1. VLF measurements of lightning induced electron precipitations and their effects on the D-region electron density profile D. Šulić, and V. D. Šulić 1, and V. Srećković 1 1 Institute of Physics, University of Belgrade, Serbia ADVANCING VLF SCIENCE THROUGH THE GLOBAL AWESOME NETWORK 30-May to 01- Jun 2009, Tunis, Tunisia

2. The response of our space environment to the constantly changing Sun is known as space weather. When the space environment is disturbed by the variable outputs of the Sun, technologies that we depend on, both in orbit and on the ground can be affected. Some of the most dramatic space weather effects occur in association with eruptions of material from the solar atmosphere into interplanetary space. Space weather

3. Over the last several decades, the monitoring of VLF transmitters has been used to study remote and transient perturbations of the lower ionosphere associated with lightning discharges. Indeed, these phenomena generate typical amplitude and phase variations of the subionospheric signals, known as the LEP effect. The perturbation begins by a rapid change in the trans- mission amplitude and/or phase, followed by a relatively slow recovery (<100 s) to the original unperturbed signal. Introduction

4. Ionosphere The ionosphere is the region extending from about 60 km to several hundreds km, where the motion of free electrons have strong effects on medium and high-frequency radiowave propagation

5. Ionosphere Precipitating electrons Propagation of VLF waves

6. Belgrade station AbsPAL (Absolute Phase & Amplitude Logger) receiver was installed at the Institute of Physics, University of Belgrade, in August 2003. Belgrade (44.85N 20.38E)

7. Belgrade station AWESOME STATION was installed at the Institute of Physics, Belgrade in June 2008.

9. List of recorded VLF signals SINGFREQ.LOC. GQD 22.10 kHz UK NAA 24.00 kHz USA DHO23.40 kHzGermany HWV20.90 kHzFrance ICV20.27 kHzItaly NWC19.80 kHzAustralia

10. Statistical results During period from 2004 to May 2009 were recorded ~ 5300 of LEP events Most of recorded LEP events occurred during local summer and autumn, very rare during winter and spring Large number of LEP events were detected on signal GQD/22.1 kHz – Belgrade Amplitude changed:  1(dB) Phase changed: few degrees

11. Method of numerical modeling This work is concerned with the numerical simulations of VLF perturbations. The method is based on changing the pair of Wait’s parameter: sharpness  in km -1 and reflection height h’ in km, along segments of GCP. The aim is to obtain calculated values:  A cal = A nonpert - A pert and  nonpert -  pert to be equal or very close with recorded values:  A rec and  rec The RANGE EXPONENTIAL model (LWPCv21 program) is used to examine a single propagation path. In this model a user specifies a range-dependent ionospheric variation.

12. Ambient ionospheric condition Wait and Spies (1964) defined a convenient quantity to describe the characteristics of the lower ionosphere as the conductivity parameter   which is:       2.5 x10 5 s -1,   the plasma frequency of the electrons, and n the electron- neutral collision frequency. The ionospheric electron density and collision frequency profiles are given by a standard nighttime ionospheric model. The collision frequency profile is given by:

13. ---- Ambient ionospheric condition The unperturbed electron density profile given by: Under nighttime conditions, the typical ranges for  and h’ are 0.40 to 0.50 km -1 and 80 to 90 km, respectively. where the pair of Wait's parameters are: sharpness  in km -1, reflection height h’ in km. The height above the Earth’s surface is h in km.

14. The intense radiation from a solar flare travels to Earth in eight minutes. SOLAR FLARE The Earth’s upper atmosphere becomes more ionized and expands.  Long distance radio signals can be disrupted by the resulting change in the Earth’s ionosphere.  A satellite’s orbit around the Earth can be disturbed from the expand atmosphere.  Satellites electronic components can be damaged.

15. Sunspot 798 in September 2005 Hyperactive sunspot 798 unleashed nine X-class solar flares including a colossal X17-flare (Sept. 07, 2005) This colossal spot made September 2005 the most active month on the Sun in almost 15 years.

16. 06 – 10 September 2005 In the period 06 – 10 Sep 2005 more than 50 LEP events were recorded each night. Most of them were recorded on signals: GQD/22.10 kHz and NAA/24.0kHz.

17. Calculated electron density on height of reflection over path

18. Location of electron density enhancement

19. One of the most important solar events from Earth's perspective is the coronal mass ejection, the solar equivalent of a hurricane One of the most important solar events from Earth's perspective is the coronal mass ejection, the solar equivalent of a hurricane. CORONAL MASS EJECTION Having escaped the Sun's gravity, a CME speeds across the gulf of space at velocities of some 400 km/s. They reach the Earth in 2.5 to 5 days. A CME is an eruption of a huge bubble of energized plasma from the Sun's outer atmosphere, or corona

20. Bel December 04/05 2004 In the night Dec 04/05 (from 17 UT to 06 UT) more than 300 LEP events were recorded. Most of them on signals: GQD/22.10 kHz and ICV/20.27kHz. Sporadically during that night LEPs were recorded on four signals -80-60-40-2002040 30 40 50 60 70

21. Transmitter Path (km) D A (dB) DF ( deg) D(km) DN max (m -3 ) GQD/22.1kHz1983-0.398.547401.22E7 NAA/ 24.0 kHz 6548-0.566119400.8E7 HWU/18.3 kHz 1493-0.34388601.03E7 ICV/20.27 kHz 970-0.74-44600.51E7 Calculated electron density

22. LEP events observed simultaneously on the four VLF paths ware the pointer to the geographical location of the region of enhancement density, over Europe. Location of electron enhancement

23. Solar eclipse on October 03, 2005 GQD/22,1 kHz

24. We would like ….

25. Summary 1.The use of VLF transmissions propagating inside the waveguide Earth – ionosphere is well developed technique for probing conditions inside the ionospheric D-region. 2.For daytime propagation conditions, the D-region is particularly stable, with reflections heights occurring at about 70-75 km. 3.Additional perturbations are driven by solar flares and total solar eclipses. Variations in the D-region lead to changes in the propagation conditions for VLF waves inside the waveguide. 4.LEP events observed simultaneously on the several VLF paths can be used as the pointer to the geographical location of the region of enhancement density, over Europe 5.Recorded data at the Belgrade station are used to study global and local conditions in the D-region in order to make relevant models.