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Long-term variations and residual trends in the E, F and sporadic E (Es) layer over Juliusruh, Europe
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  • Sivakandan Mani,
  • Jens Mielich,
  • Toralf Renkwitz,
  • Jorge L. Chau,
  • Juliana Jaen,
  • Jan Laštovička
Sivakandan Mani
Leibniz Institute of Atmospheric Physics at the University of Rostock

Corresponding Author:[email protected]

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Jens Mielich
Leibniz-Institute of Atmospheric Physics (LG)
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Toralf Renkwitz
Leibniz-Institute of Atmospheric Physics (LG)
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Jorge L. Chau
Leibniz-Institute of Atmospheric Physics at the University of Rostock
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Juliana Jaen
Leibniz Institute of Atmospheric Physics
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Jan Laštovička
Institute of Atmospheric Physics, Academy of Science, Bocni II, 14131 Prague, Czech Republic
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Abstract

In the present study, using sixty-three and fifty-six years of continuous observations, we investigate the long-term oscillations and residual trends, respectively, in the E- and F-region ionosonde measured parameters over Juliusruh, Europe. Using the Lomb-Scargle periodogram (LSP) long-term variations are estimated before the trend estimation. We found that the amplitude of the annual oscillation is higher than the 11-year solar cycle variation in the critical frequencies of the daytime E (foE) and Es (foEs) layers. A weak semi-annual oscillation is also identified in the foE. In the F-region, except for daytime hmF2, and nighttime foF2, the amplitude of the 11-year solar cycle variation is higher than the annual oscillation. The LSP estimated periods and their corresponding amplitudes are used to construct a model E- and F-region ionospheric parameters that are in good agreement with the observation. The linear trend estimation is derived by applying a least-squares fit analysis to the residuals, subtracting the model from the observation. Except for the daytime foF2, all the other parameters like nighttime foF2, day and nighttime h’F, and hmF2 show a negative trend. Present results suggest that the greenhouse effect is a prime driver for the observed long-term trend in the F-region. Interestingly, weak negative trends in the foE and foEs are found which contradicts an earlier investigation. The present study suggests that the changes in the upper stratospheric ozone and mesosphere wind shear variability could be the main driver for the observed weak negative trends in the foE, and foEs, respectively.