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Xenos, T. D.
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Xenos, T. D.
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- PublicationOpen AccessCorrelations in daily deviations from the median of f0F2, M(3000)F2 and VF(1994-05)
; ; ; ; ;Kouris, S. S.; Department of Electrical Engineering, University of Thessaloniki, Greece ;Barbatsi, K.; Ionospheric Institute of Athens, Greece ;Xenos, T. D.; Department of Electrical Engineering, University of Thessaloniki, Greece ;Zolesi, B.; Istituto Nazionale di Geofisica, Roma, Italy; ; ; The statistical analysis of the hourly daily deviations from the corresponding monthly-median values of the factor M(3000)F2 and of the critical frequency of the F2-layer, f0F2, reveals that the correlation between these parameters is poor. A similar analysis between the hourly daily deviations from the corresponding monthly-median of the height h’F and the f0F2 leads to similar results. These results indicate that the factor M(3000)F2, the height h’F and the critical frequency f0F2 may have a different daily variability.218 152 - PublicationOpen AccessThe effects of f0 F2 variability on TEC prediction accuracy(2002)
; ;Xenos, T. D.; Department of Electrical Engineering, Aristotelian University of Thessaloniki, GreeceIn this paper hourly daily F2-layer critical frequency data recorded at Rome and one minute daily TEC data recorded at Florence were used and the relevant variabiles were calculated. It was concluded that there was no clear evidence as to how they correlated. In order to obtain a measure of the f 0 F 2 and TEC variability, the normalised differences df0 F2 and d TEC from the relevant monthly median values were also considered. Since no clear evidence could be obtained as of how df0 F2 and d TEC correlate, a new parameter, the ?Ap /?R ratio was tried. ?Ap was taken as the difference between the maximum value of Ap measured at the relevant disturbance and that corresponding at the beginning of the disturbance. ?R corresponded to the two above mentioned values of Ap. This parameter was compared to the differences of the corresponding df0 F2 values called ?df and d TEC values called ?dT. In wintertime, when ?A p /? R was negative, for the vast majority of the occurrences either ?df or ?dT was negative; ?df and ?dT were never observed to be negative at the same time whereas they were both positive in fewer than 10% of the observations. When ?A p /?R was positive then either ?df or ?dT were negative. In summertime when ?A p /?R was negative both ?df and ?dT were negative. When ?A p /?R was positive, while a positive ?df corresponded almost always to a positive ?dT, a negative ?df would equiprobably indicate either a positive or a negative ?dT.120 208 - PublicationOpen AccessTen years analysis of Tropospheric refractivity variations(2004)
; ; ;Isaakidis, S. A.; Department of Electrical and Computer Engineering, Aristotle University of Thessaloniki, Greece ;Xenos, T. D.; Department of Electrical and Computer Engineering, Aristotle University of Thessaloniki, Greece; The refractivity variations of the troposphere are responsible for various effects on radio wave propagation, such as refraction, bending, radio-station interference, etc. In this work, the refractivity variations of the Hellenic troposphere are studied using data from Helliniko airport of Athens/Greece. The data were analyzed using various interpolation procedures, i.e. in a day-by-day manner for temperature and relative humidity, to transform the data according to a reference height common for the whole dataset and finally for the refractivity N with respect to time, using piece-wise hermite interpolation polynomials for the low and medium altitudes and linear interpolation factors for the high altitudes. Since refractivity varies with time and height, two height independent basic parameters were computed and analyzed: the refractivity at station height N0 and scale height Hs. These parameters can be used to calculate the refractivity profile. Using statistical tools as the moving average, the ß0 parameter and the monthly mean values, together with the corresponding standard deviations, useful results were obtained for the variations of the refractivity with respect to observation hour, height, season, month, day and level.137 392 - PublicationOpen AccessAssessment of the solar-cycle dependence of f0F2 1157(1996-12)
; ; ; ;Xenos, T. D.; Department of Electrical Engineering, University of Thessaloniki, Greece ;Kouris, S. S.; Department of Electrical Engineering, University of Thessaloniki, Greece ;Zolesi, B.; Istituto Nazionale di Geofisica, Roma, Italy; ; Comparisons between observed hourly monthly-median values of f0F2 at Slough and Rome, and calculated f0F2 values using as an index of solar activity R12 or T12, demonstrate that there is practically no difference in the results when a solar (e.g., R12) or ionospheric index (e.g., T12) is used. The choice of the index should be based on other criteria. It is also shown that there is a slight degree of favourability for a quadratic law between f0F2 and each index of solar activity. Therefore, in mapping F-layer characteristics a second-degree relation should be adopted independently of rising or falling solar-cycle. Saturation and hysteresis effects could be then minimised.189 108 - PublicationOpen AccessA single-station model suitable for f0F2 mapping(1999-02)
; ;Xenos, T. D.; Department of Electrical Engineering, University of Thessaloniki, GreeceIonospheric monthly-median values of the F2 and E layer critical frequencies from 24 mid-latitude European stations are fitted to a second degree polynomial and their correlation is discussed. The resulting model is used to predict monthly-median f0F2 values for different ionospheric stations and for high, medium and low ionospheric activity. Finally, a potential application of the single station model developed for Slough to mapping the F2-layer critical frequency is investigated. Thus prediction of the monthly median f0F2 values for eight mid-latitude European stations is attempted using the single-station model of Slough and the corresponding F0E values of the station under investigation. The f0F2 values obtained are reasonably accurate. The main advantage of this method is its simplicity and the restricted number of parameters used.142 147 - PublicationOpen AccessPreliminary results on correlation in daily f0F2 and M(3000)F2 variations(1994-05)
; ; ; ; ; ;Kouris, S. S.; Department Electrical Engineering, University of Thessaloniki, Greece ;Xenos, T. D.; Department Electrical Engineering, University of Thessaloniki, Greece ;Zolesi, B.; Istituto Nazionale di Geofisica, Roma, Italy ;Barbatsi, K.; Ionospheric Institute of Athens, Greece ;Nissopoulos, Y; Department Electrical Engineering, University of Thessaloniki, Greece; ; ; ; A statistical analysis of the hourly daily values of the factor M(3000)F2 and the F2-layer critical frequency f0F2 is carried out first for each hour of the day through-out a given month of a given year at a given station (hour-to-hour variation) and then for each day of a given month and year at a given station (day-to-day variation). This analysis shows that these ionospheric characteristics are poorly correlated. It is concluded that the daily values of the first characteristic cannot be estimated from the second by using a simple linear equation.202 157 - PublicationOpen AccessTEC and foF2 variations: preliminary results(2004)
; ; ; ; ;Kouris, S. S.; Department of Electrical and Computer Engineering, Aristotle University of Thessaloniki, Greece ;Xenos, T. D.; Department of Electrical and Computer Engineering, Aristotle University of Thessaloniki, Greece ;Polimeris, K. V.; Department of Electrical and Computer Engineering, Aristotle University of Thessaloniki, Greece ;Stergiou, D.; Department of Electrical and Computer Engineering, Aristotle University of Thessaloniki, Greece; ; ; Investigation of the relationship between TEC and (foF2)2 shows that although they are highly correlated, a «hysteresis» effect exists between them. The slab thickness is greater before than after mid-day for equal cos ?values. Moreover, a comparison of the calculated upper and lower quartiles of variability in TEC, foF2 and Nmax, respectively shows that the variability of TEC lies between those of foF2 and Nmax depending on the level of solar activity.328 575