Seasonal and Interannual Variations in the Daily Cycle of Winds over the Galápagos

Abstract

While the daily cycle of near-surface winds over the equatorial east Pacific has been studied in some detail, little is known about the daily cycle above the surface layer. Furthermore, the causes of the observed near-surface daily cycle are not well understood. A better understanding of the structure and forcing mechanisms at work on the lower-tropospheric winds over this region may increase our appreciation for the varying importance of local and remote atmospheric and oceanic processes. This study documents the daily cycle of lower-tropospheric winds over one of the Galápagos Islands during the late 1990s, as well as how it varied seasonally and interannually, using half-hourly profiler winds. The well-known zonal semidiurnal tide is evident in the data, as is a diurnal cycle that is predominantly meridional and may be driven by the results of convection over the Andes. In addition, the high vertical resolution of the wind profiles reveals a decoupling of the daily cycle of winds below ?500 m from those aloft during periods of cold (<23°C) SSTs. This decoupling, which is not evident in long-term mean profiles that effectively filter the daily cycle, may inhibit the vertical mixing of momentum or vertical propagation of tidal or wave signatures over the region.