İbrahim Ünal

Electromagnetic Wave Propagation in Ionospheric Plasma

Ionosphere physics is related to plasma physics because the ionosphere is, of course, a weak natural plasma: an electrically neutral assembly of ions and electrons [1]. The ionosphere plays a unique role in the Earth’s environment because of strong coupling process to regions below and above [2]. The ionosphere is an example of naturally occurring plasma formed by solar photo-ionization and soft x-ray radiation. The most important feature of the ionosphere is to reflect the radio waves up to 30 MHz. Especially, the propagation of these radio waves on the HF band makes the necessary to know the features and the characteristics of the ionospheric plasma media. Because, when the radio waves reflect in this media, they are reflected and refracted depending on their frequency, the frequency of the electrons in the plasma and the refractive index of the media and thus, they are absorbed and reflected by the media. The understanding of the existence of a conductive layer in the upper atmosphere has been emerged in a century ago. The idea of a conductive layer affected by the variations of the magnetic field in the atmosphere has been put forward by the Gauss in 1839 and Kelvin in 1860. Newfoundland radio signal from Cornwall to be issued by Marconi in 1901, at the first experimental evidence of the existence of ionospheric, respectively. In 1902, Kennely and Heaviside indicated that the waves are reflected from a conductive layer on the upper parts of the atmosphere. In 1902, Marconi stated that changing the conditions of night and day spread. In 1918, high-frequency band has been used by aircraft and ships. HF band in the 1920s has increased the importance of expansion. Then, put forward the theory of reflective conductive region, has been shown by experiments made by Appleton and Barnet. The data from the 1930s started to get clearer about the ionosphere and The Radio Research Station, Cavendish Laboratory, the National Braun of Standards, the various agencies such as the Carnegie Institution began to deal with the issue. In the second half of the 20th century, the work of the HF electromagnetic wave has been studied by divided into three as the fullwave theory, geometrical optics and conductivity. Despite initiation of widespread use of satellite-Earth communication systems, the use of HF radio spectrum for civilian and military purposes is increasing. Collapse of communication systems, especially in case of emergency situations, communication is vital in this band. In the ionosphere, a balance between photo-ionization and various loss mechanisms gives rise to an equilibrium density of free electrons and ions with a horizontal stratified

THE DEPENDENCE ON THE GEOMAGNETIC ACTIVITY OF CHANGES IN THE foF2 VALUES AT THE HIGH LATITUDES

Bu calismada, Aralik 1971-Eylul 1972 tarihleri arasinda yuksek enlem bolgesi olarak tanimlanan 60 o -90 o degismeyen manyetik enlem arasindaki 7 iyonsonda istasyonundan alinan saatlik foF2 verilerinin degismeyen manyetik enleme gore degisimleri, farkli jeomanyetik aktivite durumlari icin incelenmistir. Analizlerden elde edilen sonuclara gore, gunduz saatlerindeki foF2 degerlerinin, gece saatlerindeki degerlerden buyuk oldugu, ayrica bu saatlerde foF2 degerlerinin degismeyen manyetik enlem artisi ile 68 o -72 o degismeyen manyetik enlemleri arasindaki artis disinda azaldigi tespit edilmistir. Gece saatlerinde ise foF2 degerlerinin yaklasik 66 o -72 o degismeyen manyetik enlemleri arasinda arttigi, bu enlemlerden daha buyuk ve daha kucuk enlemlerde ise foF2 degerlerinin azalarak cukura benzer bir yapi olusturdugu gozlemlenmistir. Ayrica mevsimsel ve jeomanyetik aktivite degisimlerinin, foF2 degerlerinin enlemsel degisimleri uzerinde onemli bir etkiye sahip oldugu tespit edilmistir. Jeomanyetik pasif durumdaki foF2 degerleri, jeomanyetik aktif durumdaki foF2 degerlerinden buyuktur. Ozellikle jeomanyetik aktif durumdaki Aralik doneminde, polar cap ve polar oval bolgeleri daha belirgin ve bu bolgeler enlemsel olarak daha genis bir yapiya sahiptir.

Two possible approaches for ionospheric forecasting to be employed along with the IRI model

Ionospheric forecasting is a popular research area required by telecommunication and navigation system planners and operators. The problem is challenging because ionospheric processes are nonlinear. Data-driven techniques are of particular interest since they overcome most of these difficulties. In this work, two possible ionospheric forecasting approaches have been considered to be employed along with the IRI model. The authors reported these approaches previously. Ionospheric critical frequency values have been forecast using Fuzzy inference and Neural Networks considering the two possible approaches, METU-FNN and METU-NN. In parallel, the foF2 values have been calculated based on the IRI model.