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| Titel |
Seasonal and interannual variations in HCN amounts in the upper troposphere and lower stratosphere observed by MIPAS |
| VerfasserIn |
N. Glatthor, M. Höpfner, G. P. Stiller, T. von Clarmann, B. Funke, S. Lossow, E. Eckert, U. Grabowski, S. Kellmann, A. Linden, K. A. Walker, A. Wiegele |
| 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 ; 15, no. 2 ; Nr. 15, no. 2 (2015-01-16), S.563-582 |
| Datensatznummer |
250119326
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| Publikation (Nr.) |
 copernicus.org/acp-15-563-2015.pdf |
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| Zusammenfassung |
| We present a HCN climatology of the years 2002–2012, derived from FTIR limb
emission spectra measured with the Michelson Interferometer for Passive
Atmospheric Sounding (MIPAS) on the ENVISAT satellite, with the main focus on
biomass burning signatures in the upper troposphere and lower stratosphere.
HCN is an almost unambiguous tracer of biomass burning with a tropospheric
lifetime of 5–6 months and a stratospheric lifetime of about 2 years. The
MIPAS climatology is in good agreement with the HCN distribution obtained by
the spaceborne ACE-FTS experiment and with airborne in situ measurements
performed during the INTEX-B campaign. The HCN amounts observed by MIPAS in
the southern tropical and subtropical upper troposphere have an annual cycle
peaking in October–November, i.e. 1–2 months after the maximum of southern
hemispheric fire emissions. The probable reason for the time shift is the
delayed onset of deep convection towards austral summer. Because of overlap
of varying biomass burning emissions from South America and southern Africa
with sporadically strong contributions from Indonesia, the size and strength
of the southern hemispheric plume have considerable interannual variations,
with monthly mean maxima at, for example, 14 km between 400 and more than
700 pptv. Within 1–2 months after appearance of the plume, a considerable
portion of the enhanced HCN is transported southward to as far as Antarctic
latitudes. The fundamental period of HCN variability in the northern upper
troposphere is also an annual cycle with varying amplitude, which in the
tropics peaks in May after and during the biomass burning seasons in northern
tropical Africa and southern Asia, and in the subtropics peaks in July due to
trapping of pollutants in the Asian monsoon anticyclone (AMA). However,
caused by extensive biomass burning in Indonesia and by northward transport
of part of the southern hemispheric plume, northern HCN maxima also occur
around October/November in several years, which leads to semi-annual cycles.
There is also a temporal shift between enhanced HCN in northern low and mid-
to high latitudes, indicating northward transport of pollutants. Due to
additional biomass burning at mid- and high latitudes, this meridional
transport pattern is not as clear as in the Southern Hemisphere. Upper
tropospheric HCN volume mixing ratios (VMRs) above the tropical oceans
decrease to below 200 pptv, presumably caused by ocean uptake,
especially during boreal winter and spring. The tropical stratospheric tape
recorder signal with an apparently biennial period, which was detected in MLS
and ACE-FTS data from mid-2004 to mid-2007, is corroborated by MIPAS HCN data.
The tape recorder signal in the whole MIPAS data set exhibits periodicities
of 2 and 4 years, which are generated by interannual variations in biomass
burning. The positive anomalies of the years 2003, 2007 and 2011 are caused
by succession of strongly enhanced HCN from southern hemispheric and
Indonesian biomass burning in boreal autumn and of elevated HCN from northern
tropical Africa and the AMA in subsequent spring and summer. The anomaly of
2005 seems to be due to springtime emissions from tropical Africa followed by
release from the summertime AMA. The vertical transport time of the anomalies
is 1 month or less between 14 and 17 km in the upper troposphere and
8–11 months between 17 and 25 km in the lower stratosphere. |
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