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Mesoscale convective systems observed during AMMA and their impact on the NOx and O3 budget over West Africa

Huntrieser, H. and Schlager, H. and Lichtenstern, M. and Stock, P. and Hamburger, T. and Höller, H. and Schmidt, K. and Betz, H.-D. and Ulanovsky, A. and Ravegnani, F. (2010) Mesoscale convective systems observed during AMMA and their impact on the NOx and O3 budget over West Africa. Atmospheric Chemistry and Physics Discussions (10), pp. 22765-22853. Copernicus Publications. DOI: 10.5194/acpd-10-22765-2010

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Official URL: http://www.atmos-chem-phys-discuss.net/10/22765/2010/


During the "African Monsoon Multidisciplinary Analysis" (AMMA) field phase in August 2006, a variety of measurements focusing on deep convection were performed over West Africa. The German research aircraft Falcon based in Ouagadougou (Burkina Faso) investigated the chemical composition in the outflow of large mesoscale convective systems (MCS). Here we analyse two different types of MCS originating north and south of the intertropical convergence zone (ITCZ, ~10° N), respectively. In addition to the airborne trace gas measurements, stroke measurements from the Lightning Location Network (LINET), set up in Northern Benin, are analysed. The main focus of the present study is 1) to analyse the trace gas composition (CO, O3, NO, NOx, NOy, and HCHO) in the convective outflow as a function of distance from the convective core, 2) to investigate how different trace gas compositions in the boundary layer (BL) and ambient air may influence the O3 concentration in the convective outflow, and 3) to estimate the rate of lightning-produced nitrogen oxides per flash in selected thunderstorms and compare it to our previous results for the tropics. The MCS outflow was probed at different altitudes (~10–12 km) and distances from the convective core (<500 km). Trace gas signatures similar to the conditions in the MCS inflow region were observed in the outflow close to the convective core, due to efficient vertical transport. In the fresh MCS outflow, low O3 mixing ratios in the range of 35–40 nmol mol−1 were observed. Further downwind, O3 mixing ratios in the outflow rapidly increased with distance, due to mixing with the ambient O3-rich air. After 2–3 h, O3 mixing ratios in the range of ~65 nmol mol−1 were observed in the aged outflow. Within the fresh MCS outflow, mean NOx (=NO+NO2) mixing ratios were in the range of ~0.3–0.4 nmol mol−1 (peaks ~1 nmol mol−1) and only slightly enhanced compared to the background. Both lightning-produced NOx (LNOx) and NOx transported upward from the BL contributed about equally to this enhancement. On the basis of Falcon measurements, the mass flux of LNOx in the investigated MCS was estimated to be ~100 g(N) s−1. The average stroke rate of the probed thunderstorms was 0.04–0.07 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. For a better comparison with other published results, LNOx estimates per LINET stroke were scaled to Lightning Imaging Sensor (LIS) flashes. The LNOx production rate per LIS flash was estimated to 1.0 and 2.5 kg(N) for the MCS located south and north of the ITCZ, respectively. If we assume, that these different types of MCS are typical thunderstorms occurring globally (LIS flash rate ~44 s−1), the annual global LNOx production rate was estimated to be ~1.4 and 3.5 Tg(N) a−1.

Item URL in elib:https://elib.dlr.de/65566/
Document Type:Article
Title:Mesoscale convective systems observed during AMMA and their impact on the NOx and O3 budget over West Africa
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Schmidt, K.nowcast GmbH, MünchenUNSPECIFIED
Betz, H.-D.Univ. of Munich, MünchenUNSPECIFIED
Ulanovsky, A.Central Aerological Observatory, Moscow, RUNSPECIFIED
Ravegnani, F.CNR-ISAC, Bologna, IUNSPECIFIED
Journal or Publication Title:Atmospheric Chemistry and Physics Discussions
Refereed publication:Yes
Open Access:Yes
Gold Open Access:Yes
In ISI Web of Science:No
DOI :10.5194/acpd-10-22765-2010
Page Range:pp. 22765-22853
Publisher:Copernicus Publications
Keywords:deep convection, trace gases, lightning
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Aeronautics
HGF - Program Themes:L VU - Air Traffic and Environment (old)
DLR - Research area:Aeronautics
DLR - Program:L VU - Air Traffic and Environment
DLR - Research theme (Project):L - Low-Emission Air Traffic (old)
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics > Atmospheric Trace Species
Deposited By: Huntrieser, Dr.rer.nat. Heidi
Deposited On:13 Oct 2010 15:46
Last Modified:13 Dec 2019 04:07

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