Link Between the Time-Space Behavior of Rainfall and 3D Dynamical Structures of Equatorial Waves in Global Convection-Permitting Simulations

Equatorial waves (EWs) control a considerable portion of tropical rainfall variability but numerical models often struggle to capture them. Increased computing power now enables global simulations with resolved deep convection, which is believed to produce more realistic EWs. Here we identify EWs in global ICON simulations with varying horizontal resolution by (a) filtering rainfall based on space-time spectral analysis and (b) projecting wind and geopotential onto theoretical wave patterns. The simulations demonstrate that Kelvin, mixed-Rossby gravity and equatorial Rossby waves are consistently represented, regardless of model resolution and convective treatment. For smaller-scale inertio-gravity waves, however, explicit convection appears to be a prerequisite. Surprisingly, the associated rainfall signals are not accompanied by corresponding wind patterns but appear to be connected to mesoscale convective systems. This demonstrates the importance of analyzing rainfall and dynamical aspects of EWs jointly for a robust assessment.

Automated summary

Equatorial waves play a significant role in tropical rainfall variability, but current numerical models struggle to accurately represent them. However, global simulations with higher resolutions are able to capture Kelvin, mixed-Rossby gravity, and equatorial Rossby waves consistently, regardless of model resolution and convective treatment. Explicit convection is necessary for smaller-scale inertio-gravity waves. Surprisingly, the associated rainfall signals do not correspond to wind patterns but are connected to mesoscale convective systems, highlighting the importance of jointly analyzing rainfall and dynamic aspects of equatorial waves.