资源环境科技发展态势分析平台

Banded convective activity that occurred near the south coast of China on 30 January 2018 was investigated through convection-allowing simulations using a nonhydrostatic mesoscale model. The simulations capture reasonably well the observed characteristics of this event. The convective bands are found to be closely related to an episode of mesoscale gravity waves propagating northeastward with a wave speed of around 12m/s and a primary wavelength of about similar to 40-50km. Further analyses and sensitivity experiments reveal that the environment provides a wave duct for these gravity waves, with a thick low-level stable layer below 850hPa capped by a low-stability reflecting layer with a critical level. The strength and depth of the low-level stable layer determine the intrinsic phase speed and wavelength of the ducted gravity waves. In the sensitivity tests that the stable layer depth is reduced, the wave characteristics change according to what are predicted with the wave duct theory. The convective bands collocate and propagate in phase with the peak updraft regions of the gravity waves, suggesting strong interactions of convection and gravity waves, in which the ducted gravity waves can trigger and modulate convection, while latent heating from convection enhances the waves. In essence, both wave ducting and wave-convection interaction are jointly responsible for the banded convective activity.