Comprehensive Analysis of Deep Gravity Wave Propagation from Ground-Based Lidar Measurements and Numerical Simulations

Abstract:

Atmospheric gravity waves provide a major coupling mechanism between the troposphere and the middle atmosphere. However, the conditions under which they propagate into the mesosphere are still not completely understood. So far, ground-based lidar is the only remote sensing technique that can provide the high vertical and temporal resolution that has been found necessary for studying gravity wave propagation into the middle atmosphere. But most lidar systems cannot provide suitable data for the investigation of gravity waves at altitudes lower than 30 km. This study presents a new approach for closing this altitude gap by combining lidar measurements with numerical simulations.

Measurements with the Esrange lidar (68°N, 21°E) have been conducted during the first field campaign of the project “Investigation of the life cycle of gravity waves” (GW-LCYCLE) in winter 2013/14. Combining these measurements with regional numerical simulations with the Advanced Research version of the Weather Research and Forecasting (WRF-ARW) model allows for a comprehensive analysis of gravity wave propagation. Results from the numerical simulations were compared against nightly mean temperature profiles determined with the Esrange lidar’s rotational-Raman channels and measured with radiosondes launched from Esrange in intervals of 3 h. The comparison indicates that the WRF-ARW simulations are suitable for substituting the missing lidar observations below 30 km altitude.

The combination of observations and simulations shows gravity waves propagating from the tropopause region deep into the mesosphere. By calculating gravity wave potential energy densities and vertical energy fluxes the conditions conducive for gravity wave propagation are examined in detail. Our approach of reconciling lidar measurements with model simulations is found to be a promising method for gravity wave studies applicable to all lidar systems lacking temperature or density measurements below an altitude of 30 km.