Crete VLF studies of Transient Luminous Events (TLEs)

Transcription

1 The First VLF AWESOME International Workshop Tunis, Tunisia, 30 May - 01 June, 2009 Crete VLF studies of Transient Luminous Events (TLEs) C. Haldoupis and A. Mika Physics Department, University of Crete, Greece Acknowledgements: U. S. Inan and the Stanford VLF group T. Neubert and the CAL / EuroSprite team

2 Contents Background material TLE morphology, the medium, QE and EMP field effects, ionospheric VLF waves, lightning-induced VLF signatures Crete VLF studies EuroSprite campaigns and VLF measurements in Crete Early VLF events and TLEs - findings and implications Summary and concluding comments

3 Transient Luminous Events TLEs

4 Transient Luminous Events TLEs The hosting medium is the D region of the ionosphere, thus TLE effects can be studied with VLF electromagnetic waves

5

6 Q ~ L

7

8 Crete VLF studies of TLEs

9 VLF signals

10

11 Lightning-generated generated sub-ionospheric VLF Perturbations Crete VLF station recordings - November 15, 2005 Narrowband VLF signal time series and perturbations. It allows one to study indirect and direct lightning effects in the upper atmosphere lower ionosphere

12 Lightning-generated Figure and text is from Stanford group publications

13 Early VLF perturbations due to scattering from irregularities in conductivity VLF Scattering narrow angle forward scattering caused by a horizontally extended region of perturbed electron density (l > λ, h< λ) Wait (1964); Poulsen et al. (1990, 1993) wide angle scattering by induced currents from an assembly of conducting vertical structures (d << λ ). Wait (1995); Rodger et al. (1997, 1999) Observations imply: Most Early VLF events are likely due to laterally extended regions of electron density enhancements in the upper D region

14 Crete VLF studies of TLEs (Sprites and Elves) Generation mechanisms

15 Crete VLF studies of TLEs (Sprites and Elves) Generation mechanisms

16

17

18

19

20 Crete VLF Studies of TLEs

21 VLF Measurements in Crete (started July 18, 2003)

22

23 Coupling of Atmospheric Layers - EU / RTN

24 HAIL Software (Analysis of Narrowband VLF recordings)

25 Narrowband VLF time series VLF Wavelet analysis More work is needed

26 Narrowband VLF time series VLF Wavelet analysis More work is needed Broadband VLF time and frequency domain analysis

27 Crete VLF / TLE Studies (PhD Thesis, Agnes Mika) * *:

28 Relation between Early VLF events and sprites

29 Early VLF Events and Sprites July 21, 2003, storm 02:00-03:15 UT: 28 sprites

30 Sprite related Early/Slow and LEP VLF Signatures LEP Early VLF Sprite at 02:38: UT

31 A large amplitude Early VLF event

32

33 Early VLF events and Sprites : EuroSprite 2007 November 15, 2007 Storm : 22:15 23:40 UT- 14 sprites 3 VLF links (HWU, NAA, HWV) have identical GCPs 0.3 MW Inactive 15 Early 1.2 MW kw 7 Early

34 Early VLF and Sprites : one to one relation November 15, 2007 Storm : 22:15 23:40 UT - 14 sprites NAA CR Link 24.0 khz, 1000 kw 9 sprites - 8 Early VLF (88%) 14 Sprites 14 early VLF (100%) 2 Early (with +CG causatives) -- No sprites? +CG causative missed Sprite /elve? 14 Sprites, 12 +CGs, 14 Early VLF events accompanied, 100 % 1Early event (with +CG causative) but no sprite 664 -CGs and the rest (190) +CGs had NO Early-like VLF signature

35 Need for more work

36 Need for more work

37

38 Need for more work

39

40

41 Need for more work

42

43 early/slow vs early/fast VLF events Early/slow Early/fast

44

45

46 Terminology : E/F and E/S, thus better call Early VLF events Need for more work

47

48

49 Typical Early VLF signature. Recovery time ~ 200 s

50 ISUAL Observations July July Elves over US/Mexico 45 elves and VLF data No VLF-perturbations

51 Need for more work

52 Modeling the relaxation of Early VLF events Early VLF event recoveries range from several seconds to several tens of seconds mostly between 20 s and 200 s what can we learn?

53

54

55

56 Best fit at 75 km 80 km 85 km Need for more work

57 Need for more work

58

59

60 Sub-Ionospheric VLF events There is now a good deal of understanding. But there are remaining problems/questions and need for more work. The AWESOME network offers new opportunities-possibilities for more VLF-lightning research, also with EuroSprite, TARANIS and ASIM projects

61 6-Tutorials on Ionospheric physics topics Tutorial by U. S. Inan on: Lower and middle atmospheric electrodynamics

62