Examining Diurnal Variability across the Equatorial Pacific Basin associated with ENSO

Many questions remain regarding driving mechanisms behind the diurnal cycle across ocean basins and factors that influence it. This study utilizes buoy data to examine diurnal variability of rainfall across the equatorial Pacific basin during the December through February (DJF) seasonal period from 1998 through 2012. Daily mean, diurnal amplitude and phase were calculated for rainfall data assessment and their variability with ENSO phases were examined using composites and probability distributions. Air and sea-surface temperature, relative humidity and surface winds were similarly examined to evaluate potential relationship with the diurnal variability of rainfall. Buoy data were assessed against results from a previous study that performed similar diurnal variability analysis through use of TRMM 3B42 rainfall data. Analysis indicated increased frequency of heavier rainfall during ENSO warm phase (El Niño) events, suggested by larger diurnal amplitude and greater variability in observed rainfall rates across the central Pacific basin. Associated with the increased diurnal amplitude of rainfall rates during El Niño, the diurnal amplitudes of relative humidity and surface winds also increased, while the diurnal amplitudes of air temperature and sea-surface temperature decreased. Observed variability of atmospheric variables was primarily diurnal, although surface pressure and near-surface winds exhibited a semi-diurnal phase signal.