Lifecycle and Impacts of MCS Convectively Generated Low-Frequency Gravity Waves

Mesoscale Convective Systems (MCSs) frequently generate low-frequency gravity waves that propagate away from the system and modify the surrounding environment. Idealized MCS simulations are performed using the CM1 model with initial environments having a range of shear and instability values. Common events that are part of an MCS lifecycle are found to correspond to low-frequency wave generation, including: initial convective development, initial development of precipitation, the first appearance of stratiform precipitation, and substantial increases in rear inflow. Each of these events are associated with modifications in the vertical latent heating profile, and thus generate low-frequency gravity waves associated with either sinking and stabilization, or lifting and destabilization, of the atmosphere. Events with cooling, and hence, lifting concentrated in the lower levels had a larger impact on the surrounding environmental stability field than if it was concentrated in the mid-levels. Subsequently, updraft speeds within the convective line of the MCS vary in response to the gravity wave-generated modifications in instability ahead of the convective line.

Ambient environmental factors were found to control the location and depth of the latent cooling, and hence also control the magnitude of the impact of the generated gravity wave on the surrounding environment. MCSs in environments with moderate amounts of shear, or higher instability levels, displayed more frequent and intense gravity wave responses compared to MCSs in environments with low or high shear, or low instability levels.

Gravity wave impacts were also compared to those produced in similar MCS simulations but with modified graupel microphysical characteristics.