ENSO's impact on the annual cycle: The view from Galápagos

Abstract

UHF profiler observations of lower tropospheric winds at San Cristóbal in Ecuador's Galápagos Islands commenced in October 1994. The available data give a detailed picture of the lower troposphere‧s annual cycle over this portion of the East Pacific cold tongue. The profiler tracks the low‐level southerly wind maximum from its weakest state in austral summer, when it may briefly rise above 1 km, to its strongest state mid‐year, when it is often found below 400 m. The profiler operated during much of the 1997–98 El Niño and gives us an unprecedented look at dramatic changes in the flow over the cold tongue during a warm event. The seasonal deepening of the low‐level flow was enhanced as the ITCZ moved into the Southern Hemisphere for a few months and the lower tropospheric winds became northerly.