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| Titel |
In situ observations of meteor smoke particles (MSP) during the Geminids 2010: constraints on MSP size, work function and composition |
| VerfasserIn |
M. Rapp, J. M. C. Plane, B. Strelnikov, G. Stober, S. Ernst, J. Hedin, M. Friedrich, U.-P. Hoppe |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 30, no. 12 ; Nr. 30, no. 12 (2012-12-12), S.1661-1673 |
| Datensatznummer |
250017293
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| Publikation (Nr.) |
 copernicus.org/angeo-30-1661-2012.pdf |
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| Zusammenfassung |
| We present in situ observations of meteoric smoke particles (MSP) obtained
during three sounding rocket flights in December 2010 in the frame of the
final campaign of the Norwegian-German ECOMA project (ECOMA = Existence and
Charge state Of meteoric smoke particles in the Middle Atmosphere). The flights
were conducted before, at the maximum activity, and after the decline of the
Geminids which is one of the major meteor showers over the year. Measurements
with the ECOMA particle detector yield both profiles of naturally charged
particles (Faraday cup measurement) as well as profiles of photoelectrons
emitted by the MSPs due to their irradiation by photons of a xenon-flash
lamp. The column density of negatively charged MSPs decreased steadily from
flight to flight which is in agreement with a corresponding decrease of the
sporadic meteor flux recorded during the same period. This implies that the
sporadic meteors are a major source of MSPs while the additional influx due
to the shower meteors apparently did not play any significant role.
Surprisingly, the profiles of photoelectrons are only partly compatible with
this observation: while the photoelectron current profiles obtained during
the first and third flight of the campaign showed a qualitatively similar
behaviour as the MSP charge density data, the profile from the second flight
(i.e., at the peak of the Geminids) shows much smaller photoelectron
currents. This may tentatively be interpreted as a different MSP composition
(and, hence, different photoelectric properties) during this second flight, but
at this stage we are not in a position to conclude that there is a cause and
effect relation between the Geminids and this observation. Finally, the ECOMA
particle detector used during the first and third flight employed three
instead of only one xenon flash lamp where each of the three lamps used for
one flight had a different window material resulting in different cut off
wavelengths for these three lamp types. Taking into account these data along
with simple model estimates as well as rigorous quantum chemical calculations,
it is argued that constraints on MSP sizes, work function and composition
can be inferred. Comparing the measured data to a simple model of the
photoelectron currents, we tentatively conclude that we observed MSPs in the
0.5–3 nm size range with generally increasing particle size with decreasing
altitude. Notably, this size information can be obtained because different
MSP particle sizes are expected to result in different work functions which
is both supported by simple classical arguments as well as quantum chemical
calculations. Based on this, the MSP work function can be estimated to lie in
the range from ~4–4.6 eV. Finally, electronic structure calculations
indicate that the low work function of the MSP measured by ECOMA indicates
that Fe and Mg hydroxide clusters, rather than metal silicates, are the major
constituents of the smoke particles. |
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