1. 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

2. 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

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

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

5. 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:

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

7. 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

8. 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

9. 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 а, r and RF Ministry of education and science by state contract