1. 1 On remote sensing of TLEs by ELF/VLF wave measurements on board a satellite F. Lefeuvre 1, R. Marshall 2, J.L. Pinçon 1, U.S. Inan 2, D. Lagoutte 1, M. Parrot 1, J.J. Berthelier 3 1 LPCE/CNRS, 3 A, Av de la Recherche scientifique, 45071, Orléans cedex 2, France, lefeuvre@cnrs-orleans.fr 2 STARLAB, Stanford Univ., Stanford CA 94305-9515, USA 3 CETP, 4, av de Neptune, 94107 Saint Maur des Fossés, France lefeuvre@cnrs-orleans.fr

2. 2 Context Ground-based EM observations in the ELF/VLF band allow the detection of: - parent lightning - currents in the heart of sprites - ELF slow-tails, etc. Space-based EM observations - space based characterization of parent lightning in the VHF band (FORTE)

3. 3 The present paper based on simultaneous observations: - at ground: Stanford Langmuir (and Palmer ) stations - on the French DEMETER satellite is a first attempt to try to point out information we can get from EM measurements: - in the ELF/VLF frequency range - with an extension on higher frequency bands

4. 4 Central question: How does EM waves radiated by lightning flashes cross the ionosphere ? According to the « sharp-boundary » model ? According to a « radio-window » model ? B0B0 B0B0 P k sferics 0+ whistlers

5. 5 PLAN 1. Introduction 2. Instrumentation 3. data and interpretation of results 4. discussion 5. conclusion

6. 6 2. INSTRUMENTATION Ground-based measurements ● Langmuir station (33° 9 N, 252°8 E) - low-light camera system, photometer data at 25 kS/s - ELF/VLF measurements (~350 Hz to 45 kHz) The locations of causative lightning strokes were determined to an accuracy of ± 0.5 km by the US National Lightning Detection Network ● Palmer station, Antarctica (64°77 S, 296° E)

7. 7 DEMETER measurements ● Orbit - circular Sun-synchronous polar orbit at an altitude of 710 km - night time passes over Langmuir around 22:30 MLT. ● TBF experiment - ELF band (≤ 1 kHz), 2 electric and 3 magnetic wave field components - VLF band (≤ 17 kHz), 1 electric at 1 magnetic wave field components - burst modes (waveform data) over predefined geographical zones

8. 8 L Juillet 28 2005 DEMETER orbit above the New Mexican Langmuir station (L )

9. 9 Sf1Sf2Sf3 GROUND-BASED Two TLEs are observed - TLE1, 05:02:44.678 UT - TLE2, 05:02:44.751 UT Thee sferic events - Sf1 (7ms before TLE1, at the time of a lightning (CG+, 75.2 kA) - Sf2 (41 ms before TLE2, at the time of a lighting (CG+, 28 kA) - Sf3 (cluster of sferics starting 10 ms before TLE2 Palmer data - 34 ms after Langmuir - amplitude 10 time less Waveforms - Langmuir, EM signature of ELF - Palmer, slow tail

10. 10 0+20+30+1 0+30+2 DEMETER Three EM (E and B spectra ) 0+ whistlers associated with the three sferics observed at Langmuir Power : 65 dB less than at Langmuir However, distance between the DEMETER magnetic Foot line and Langmuir ~ 880 km

11. 11 248° 252° 256° 258° E 36° 32° 28° 24° Geographical location of: the lightning area ( ), the Langmuir station ( ), the DEMETER magnetic foot line ( )

12. 12 Note : Langmuir spectrogram the lack of substantial attenuation < 1.8 kHz could mean that the wave propagates directly upward Palmer spectrogram the lower frequency cut-off at ~ 1.6 kHz suggests that the wave does not propagate in the wave guide QTEM mode

13. 13 16 - 20 kHz ~ 1ms Pulse like feature before 0+ whistler 1 (as Kelley et al. 1990), but Kelley et al. (1997) show maximum power of lightning EM in the 50 – 125 kHz) frequency range

14. 14 Proton whistlers -upgoing by definition - R part (electron whistler) - L part (proton whistler) Observation : - R and L waves seen on E and B spectra - no energy gap on the R wave between f cr and f H + Agreement with the Wang (1971) model : -the « electron whistler » propagates with θ~0°, -the « proton whistler » propagates with large θ values -The DEMETER observation explained for 0 < θ < 30°.

15. 15 3. Discussion

16. 16 RADIO – WINDOW THEORY (Ellis, 1956; Budden, 1985) n 2 = 1 – A/ ( B± C) A = X(U-X) B = U(U-X) - 0.5Y T 2 C ={ 0.25 Y T 4 + Y L 2 (U-X)} 1/2 X = f pe 2 /f 2 Y = f ce /f θ = (B 0, K) Y T = Y sin θ Y L = Y cos θ U = 1 – iZ Z = ν/2πf, with ν electron collision frequency

17. 17 Variation of n 2 as a function of X = f pe 2 /f 2 for a cold collisionless electron plasma at Y = f ce /f = 100.

18. 18 IRI 2001 model of ionosphere for July 28 2005 at the UT time and at the geographical coordinates of the observations at Langmuir and DEMETER. Collision frequency model ν= K exp {-0.15(h-h 0 )}

19. 19

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21. 21 300 kHz

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23. 23 CONCLUSION The analysis of the 28 July 2005 events, simultaneously observed at the Langmuir station and on-board DEMETER, at the time of TLEs detection, show that: The analysis of the 28 July 2005 events, simultaneously observed at the Langmuir station and on-board DEMETER, at the time of TLEs detection, show that: - parent lightning flashes may be identified from satellite measurements in the ELF/VLF band, - proton whistlers characteristics may be used for fast estimation of propagation characteristics after ionospheric crossing

24. 24 The Ellis, Budden « radio window » concept The Ellis, Budden « radio window » concept - explains the July 28 2005 observation - suggests that its effects are quite general To better understand the effects of the ionospheric crossing, one needs To better understand the effects of the ionospheric crossing, one needs - better models of the D and E layers - ray-tracing programs taking into account collisions, heavy ions, etc.

25. 25 NOTE : The theory predicts that the condition for a wave energy transmission depends on the latitude of the transmission point, and so that is only possible for Y > 0.5 (1+l z -2 ), with lz the direction cosine of the axis of the refractive index surface. As a consequence waves which may be transmitted must have angles between B0 and the vertical - 0.5 (1+l z -2 ), with lz the direction cosine of the axis of the refractive index surface. As a consequence waves which may be transmitted must have angles between B0 and the vertical - < 85° at 1 kHz, - < 80° at 5 kHz, etc

26. 26 From J.L. Pinçon