Figure 2. Daily time series of SST at 0°, 125°W. Dashed line is climatology.
In early 1997, surface winds along the equator were punctuated by a series of westerly events of increasing intensity and eastward fetch (Fig.1). These westerly episodes, associated with enhanced Madden and Julian Oscillations (MJO) in the atmosphere, locally drove warm water eastward near the equator. These westerly events also excited downwelling equatorial Kelvin waves that propagated into the eastern Pacific, depressing the thermocline by over 90m in late 1997. At the same time, the thermocline in the westem Pacific shoaled by 20-40m in response to anomalous upwelling Rossby wave generatron.
Prior to the termination of the event in May 1998, thermocline shoaling progressed slowly into the central and eastern Pacific even while SSTs remained above normal (Figs.1 and 3). It was not until the trade winds returned to near normal strength in the eastern Pacific in mid-May 1998 that the unusually cold water residing just below the surface could be upwelled. When that happened, SSTs plummeted dramatically.
