Space weather effects on Communication: Geomagnetic activity and Radio wave absorption in the equatorial region

1. Space weather effects on Communication:Geomagnetic activity and Radio wave absorption in the equatorial region Victor U Chukwuma* + Department of Physics, Olabisi Onabanjo University, P. O Box 351, Ago-Iwoye, Nigeria E-mail: victorchukwuma@yahoo.com *On Sabbatical Leave at Lagos State University + For all correspondence Space weather research group

2. Outline • Introduction • Interplanetary and Geomagnetic phenomenon. • Ionospheric response. • Storm effects on radio wave propagation Space weather research group

3. Space weather refers to the conditions on the Sun , the solar wind, magnetosphere, ionosphere and the thermosphere that can influence the performance and reliability of satellite- and ground – based technological systems. Central to space weather are intense geomagnetic storms. This paper presents the results of two independent studies that reinforce one another in implying that space weather, as manifested in intense geomagnetic storms, adversely affect HF radio communication. This is due to the fact that HF radio communication depends on the ionosphere. The first part of the paper presents the interplanetary origin of an intense storm, the geomagnetic and ionospheric response to the interplanetary structures The second part presents the effect of geomagnetic activity on radio wave absorption Introduction Space weather research group

4. Interplanetary and Geomagnetic Observationdata These are OMNI hourly averaged definitive multi-spacecraft interplanetary parameters data and are the proton number density, the solar wind flow speed, the interplanetary magnetic field component Bz, the plasma beta and the dawn-dusk electric field. These data are obtained from NSSDC’s OMNIWeb Service (http://nssdc.gsfc.nasa.gov/omniweb). Hourly values of the low-latitude magnetic index, Dst which are derived from low-latitude stations and are obtained from the National Geophysical Data Centre's SPIDR OMNI IMF data (http// spidr.ngdc.noaa.gov). Space weather research group

5. Solar wind, IMF & Magnetosphere Space weather research group

6. Coronal Mass Ejection Space weather research group

7. Magnetic reconnection Space weather research group

8. Interplanetary and Geomagnetic phenomenon Space weather research group

9. Space weather research group

10. Ionospheric data The Ionospheric data used in this study consists of hourly values of foF2 obtained from some of the National Geophysical Data Centre's SPIDR Space Physics Interactive Data Resource) a network of ionosonde stations located in the East Asian sector: Yakutsk, Wakkanai, Akita, Kokubunji, Yamagawa, Okinawa and Manila. These stations are listed in Table 1. The present study is concerned with variations in foF2 due to the geomagnetic storms of July 13-14, 1982. However, the F2 region response to geomagnetic storms is most conveniently described in terms of D(foF2) , that is the normalized deviations of the critical frequency foF2 from the reference (Chukwuma, 2003b): Space weather research group

11. Ionosonde Stations Space weather research group

12. Ionospheric response Space weather research group

13. Storm effects on radio wave propagation Space weather research group

14. Determination of Absorption Absorption data for the present study was obtained at 4.87 MHz at 1000hrs LT at Lagos (3.40oE, 6.55oN) using A3 method The transmitter (Radio Cotonou) is located at Cotonou 2.43oE, 6.35oN.The storm data are obtained from the IUGG bulletin published by Institut Fur Geophysik, Gottingen, Germany. The absorption of HF radio wave for any circuit when the height of reflection of the radio wave, as in the case of the Cotonou –Lagos circuit, is the same for both daytime and night time is given as: The absorption data represents the total absorption from: • the F region in which the radio wave is reflected; a considerable amount of the total absorption occurs near the top of the radio wave trajectory in the deviating region. • the E region, where the collisional frequency is relatively high, while the refractive index is still nearly unity. Space weather research group

15. Variations in geomagnetic activity and ionospheric absorption around all severe storms. Space weather research group

16. Variations in geomagnetic activity and ionospheric absorption around severe storms with SSC . Space weather research group

17. Summary A study of the effect of space weather on HF radio communication has been presented. The paper consists of the investigation of the intense storm of July 13-14, 1982(Dst≈ -325 nT) on the one hand and the investigation of the effect of geomagnetic storms on equatorial radio wave absorption on the other hand.In the first part of the study, the structure of the storm of July 13-14, 1982(Dst≈ -325 nT) is presented using the low-latitude magnetic index, Dst and is interpreted using solar wind interplanetary data, while the F2 region structure response to the geomagnetic storm was studied using foF2 data obtained during the storms from a network of ionosonde stations. In the second part, the effect of geomagnetic storms on equatorial radio wave absorption was investigated using severe storms (Ap 54) and HF absorption data obtained on 4.87 MHz at 10:00 hours LT at Lagos (3.40oE, 6.55oN).The results of these independent investigations have been found to reinforce one another in implying that space weather, as manifested in intense geomagnetic storms, adversely affect HF radio communication. Space weather research group

18. Conclusion Earlier investigations of the influence of geomagnetic storms on radio wave absorption were based on storm selection criterion that lumped together weak, moderate, and strong storms together, and favouring weak and moderate weak storms the selection made it impossible for the investigations to detect any change in equatorial radio wave absorption following geomagnetic storms. The present result obtained using the superposed epoch method showsthat HF absorption in the equatorial ionosphere increases after severe geomagnetic activity. Space weather research group