Convective gravity wave propagation and breaking in the stratosphere: comparison between WRF model simulations and lidar data

摘要

In this work we perform numerical simulations of convective gravity waves(GWs), using the WRF (Weather Research and Forecasting) model. We first runan idealized, simplified and highly resolved simulation with model top at 80 km. Below 60 km of altitude, a vertical grid spacing smaller than 1 km issupposed to reliably resolve the effects of GW breaking. An eastward linearwind shear interacts with the GW field generated by a single convectivethunderstorm. After 70 min of integration time, averaging within a radius of300 km from the storm centre, results show that wave breaking in the upperstratosphere is largely dominated by saturation effects, driving an averagedrag force up to ?41 m s?1 day?1. In the lower stratosphere,mean wave drag is positive and equal to 4.4 m s?1 day?1.In a second step, realistic WRF simulations are compared with lidarmeasurements from the NDACC network (Network for the Detection ofAtmospheric Composition Changes) of gravity wave potential energy (E_p) overOHP (Haute-Provence Observatory, southern France). Using a vertical gridspacing smaller than 1 km below 50 km of altitude, WRF seems to reliablyreproduce the effect of GW dynamics and capture qualitative aspects of wavemomentum and energy propagation and transfer to background mean flow.Averaging within a radius of 120 km from the storm centre, the resultingdrag force for the study case (2 h storm) is negative in the higher (?1 m s?1 day?1) and positive in the lower stratosphere (0.23 m s?1 day?1).Vertical structures of simulated potential energy profiles are found to bein good agreement with those measured by lidar. E_p is mostly conserved withaltitude in August while, in October, E_p decreases in the upper stratosphereto grow again in the lower mesosphere. On the other hand, the magnitude ofsimulated wave energy is clearly underestimated with respect to lidar databy about 3–4 times.