Generation of Multiple Gravity Wave Couplets from Convection

Abstract

Abstract The generation of multiple wave couplets with deep tropospheric downdrafts/updrafts by convection is explored through idealized 2D moist numerical simulations as well as dry experiments with prescribed artificial latent heating. These wave couplets are capable of horizontally propagating over a long distance at a fast speed with vertical motions spanning the entire troposphere. The timing of wave generation is determined by the variation in the local heating rate, which arose from the imbalances among latent heating, nonlinear advection, and adiabatic heating/cooling. The amplitudes of wave couplets also correspond well with the strength of the local heating rate. The heat budget analysis highlights the crucial roles of both latent heating and nonlinear advection in the generation of the tropospheric wave couplets. Strong latent heating induces the thermodynamic imbalance and thus triggers waves. Meanwhile, latent heating also increases vertical motion in the source region and thus enhances nonlinear advection through transferring heat upward. Nonlinear advection, which has a comparable magnitude to latent heating in the upper troposphere, partially offsets the balancing effect of adiabatic heating/cooling, and results in a more persistent imbalance at high levels, allowing for the emission of consecutive waves even when latent heating becomes weak. In the simulation with weak nonlinear advection, fewer wave couplets are found, as the effect of latent heating is more easily offset by adiabatic cooling before it weakens. Significance Statement The generation of gravity waves in the troposphere by convection is of significant importance in the fields of atmospheric science and meteorology. The waves play a crucial role in the initiation and organization of convection, and the parameterization of wave momentum flux in global numerical models. This study aimed to investigate the generation of wave couplets in the troposphere through idealized numerical simulations with varying prescribed latent heating. The results showed that gravity wave couplets were generated in succession as a result of the imbalances among latent heating, nonlinear advection, and adiabatic heating/cooling. This study highlighted an important but yet complex issue of gravity waves being generated within convection by nonlinear sources other than latent heating, which had been neglected in many recent studies on the topic. These findings deepened our understanding of convectively generated gravity waves and paved the way for coupled wave–convection relationship studies.