The Modulation of the Diurnal Cycle of Rainfall by Convectively Coupled Equatorial Waves

This study examines the variability of the diurnal cycle of rainfall associated with convectively coupled equatorial waves within the tropics using satellite-based observations of rainfall and cloudiness. Independent of the wave modes, the amplitude of the diurnal cycle increases and the phase of the diurnal cycle is delayed within the convectively enhanced envelopes of all waves, while the opposite is true within the suppressed envelopes. Although the amplitude of the diurnal cycle increases within the enhanced envelopes, its fractional contribution to the total variance of rainfall within the envelope decreases. This result indicates that the increase of total rainfall within the enhanced envelopes cannot be explained solely by the diurnal cycle. The delay in the peak time of day within the enhanced envelopes occurs due to increased development of stratiform-anvil clouds following the development of deep convective rainfall. Similar variability of the diurnal cycle within all wave modes suggest that the diurnal cycle may not contribute to the development of any particular wave mode, but rather it is modulated by the changes in the atmosphere due to large-scale variability.