386 research outputs found
Ionospheric response during low and high solar activity
We analyse solar extreme ultraviolet (EUV) irradiance observed by the Solar EUV Experiment (SEE) onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite, and solar proxies (the F10.7 index, and Mg-II index), and compare their variability with the one of the global mean Total Electron Content (GTEC). Cross-wavelet analysis confirms the joint 27 days periodicity in GTEC and solar proxies. We focus on a comparison for solar minimum (2007-2009) and maximum (2013-2015) and find significant differences in the correlation during low and high solar activity years. GTEC is delayed by
approximately 1-2 days in comparison to solar proxies during both low and high solar activity at the 27 days solar rotation period. To investigate the dynamics of the delay process, Coupled Thermosphere Ionosphere Plasmasphere electrodynamics model simulations have been performed for low and high solar activity conditions. Preliminary results using cross correlation analysis show an ionospheric delay of 1 day in GTEC with respect to the F10.7 index during low and high solar activity.Wir analysieren vom Solar Extreme Ultraviolet Experiment (SEE) an Bord des Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) Satelliten gemessene solare EUV-Irradianzen, solare Proxies (den F10.7-Index und denMg-II-Index), und vergleichen deren VariabilitĂ€t mit derjenigen des global gemittelten Gesamtelektronengehalts (GTEC). Kreuzwaveletanalysen bestĂ€tigen eine gemeinsame VariabilitĂ€t im Periodenbereich der solaren Rotation (27 Tage). Wir vergleichen insbesondere den Zusammenhang wĂ€hrend des solaren Minimums (2007- 2009) und Maximums (2013-2015), wobei signifikante Unterschiede der Korrelation zwischen solaren und ionosphĂ€rischen Parametern auftreten. Es tritt eine Verzögerung der Maxima und Minima von GTEC gegenĂŒber denjenigen der solaren Proxies von
einem Tag sowohl im solaren Minimum als auch im solaren Maximum auf
The response of the ionospheric peak electron density (NmF2) to solar activity)
The ionospheric peak electron density NmF2, simulated with the Coupled
Thermosphere Ionosphere Plasmasphere electrodynamics (CTIPe) model was used to
study the ionospheric response to solar flux in years of low (2008) and high (2013)
solar activity. The CTIPe NmF2 was compared to the Whole Atmosphere Community
Climate Model with Thermosphere and Ionosphere Extension (WACCM-X) and the
Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC)
NmF2 in March and July of 2008 and 2013. The comparison shows that the CTIPe NmF2 is lower than the COSMIC andWACCM-X NmF2. Both models successfully reproduce the semi-annual variations seen in the COSMIC observations. Analysis of the 27-day variations of the CTIPe NmF2 shows that the midnight NmF2 deviations are stronger than the midday deviations. In addition, at low solar activity, the 27-day variations of NmF2 are larger in the Southern Hemisphere, while at high solar activity, the 27-day variations of NmF2 are larger at the equator and in the Northern Hemisphere.
An ionospheric delay was estimated with CTIPe simulated NmF2 at the 27-day solar
rotation period during low and high solar activity. During low (high) solar activity, an
ionospheric delay of about 12 (34) hours is predicted indicating an increasing ionospheric delay with solar activity.Die maximale ionosphÀrische Elektronendichte NmF2, die mit dem Coupled Thermosphere Ionosphere Plasmasphere electrodynamics (CTIPe) Modell
simuliert wurde, wurde zur Untersuchung der ionosphÀrischen Reaktion in Jahren
mit geringer (2008) und hoher (2013) SonnenaktivitÀt verwendet. CTIPe vorhergesagte NmF2 wurde mit derjenigen des Whole Atmosphere Community Climate Model with Thermosphere and Ionosphere Extension (WACCM-X) und Messwerten des Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) im MÀrz und Juli der Jahre 2008 und 2013 verglichen. Der Vergleich zeigt, dass NmF2
aus CTIPe geringer ist als das COSMIC gemessene und von WACCM-X simulierte.
Beide Modelle reproduzieren erfolgreich die von COSMIC beobachteten halbjÀhrlichen
Schwankungen. Die Analyse der 27-tÀgigen Schwankungen des CTIPe NmF2 zeigt,
dass die mitternÀchtlichen NMF2-Abweichungen stÀrker sind als diejenigen am Mittag.
AuĂerdem sind bei geringer SonnenaktivitĂ€t die 27-Tage-Abweichungen von NmF2 in der SĂŒdhemisphĂ€re gröĂer, wĂ€hrend bei hoher SonnenaktivitĂ€t die 27-Tage-Abweichungen von NmF2 am Ăquator und in der NordhemisphĂ€re gröĂer sind.
Die ionosphÀrische Verzögerung wÀhrend geringer und hoher SonnenaktivitÀt wurde
fĂŒr die 27-tĂ€gige Sonnenrotation mit CTIPe simuliert. Bei geringer (hoher) SonnenaktivitĂ€t wird eine ionosphĂ€rische Verzögerung von etwa 12 (34) Stunden beobachtet, was auf eine zunehmende ionosphĂ€rische Verzögerung mit zunehmender SonnenaktivitĂ€t hinweist
First Energy and Angle differential Measurements of e^+e^- -pairs emitted by Internal Pair Conversion of excited Heavy Nuclei
We present the first energy and angle resolved measurements of e+e- pairs
emitted from heavy nuclei (Z>=40) at rest by internal pair conversion (IPC) of
transitions with energies of less than 2MeV as well as recent theoretical
results using the DWBA method, which takes full account of relativistic
effects, magnetic substates and finite size of the nucleus. The 1.76MeV E0
transition in Zr90 (Sr source) and the 1.77MeV M1 transition in Pb207 (Bi
source) have been investigated experimentally using the essentially improved
set-up at the double-ORANGE beta-spectrometer of GSI. The measurements prove
the capability of the setup to cleanly identify the IPC pairs in the presence
of five orders of magnitude higher beta- and gamma background from the same
source and to yield essentially background-free sum spectra despite the large
background. Using the ability of the ORANGE setup to directly determine the
opening angle of the e+e- pairs, the angular correlation of the emitted pairs
was measured. In the Zr90 case the correlation could be deduced for a wide
range of energy differences of the pairs. The Zr90 results are in good
agreement with recent theory. The angular correlation deduced for the M1
transition in Pb207 is in strong disagreement with theoretical predictions
derived within the Born approximation and shows almost isotropic character.
This is again in agreement with the new theoretical results.Comment: LaTeX, 28 pages incl. 10 PS figures; Accepted by Z.Phys.
Positron spectra from internal pair conversion observed in {238}U + {181}Ta collisions
We present new results from measurements and simulations of positron spectra,
originating from 238U + 181Ta collisions at beam energies close to the Coulomb
barrier. The measurements were performed using an improved experimental setup
at the double-Orange spectrometer of GSI. Particular emphasis is put on the
signature of positrons from Internal-Pair-Conversion (IPC) processes in the
measured e+ energy spectra, following the de-excitation of electromagnetic
transitions in the moving Ta-like nucleus. It is shown by Monte Carlo
simulations that, for the chosen current sweeping procedure used in the present
experiments, positron emission from discrete IPC transitions can lead to rather
narrow line structures in the measured energy spectra. The measured positron
spectra do not show evidence for line structures within the statistical
accuracy achieved, although expected from the intensities of the observed
transitions (E keV) and theoretical conversion
coefficients. This is due to the reduced detection efficiency for IPC
positrons, caused by the limited spatial and momentum acceptance of the
spectrometer. A comparison with previous results, in which lines have been
observed, is presented and the implications are discussed.Comment: LaTeX, 20 pages including 5 EPS figures; Accepted by Eur. Phys.Jour.
New Results on e+e- Line Emission in U+Ta Collisions
We present new results obtained from a series of follow-up e+e- coincidence
measurements in heavy-ion collisions, utilizing an improved experimental set-up
at the double-Orange beta-spectrometer of GSI. The collision system U+Ta was
reinvestigated in three independent runs at beam energies in the range
(6.0-6.4)xA MeV and different target thicknesses, with the objective to
reproduce a narrow sum-energy e+e- line at ~635 keV observed previously in this
collision system. At improved statistical accuracy, the line could not be found
in these new data. For the ''fission'' scenario, an upper limit (1 sigma) on
its production probability per collision of 1.3x10^{-8} can be set which has to
be compared to the previously reported value of [4.9 +- 0.8 (stat.) +- 1.0
(syst)]x10^{-7}. In the light of the new results, a reanalysis of the old data
shows that the continuous part of the spectrum at the line position is
significantly higher than previously assumed, thus reducing the production
probability of the line by a factor of two and its statistical significance to
< 3.4sigma.Comment: 15 pages, standard LaTeX with 3 included PS figures; Submitted to
Physics Letters
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