Long-term high-resolution temperature data of the Compact Rayleigh Autonomous Lidar (CORAL) is used to evaluate temperature and gravity wave (GW) activity in ECMWF Integrated Forecasting System (IFS) over R\’io Grande (53.79$^{\circ}$S, 67.75$^{\circ}$W), which is a hot spot of stratospheric GWs in winter. Seasonal and altitudinal variations of the temperature differences between the IFS and lidar are studied for 2018 with a uniform IFS version. Moreover, interannual variations are considered taking into account updated IFS versions. We find monthly mean temperature differences $<2$~K at 20-40~km altitude. At 45-55~km, the differences are smaller than 4~K during summer. The largest differences are found during winter (4~K in May 2018 and -10~K in August 2018, July 2019 and 2020). The width of the difference distribution (15th/85th percentiles), the root mean square error, and maximum differences between instantaneous individual profiles are also larger during winter ($>\pm10$~K) and increase with altitude. We relate this seasonal variability to middle atmosphere GW activity. In the upper stratosphere and lower mesosphere, the observed temperature differences result from both GW amplitude and phase differences. The IFS captures the seasonal cycle of GW potential energy ($E_p$) well, but underestimates $E_p$ in the middle atmosphere. Experimental IFS simulations without damping by the model sponge for May and August 2018 show an increase in the monthly mean $E_p$ above 45~km from only $\approx10$~\% of the $E_p$ derived from the lidar measurements to 26~\% and 42~\%, respectively. GWs not resolved in the IFS are likely explaining the remaining underestimation of the $E_p$.

We use observations from one of the SOUTHTRAC (Southern Hemisphere Transport, Dynamics, and Chemistry) Campaign flights in Patagonia and the Antarctic Peninsula during September 2019 to analyze possible sources of gravity wave (GW) in this hotspot during austral late winter and early spring. Data from two of the instruments onboard the German High Altitude and Long Range Research Aircraft (HALO) are employed: the Airborne Lidar for Middle Atmosphere research (ALIMA) and the Basic HALO Measurement and Sensor System (BAHAMAS). The former provides vertical temperature profiles along the trajectory while the latter gives the three components of velocity and temperature at the flight position. GW induced perturbations are obtained from these observations. We include numerical simulations from the Weather Research and Forecast (WRF) model to place a four-dimensional context for the GW observed during the flight and in order to present possible interpretations of the measurements, as for example the orientation or eventual propagation sense of the waves may not be inferred using only data obtained onboard. We first evaluate agreements and discrepancies between the model outcomes and the observations. This allowed us an assessment of the WRF performance in the generation, propagation and eventual dissipation of diverse types of GW through the troposphere, stratosphere and lower mesosphere. We then analyze the coexistence and interplay of mountain waves (MW) and non-orographic (NO) GW. The MW dominate above topographic areas and in direction of the so-called GW belt whereas the latter waves are mainly relevant above oceanic zones.

To understand the main orographic and non-orographic sources of gravity waves (GWs) over South America during an Experiment (Rapp et al, 2021, https://doi.org/10.1175/BAMS-D-20-0034.1), we propose the application of a rotational spectral analysis based on methods originally developed for oceanographic studies. This approach is deployed in a complex scenario of large-amplitude GWs by applying it to reanalysis data. We divide the atmospheric region of interest into two height intervals. The simulations are compared with lidar measurements during one of the flights. From the degree of polarization and the total energy of the GWs, the contribution of the upward and downward wave packets is described as a function of their vertical wavenumbers. At low levels, a larger downward energy flux is observed in a few significant harmonics, suggesting inertial GWs radiated at polar night jet levels, and below, near to a cold front. In contrast, the upward GW energy flux, per unit area, is larger than the downward flux, as expected over mountainous areas. The main sub-regions of upward GW energy flux are located above Patagonia, the Antarctic Peninsula and only some oceanic sectors. Above the sea, there are alternating sub-regions dominated by linearly polarized GWs and sectors of downward GWs. At the upper levels, the total available GW energy per unit mass is higher than at the lower levels. Regions with different degrees of polarization are distributed in elongated bands. A satisfactory comparison is made with an analysis based on the phase difference between temperature and vertical wind disturbances.

Gravity waves (GWs) generated by orographic forcing, also known as mountain waves (MWs) have been studied for decades. First measured in the troposphere, then in the stratosphere, they were only imaged at mesospheric altitude in 2008. Their characteristics have been investigated during several recent observation campaigns, but many questions remain concerning their impacts on the upper atmosphere, and the effects of the background environment on their deep propagation. An Advanced Mesospheric Temperature Mapper (AMTM) and the Southern Argentina Agile MEteor Radar (SAAMER) have been operated simultaneously during the Austral winter 2018 from Rio Grande, Argentina (53.8°S). This site is located near the tip of South America, in the lee of the Andes Mountains, a region considered the largest MW hotspot on Earth. New AMTM image data obtained during a 6-month period show almost 100 occurrences of MW signatures penetrating into the upper mesosphere. They are visible ~30% of time at the height of the winter season (mid-May to mid-July). Their intermittency is highly correlated with the zonal wind controlled by the semi-diurnal tide, revealing the direct effect of the atmospheric background on MW penetration into the Mesosphere Lower Thermosphere (MLT, altitude 80-100 km). Measurements of their momentum fluxes (MF) were determined to reach very large values (average ~250 m/s), providing strong evidence of the importance and impacts of small-scale gravity waves at mesospheric altitudes.

Polar mesospheric cloud (PMC) imaging and lidar profiling performed aboard the 5.9 day PMC Turbo balloon flight from Sweden to northern Canada in July 2018 revealed a wide variety of gravity wave (GW) and instability events occurring nearly continuously at approximately 82 km. We describe one event exhibiting GW breaking and associated vortex rings driven by apparent convective instability. Using PMC Turbo imaging with spatial and temporal resolution of 20 m and 2 s, respectively, we quantify the GW horizontal wavelength, propagation direction, and apparent phase speed, and we identify vortex rings with diameters of 3-5 km and horizontal spacing of ~5 km. Lidar data show GW vertical displacements of ±0.3 km. From the data, we find a GW intrinsic frequency and vertical wavelength of 0.009 ± 0.003 rad s-1 and 9 ± 4 km, respectively. We show that these values are consistent with the predictions of numerical simulations of idealized GW breaking. We estimate the momentum deposition rate per unit mass during this event to be 0.04 ± 0.02 m s-2 and show that this value is consistent with the observed GW. Comparison to simulation gives a mean energy dissipation rate for this event of 0.05-0.4 W kg-1, which is consistent with other reported in-situ measurements at the Arctic summer mesopause.