Examining the Variability of the Diurnal Cycle of Rainfall over the Pacific Basin associated with El Niño

Accurately reproducing the diurnal cycle of rainfall for atmospheric modeling represents a potential challenge for improving the reliability of weather and climate forecasting.  Scientific advances such as the Tropical Rainfall Measuring Mission and Global Precipitation Measurement have provided invaluable rainfall data for detailed research.  Moreover, large-scale decadal- to multi-decadal climate variations such as El Niño create significant deviations in atmospheric conditions and rainfall, particularly within the tropics.  El Niño and its counterpart La Niña represent the respective warm and cool phase of the global-scale phenomenon known as El Niño – Southern Oscillation (ENSO), and distinct variations in the diurnal cycle of rainfall are associated with each phase.  This research focuses on the December through February (DJF) period of each ENSO phase, when it has historically been strongest.  Daily mean rainfall, diurnal amplitude and phase values from 1998-2016 were compared to observations during individual and averaged El Niño and La Niña events.  Probability distributions were calculated for statistical analysis of diurnal amplitude and phase, and results indicated a statistically significant relationship between ENSO phase and the diurnal cycle.  Diurnal amplitude was enhanced and suppressed, respectively, during El Niño and La Niña events.  Diurnal phase during El Niño closely mirrored climatology, with maximum phase probability during the mid-morning hours, along with an additional maximum in phase probability during the afternoon.  Phase maximum and minimum probability during La Niña occurred during the mid-morning and mid-afternoon hours, respectively.