The summertime diurnal cycle of precipitation derived from IMERG

Abstract

The Integrated Multi-satellitE Retrievals for GPM (IMERG) precipitation product derived from the Global Precipitation Measurement (GPM) constellation offers a unique opportunity of observing the diurnal cycle of precipitation in the latitudinal band 60°N-S at unprecedented 0.1° × 0.1° and half-hour resolution. The diurnal cycles of occurrence, intensity and accumulation are determined using four years of data at 2° × 2° resolution; this study focusses on summertime months when the diurnal cycle shows stronger features. Harmonics are fitted to the diurnal cycle using a non-linear least squares method weighted by random errors. Results suggest that mean-to-peak amplitudes for the diurnal cycles of occurrence and accumulation are greater over land (generally larger than 25% of the diurnal mean), where the diurnal harmonic dominates and peaks at ~16-24 LST, than over ocean (generally smaller than 25%), where the diurnal and semi-diurnal harmonics contribute comparably. Over ocean, the diurnal harmonic peaks at ~0-10 LST (~8-15 LST) over open waters (coastal waters). For intensity, amplitudes of the diurnal and semi-diurnal harmonics are generally comparable everywhere (~15-35%) with the diurnal harmonic peaking at ~20-4 LST (~3-12 LST) over land (ocean), and the semi-diurnal harmonic maximises at ~5-8 LST and 17-20 LST. The diurnal cycle of accumulation is dictated by occurrence as opposed to intensity.