Ángel Francisco Adames Corraliza , Victor Mayta, Fiaz Ahmed, Brandon Wolding, Kathleen Schiro

The "damped gravity wave" (DGW) approximation occurs when convective momentum dissipation is balanced by the pressure gradient force of convectively forced gravity waves. While this balance has been used to parameterize large-scale lifting in limited-domain models of tropical deep convection, its applicability to observed phenomena has not been carefully examined. A scale analysis indicates that DGW balance can occur in tropical cloud clusters occurring in low shear environments, with horizontal scales of ~ 100 km or greater and timescales of a day. The DGW balance is then used to explain three well-known properties of tropical deep convection. First, DGW balance implies that the average mesoscale vertical velocity in cloud clusters will be closer to first baroclinic, with second baroclinic motions contributing a smaller fraction of the total ascent. The first baroclinic mode is dominant because gravity waves and momentum diffusion induce a nonlocal velocity response to buoyancy, making ascent over regions of negative buoyancy possible. Second, a combination of the weak temperature gradient (WTG) and DGW balances yields a form of convective quasi-equilibrium, with adjustment timescales comparable to those previously estimated. Third, the use of WTG-DGW approximations in an entraining plume model reproduces the empirical precipitation-buoyancy relationship from Ahmed and Neelin. The sensitivity of precipitation to mean CAPE is interpreted as a small excursion from the zero buoyancy approximation where the undilute buoyancy and dilution by entrainment nearly, but not completely, cancel. Overall, these results support viewing cloud clusters as a coupling between deep convection and gravity waves.