Sources of concentric gravity waves generated by a moving mesoscale convective system in southern Brazil

Abstract

The studies on the sources of three concentric gravity waves (CGWs) excited by a moving mesoscale convective system (MCS) on the night of 1–2 October 2019 are investigated. These CGWs were observed using a hydroxyl (OH) all-sky imager, whereas the MCS was observed by the Geostationary Operational Environmental Satellite (GOES). Using 2D spectral analysis, we observed that the three CGWs have horizontal wavelength λH between ∼30–55 km, phase speed cH∼70–90 m s−1, and period τ∼7–12 min. Using backward ray tracing, we found that two of the CGWs were excited from convective cores within the MCS. We also found that the epicenters of the two waves were close to the tropopause positions of the ray-traced paths and nearby convective cores. Regarding the source, we verified that on this night the tropopause was ∼-80 ∘C, which was ∼10 ∘C colder than the days preceding and after the MCS and also colder than usually observed. Since the tropopause height and temperature are fundamental parameters underlying the analysis of the overshooting extent, we developed our own methodology to establish a reference tropopause that would enable a quantitative estimate of this parameter. Since the MCS (CGWs source) was moving, the overshooting convective cores were tracked in space and time. Using the tracking of the overshooting tops (OTs) in space and time with the aid of reverse ray tracing, we found that two out of the three CGWs were excited by the MCS, whereas the source of the remaining one was not directly associated with the MCS.