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| Titel |
Response of polar mesosphere summer echoes to geomagnetic disturbances in the Southern and Northern Hemispheres: the importance of nitric oxide |
| VerfasserIn |
S. Kirkwood  , E. Belova, P. Dalin, M. Mihalikova, D. Mikhaylova, D. Murtagh, H. Nilsson, K. Satheesan, J. Urban, I. Wolf |
| 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 ; 31, no. 2 ; Nr. 31, no. 2 (2013-02-27), S.333-347 |
| Datensatznummer |
250018996
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| Publikation (Nr.) |
 copernicus.org/angeo-31-333-2013.pdf |
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| Zusammenfassung |
| The relationship between polar mesosphere summer echoes (PMSE) and
geomagnetic disturbances (represented by magnetic K indices) is examined.
Calibrated PMSE reflectivities for the period May 2006–February 2012 are
used from two 52.0/54.5 MHz radars located in Arctic Sweden (68° N,
geomagnetic latitude 65°) and at two different sites in Queen Maud
Land, Antarctica (73°/72° S, geomagnetic latitudes
62°/63°). In both the Northern Hemisphere (NH) and the
Southern Hemisphere (SH) there is a strong increase in mean PMSE reflectivity
between quiet and disturbed geomagnetic conditions. Mean volume
reflectivities are slightly lower at the SH locations compared to the NH, but
the position of the peak in the lognormal distribution of PMSE reflectivities
is close to the same at both NH and SH locations, and varies only slightly
with magnetic disturbance level. Differences between the sites, and between
geomagnetic disturbance levels, are primarily due to differences in the
high-reflectivity tail of the distribution. PMSE occurrence rates are
essentially the same at both NH and SH locations during most of the PMSE
season when a sufficiently low detection threshold is used so that the peak
in the lognormal distribution is included. When the local-time dependence of
the PMSE response to geomagnetic disturbance level is considered, the
response in the NH is found to be immediate at most local times, but delayed
by several hours in the afternoon sector and absent in the early evening. At
the SH sites, at lower magnetic latitude, there is a delayed response (by
several hours) at almost all local times. At the NH (auroral zone) site, the
dependence on magnetic disturbance is highest during evening-to-morning
hours. At the SH (sub-auroral) sites the response to magnetic disturbance is
weaker but persists throughout the day. While the immediate response to
magnetic activity can be qualitatively explained by changes in electron
density resulting from energetic particle precipitation, the delayed response
can largely be explained by changes in nitric oxide concentrations.
Observations of nitric oxide concentration at PMSE heights by the Odin
satellite support this hypothesis. Sensitivity to geomagnetic disturbances,
including nitric oxide produced during these disturbances, can explain
previously reported differences between sites in the auroral zone and those
at higher or lower magnetic latitudes. The several-day lifetime of nitric
oxide can also explain earlier reported discrepancies between high
correlations for average conditions (year-by-year PMSE reflectivities and
K indices) and low correlations for minute-to-day timescales. |
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