Impact of convectively coupled tropical waves on the composition, vertical structure of the atmosphere, and tropical cyclogenesis in the region of Cabo Verde in September 2021 during the CADDIWA campaign

Abstract

Abstract. In summer, mixed Rossby gravity waves–tropical depressions (MRG-TD) are known to drive intraseasonal humidity variability in the northeastern Atlantic troposphere, modulated by equatorial Rossby (ER) and Kelvin waves. However, their impact on dust remains poorly understood, and methods in the literature struggle to distinguish the two MRG-TD tracks. During the Clouds–Atmosphere Dynamics–Dust Interaction in West Africa (CADDIWA) campaign in September 2021, in situ data (from dropsondes and radiosondes) and remote sensing data (Global Navigation Satellite System data and Infrared Atmospheric Sounding Interferometer data) were used to investigate the three-dimensional impact of tropical waves on dust and thermodynamics over Cabo Verde. The distinct contributions of Kelvin waves, ER, and MRG-TD were isolated using frequency–wavenumber filtering of total column water vapor. The latter was efficiently split into southern- and northern-track African easterly waves using distinct frequency windows (MRG-TD1 and MRG-TD2) and enabled us to demonstrate their distinct horizontal structures and impacts. ER waves mainly impacted thermodynamics above 750 hPa, MRG-TD1 affected jet-level thermodynamics, and MRG-TD2 modulated moisture in the lower troposphere. MRG-TD2 was identified as the main driver of dust events over Cabo Verde in September 2021. Tropical cyclogenesis was linked to interactions among multiple tropical waves. Notably, a delay of up to 2 d was observed between Kelvin wave interactions with MRG-TD1 and cyclone formation, consistent with previous findings. These results highlight the critical role of tropical wave interactions in cyclogenesis and underscore their potential to improve forecasting.