Abstract
AbstractWe investigate for the first time the variability of the F2 layer critical frequency (foF2), its peak height (hmF2), the thickness parameter B0, and the E region critical frequency (foE) over Santa Maria (29.7° S, 53.7° W, dip angle = −37°), a station located in the central region of the South American Magnetic Anomaly. The selected ionospheric parameters were obtained from ionograms recorded by a recent Digisonde Portable Sounder 4‐D. The time period covers 309 days from 1 September 2017 to 30 August 2018. The diurnal analyses revealed a large day‐to‐day ionospheric variability, with some peculiarities as a strong semiannual pattern superimposed to expected ionospheric behavior. Furthermore, the results show significant differences between the averaged foF2 in December and June solstices, revealing a possible presence of the annual asymmetry. The coefficient of variation (CV) is used as a quantitative description of the variability of each parameter versus time and season. Considering low solar flux and geomagnetically quiet days only, we note that CV is smaller during the daytime and larger during nighttime for all parameters. The least variable ionospheric parameter in our study is foE, while the most variable one is B0. Regarding the F2 layer parameters, we observe that foF2 is much more variable than hmF2. We attribute the observed CV to the neutral atmosphere source over Santa Maria. The ionospheric variability is in general enhanced during geomagnetically disturbed periods. The estimated CV is higher over Santa Maria than Wuhan, China (30.5° N, 114.4° E, dip angle = 46°), a station with no influence of the South American Magnetic Anomaly.
Highlights
It is well established that production, loss, and transport processes that occur in the ionosphere is subject to many influences from the Sun, magnetosphere, and lower and middle atmosphere, which deviate it from the climatological mean
We investigate for the first time the variability of the F2 layer critical frequency, its peak height, the thickness parameter B0, and the E region critical frequency over Santa Maria (29.7° S, 53.7° W, dip angle = −37°), a station located in the central region of the South American Magnetic Anomaly
The universal time (UT) runs along the horizontal axes, and the local time (LT) scale is at the top of the Figures 3a and 3e
Summary
It is well established that production, loss, and transport processes that occur in the ionosphere is subject to many influences from the Sun, magnetosphere, and lower and middle atmosphere, which deviate it from the climatological mean. Batista and Abdu (2004) analyzed the parameters foF2, hmF2, and B0 obtained by digital ionosondes over two stations in Brazil, São Luís (2.6° S, 44.2° W, dip angle = −0.5°) at the magnetic equator and Cachoeira Paulista (22.7° S, 45° W, dip angle = −28°), close to the southern crest of the Equatorial Ionization Anomaly (EIA) The authors compared their observational data with the modeled results by International Reference Ionosphere, in which it showed some discrepancies in specific hours. The main objectives of this work are (1) to discuss the characteristics of the data and the system recently installed in Santa Maria, (2) to analyze the diurnal and seasonal patterns of the ionospheric variability through the selected parameters for the whole year of data, (3) to analyze the sources of ionospheric variability over Santa Maria, (4) to compare the results over Santa Maria with Wuhan during two geomagnetic storms, and (5) to discuss the physical reasons of the obtained results
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