El Nino and La Nina Practice Test

A fisheries manager in Peru reports a sharp decline in anchovy populations coinciding with reduced nutrient upwelling and unusually warm coastal waters in the eastern Pacific. At the same time, trade winds across the equatorial Pacific are weaker than average. Which ENSO phase is most likely occurring?

A climatology student notes that during an ENSO event, warm surface water shifts eastward across the equatorial Pacific, convection increases over the central/eastern Pacific, and the trade winds weaken. Which mechanistic explanation best links these observations to the Walker circulation?