DAILY SURFACE WIND VARIATIONS OVER THE EQUATORIAL PACIFIC-OCEAN

Daily surface wind variations over the equatorial eastern Pacific Ocea n during summer 1992 are documented, using hourly observations from th e tropical atmosphere ocean moored buoy array. Diurnal and semidiurnal variations are apparent in the zonal wind component, with peak-to-pea k amplitudes of a few tenths of a meter per second. The phase of the s emidiurnal cycle in zonal wind is approximately uniform across the equ atorial eastern Pacific Ocean, with westerly wind maxima at similar to 0300 and 1500 LT. The diurnal cycle dominates the daily march of meri dional wind. The range of the diurnal meridional wind variations is si milar to 0.6-0.8 ms(-1) at most locations: more than twice as large as the daily zonal wind changes. The low-level flow is southward across the equator at night (relative to the daily mean), regardless of wheth er the mean winds are southerly or northerly. The diurnal meridional w ind variations along the equator may be related to the diurnal cycle o f deep convection in the Intertropical Convergence Zone (ITCZ) to the north. In particular, surface wind divergence along the equator (which is dominated by the meridional component) exhibits a pronounced diurn al cycle, with the strongest divergence in the early morning when deep convection in the ITCZ is at a maximum. The average daily range of th e equatorial surface wind divergence is 1.5 x 10(-6) s(-1), or similar to 30% of the daily mean. The semidiurnal zonal wind variations are d ynamically consistent with the well-known semidiurnal cycle in surface pressure, which is thought to be a manifestation of the atmospheric t hermal tide.