Case Studies on Concentric Gravity Waves Source Using Lightning Flash Rate, Brightness Temperature and Backward Ray Tracing at São Martinho da Serra (29.44°S, 53.82°W). Issue 10 (21st May 2021)

• Record Type: Journal Article
• Authors: Nyassor, P. K.; Wrasse, C. M.; Gobbi, D.; Paulino, I.; Vadas, S. L.; Naccarato, K. P.; Takahashi, H.; Bageston, J. V.; Figueiredo, C. A. O. B.; Barros, D.
• Is Part Of: Journal of geophysical research. Volume 126:Issue 10(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-05-21
• Subjects: concentric gravity wave -- convective overshoot -- lightning flash rate; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2020JD034527
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: We relate the spatial and temporal distribution of lightning flash rates and cloud top brightness temperature (CTBT) to concentric atmospheric gravity wave (CGW) events observed at the Southern Space Observatory (SSO) in São Martinho da Serra (29.44°S, 53.82°W, 488.7 m) in southern Brazil. The selected identified cases from 2017 to 2018 were observed by a hydroxyl (OH) all‐sky imager. Backward ray tracing shows that the time of gravity wave excitation agrees with the highest values of lightning flash rates (indicating lightning jump) as well as the coldest brightness temperatures that indicate the time of convective overshoot. Radiosonde measurements show high convective available potential energy (CAPE), associated with a maximum updraft velocity just prior to the wave events. We find that these possible source locations correspond to the positions and times that convective plumes overshot the tropopause (seen in GOES‐16 CTBT images). We also show that higher spatial lightning density (i.e., number of lightning flashes at a given longitude and latitude) agree with the overshoot locations from the GOES satellite. We also find that the overshoot times from the GOES‐16 satellite agree with the times lightning jumps were observed in the lightning flash rate. Finally, we find that the periodicities in the lightning flash rate agree with the periods of the observed CGWs, which further strengthens the result that the CGWs were excited by the deep convective systems determined from backward ray tracing. Plain Language Summary: A column of rising warm air (convective plume) in a cloud is capable of vertically overshooting the tropopause into the stratosphere by ∼1–3 km, thereby generating concentric atmospheric gravity waves. The updraft of the plume is the driving factor of the charge separation within the cloud, which results in lightning discharge. Since the lightning flash rate is a direct consequence of the updraft and overshooting, the intensity of the updraft modulates the lightning flash rate. If the plume overshoots the tropopause, the rate of the overshooting is related to the lightning flash rate and also to the waves excited from this overshooting. By backward tracing the waves, the position and time the ray path coincides with the tropopause agrees with the position and time of the overshooting plumes and high spatial density of the lightning. From the lightning flash rate, we also find that lightning jumps occurred at the same times as the overshooting. The spatial and temporal distributions of the overshooting plumes, their respective lightning density, and jumps, the position and time of the ray path as well as the concentric ring centers were used to locate the sources of these concentric waves that we investigate in this work. Key Points: The first ground‐based observation of concentric gravity waves over Brazil is presented Spatial and temporal distribution of lightning activities were related to cloud top brightness temperature to locate overshooting plumes Periodicities in the lightning flash rate were related to the observed concentric gravity wave periods