International Journal of Marine Science2016, Vol.6, No.56, 1-9
3
Pacific has colder SST anomalies. The maximum values of the warm SST are located in the coastal region of the
eastern boundary. As the El Nino develops further, the SST pattern is mostly stationary in spite of a slightly
westward shift of the maximum SST anomaly with magnitude of 3.5
˚
C. Figure 2 displays anomalies of (a) along
shore wind stress, (b) Ekman pumping, (c) MLD and (d) SST, averaged over 90˚W-88˚W and13˚S-15˚S region
(viz. 2˚x2˚ box near the south east Pacific coast), from January 1994 to December 1998. During the mature phase
of 1997 El Nino event i.e. July /August 1997 higher τ
alongshore
anomalies with magnitude of (~2*10
-2
Nm
-2
) along
with deeper thermocline are seen in the south eastern tropical Pacific. Ekman suction is replaced by Ekman
pumping with magnitude of anomalies -0.9 *10
-6
m/s (figure 2b).
Figure 1 SST anomalies (
˚
C) during El Nino event 1997-1998 in the tropical Pacific for the months MAY, JUN, JUL, AUG, SEP,
OCT, NOV, DEC, JAN, FEB, MAR, APR
Weakened trade winds during the El Nino allow warmer water from the western Pacific to surge eastward. This
leads to a buildup of warm surface water and a sinking or deepening of the thermocline in the eastern Pacific. The
anomalous trade winds flow from west to eastern Pacific in El Nino event, where the Ekman pumping is negative
(downwelling). Positive MLD anomalies of the order of 40 m are seen in eastern tropical Pacific Ocean Figure
2(c). In the El Nino event deeper thermocline is present in the eastern tropical Pacific and has negative Ekman
pumping which cause mixed layer depth to increase and hence positive MLD anomalies occur. This demonstrates
the increase in τ
alongshore
field over the coastal waters off Peru during the 1997–1998 El Nino, which should have
raised the thermocline. However, Ekman pumping is playing important role in deepening of thermocline. Positive
SST anomalies of the order of (~2˚C) are seen during this event from figure 2(d).
