Comment on acp-2021-79

Abstract

Hurricane Florence was the sixth named storm in the Atlantic hurricane season 2018. It caused dozens of deaths and major economic damage. In this study, we present in situ observations of trace gases within tropical storm Florence on September 2, 2018 after it had developed a rotating nature, and of a tropical wave observed close to the African continent on August 29, 2018 as part of the research campaign CAFE Africa (Chemistry of the Atmosphere -Field Experiment in Africa) with the HALO (High Altitude Long Range) research aircraft. We show the impact of deep convection on atmospheric composition by measurements of the trace gases nitric oxide (NO), ozone (O 3 ), carbon monoxide (CO), hydrogen peroxide (H 2 O 2 ), dimethyl sulfide (DMS) and methyl iodide (CH 3 I), and by the help of color enhanced infrared satellite imagery taken by GOES-16. While both systems, the tropical wave and the tropical storm, are deeply convective, we only find evidence for lightning in the tropical wave using both in situ NO measurements and data from the World Wide Lightning Location Network (WWLLN). 1 Introduction Tropical cyclones are low-pressure systems evolving over warm tropical waters usually close to the equator (± 20 • ) -an area which is referred to as the Intertropical Convergence Zone (ITCZ) (Frank and Roundy, 2006; Deutscher Wetterdienst).The ITCZ is a global band of convection where south-and northeasterly trade winds converge. It is characterized by rapidly changing weather events. Air heated by the sun near the equator rises, creating low pressures near the surface, which initiates flows from adjacent areas (Waliser and Gautier, 1993;Wang and Magnusdottir, 2006;Deutscher Wetterdienst). In this region of high ocean temperature and intense solar radiation humid air can rise deeply into the troposphere up to 15 km (Collier and Hughes, 2011;Deutscher Wetterdienst). This is associated with the formation of deep, convective cumulonimbus clouds accompanied by heavy rainfall and thunderstorm activity (Zipser, 1994;Xu and Zipser, 2012). In the early stages, these systems are referred to as tropical waves or disturbances which together with low wind shear and high ocean temperature of 26.5 • C or higher can form tropical cyclones (