Case Studies of Middle Atmospheric Gravity Waves Resolved in EOS Aura and EOS Aqua Satellite Radiances and High-Resolution High-Altitude Global Numerical Weather Prediction Models

Global insights into the way gravity waves drive the middle atmospheric circulation have been hampered by resolution constraints on both the observational and modeling side. Limb and nadir viewing satellite instruments have lacked sufficient horizontal and/or vertical resolution to resolve these waves in acquired along-track radiances. Similarly, finite computing resources have meant that global atmospheric models could not be run at the necessary high spatial resolutions from the ground to the mesosphere to resolve gravity wave generation in the troposphere and propagation/breakdown in the middle atmosphere. Both of these resolution constraints are now being progressively overcome. Here, we present case studies of long wavelength gravity waves that are explicitly resolved in radiances acquired by several high-resolution satellite remote sensors, including the Microwave Limb Sounder (MLS) on the EOS Aura satellite, the Advanced Infrared Sounder (AIRS) on EOS Aqua, and the Advanced Microwave Sounding Unit-A (AMSU-A) instruments on EOS Aqua and various NOAA meteorological satellites. We then “hindcast” wave events seen in these data on certain days using a high-altitude advanced-level physics (ALPHA) version of the Navy Operational Global Atmospheric Prediction System's (NOGAPS) global spectral model (GSM). NOGAPS is the Department of Defense's (DoD's) high-resolution operational global numerical weather prediction (NWP) system, which issues 6-day weather forecasts every 6 hours at T239L30 (~0.5o resolution) from the Fleet Numerical Meteorology and Oceanography Center (FNMOC). The NOGAPS-ALPHA GSM includes a prognostic middle atmosphere, extending NOGAPS from its current upper forecast level of ~35 km to altitudes ~80-100 km. Here we run NOGAPS-ALPHA at various horizontal spectral resolutions (T79, T159, T239) and vertical resolutions (L54, L68, etc.) and compare the long wavelength gravity waves that are explicitly resolved and predicted with those measured by the satellite sensors. These comparisons reveal large amplitude mountain waves in the Arctic winter stratosphere. We support these findings with regional mountain wave model simulations. We also show evidence for some of these wave events in operational forecast fields issued at the time by the European Center for Medium Range Weather Forecasting's (ECMWF) Integrated Forecast System (IFS), which runs operationally at TL511L60. Some of the model-data comparisons also reveal nonorographic gravity waves emanating from tropical convection and jet stream instabilities/imbalances. Both the satellite instruments and the models still resolve these gravity waves imperfectly, and cannot resolve other smaller-wavelength waves at all. Thus, we argue that useful model-data comparisons only result after careful consideration of the space-time resolution characteristics of both the data acquired by satellite instruments and the atmospheric fields generated by global models, since waves present in one may not be “visible” in the other.