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The spatial and temporal variability of gravity waves (GWs) potential energy (Ep) over South America (SA) was examined by analyzing temperature profiles obtained through the utilization of Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) from January 2002 to December 2021. We used the empirical orthogonal function (EOF) analysis to decompose GWs parameters and to analyze the GW variations over SA. We considered the first three eigenmodes (EOF1, EOF2, and EOF3) and their principal components (PC1, PC2, and PC3) of the EOF decomposition, which accounts for ∼80–90% of the total GWs variation over SA. Further, we analyzed the coupled variation of Ep and zonal mean wind ( U ) to verify their inter-dependencies using the singular value decomposition (SVD). The spatial variation showed that different localized mechanisms generate GWs at different sectors of the continent. The EOF1 of Ep comprised more than 50%, the EOF2 ∼20–25%, and the third ∼10–15% of the total GWs variation. The positive variation of GWs energy in the EOF1 is localized in the tropical region from the lower stratosphere to the lower mesosphere and southward below 1.5° S in the upper mesosphere. The spectral analysis of GWs energy showed biannual, annual, semiannual, and 11-year variations at different eigenvectors. Relative Ep (REp) showed an asymmetric hemispheric response to solar flux over South America. The REp response to QBO showed a modulating effect below 70 km and a positive response above 70 km. There is a good positive correlation between the temporal component of EOF2 of Ep and the quasi-biennial oscillation (QBO) at 30 mb and 50 mb in the PC2 temporal variation. Graphical Abstract

Using COSMIC-2 and METOP radio occultation measurements during the years 2020 and 2021, the study presents the first direct and independent relationship between the potential energy (Ep) in the stratosphere, precipitable water vapour (PWV), tropopause heights (TPH), and cold-point heights (CPH) over South America. The South American continent comprises the tropical region, the Andes Mountain range, and mid-latitude climates. The seasonal mean of the potential energy (Ep), the PWV, and the tropopause parameters height (TPH and CPH) were obtained to investigate the relationship between the stratospheric gravity wave (SGW) Ep and the tropospheric parameters (PWV, TPH, and CPH). Around the Andes Mountains to the east, there is significantly less water vapour (PWV < 10 mm) and a relatively high gravity wave Ep (Ep > 8 kJ kg−1). A good correlation of variability was found between the PWV and the lower SGW Ep in summer over the tropical region (± 20◦). Generally, good and strong correlations were observed in the summer and spring, with negative/no correlations in the winter in 2020 and 2021. Also, good and strong correlations between SGW, PWV, and TPH were observed in the summer at 20oN-10oN in 2020 and 2021. Our result demonstrated the possibility that convective activity was a major driver of the tropical gravity waves over South America. In the subtropical (30∘–40∘) region, especially in the winter, the tropospheric parameters make little or no contribution to gravity wave activity in the region. The CPH generally showed a no/negative with SGW over the South American tropics. The SGW activities in the tropical region showed an impact on the structure of the tropopause parameters, which could be a result of the convective activity in this region.

The Intertropical Convergence Zone (ITCZ) is a dominant feature of tropical climate characterized by intense convection that influences global atmospheric circulation and serves as a primary source of stratospheric gravity waves (GWs), which transport energy and momentum vertically through the atmosphere. This study investigates the modulation of the tropical ITCZ position and stratospheric gravity wave activity by the El Niño–Southern Oscillation (ENSO), the Madden–Julian Oscillation (MJO), and the Quasi-Biennial Oscillation (QBO) using 11 years (2011–2021) of radio occultation and reanalysis data. ITCZ latitude (from 850 hPa refractivity) and gravity wave potential energy maxima (from stratospheric temperatures) were identified via Gaussian fitting. Both ITCZ and gravity wave potential energy maxima exhibit coherent seasonal migration (∼10 and ∼5° latitudinal shifts, respectively), with potential energy maxima typically equatorward of the ITCZ. ENSO is the primary modulator: El Niño conditions shift the ITCZ northward in the American sector but southward in the African and Asian sectors. For gravity wave potential energy maxima, El Niño induces southward shifts in the American sector but northward shifts in the Asian sector, while enhancing overall GW activity. The MJO prompts regionally complex southward shifts in the ITCZ/potential energy maxima. The QBO predominantly influences gravity wave potential energy, with westerly phases associated with southward shifts in the potential energy maxima in the African and Asian sectors. While long-term latitudinal trends are weak, climate modes significantly impact ITCZ/GW peak values. The radio occultation data captured finer-scale features than reanalysis products, highlighting the importance of observational constraints in understanding troposphere–stratosphere coupling mechanisms.

Medium-scale gravity waves (MSGWs) are atmospheric waves with horizontal scales ranging from 50 to 1000 km that can be observed through airglow all-sky images. This research introduces a novel algorithm that automatically identifies MSGWs using the keogram technique to study the waves over the Antarctic Peninsula. MSGWs were observed with an all-sky airglow imager located at the Brazilian Comandante Ferraz Antarctic Station (CF, 62° S), near the tip of the Antarctic Peninsula. Several preprocessing techniques are necessary to extract the parameters of MSGWs from the airglow images. These include projecting the images into geographical coordinates, applying a flat-field correction, performing consecutive image subtraction, and employing a Butterworth filter to enhance the visibility of the MSGWs. Additionally, a wavelet transform is used to identify the primary oscillations of the MSGWs in the keograms. Subsequently, a wavelet transform is also used to reconstruct the MSGWs and obtain the fitting coefficients of phase lines. The fitting coefficients are then used to calculate the MSGW parameters and assess the quality of the results. Simulations with synthetic images containing typical propagating gravity waves were conducted to evaluate the errors generated during the MSGW calculations and to determine the threshold for the fitting parameters. This methodology processed a year's worth of data in less than 1 h, successfully identifying most waves with errors lower than 5 %. The observed wave parameters are generally consistent with expected results; however, they show differences from other observation sites, exhibiting larger phase speeds and wavelengths.