Abstract
In this study, probable signature of mid-latitude electron density trough at the ionospheric critical frequencies is investigated. For this purpose, hourly ionospheric critical frequency (foF2) data obtained from ionosonde stations for the year 1972 is used. These stations are situated at between 45 o - 66 o invariant magnetic latitudes (Λ) of the Northern hemisphere. foF2 data is investigated in terms of local time (LT), seasons, Λ and geomagnetic activity (K p ) variations. The results show that the troughs occur at nighttime hours between dusk and dawn sector for all situations. The troughs at geomagnetic active (K p >2 + ) conditions are more prominent and apparent than that at geomagnetic quiet (K p ≤2 + ) conditions. The troughs and their minimum positions tend to occur at lower Λ for all four seasons at geomagnetic active conditions. Also, the average of foF2 values in the minimum points of the troughs has lower values at geomagnetic active conditions. It is observed that the seasonal variations have important effects on the structure of trough, especially for December Solstice. The results of this study will contribute a better description and prediction of the mid-latitude electron density trough features for the ionospheric F2 peak heights and better understanding the role of the mid-latitude electron density trough on the ionospheric variability.
Highlights
Solar flares and solar wind streams affect the Earth’s magnetic field significantly and this interaction causes large and sudden changes in the electron density of the ionosphere
Earlier studies [Rothkaehl et al 2000, Tulunay et al 2003] concluded that (i) It would be advisable to adopt a practical, simple convection model which changes in steps with the planetary geomagnetic activity index (Kp) or interplanetary magnetic field (IMF) reversals or any other effective event in order to reflect the influence of the trough phenomena on the ionospheric foF2 predimid-latitude electron density trough [Muldrew 1965, ction or forecasting algorithms. (ii) Since the foF2 peak Calvert and Van Zandt 1966, Sharp 1966, Carlson 1968, can extend above 500 km, the signature of the trough is TİMOÇİN AND ÜNAL
The purpose of our study is to investigate possible signature on foF2 of the structure called the mid-latitude electron density trough depending on local time, seasons, Λ and geomagnetic activity changes and is to compare obtained the results from this study with obtained the results from previous studies which were performed for different altitudes
Summary
Solar flares and solar wind streams affect the Earth’s magnetic field significantly and this interaction causes large and sudden changes in the electron density of the ionosphere. Earlier studies [Rothkaehl et al 2000, Tulunay et al 2003] concluded that (i) It would be advisable to adopt a practical, simple convection model which changes in steps with the planetary geomagnetic activity index (Kp) or interplanetary magnetic field (IMF) reversals or any other effective event in order to reflect the influence of the trough phenomena on the ionospheric foF2 predimid-latitude electron density trough [Muldrew 1965, ction or forecasting algorithms. TİMOÇİN AND ÜNAL expected to fall in the foF2 variations all over the world. From this point of view it must be essential to include the influence of the trough in foF2 predictions or forecasts for practical applications and modeling. In practical applications of the HF radio communications in any model that does not include the trough are not a complete model
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