Tropical Wave Observations From the Reel-Down Atmospheric Temperature Sensor (RATS) in the Lowermost Stratosphere During Strateole-2

Tropical waves play an important role in driving the quasi-biennial oscillation of zonal winds in the tropical stratosphere. In our study we analyze these waves based on temperature observations from the 2021–2022 Strateole-2 campaign when the Reel-down Atmospheric Temperature Sensor (RATS) was successfully deployed for the first time. RATS provides long-duration, continuous and simultaneous high-resolution temperature observations at two altitudes (balloon float level and 200 m below) allowing for an analysis of vertical wavelengths. This separation distance was chosen to focus on waves near the resolution limit of reanalyses. Here, we found tropical waves with periods between about 6 hr and 2 days, with vertical wavelengths between 1.5 and 5 km, respectively. Comparing our results to Fifth generation European Centre for Medium-Range Weather Forecasts (ERA5) reanalyses we found good agreement for waves with a period longer than 1 day. However, the ERA5 amplitudes of higher-frequency waves are under-estimated, and the temporal evolution of most wave packets differs from the observations.