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| Titel |
Lightning activity in Brazilian thunderstorms during TROCCINOX: implications for NOx production |
| VerfasserIn |
H. Huntrieser, U. Schumann, H. Schlager, H. Höller, A. Giez, H.-D. Betz, D. Brunner, C. Forster, O. Pinto, R. Calheiros |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 8, no. 4 ; Nr. 8, no. 4 (2008-02-25), S.921-953 |
| Datensatznummer |
250005675
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| Publikation (Nr.) |
 copernicus.org/acp-8-921-2008.pdf |
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| Zusammenfassung |
| During the TROCCINOX field experiment in January and February 2005, the
contribution of lightning-induced nitrogen oxides (LNOx) from tropical and
subtropical thunderstorms in Southern Brazil was investigated. Airborne trace
gas measurements (NO, NOy, CO and O3) were performed up to
12.5 km with the German research aircraft Falcon. During anvil
penetrations in selected tropical and subtropical thunderstorms of 4 and 18
February, NOx mixing ratios were on average enhanced by 0.7–1.2 and
0.2–0.8 nmol mol−1 totally, respectively. The relative contributions
of boundary layer NOx (BL-NOx) and LNOx to anvil-NOx were
derived from the NOx-CO correlations. On average ~80–90% of
the anvil-NOx was attributed to LNOx. A Lightning Location
Network (LINET) was set up to monitor the local distribution of
cloud-to-ground (CG) and intra-cloud (IC) radiation sources (here called
"strokes") and compared with lightning data from the operational Brazilian
network RINDAT (Rede Integrada Nacional de Detecção de
Descargas Atmosféricas). The horizontal LNOx mass flux out of the
anvil was determined from the mean LNOx mixing ratio, the horizontal outflow
velocity and the size of the vertical cross-section of the anvil, and related
to the number of strokes contributing to LNOx. The values of these parameters
were derived from the airborne measurements, from lightning and radar
observations, and from a trajectory analysis. The amount of LNOx produced per
LINET stroke depending on measured peak current was determined. The results
were scaled up with the Lightning Imaging Sensor (LIS) flash rate
(44 flashes s−1) to obtain an estimate of the global LNOx production
rate. The final results gave ~1 and ~2–3 kg(N) per LIS flash
based on measurements in three tropical and one subtropical Brazilian
thunderstorms, respectively, suggesting that tropical flashes may be less
productive than subtropical ones. The equivalent mean annual global LNOx
nitrogen mass production rate was estimated to be 1.6 and 3.1 Tg a−1,
respectively. By use of LINET observations in Germany in July 2005, a
comparison with the lightning activity in mid-latitude thunderstorms was also
performed. In general, the same frequency distribution of stroke peak
currents as for tropical thunderstorms over Brazil was found. The different
LNOx production rates per stroke in tropical thunderstorms compared with
subtropical and mid-latitude thunderstorms seem to be related to the
different stroke lengths (inferred from comparison with laboratory data and
observed lengths). In comparison, the impact of other lightning parameters as
stroke peak current and stroke release height was assessed to be minor. The
results from TROCCINOX suggest that the different vertical wind shear may
be responsible for the different stroke lengths. |
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