Comparing gravity waves sampled from a kilometre-scale IFS run to AIRS satellite observations

Abstract

Gravity waves are small-scale atmospheric waves which transport energy and momentum. These waves impact the large scale circulation and increasing our understanding of them is therefore important to support improvements to weather and climate models. This presentation focusses on gravity waves in the stratosphere using data from a high resolution run of the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System (IFS) operated at a kilometre-scale spatial resolution, the Atmospheric Infrared Sounder (AIRS) on NASA’s Aqua satellite and the ECMWF ERA5 reanalysis. For this comparison, the IFS run and ERA5 are resampled using the AIRS observational filter. Data are examined during the first 2 weeks of November, as the high resolution model was initialised on the 1st of this month. Wave properties were found using the 2D+1 S-Transform, a spectral analysis technique, which has been previously applied to AIRS data. Asia and surrounding regions are investigated, because preliminary studies of AIRS data suggested strong gravity wave activity in this region during this time period. Gravity waves can also be seen in the high resolution model and ERA5 data at similar times and locations as those in the observations. Higher amplitude gravity waves can be seen in nighttime AIRS data compared to the resampled models. The horizontal wavelengths in the data sets are generally similar in areas of peak gravity wave activity for nighttime data. Weather models are advancing rapidly and kilometre scales, such as the experimental IFS run, could become operational in the next decade. At these grid scales, gravity waves must be resolved instead of parameterized so the models need to be tested to see if they do this correctly. This work provides information on how a cutting edge model resolves gravity waves compared to observations.