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 Variabilität mit derjenigen des global gemittelten Gesamtelektronengehalts (GTEC). Kreuzwaveletanalysen bestätigen eine gemeinsame Variabilität im Periodenbereich der solaren Rotation (27 Tage). Wir vergleichen insbesondere den Zusammenhang während des solaren Minimums (2007- 2009) und Maximums (2013-2015), wobei signifikante Unterschiede der Korrelation zwischen solaren und ionosphärischen Parametern auftreten. Es tritt eine Verzögerung der Maxima und Minima von GTEC gegenüber 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 ionosphärische Elektronendichte NmF2, die mit dem Coupled Thermosphere Ionosphere Plasmasphere electrodynamics (CTIPe) Modell simuliert wurde, wurde zur Untersuchung der ionosphärischen Reaktion in Jahren mit geringer (2008) und hoher (2013) Sonnenaktivität 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 März 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 halbjährlichen Schwankungen. Die Analyse der 27-tägigen Schwankungen des CTIPe NmF2 zeigt, dass die mitternächtlichen NMF2-Abweichungen stärker sind als diejenigen am Mittag. Außerdem sind bei geringer Sonnenaktivität die 27-Tage-Abweichungen von NmF2 in der Südhemisphäre größer, während bei hoher Sonnenaktivität die 27-Tage-Abweichungen von NmF2 am Äquator und in der Nordhemisphäre größer sind. Die ionosphärische Verzögerung während geringer und hoher Sonnenaktivität wurde für die 27-tägige Sonnenrotation mit CTIPe simuliert. Bei geringer (hoher) Sonnenaktivität wird eine ionosphärische Verzögerung von etwa 12 (34) Stunden beobachtet, was auf eine zunehmende ionosphärische Verzögerung mit zunehmender Sonnenaktivität 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 $\gamma$ transitions (E$_{\gamma}~1250-1600$ 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