Influence of modes of climate variability on stratospheric gravity waves in the tropics using Radio Occultation and Reanalysis Data

Abstract. The Intertropical Convergence Zone (ITCZ) is a critical driver of tropical climate, characterized by convective activity that transfers energy, influences atmospheric circulation, and modulates precipitation. These processes generate atmospheric disturbances, making the ITCZ a significant source of stratospheric gravity waves (GWs). This study investigates the relationship between the ITCZ and stratospheric GWs, as well as the influence of climate variability modes—Madden-Julian Oscillation (MJO), El Niño–Southern Oscillation (ENSO), and Quasi-Biennial Oscillation (QBO)—on GW activity and ITCZ dynamics. Using GNSS radio occultation (RO) data from COSMIC-1, COSMIC-2, and METOP satellites (2011–2021), we derive the latitudinal positions of the ITCZ and GW potential energy (Ep) maxima via Gaussian fitting. ERA5 and NCEP reanalysis data are used to validate ITCZ positions and estimate refractivity. Results show the ITCZ migrates ~10° latitudinally, with ~5° seasonal shifts between boreal winter and summer, while its strength remains relatively stable. Stratospheric GW Ep maxima exhibit seasonal patterns similar to the ITCZ, with smaller latitudinal gaps in the Northern and Southern Hemispheres. Multilinear regression reveals significant zonal variations in the impacts of QBO, ENSO, and MJO on ITCZ position and Ep, particularly over the American, African, and Asian sectors. ENSO and MJO drive substantial negative trends in ITCZ position, Ep, and refractivity, especially in Asian and African regions. However, zonal trends in Ep maxima and ITCZ positions remain stable, likely due to consistent Gaussian peak locations. Discrepancies in ITCZ trends and refractivity values between RO, ERA5, and NCEP data are attributed to differences in resolution, coverage, and assimilation techniques. This study highlights the complex interplay between the ITCZ, GWs, and climate variability modes.