Comparison of High- Altitude WRF Simulations with AIRS Satellite Data

Weather conditions at high altitudes, i.e., 50-100 km, may be of interest to some end users. This layer comprises of the stratosphere and the mesosphere. One example where knowing weather conditions at high altitude would be relevant is hypersonic vehicles. These vehicles operate at high altitudes at speeds above Mach 5. Although the air density is rare, the wind speed is extremely high at these altitudes.For example, the experimental Hypersonic Technology Vehicle 2 (HTV-2) was developed by the Defense Advanced Research Projects Agency (DARPA) Falcon Project to fly at Mach 20 at 80 km altitude.

The Weather Research and Forecasting (WRF) model has typically been applied to simulate weather in the troposphere. Nonetheless, WRF has been successfully run with a model top at 80 km altitude (Kruse et al. 2022). In this study, a series of high- altitude WRF simulations is run over the western United States with a horizontal grid size of 10 km and 250 vertical levels with model top at 1 Pa. One set of experiments is from the winter in 2023 with 4 initializations per day for a 10-day period with a 48-h forecast per initialization. A second set of experiments is from the summer in 2024 with 4 initializations per day for a 10-day period with a 48-h forecast per initialization.

Previous results with the above WRF setup reveal that the model produced gravity waves in the stratosphere and the mesosphere. Indeed, gravity waves are an important phenomena in these layers. Furthermore, gravity waves propagate in the horizontal and the vertical directions, transferring momentum and re-distributing energy. Data from the Stratospheric Atmospheric Infrared Sounder (AIRS) aboard NASA's Aqua satellite are used to derive stratospheric gravity wave activities. Comparing the gravity wave activities from WRF and AIRS will be used to assess the realism of these WRF simulations of weather at high altitudes.