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1Introduction
Interactions between the atmosphere and the ocean are very important in the climate system. The oceans play an important role in the climate system owing in part to their large heat-storage Capacity. Vertical water movement in the ocean changes sea surface temperatures (SST) and vice versa and thus causing changes in MLD. In this paper the main focus is to understand the variability of Ekman pumping representing vertical mixing and mixed layer depth during strong El Nino/La Nina and IOD events. Ekman pumping is represented by τ/(ρf), where τ is the surface wind stress, ρ is seawater density (1025 kg m^sup -^3), and f is the Coriolis parameter (=2Ωsin[theta], with Ω and [theta] equal to Earth's angular velocity and latitude, respectively). The surface wind stress τ is calculated using the bulk formulation,
τ = [τx, τy] = ρaCD V [u, v], (1)
Where, τx and τy are east-west and north-south components, respectively. The surface wind (nominally at 10 m) is assumed to be parallel to the stress vector, with components [u, v] and magnitude V (= wind speed). ρa is the density of surface air, CD is the drag coefficient. Vertical velocity at the bottom of the Ekman layer (effective depth of frictional influence) from wind stress, WEK, is named Ekman suction if upward and Ekman pumping if downward as in (Stommel, 1958). Ekman transport is proportional to the wind stress and inversely proportional to the sine of the latitude as discussed by (Sverdrup et al., 1942). Ekman pumping analysis is given as
WEK = (curl τ)/ (ρf), (2)
Fennel (1999) showed theoretically that wind stress curl could have a substantial impact in coastal upwelling. Off Oregon west coast of North America, Ekman suction was a major contributor to the total upward velocity during coastal upwelling as discussed by (Halpern, 1976). Off the west coast of South America, El Nino conditions include a deepening of the coastal thermocline (Strub, et al., 1998). During the 1997-98 El Nino, the thermocline deepened by 75 m near the coast of southern Peru. Wooster and Guillen (1974) posited that the deepened coastal thermocline off Peru during El Nino was a consequence of the Bjerknes (1969) breakthrough explanation about the weakening of the southeasterly trade wind as the fundamental...