Representation of Convective Gravity Waves in High-Vertical-Resolution Global Simulations

Atmospheric gravity waves (GWs) play an important role in forcing large-scale atmospheric circulation that significantly impact seasonal and near-term climate predictions. Collectively these waves are known to drive long-term, slowly varying global circulation patterns as e.g. the quasi-biennial oscillation (QBO) in the tropical lower stratosphere. Recent observational case studies found that large QBO forces in the lowermost stratosphere were associated with long-period, long-horizontal-wavelength GWs with very short vertical wavelengths on the order of several hundred meters. Due to their extreme aspect ratio with short vertical wavelengths the simulation of these waves in state-of-the-art global circulation models is challenging and ultra-high vertical resolution in the stratosphere is necessary.

We present very-high vertical resolution global simulations with a grid spacing of 50m in the stratosphere. In our study we use the European Center for Medium-Range Weather Forecasts integrated forecasting system (ECMWF IFS) and Japanese Atmospheric General circulation model for Upper Atmosphere Research (JAGUAR) simulations to study these tropical waves with extreme aspect ratios and determine their impact on the QBO. Furthermore, we validate these simulations with Strateole-2 balloon observations and analyze the differences of the simulated and observed wave fields.