Abstract
The main climatological features of the ionospheric equivalent slab thickness (τ) for the Northern hemisphere midlatitudes are analyzed. F2-layer peak electron density values recorded at three midlatitude ionospheric stations (Chilton 51.5° N, 0.6° W, U.K.; Roquetes 40.8° N, 0.5° E, Spain; Wallops Island 37.9° N, 75.5° W, USA) and vertical total electron content values from colocated ground-based Global Navigation Satellite System receivers are used to calculate a dataset of τ values for the last two solar cycles, considering only magnetically quiet periods. Results are presented both as grids of binned medians and as boxplots as a function of local time and month of the year, for different solar activity levels. Corresponding trends are first compared to those output by the midlatitude empirical model developed by Fox et al. (Radio Sci 26:429–438, 1991) and then discussed in the light of what is known so far. From this investigation, the strong need to implement an improved empirical model of τ has emerged. Both Space Weather and Space Geodesy applications might benefit from such model. Therefore, both the dataset and the methodology described in the paper represent a first fundamental step aimed at implementing an empirical climatological model of the ionospheric equivalent slab thickness. The study highlighted also that at midlatitudes τ shows the following main patterns: daytime values considerably smaller than nighttime ones (except in summer); well-defined maxima at solar terminator hours; a greater dispersion during nighttime and solar terminator hours; no clear and evident solar activity dependence.
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Data availability
Ionosondes’ data are available via the public access portal of the Digital Ionogram Database (http://ulcar.uml.edu/DIDBase/) of the Global Ionosphere Radio Observatory in Lowell. RINEX files are available from NASA’s GNSS FTP repository (ftp://cddis.nasa.gov/). Magnetic activity indices are available from NASA’s Space Physics Data Facility of the Goddard Space Flight Center (https://spdf.gsfc.nasa.gov/pub/data/omni/high_res_omni/). Solar activity indices are available from OMNIWeb Data Explorer website (https://omniweb.gsfc.nasa.gov/form/dx1.html) and from Sunspot Index and Long-term Solar Observations (SILSO) website (http://www.sidc.be/silso/home). Slab thickness datasets generated in this study are available from the corresponding author on reasonable request.
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Acknowledgements
This publication uses data from ionospheric observatories made available via the public access portal of the Digital Ionogram Database (http://ulcar.uml.edu/DIDBase/) of the Global Ionosphere Radio Observatory in Lowell, MA. The authors are indebted to the observatory directors and ionosonde operators for the significant investments of their time, effort, expertise, and funds needed to acquire and provide measurement data to academic research. Thanks to the International GNSS Service (IGS, http://www.igs.org/) team for providing and making freely available GNSS data, and for their huge efforts in setting, maintaining, and developing their GNSS stations network. RINEX files used in this study were downloaded from NASA’s GNSS repository (https://cddis.nasa.gov/Data_and_Derived_Products/CDDIS_Archive_Access.html). The authors thank Dr. Luigi Ciraolo for providing us a tailored version of his vTEC calibration software. Magnetic activity indices used in this study were downloaded from NASA’s Space Physics Data Facility of the Goddard Space Flight Center (https://spdf.gsfc.nasa.gov/pub/data/omni/high_res_omni/). The F10.7 solar index was downloaded through OMNIWeb Data Explorer website (https://omniweb.gsfc.nasa.gov/form/dx1.html) maintained by the NASA. SSNnew and SSNold solar indices were downloaded from Sunspot Index and Long-term Solar Observations (SILSO) website (http://www.sidc.be/silso/home).
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This research is partially supported by the Italian MIUR-PRIN grant 2017APKP7T on Circumterrestrial Environment: Impact of Sun-Earth Interaction.
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AP contributed to conceptualization, methodology, software, validation, formal analysis, investigation, and writing-original draft. BN contributed to conceptualization, writing-review and editing, investigation, and validation. MPi contributed to writing-original draft, investigation, and validation. CC contributed to writing-review and editing, investigation, and validation. MPe contributed to supervision, writing-review and editing, funding acquisition, investigation, and validation.
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Pignalberi, A., Nava, B., Pietrella, M. et al. Midlatitude climatology of the ionospheric equivalent slab thickness over two solar cycles. J Geod 95, 124 (2021). https://doi.org/10.1007/s00190-021-01577-7
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DOI: https://doi.org/10.1007/s00190-021-01577-7