Horizontal propagation of large amplitude mountain waves in the vicinity of the polar night jet

We analyze a large-amplitude mountain wave event, which was observed by a ground-based lidar above New Zealand between 31 July and 1 August 2014. Besides the lidar observations, European Centre for Medium-Range Weather Forecasts (ECMWF) data, satellite observations, and ray tracing simulations are utilized in this study. It is found that the propagation of mountain waves into the middle atmosphere is influenced by two different processes at different stages of the event. At the beginning of the event, instabilities in a weak wind layer cause wave breaking in the lower stratosphere. During the course of the event the mountain waves propagate to higher altitudes and are refracted southward toward the polar night jet due to the strong meridional shear of the zonal wind. As the waves propagate out of the observational volume, the ground-based lidar observes no mountain waves in the mesosphere. Ray tracing simulations indicate that the mountain waves propagated to mesospheric altitudes south of New Zealand where the polar night jet advected the waves eastward. These results underline the importance of considering horizontal propagation of gravity waves, e.g., when analyzing locally confined observations of gravity waves

Observed versus simulated mountain waves over Scandinavia – improvement of vertical winds, energy and momentum fluxes by enhanced model resolution?

Two mountain wave events, which occurred over northern Scandinavia in December 2013 are analysed by means of airborne observations and global and mesoscale numerical simulations with horizontal mesh sizes of 16, 7.2, 2.4 and 0.8 km. During both events westerly cross-mountain flow induced upward-propagating mountain waves with different wave characteristics due to differing atmospheric background conditions. While wave breaking occurred at altitudes between 25 and 30 km during the first event due to weak stratospheric winds, waves propagated to altitudes above 30 km and interfacial waves formed in the troposphere at a stratospheric intrusion layer during the second event. Global and mesoscale simulations with 16 and 7.2 km grid sizes were not able to simulate the amplitudes and wavelengths of the mountain waves correctly due to unresolved mountain peaks. In simulations with 2.4 and 0.8 km horizontal resolution, mountain waves with horizontal wavelengths larger than 15 km were resolved, but exhibited too small amplitudes and too high energy and momentum fluxes. Simulated fluxes could be reduced by either increasing the vertical model grid resolution or by enhancing turbulent diffusion in the model, which is comparable to an improved representation of small-scale nonlinear wave effects

Gazette de Bayonne, de Biarritz et du Pays basque

14 janvier 19251925/01/14.Appartient à l’ensemble documentaire : Aquit

Stratospheric Gravity Wave Products from Satellite Infrared Nadir Radiances in the Planning, Execution, and Validation of Aircraft Measurements during DEEPWAVE

Gravity wave perturbations in 15-μm nadir radiances from the Atmospheric Infrared Sounder (AIRS) and Cross-Track Infrared Sounder (CrIS) informed scientific flight planning for the Deep Propagating Gravity Wave Experiment (DEEPWAVE). AIRS observations from 2003 to 2011 identified the South Island of New Zealand during June–July as a “natural laboratory” for observing deep-propagating gravity wave dynamics. Near-real-time AIRS and CrIS gravity wave products monitored wave activity in and around New Zealand continuously within 10 regions of scientific interest, providing nowcast guidance and validation for flight planners. A novel technique used these gravity wave products to validate upstream forecasts of nonorographic gravity waves with 1–2-day lead times, providing time to plan flight intercepts as tropospheric westerlies brought forecast source regions into range