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International Journal of Marine Science 2013, Vol.3, No.18, 145-150
http://ijms.sophiapublisher.com
146
the Arabian Sea (Figure 1) were extracted from the
Hadley Center's SST data for the period 1961 to 2009.
HadISST1 temperatures are reconstructed using a
two-stage reduced-space optimal interpolation procedure,
followed by superposition of quality-improved
gridded observations onto the reconstructions to
restore local detail (Rayner et al., 2003). The SST
anomalies (SSTA) are calculated as SST minus mean
SST of the entire period (1961~2009).
Figure 1 Study region and the areas selected (1×1 degree boxes)
for present analysis
Monthly average SST for the years 1961 to 2009 was
modeled using the following equation and was
performed separately for each location:
Where T is the predicted monthly average SST, A
1
, P
1
and α
1
are the amplitude, period and phase shifts,
respectively of the first mode and A
2
, P
2
and α
2
are the
amplitude, period and phase shift of the second mode.
The slope and the y-intercept (C) are the linear
parameters that describe the trendline of the whole
data set. The latter constants were estimated prior to
estimating the modal parameters and all parameters
were estimated by minimizing the negative log
likelihood assuming that the errors were normally
distributed with mean zero and variance σ2. The
likelihood profile technique (Lebreton et al., 1992)
was used for estimating 95% confidence intervals (CI).
The slopes of the linear trendlines were tested to
determine if they were significantly different from
zero (Zar, 1999).
We obtained gridded SSH data from Archiving,
Validation, and Interpretation of Satellite Oceanographic
data (AVISO,
http://www.aviso.oceanobs.com/
) for
the two locations for the period 1993~2010. This data
is an optimal merging of SSH from multiple platforms:
Ocean Topography Experiment (TOPEX)/Poseidon,
Jason, (European Remote Sensing Satellite) ERS-1/2,
and Environmental Satellite (Envisat).
3 Results
The sea surface temperature for the period from 1961
to 2010 gave a mean SST that is significantly higher
in Muscat than in Masirah (t-stat0.05, DF=1174=7.48;
P=7.5×10-14). Showing interannual and longer time
fluctuations in SST (Table 1), SST is noticeably higher
post-1985 at Masirah.
Table 1 Statistics of annual SST off Muscat and Masirah during
the study period
Parameter
Muscat
Masirah
Mean SST (1961
-
2010)
26.61
25.82
Standard Deviation (1961
-
2010)
0.25
0.37
Variance (1961
-
2010)
0.06
0.13
Mean SST (1961
-
1984)
26.45
25.55
Mean SST (1985
-
2010)
26.77
26.08
Standard Deviation (1961
-
1984)
0.18
0.21
Variance (1961
-
1984)
0.03
0.04
Standard Deviation( 1985
-
2010)
0.21
0.29
Variance (1985
-
2010)
0.04
0.09
The SST anomaly (SSTA) from 1961 to 2009 showed
a distinct shift in the SST distribution after 1984
(Figure 2). A quantum jump of about 0.5
℃
is seen in
the SSTA post-1984 at both locations. At both
locations, there was a positive increase in SST over
the period of the study and for both locations the
slopes were significantly different from zero (Masirah:
t-stat0.05, DF=586=3.88, P=0.0001; Muscat: t-stat0.05,
DF=586=2.50, P=0.01). The rate of increase of
temperature over the study period was higher in
Muscat than Masirah (larger slope value). Muscat
shows two prominent peaks with the most prominent
one occurring every 12 months while the smaller
mode occurring approximately every 6 months (Table
2). The difference between the amplitudes is 0.32
℃
indicating that the two modal peaks are similar in
amplitude. The most prominent peak occurs annually
during the month of July and the smaller peak during
May. In the case for Masirah, though bi-modal in
nature it has its prominent peak occurs every 6 months