimeters, degrees Celcius, and milligrams per cubic meter for SSHA, SST, and chl-a 
data, respectively. 
Spatial and temporal modes of ocean variability 
The remote forcing in the timescale of interannual 
and seasonal variations due to ENSO and monsoons 
are represented by the first and second EOF modes of 
SSHA, SST, and chlorophyll-a concentrations, with the 
total energy variance from these 2 modes about 78.60% 
for chlorophyll-a values, 71.39% for SSHA, and 34.53% 
for SST (Table 1). The first spatial mode of SSHA con- 
tributed 48.82% of the total variance, indicating waters 
with relatively low temperatures and with negative 
SSHA concentrated along the southern coast of Java 
(Fig. 4A). The second spatial mode of SSHA contrib- 
uted 22.57% of the total variance and showed that wa- 
ters with relatively low temperatures were distributed 
along the southern coast of the Indonesian archipelago 
(Fig. 4B). The first spatial mode of SSHA corresponded 
with interannual variability, as shown by the first tem- 
poral mode (Fig. 5A). A map of the second spatial mode 
of SSHA clearly shows that this mode corresponded 
with seasonal variability, as indicated by the second 
temporal mode (Fig. 5B). 
The SSHA results were associated with the first and 
second spatial modes of SST, with total variances of 
25.93% and 8.60%, respectively. The first spatial mode 
of SST showed that waters with relatively low tem- 
peratures were concentrated along the southern coast 
of Java, extending to the offshore area (7-13°S) (Fig. 
Table 1 
Summary of the amplitude function (percentage of 
the total variability) of the first and second empirical 
orthogonal function modes of the sea-surface-height 
anomaly (SSHA), sea-surface temperature (SST), and 
chlorophyll-a (chl-a) concentrations in the eastern In- 
dian Ocean off Java from September 1997 to December 
2000 . 
Total modes 
Parameter Mode 1 (%) Mode 2 (%) 1 and 2 (%) 
SSHA 48.82 22.57 71.39 
SST 25.93 8.60 34.53 
Chl-a 63.39 15.21 78.60 
4C). The second spatial mode of SST showed that those 
waters were spread along the western coast of Java (7- 
12°S), while waters with relatively high temperatures 
covered the eastern part of the EIO off Java (Fig. 4D). 
The amplitude function of the first mode of SST corre- 
sponded with interannual variability (Fig. 50, and the 
second mode corresponded with the seasonal cycle in 
which the maximum and minimum SST occurred during 
the northwest monsoon (November-April) and southeast 
monsoon (May— October), respectively (Fig. 5D). 
