Daily surface wind variations over the equatorial Pacific Ocean

Daily surface wind variations over the equatorial eastern Pacific Ocean during summer 1992 are documented, using hourly observations from the tropical atmosphere ocean moored buoy array. Diurnal and semidiurnal variations are apparent in the zonal wind component, with peak-to-peak amplitudes of a few tenths of a meter per second. The phase of the semidiurnal cycle in zonal wind is approximately uniform across the equatorial eastern Pacific Ocean, with westerly wind maxima at -0300 and 1500 LT. The diurnal cycle dominates the daily march of meridional wind. The range of the diurnal meridional wind variations is -0.6-0.8 ms -• 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 whether the mean winds are southerly or northerly. The diurnal meridional wind variations along the equator may be related to the diurnal cycle of 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 diurnal cycle, with the strongest divergence in the early morning when deep convection in the ITCZ is at a maximum. The average daily range of the equatorial surface wind divergence is 1.5 x 10 -6 s -1 or --30% of the daily mean The semidiurnal zonal wind 9 ø variations are dynamically consistent with the well-known semidiurnal cycle in surface pressure, which is thought to be a manifestation of the atmospheric thermal tide.