Vol52,5,2009 453 ANNALS OF GEOPHYSICS, VOL. 52, N. 5 October 2009 Key words radio propagation – geomagnetic and ionospheric storm 1. International observations on geomagnetic and ionospheric variations A model comparison of noon International Reference Ionosphere (IRI, Bilitza, 1988) pro- files obtained from both ionospheric stations of Istanbul (IST; 41°N; 29°E, LT=(UT+2h), DIP=57°.2, L=1.6) and Rome (RO; 41°N; 12°E, LT=(UT+1h), DIP=57°.4 L=1.6) is re- ported in fig. 1. Some references to these proce- dures can be found in Davies, 1981; Agopyan, 1982; Titheridge, 1988; Rawer and Bilitza, 1989; Schunk, 1996 and Bilitza, 2008. The electron density (Ne) noon profiles for the two stations, obtained by the IRI model, show a slab thickness of τ ~150 km for the F region. A similarity between the two stations situat- ed at the same L shell (1.6) and with only ∆h=1h difference of universal standard time (UTS) as well a slightly different behavior typ- ical of disturbed days, can also be clearly seen in fig. 2. The plasmapause is typically located at L=4-6 but may be found at L ~ 2 during very ac- tive periods; for both observation sites at L =1.6 and with (magnetic planetary index Kp) Kp ≥7 then the saturation of the protonospheric reser- voir value should take (see Kamide and Rich- mond, 1986) ts = 0.17(L)4 = ~_ 1.1 days, so that one day becomes insufficient for its replenish- ment as seen in fig. 3. The method of analysis applied to RO and IST measurements used here was described in previ- ous papers (Bulat et al., 1997 and Agopyan, 2002). The hourly values of frequency (MHz) measurements of ∆foF2(%) are based on foF2 Bibl ionosonde data from Istanbul University Ionosphere Research Station Ayazaga IST-IIAI Revised comparison and analysis of severe magnetic storm effects measured over Istanbul and Rome Harutyun Agopyan Vocational School of Technical Sciences, Telecommunication Program, Istanbul University, Turkey Abstract Geomagnetic Storms (GS) and Ionospheric Storms (IS) for high geomagnetic activity conditions are studied in Istanbul (IST) and in Rome (RO). Further and revised results that led to new interpretations are briefly present- ed here following a previous paper on the severe storm effects on the ionosphere over Istanbul. The series of storms started on 28th October 1968 and went on to 2nd November 1968 with the geomagnetic index Kp reach- ing values up to 8. Deviations of the critical frequency of the F2 layer, ∆foF2(%), from monthly medians up to 100% were observed. Power spectral results show here that not only the Diurnal Planetary Waves (PW) of 2.3 day periodicity but also tidal waves with semidiurnal (12h), teridiurnal (8h) and quaterdiurnal (6h) characteris- tic times are present. Mailing address: Dr. Harutyun Agopyan, Istanbul University, Vocational School of Technical Sciences, Tele- communication Program, 34320 Avcilar, Istanbul, Turkey: e-mail: harutyun@istanbul.edu.tr Vol52,5,2009 1-12-2009 13:29 Pagina 453 454 H. Agopyan with geographic coordinates ϕ=41°08’11’’ N; λ=29°01’58’’ E and geomagnetic coordinates φ=38°40’N; Λ=107°.76E; geocentric DIP=57°.2. IIAI ionosonde used automatic sweep 1.4-20 MHz and operated 40 kW pp during the complete 20th solar cycle (1963-1974) (Agopyan, 1994; Ozguc et al., 1998; Ozcep and Orbay, 1999). Magnetic recordings of GSs and ionospher- ic soundings for ISs from 28th October 1968 to 2nd November 1968 with geomagnetic 3- hourly magnetic activity index Kp reaching up to 7 to 8 values are considered. During the month of October H mean was -16.1 nT but in November the H mean was = –32.5 nT (around twice of the annual mean value = –16.1 nT). The geomagnetic field disturbances during this time interval are reported in Agopyan, 2002, figure 6. The maximum disturbance in H component is reached on 31st October around 21UT. In the first storm day the ionospheric height changes are well over 250 km. Leitinger et al., (2004) give slab thickness (τ) values at midday as 320 km and at midnight as 340 km over RO using SIRO data during October 1981. Whereas on 29th October IST measured NmF2= 7x1011 e/m3, Zhang et al., (2003) give values for RO as NmF2=1x10-6 /cm-3 for 15th July 2000. Using new IRI 2007 model (http://IRI.gs- fc.nasa.gov 2008) no changes in height occurs during sunlight hours but electron density (Ne) changes are very significant during 18LT hrs for RO and 19LT hrs for IST simultaneously. At h=300 km the maximum electron density (Nm) of RO (Nm=8x1011m-3) shows approximately ∆Nm=4x1011m-3 concentration difference as max Fig. 1. Comparisons of the ionospheric heights (km) versus electron density (Ne/cc) generated noon profiles of IRI for Istanbul solid-line (stars) and Rome broken-line (circles) plotted simultaneously. 0 670 475 275 75 500000 1000000 1500000 2000000 N ELECTRON DENSITY el/cc H H E IG H T S i n K m OCTOBER 1968 ISTANBUL DIP=57.2 L=1.6 SOLID LINE (STARS) OCTOBER 1968 ROME DIP=57.4 L=1.6 BROKEN LINE (CIRCLES) IRI NOON PROFILE RZ=108 F10.7=152.8 Vol52,5,2009 1-12-2009 13:29 Pagina 454 455 Revised comparison and analysis of severe magnetic storm effects measured over Istanbul and Rome Ne value deviation from IST (Nm=4x1011m-3) and this amount of ∆Nm=4x1011m-3 means 0.4 Tera electrons per meter cube or an excess con- centration of 400 billion of electrons per cubic meter. Then, between IST and RO, for the Day 28th October 1968, IST shows a height of 325 km and Nm=4x1011m-3 at 18LT, simultaneously RO shows the same height and Nm=8x1011m-3 at 19LT. Consecutively, ∆Nm, max Ne value devi- ations at the same UTS hours of the stormy days at IST (at 18LT) and RO (at 19LT) are the fol- lowing empirical reproductions generated from IRI 2007 model: ∆Nm=0.37x1012 m-3 on 28th.10.1968 (prestorms), ∆Nm=0.42x1012 m-3 on 29.10.1968 (storms), ∆Nm=0.40x1012 m-3 on 30th.10.1968 (post- storms, positive phases of positive ISs ∆Nm=0.43x1012 m-3 on 31st.10.1968 (negative phases and negative ISs) ∆Nm=0.43x1012 m-3 on 01st.11.1968 (positive and negative phases of ISs) ∆Nm=0.44x1012 m-3 on 02nd.11.1968 (post- storms, negative phases of ISs) respectively. According to the reports by Prölss and Werner (2002) the largest storm effects have been observed at RO. By using the IRI-2000 ionospheric model, applied to RO data, a high degree of reliability during quiet conditions and inadequate degree of reliability during storm events has been shown (Cander, 2003; Zolesi and Cander, 2004). 2. Results of comparisons The percentage frequency (MHz) deviations ∆foF2 (%) reached up to 70%. The comparison plots of normalized prestorm analysis in fig. 2 showed a deviation of about ± 2%. In both ionospheric stations the maximum electron densities were approximately Nm=1.45x106 e/cc, while the heights of the maximum were about h=280 km. Figure 3 shows the percentage deviation of foF2 (MHz) during the magnetic storm period of 5 days. Planetary waves (periods of about 2–30 days) were predominantly of tropospheric ori- gin and penetrated directly to heights slightly above 100 km. They have to propagate upwards into the F-region ionosphere via an indirect Fig. 2. Comparisons of normalized prestorm analysis as percentage deviations of foF2 (MHz) from monthly medians for Istanbul (black-line) and Rome (dashed-line) plotted simultaneously. P R E S TO R M 2 8 - 29 OCTOBER 1968 SAMPLE 1 - 9 NORMALIZED ISTANBUL (Black Line) L=1.6 ROME (Dashed Line) L=1.6 9UT SC1-2-2 -1 0 1 2 3 1 2 3 4 5 6 7 8 9 UT -2% -1% 0% 1% 2% 3% PE R C EN TA G E D EV IA TI O N S O F fo F2 (M H z) Vol52,5,2009 1-12-2009 13:29 Pagina 455 456 H. Agopyan route. Their effects were observed in the lower ionosphere, in the ionospheric E region in h’E and sporadic-E (Es) layer and in the F2 region (e.g., Altadill and Apostolov, 2001; Lastovicka et al., 2006; Mikhailov et al., 2004). The quasi- 2-day wave in the Mesosphere Lower Thermos- phere (MLT) was the most studied. Summariz- ing, it has been reported that the 2-day wave is a manifestation of both a global normal Rossby mode and a local unstable wave. Its activity is maximum during local summer and especially close to equinoxes (e.g., Altadill and Apos- tolov, 2001). Tides in the atmosphere are pre- dominantly thermal, not gravitational tides. They are generated by the periodic solar heat- ing. Dominant tidal periods in the ionosphere are 24 h and 12 h. The spectral analysis was applied to the Rome and Istanbul data. The power spectra in- cluding the Hanning windowing showed the ef- fects of planetary waves (PW) with peaks at 2.3 days and tidal waves with diurnal and semidiur- nal peaks, fig. 4. It is also notable that during the negative phases of the IS, ∆foF2 minimum value mostly restricting telecommunication channels and radio propagations observed over IST (∆foF2=–33%) was 10% greater than that observed over RO (∆foF2=–22%); whereas during the positive phases of the IS ∆foF2=+70% was observed over IST while in RO ∆foF2= was +75%. 3. Conclusions Results of the analysis of the studied severe GSs presented here show complex mechanisms for the ionosphere at medium range scale as al- so partly seen in previous papers on IST using storm sudden commencements (SC) and ionos- pheric storms (IS) (Agopyan, 1986 and 2002). In this paper a comparison between RO and IST Fig. 3. Comparisons of percentage deviations of foF2 (MHz) from monthly medians versus time of 5 days af- ter 29 October to 2 November 1968 for Istanbul solid-line (stars) and Rome broken-line (circles) plotted simul- taneously. ISTANBUL L=1.6 SOLID LINE (Stars) ROME L=1.6 BROKEN LINE (Circles) 100 50 0 0 50 100 120 -50 -100 PE R C EN TA G E D EV IA TI O N S O F fo F2 (M H z) 5 DAYS AFTER 28 OCTOBER 1968 (UT HOURS) Vol52,5,2009 1-12-2009 13:29 Pagina 456 457 Revised comparison and analysis of severe magnetic storm effects measured over Istanbul and Rome for the power spectral analysis on foF2 data showed peaks at 2.3 days and at 24h (diurnal), 12h (semidiurnal), 8h (teridiurnal) and 6h (qua- terdiurnal) characteristics in both stations. The peaks magnitude was however weaker in RO. The morphological analysis of the two stations magnetic and ionospheric effect can be now compared and summarized as follows: – FIRST STORM (1st SC at 09h09 UT on 29th October 1968, Kp=7): After the sudden commencement following weak ring currents, a rapid decrease of ∆H and increase of ∆foF2 on 30th October 1968 at 02h LT in IST, and 00h LT in RO, was observed simultaneously. – SECOND STORM (2nd SC at 09h00 UT on 31st October 1968, Kp=8): A very strong negative phase for ∆H started immediately after the SC indicating the strong effect of the ring current increase; the foF2 data show small ex- cursions following SCs exhibiting positive phase for RO but negative for IST. The largest positive response came with a delay about 8 hs for IST but 12 hs for RO with respect to SC. – THIRD STORM (3rd SC at 09h17 UT on 1st November 1968, Kp=7): An apparent ∆H peak, with the rapid increase and decrease in negative phase which proves recovery of the in- tensive ring currents coinciding with a positive phase in ∆foF2 and an elevation of the F layer for both stations IST and RO were observed consecutively. The ionospheric positive and negative wavelike fluctuations were less signif- icant in RO than in IST (Agopyan, 1994). Negative phases last for a long time, even sev- eral hours after a SC and were observed in all three cases. Negative long-duration F2-layer storms are known to result from thermospheric neutral composition variations, namely, O/N2 decrease (e.g., Prölss, 1995). Acknowledgements I wish to express my gratitude to Professors E. Boschi, P. Dominici, P. Spalla and also to S.M. Radicella, for their invitation, for provid- Fig. 4. Comparison results of power spectra of electron density values of the ionospheric severe storm includ- ing Hanning windowing for Istanbul (black-line) and Rome (dashed black-line) plotted simultaneously. 0.80 1.00 Power Frequency (microcycle/s) 0.90 0.60 0.70 0.40 0.50 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 0.20 0.30 0.00 0.10 ISTANBUL (Black Line) L=1.6 ROME (Dashed Line) L=1.6 Vol52,5,2009 1-12-2009 13:29 Pagina 457 458 H. Agopyan ing storm data, for the means used, and also for the international collaboration during the es- tablishment of the Aeronomy and Radio prop- agation Laboratory in Italy where I carried out this study with the support of ICTP-TRIL Pro- gram. REFERENCES AGOPYAN, H. (1982): Ionospheric storms in connection with Geomagnetic storms, EGS and ESC Joint Meeting, Program and Abstracts Handbook, (August, Leeds, England), 110-17, A15, 23-27. AGOPYAN, H. (1986): Ionospheric behavior on geomagnetic storms, in Proceedings of the International Symposium on «Radio Beacon Contribution to Study of Ionization and Dynamics of the Ionosphere and Corrections to Geodesy», edited by ANTTI TAURAINEN (Oulu, Fin- land), 1, 11-25, ISBN 951-42-2256-3. AGOPYAN, H. (1994): Magnetic and Ionospheric Storms in IST: An Observational Review, Journal of The Cham- ber of Geophysical Egineers of Turkiye, Geophysics, Jeofizik, edited by A.T. BASOKUR, 8 (2), 105-121, ISSN 0259-1472. AGOPYAN, H. (2002): Severe magnetic storm effects on the ionosphere over Istanbul: a case study, Annals of Geo- physics, 45 (5), 621-628. ALTADILL, D. and E.M. APOSTOLOV (2001): Vertical propa- gating signatures of wave-type oscillations (2- and 6.5- days) in the ionosphere obtained from electron density profiles, Journal of Atmospheric and Solar-Terrestrial Physics, 63, 823-834. BILITZA, D. (1988 and 2008): Private Communications, (IRI 2008, URL:http://IRI.gsfc.nasa.gov). BULAT, T., B. ZOLESI, S., M. RADICELLA and H. AGOPYAN (1997): Comparison of ISs Observed Simultaneously in Istanbul and Rome, (ST3), XXII G. Assembly of the European Geophysical Society, 21-25 April 1997, Vi- enna, Austria, Ionosphere and Thermosphere, Space and Planetary Sciences, Editor: Prof. Dr. Arne K. RICHTER, Annals Geophysicae, Part III, (ST034), vol. 15, supp. III, 628. CANDER, L.J.R. (2003): Toward Forecasting and Mapping Ionospheric space weather under the COST actions, Adv. Space Res., 31 (4), 957-964. DAVIES, K. (1981): Review of recent in Ionospheric predic- tions, Radio Science, 16, 1407-1430. KAMIDE, Y. and A.D. RICHMOND (1986): Recent advances in studies of Magnetosphere-Ionosphere coupling, J. Geomagnetism and Geo-electricity, 38 (7), 653. LAŠTOVIČKA, J., A.V. MIKHAILOV, T. ULICH, J. BREMER, A.G. ELIAS, N. ORTIZ DE ADLER, V. JARA, R. ABARCA DEL RIO, A.J. FOPPIANO, E. OVALLE and A.D. DANILOV (2006): Long-term trends in foF2: A comparison of various methods, Journal of Atmospheric and Solar- Terrestrial Physics, 68 (17), 1854-1870. LEITINGER, R., L. CIRAOLO, L. KERSLEY, S.S. KOURIS and P. SPALLA (2004): Relations between electron content and peak density: regular and extreme behaviour, in «COST 271 Action, Effects of Upper Atmosphere on Terrestrial and Earth Space Communications, Final Re- port», Annals of Geophysics, suppl. vol. 47 (2-3), 1097-1107. MIKHAILOV, A.V., A.KH. DEPUEVA and T.YU. LESCHIN- SKAYA (2004): Morphology of quiet-time F2-layer dis- turbances: high to lower latitudes, Int. J. Geomagn. Aeronom., 5 (1), GI-1006. OZCEP, F. and N. ORBAY (1999): Interaction between Physics and the Earth: Geophysics in the 75th year of the republic of Turkey (Yerküre ile Fiziksel iletisim: Cumhuriyetin 75.yilinda ülkemizde Jeofizik) Istanbul University Engineering Faculty’s Earth Sc. Rev., 12 (1), 99-105. OZGUC, A., T. ATAC, Y. TULUNAY and L. STANISLAWSKA (1998): The ionospheric foF2 data over Istanbul and their response to solar activity for the years 1964-1969 and 1993, Studia Geoph. et Geod., 42, 112-118. PRÖLSS, G.W. (1995): Ionospheric F-region Storms, Hand- book of Atmospheric Electrodynamics, edited by H. VOLLAND, , vol. II, (CRC Press, Boca Raton), pp. 195- 248. PRÖLSS, G.W. and S. WERNER (2002): Vibrationally excited nitrogen and oxygen and the origin of negative ionos- pheric storms, Journal Geophys. Res., 107, A2,10.1029/2001JA900126, SIA 1-6. RAWER, K and D. BILITZA (1989): Electron density profile description in the IRI, Journal of Atmospheric and So- lar-Terrestrial Physics, 51, 781-790. SCHUNK, R.W. (1996): Handbook of Ionospheric Models Solar-Terrestrial Energy Program, August, STEP, 1, 73-295. TITHERIDGE, J.E. (1988): Private Communications. ZOLESI, B. and L.J.R. CANDER (eds) (2004): Cost 271 Ac- tion, Effects of the upper atmosphere on terrestrial and earth space communications: introduction, Final Re- port, First Section, Annals of Geophysics, Suppl. vol. 47 (2/3), 915-925. ZHANG, Y, L.J. PAXTON, H. KIL, C.-I MENG, S.B. MENDE, H.U. FREY and T.J. IMMEL (2003): Negative ionospher- ic storm seen by the IMAGE FUV instrument, Journal Geophys. Res., 108 (A9), 1343, doi: 10. 1029/2002JA009797, 2003 (SIA, 4-7). (received, July 14, 2008; accepted, May 28, 2009) Vol52,5,2009 1-12-2009 13:29 Pagina 458