Long‐Term Variations and Residual Trends in the E, F, and Sporadic E (Es) Layer Over Juliusruh, Europe. Issue 4 (4th April 2023)

• Record Type: Journal Article
• Authors: Sivakandan, M.; Mielich, J.; Renkwitz, T.; Chau, J. L.; Jaen, J.; Laštovička, J.
• Is Part Of: Journal of geophysical research. Volume 128:Issue 4(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-04-04
• Subjects: long‐term variations -- trends -- ionosphere -- ionosonde; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2022JA031097
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Using 63 and 56 yr of continuous observations, we investigate the long‐term oscillations and residual linear trends, respectively, in the E‐ and F‐region ionosonde measured parameters of frequencies and height over Juliusruh, Europe. Using the Lomb‐Scargle periodogram (LSP) long‐term variations are estimated before the trend calculation. We found that the amplitude of the annual oscillation is higher than the 11‐yr solar cycle variation in the critical frequencies of the daytime E (foE) and Es (foEs) layers. In the F‐region, except for daytime hmF2, and nighttime foF2, the amplitude of the 11‐yr solar cycle variation is higher than the annual oscillation. The combination of the LSP estimated periods and their corresponding amplitudes and traditional regression analysis are used to construct a model for E‐ and F‐region ionospheric parameters. The modeled estimates are in good agreement with the observations. The trend calculation is derived by applying a least‐squares fit analysis to the residuals, subtracting the model from the observation. In the F‐region, both day (nighttime) foF2 and hmF2 show negative trends of −4.44 ± 1.78 (−4.30 ± 1.63) kHz/yr and −413 ± 47 (−574 ± 75) m/yr, respectively. The Piecewise linear trend of foF2 provides negative and positive trends in 1964–1996 and 1997–2019, respectively. In the E‐region, foEs show a negative trend of −2.00 ± 0.61 kHz/yr. The present investigation suggests that the greenhouse cooling effect and negative trend in the atomic oxygen (O) as well as wind shear variability could be the main drivers for the observed negative trends in the hmF2, foF2, and foEs, respectively. Plain Language Summary: Studies on long‐term changes are essential for understanding and quantifying the climate change impact on the Earth's ionosphere if it exists. In this investigation, we used 56 yr of ionosonde‐measured E‐ and F‐region parameters like frequencies and altitude of maximum electron concentration for trend estimation. We found a negative trend in the F‐region ionospheric peak critical frequency (foF2), and its associated peak altitude (hmF2). More importantly, the nighttime hmF2 trend is slightly higher than the daytime. The foF2 trend is negative from 1964 to 1996 and positive during 1997–2019. The present study suggests that the anthropogenic forcing originated negative trends in the atomic oxygen, and the greenhouse cooling effect could be the driver for the F‐region ionospheric trends. In the E‐region, foE shows a weak and statistically insignificant positive trend. For the first time, we also report a negative trend in the foEs that could be caused by the wind shear variabilities. Key Points: The amplitude of annual and solar cycle oscillations are predominant in peak frequencies, and altitude of the E‐and F‐region, respectively In the E‐region, daytime foEs shows a weak negative trend −2.00 ± 0.61 kHz/yr during 1964–2019 Day and nighttime F‐region critical frequency, and peak height trends are negative. The daytime hmF2 trend is weaker than the nighttime