The combined daily cycle of the upper ocean and lower troposphere over the East Pacific Cold Tongue

Historically, the East Pacific Cold Tongue has been poorly observed. However, over the course of the last two decades the situation has improved. Special observations have been taken during cruises of opportunity, e.g. series of radiosonde launches along 110°W and 95°W, as well as during various field campaigns such as EPIC2001. In addition, multi-year series of high-resolution data have been collected from relatively fixed platforms. Half-hourly profiles of lower-tropospheric winds over San Cristóbal (1°S, 90°W) in the Galápagos Islands have been collected during much of the last 11 years, while the Tropical Atmosphere-Ocean (TAO) buoys along 110°W and 95°W provide up to 15 years worth of dynamic and thermodynamic information about both the ocean and the atmosphere just above the surface. Data collection along 95°W was augmented for a few years centered on the EPIC2001 campaign by the deployment of buoys at 3.5°N, 10°N, and 12°N, and by the installation of additional sensors, including barometers, radiometers and rain gauges, at all buoys along the meridian.

Previous studies, using data from various periods over the last 15 years, have examined the daily cycle of near-surface winds in the TAO array; the complex seasonal and interannual changes in mixed layer depths and the daily cycle of SST at (0°N, 110°W); and the seasonal and interannual variability of the lower troposphere's daily cycle over the Galápagos. Here, we explore the daily cycle at and just below the ocean surface along 95°W and compare it with the daily cycle at San Cristóbal during the same time periods. We focus in particular on changes in the ocean daily cycle during periods of "coupled" and "decoupled" lower-tropospheric daily cycles, using balloon soundings collected along 95°W to provide thermodynamic context in the lower troposphere.