International Journal of Marine Science2016, Vol.6, No.56, 1-9
8
Table 1 Amplitudes of SST, MLD and W
EK
anomalies in the El Nino and IOD events
Event
SST(
o
C)
MLD(m)
W
EK
(*10
-6
m/s) for El Nino/La
Nina and W
EK
(*10
-5
m/s ) for
positive and negative IOD
El Nino in 1997-98
> 3.5
20 to 30
-0.5
El Nino in 1982-82
> 3
10 to 20
-0.5
La Nina in 1988-89
< -2
-10 to -20
0.5
Composite of El Nino
3 to 3.5
10 to 20
-0.5
Composite of La Nina
-1 to -2
-10 to -20
0.5
PIOD in 1997(East-box)
-1.4
-30 to -40
2 to 3
PIOD in 1994(East-box)
-1.4
-20 to -30
4 to 4.5
NIOD in 1992(East-box)
0.8 to 1.0
20 to 30
-1
PIOD in 1997(West-box)
0.5 to 1.2
30 to 40
-0.5
PIOD in 1994(West- box)
0.6 to 1.2
10 to 15
-0.5
NIOD in 1992(West-box)
-0.4 to -0.6
0 to -10
0.3
Composite of PIOD(East-box)
-1.8 to -2.1
-25 to -35
3 to 4
Composite of PIOD (West-box)
0.3 to 0.6
15 to 20
0 to -1
Composite of NIOD (East-box)
0.8 to 1.0
20 to 30
0.5 to -1
Composite of NIOD (West-box)
-0.4 to -0.6
0 to -10
0 to 0.5
4. Conclusions
In the present study Ekman pumping and MLD variability is examined during El Nino and IOD events in the
Indo-Pacific region. In the El Nino years negative Ekman pumping anomalies occur in the eastern tropical Pacific
Ocean in accordance with positive MLD anomalies and warmer SSTs with deeper thermocline depth present there.
Stronger MLD deviations are found during stronger El Nino event of 1997-98. The alongshore wind stress
component increased during this event which would act to lift the thermocline. In spite of this, downwelling
occurred and hence importance of Ekman pumping in deepening of thermocline is emphasized. During La Nina
event, positive Ekman pumping anomalies and negative MLD anomalies occur in eastern tropical Pacific Ocean.
Magnitude of Ekman pumping remains approximately same during El Nino or La Nina in the south east pacific.
During positive IOD events eastern box has positive Ekman pumping and negative MLD anomalies, and vice
versa for the negative IOD events. More Ekman pumping anomalies are found in the eastern box during strong
positive IOD event in 1994. Stronger deviations in Ekman pumping and MLD are seen during IOD event as
compared to those in El Nino/La Nina events.
Acknowledgements
The authors wish to thank the Director, I.I.T.M. from providing the facilities. Wind data from ECMWF and MLD & SST data from
APDRC website is gratefully acknowledged. Authors are thankful to Dr. Brian Doty for the GrADS software.
References
Bakun A., and Nelson C.S., 1991, The seasonal cycle of wind-stress curl in the sub-tropical eastern boundary current regions, J. Phys. Oceanogr., 21, 1815–
1834
