Tracking gravity waves in moist baroclinic jet-front systems

A series of four-dimensional ray-tracing experiments are performed to investigate the propagating wave characteristics, source mechanisms, and wave number vector refraction budget of six groups of lower-stratospheric gravity waves in the moist baroclinic jet-front systems with varying degree of convective instability. On one hand, the resemblance of ray trajectories and propagating characteristics between gravity waves in the dry experiment versus those in the experiment with weak diabatic heating demonstrates the limited role of moist convection in modifying those wave modes that are dominated by dry dynamics, including both the short-scale northward-propagating mode and the intermediate-scale northward-propagating mode in the jet exit region (likely induced by upper-level jet imbalance and/or tropospheric frontogenesis), the intermediate-scale eastward-propagating mode from the jet exit region in the ridge down to the jet entrance region in the trough (likely induced by upper-level jet imbalance), and the short-scale southward-propagating mode located far to the south of the jet right above the surface cold front (likely induced by tropospheric frontogenesis). On the other hand, comparisons of the gravity waves in the two aforementioned experiments through the ray tracing analysis further demonstrate that moist convection may force new wave modes, modify existing dry wave modes through latent heat release, or modify the new/existing waves through modification of large-scale flow. Convectively generated gravity waves could propagate both upstream and downstream of the latent heating. Lastly, it is indicated in the budget analysis of wave number vector refraction equations that the wind effect on changing the characteristics of propagating gravity waves generally dominates over the thermodynamics effect, and that the thermodynamics effect may counteract, enhance, or even take over the effect of background wind for those wave packets crossing the tropopause or frontal systems.