Crete VLF studies of Transient Luminous Events TLEs

1
Crete VLF studies ofTransient Luminous Events
(TLEs)
The First VLF AWESOME International Workshop
Tunis, Tunisia, 30 May - 01 June, 2009

• 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
(No Transcript)
6
Q L
7
(No Transcript)
8
Crete VLF studies of TLEs
9
VLF signals
10
(No Transcript)
11
Lightning-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 gt ?, hlt ?) Wait (1964)
Poulsen et al. (1990, 1993)
Observations imply Most Early VLF events are
likely due to laterally extended regions of
electron density enhancements in the upper D
region
wide angle scattering by induced currents from
an assembly of conducting vertical structures (d
ltlt ? ). Wait (1995) Rodger et al. (1997, 1999)
14
Crete VLF studies of TLEs (Sprites and Elves)
Generation mechanisms
15
Crete VLF studies of TLEs (Sprites and Elves)
Generation mechanisms
16
(No Transcript)
17
(No Transcript)
18
(No Transcript)
19
(No Transcript)
20
Crete VLF Studies of TLEs
21
VLF Measurements in Crete (started July 18,
2003)
22
(No Transcript)
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)

http//cal-crete.physics.uoc.gr/VLF-sprites/pu
blications.html
28
Relation between Early VLF events and sprites
29
Early VLF Events and Sprites
1274
July 21, 2003, storm 0200 - 0315 UT 28 sprites
207
28
30
Sprite related Early/Slow and LEP VLF
Signatures
LEP
Early VLF
Sprite at 023840.640 UT
31
A large amplitude Early VLF event
32
(No Transcript)
33
Early VLF events and Sprites EuroSprite 2007
November 15, 2007 Storm 2215 2340 UT- 14
sprites
3 VLF links (HWU, NAA, HWV) have identical GCPs
Inactive
0.3 MW
15 Early
1.2 MW
100 - kW
7 Early
34
Early VLF and Sprites one to one relation
November 15, 2007 Storm 2215 2340 UT - 14
sprites
9 sprites - 8 Early VLF (88)
14 Sprites 14 early VLF (100)
NAA CR Link 24.0 kHz, 1000 kW
?
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
(No Transcript)
38
Need for more work
39
(No Transcript)
40
(No Transcript)
41
Need for more work
42
(No Transcript)
43

• early/slow vs early/fast VLF events

Early/fast
Early/slow
44
(No Transcript)
45
(No Transcript)
46
Terminology E/F and E/S, thus better call
Early VLF events
Need for more work
47
(No Transcript)
48
(No Transcript)
49
Typical Early VLF signature. Recovery time 200
s
50
ISUAL Observations July 2004 - July 2005 282
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
(No Transcript)
54
(No Transcript)
55
(No Transcript)
56
Best fit at
75 km


80 km

85 km
Need for more work
57
Need for more work
58
(No Transcript)
59
http//cal-crete.physics.uoc.gr/VLF-sprites/public
ations.html
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
http//isea12.physics.uoc.gr/
62
(No Transcript)