NO<sub>x</sub> production by lightning in Hector: first airborne measurements during SCOUT-O3/ACTIVE

Abstract

Abstract. During the SCOUT-O3/ACTIVE field phase in November–December 2005 airborne in situ measurements were performed inside and in the vicinity of thunderstorms over northern Australia with several research aircraft (German Falcon, Russian M55 Geophysica, and British Dornier-228). Here a case study from 19 November is presented in large detail on the basis of airborne trace gas measurements (NO, NOy, CO, O3) and stroke measurements from the German LIghtning Location NETwork (LINET), set up in the vicinity of Darwin during the field campaign. The anvil outflow from three different types of thunderstorms was probed by the Falcon aircraft: 1) a continental thunderstorm developing in a tropical airmass near Darwin, 2) a mesoscale convective system (MCS) developing within the tropical maritime continent (Tiwi Islands) known as Hector, and 3) a continental thunderstorm developing in a subtropical airmass ~200 km south of Darwin. For the first time detailed measurements of NO were performed in the Hector outflow. The highest NO mixing ratios were observed in Hector with peaks up to 7 nmol mol−1 in the main anvil outflow at ~11.5–12.5 km altitude. The mean NOx (=NO+NO2) mixing ratios during these penetrations (~100 km width) varied between 2.2 and 2.5 nmol mol−1. The NOx contribution from the boundary layer (BL), transported upward with the convection, to total anvil-NOx was found to be minor (<10%). On the basis of Falcon measurements, the mass flux of lightning-produced NOx (LNOx) in the well-developed Hector system was estimated to 0.6–0.7 kg(N) s−1. The highest average stroke rate of the probed thunderstorms was observed in the Hector system with 0.2 strokes s−1 (here only strokes with peak currents ≥10 kA contributing to LNOx were considered). The LNOx mass flux and the stroke rate were combined to estimate the LNOx production rate in the different thunderstorm types. For a better comparison with other studies, LINET strokes were scaled with Lightning Imaging Sensor (LIS) flashes. The LNOx production rate per LIS flash was estimated to 4.1–4.8 kg(N) for the well-developed Hector system, and to 5.4 and 1.7 kg(N) for the continental thunderstorms developing in subtropical and tropical airmasses, respectively. If we assume, that these different types of thunderstorms are typical thunderstorms globally (LIS flash rate ~44 s−1), the annual global LNOx production rate based on Hector would be ~5.7–6.6 Tg(N) a−1 and based on the continental thunderstorms developing in subtropical and tropical airmasses ~7.6 and ~2.4 Tg(N) a−1, respectively. The latter thunderstorm type produced much less LNOx per flash compared to the subtropical and Hector thunderstorms, which may be caused by the shorter mean flash component length observed in this storm. It is suggested that the vertical wind shear influences the horizontal extension of the charged layers, which seems to play an important role for the flash lengths that may originate. In addition, the horizontal dimension of the anvil outflow and the cell organisation within the thunderstorm system are probably important parameters influencing flash length and hence LNOx production per flash.

Lightning‐generated NOx seen by the Ozone Monitoring Instrument during NASA's Tropical Composition, Cloud and Climate Coupling Experiment (TC4)

“…The Huntrieser et al analysis suggests that longer flash length occurs with stronger upper level winds and that the greater length is responsible for greater production per flash. Huntrieser et al [2009] suggest that even within the tropics, substantial variability in production per flash can occur, and may also be related to flash length and associated wind profiles.…”

Lightning NOx Production in the Tropics as Determined Using OMI NO2 Retrievals and WWLLN Stroke Data

“…The slightly smaller contrast between marine and continental PE over the tropical Pacific may be due to the mixed character of continental convection in this region. The relatively high continental values of LNO x PE in the tropical Pacific could be caused by the fact that much of the land‐based lightning in this region occurs over islands, where differential heating increases sea‐breeze convergence and storm intensity (Cummings et al, ; Huntrieser et al, ).…”

Tropospheric nitric acid columns from the IASI satellite instrument interpreted with a chemical transport model: Implications for parameterizations of nitric oxide production by lightning

“…Lightning NO x emitted into the GEOS‐Chem grid boxes produce dilute NO plumes with typical concentrations less than 1 ppbv. Aircraft observations found that lightning can create highly concentrated NO plumes inside cumulonimbus clouds, with concentrations generally between 1 and 7 ppbv and occasionally rising as high as 25 ppbv [ Huntrieser et al ., , ; Ott et al ., ]. These concentrated plumes can have spatial scales as small as 300 m [ Huntrieser et al ., ], which are not resolved in global models with typical scales of 50–500 km.…”