International Journal of Marine Science2016, Vol.6, No.56, 1-9
4
Figure 2 Monthly mean anomalies of (a) alongshore wind stress (τ
alongshore
), (b) Ekman pumping/suction (W
EK
), (c) mixed layer depth
and (d) sea surface temperature (SST), averaged over the region 90˚W-88˚W and13˚S-15˚S
Monthly Ekman pumping anomalies for 5 years covering 1982-83 El Nino event and 1988-1989 La Nina event
averaged over the same region as above , are shown in figure 3(a &b). Negative Ekman pumping anomalies (Peak
of the order of 0.5 *10
-6
m/s in 1982 August) and positive Ekman pumping anomalies (peak ~ 0.9 *10
-6
m/s in
1988 September) are easily evident from the figure which would cause deepening and shoaling of thermocline
respectively. Comparing the two El Nino events amplitude of Ekman pumping is more during 1997 -98 than that
during 1982-83 attributing to the stronger former event. MLD anomalies in the eastern Pacific averaged over
complete event are more (~20-30m) in the 1997-98 event than in the 1982-83 event (~10-20m) (Figure not
shown).Ekman pumping anomalies are of the same order (~0.9 *10
-6
m/s) in the strong El Nino and strong La
Nina event. Ekman pumping is replaced with Ekman suction in the eastern tropical Pacific and hence shallow
thermocline is present during La Nina.
Figure 4 shows composite of SST anomalies, Ekman pumping anomalies and MLD anomalies in the El Nino and
La Nina event. It is clearly seen that during El Nino events positive SST anomalies, negative Ekman pumping
anomalies causing downwelling and hence positive MLD anomalies that is deepening of MLD exist in the eastern
tropical Pacific Ocean whereas negative SST anomalies, positive Ekman pumping anomalies and negative MLD
anomalies exist during La Nina event. In the west Pacific Ocean this becomes opposite. This composite picture
also points that the amplitude of Ekman pumping and MLD anomalies remains unaltered in the south east Pacific
during El Nino or La Nina event.
