Concentric traveling ionosphere disturbances (CTIDs) in total electron content triggered by Super Typhoon Meranti on 13 September 2016 are detected by using the ground‐based Global Navigation Satellite Systems network in Taiwan. The CTIDs emanated outward before the typhoon landfall and lasted for more than 10 h. The characteristics of CTIDs agree with the gravity wave theory and exhibit spatial and temporal scales in wave periods of ~8–30 min, horizontal wavelengths of ~160–200 km, and horizontal phase velocities of ~106–220 m/s. We also observe the CTIDs showing the stationary wave character. Broad spectra of CTIDs are excited after the rainbands of typhoon impinged on Central Mountain Range of Taiwan. The ray‐tracing technique confirms that the CTIDs were excited by convective clouds, spiral rainbands, and the eyewall of Typhoon Meranti. This study provides new evidence of typhoon‐induced concentric gravity waves in the ionosphere.

We examine the thermal structure of the mesosphere and lower thermosphere (MLT) using observations from 2002 through 2021 from the SABER instrument on the NASA TIMED satellite. These observations show that the MLT has significantly cooled and contracted between the years 2002 and 2019 (the year of the most recent solar minimum) due to a combination of a decline in the intensity of the 11‐year solar cycle and increasing carbon dioxide (CO₂.) During this time the thickness of atmosphere between the 1 and 10⁻⁴ hPa pressure surfaces (approximately 48 and 105 km) has contracted by 1,333 m, of which 342 m is attributed to increasing CO₂. All other pressure surfaces in the MLT have similarly contracted. We further postulate that the MLT in the two most recent solar minima (2008–2009 and 2019–2020) was very likely the coldest and thinnest since the beginning of the Industrial Age. The sensitivity of the MLT to a doubling of CO₂ is shown to be −7.5 K based on observed trends in temperature and growth rates of CO₂. Colder temperatures observed at 10⁻⁴ hPa in 2019 than in the prior solar minimum in 2009 may be due to a decrease of 5% in solar irradiance in the Schumann‐Runge band spectral region (175–200 nm).

We report the first joint observations of convectively generated gravity waves (GWs) using an OH airglow imager in Colorado and the Atmospheric Infrared Sounder (AIRS) onboard the Aqua satellite. Convective GWs, appearing as concentric rings, are observed over the western Great Plain regions of North America in the evening of 3 June 2008 in the airglow images. Inspecting both weather radars and AIRS radiances at 8.1 µm, strong convective clouds are found near the center of the concentric rings. The AIRS data at 4.3 µm show semicircular GWs with horizontal wavelengths of 60–80 km at 0900 UT, whereas the airglow imager observed circular GWs with horizontal wavelengths of ~44 km and airglow emission perturbation of ~6% at the same geographic location at 0910 UT. Large‐scale GWs (horizontal wavelengths greater than 100 km) emanating northwestward can be seen in both AIRS data and airglow images at different times. The imager observed small‐scale ripples associated with unstable concentric GWs in the mesopause in the early evening. Given that the brightness temperature perturbation of the GWs in the AIRS data is about 0.16 K and assuming that the GWs propagate without dissipation from the stratosphere to the upper mesosphere, the expected airglow emission perturbation caused by the GWs would be 4%–17%. Ray tracing simulations are performed to demonstrate that the GWs seen in AIRS and in the imager were likely excited by the same convective system.

We use Whole Atmosphere Community Climate Model simulations made under various climate change scenarios to study the evolution of the global‐mean temperature trend in the late twentieth century and the twenty‐first century. Results are compared with available satellite observations, including new trend estimates derived from the Sounding of the Atmosphere using Broadband Emission Radiometry instrument on NASA's TIMED spacecraft. Modeled and observed trends are shown to be consistent throughout the entire middle atmosphere, from near the tropopause (~16 km) to the lower thermosphere (~95 km) in the period covered by the satellite data. Simulations are extended into the twenty‐first century to document the evolution of the global‐mean temperature trend profile. We find, consistent with previous studies, a marked change in the trend profile at the turn of the twenty‐first century, which is driven by the recovery of stratospheric ozone following the adoption of the Montreal Protocol. In the twenty‐first century, the trend profile becomes more uniform with altitude, but its overall shape and magnitude are conditioned by the scenario adopted for future emissions of greenhouse gases. Our results suggest that the vertical profile of temperature trends in the middle atmosphere will remain an important signature of global climate change, and they underscore the importance of global, continuous monitoring of this region of the atmosphere.