Determining the ULF source altitude using phase measurements in experiments on the Sura facility Alexander Ryabov Dmitry Kotik Radiophysical Research Institute AGU Fall Meeting 2012

Motivation During last 40 years, it was proposed several mechanisms for explaining the generation of ULF/VLF waves in the ionosphere: modulation of ionospheric currents based on thermal nonlinearity, ponderomotive mechanisms for generation both VLF and ULF signals, cubic nonlinearity. It was shown in Chia-Lie Chang report “ELF/VLF Generation Without Electrojet” that ULF-ELF source can be located at the F-layer. Dennis Papadopoulos in his work “Fundamental physics issues on radiation belts and remediation” explains the Ionospheric Current Drive (ICD) ULF/VLF generation mechanism. In this study we propose a method for time delay calculation based on phase measurements. By measuring propagation delay it is possible to determine the altitude of radiation source

Experimental setup Radiating 6,5 MHz with AM 10,8—11,2 Hz

Transmitter and receiver timing Instrument delay was measured directly: 30 ms

Calculating the ULF signal time delay Split the trajectory for a number of pieces and write the expression for the phase shift and propagation delay: Subtract expressions for a two nearby frequencies: ~0,15 ~0,035 L – Distance V – Group velocity τ – Time delay Ф – Phase Final equation for time delay calculation:

June, 12. Amplitudes and phases O-mode, 6,5 MHz, 16º to south Time delay: 310±56 ms Time delay: 385 ms

June, 16. Amplitudes and phases O-mode, 6,5 MHz, 12º to south In this measurement ULF signal was registered both in N-S and E-W components Time delay: 265±120 ms 201±110 ms

Ionogram and calculated refraction index for June,16 Time delay: 257 ms The results of time delay calculation from the experimental data and IRI model Experiment Antenna Time delay τ, ms Time delay (IRI), ms 12-Jun-2012 S-N 310±56 385 16-Jun-2012 265±120 257 W-E 201±110

Summary Acknowledgements The VLF/ULF signal source could be located in the upper ionosphere using time delay measurement of the received signals at the earth surface. This time delay could be determined by measuring the phase difference between received and reference signals, which are GPS synchronized. The comparison with numerical simulation of the time delay using the adjusted IRI model and ionosonde data shows well agreement with the experimental observations. Measured time delay of ULF signal is about 300 ms, that means the ULF source is located at the F-layer maximum altitude. Acknowledgements This work has been supported by RFBR grants 11-02-00419-а, 11-02-97104-r and RF Ministry of education and science by state contract 16.518.11.7066