Diurnal variability in rainfall, surface meteorological parameters, and sea surface temperature and salinity in the tropical Pacific and Atlantic Oceans

Understanding the interplay between sea surface temperature and atmospheric surface layer variability on diurnal time scales can contribute to our understanding of atmospheric convection and ocean mixing in the tropics. Thus, we document and interpret diurnal cycles of rainfall, surface meteorological parameters, and sea surface temperature and salinity for the period 1997-2001 using measurements from ATLAS buoys of the TAO/TRITON and PIRATA moored buoy arrays in the tropical Pacific and Atlantic Oceans. Regional and seasonal differences in the diurnal cycle for seven areas representing different climatological regimes in each basin are presented. Significant diurnal cycles are found in all atmospheric surface layer parameters. A diurnal cycle in the tropical surface layer stability and mixed layer structure is described consistent with these results. Analysis of the rainfall at the buoys suggests there is a maximum between midnight and 0800 LT, in agreement with previous studies of oceanic rainfall variability. An additional afternoon maximum is observed at several locations, and is mainly present during the season of maximum solar insolation implying it results from surface forced convection. The surface buoyancy flux corresponding to the heat and fresh water fluxes measured at the buoys indicates negative (stable) values during the day, and positive (unstable) values at night. Thus, fresh water flux contributes to stabilizing the water column in the afternoon. At night, however, surface cooling overwhelms any stabilization of the column due to fresh water flux, despite the nighttime precipitation maximum.