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NonThermal Continuum Radiation Observed from the CLUSTER Fleet
Pierrette Décréau, S. Grimald, Michel Parrot, O. Randriamboarison, Jean-Louis Rauch, Jean-Gabriel Trotignon, X. Vallieres, P. Canu, Nicole
Cornilleau, J. Pickett, et al.
To cite this version:
Pierrette Décréau, S. Grimald, Michel Parrot, O. Randriamboarison, Jean-Louis Rauch, et al.. Non-Thermal Continuum Radiation Observed from the CLUSTER Fleet. Cluster and Double Star sym-posium. 5th Anniversary of Cluster in Space, Sep 2005, Noordwijk, Netherlands. �hal-00154413�
Non Thermal Continuum radiation
observed from the Cluster fleet
5th Anniversary of Cluster in Space 19-23 September, ESTEC
P. Décréau, S. Grimald, M. Parrot, O. Randriamboarison, J.-L. Rauch, J._G. Trotignon, X. Vallières, LPCE Orléans, F.
P. Canu, N. Cornilleau, CETP Vélizy, F. J. Pickett, Iowa Univ., USA
O. Santolik, St Charles Univ., Prague, Czech Rep.
M. P. Gough, A. M. Buckley, T. D. Carozzi, SSS, Sussex Univ., GBR A. Masson, RSSD, Noordwijk, The Netherlands
2
1.
Generalities
2.
Advances with Cluster observations
Ray path from multipoint observatory
Sources
3.
Summary and perspectives
5th anniversary of Cluster 19-23 Sept. 2005 ESTEC 3 C4 7 June 2003 Escaping Continuum Magnetosheath Type III Plasmasphere Plasmasphere
1.1 What is Non Thermal Continuum (NTC)?
NTC radiations are:
•
weak, long lasting, narrow band, EM emissions•
observed (since 1970s), in almost all regions ofmagnetosphere, they can escape in the interplanetary medium
NTC and Type III:
~ 10-16 V2 M-2 Hz-1
4
1.2 What is the source of NTC?
General scheme of NTC generation:
ES
emissions EM radiation
Particles free energy
This happens at the plasmapause boundary layer
NTC formation is largely not understood. How to explain:
Duration of emissions?
Spectral characteristics (narrow bands, harmonic structures)?
Wave intensity? Beaming properties? Radio window at grad (Ne) Jones, 1982 N.L. processes • coalescence with LF waves Melrose, 1981 • decay of Bernstein waves Rönmark, 1985 Models
5th anniversary of Cluster 19-23 Sept. 2005 ESTEC
5
Sources
Several generation models Few observations
Remote Observations Increasing data set:
Injun 5, Hawkeye, ISEE, GEOS, DE1, Polar, Geotail, IMAGE, Cluster
Various behaviors
Link to be understood
6
Y
X
Y
X
1.4 How does NTC propagate?
Magnetosheath MPause Magnetosphere B. Shock Trapped NTC NTC is reflected at magnetosheath density irregularities.
It seems to create band splitting (via Doppler shift?)
26/02/2001
Gurnett, 1975
Cusp
•
NTC radiation emerges from sources at PPause boundary layer. It is beaming predominantly near equatorial plane.•
The lower frequency band is trapped inside the magnetospheric cavity, bouncing between MPause(/cusp) and Plasmapause5th anniversary of Cluster 19-23 Sept. 2005 ESTEC
7
2.
Advances with Cluster observations
Ray path from multipoint observatory
2 examples
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26/09/03 Separation ~ 250 km
Example 1: Beaming properties
•
No definitive conclusion has been reached, concerning the validity of Jones theory•
Cluster orbit does not cross a beam pair issued from the same source200 km separation
Test of Jones theory ( ES to EM conversion )
2 narrow beams, symetric / equator
α
α = arctan(f
5th anniversary of Cluster 19-23 Sept. 2005 ESTEC
9
Example 2: Observation of narrow band emissions
Far from equator, the four SC see exactly the same emission Only part of the constellation is illuminated near the equator
10 20 30 40 50 dB above 10 -7 V rms .Hz -1/2 2 20 40 60 80 Frequency (kHz) C1 10 20 30 40 50 dB above 10 -7 V rms .Hz -1/2 2 20 40 60 80 Frequency (kHz) C2 10 20 30 40 49 dB above 10 -7 V rms .Hz -1/2 2 20 40 60 80 Frequency (kHz) C3 10 20 30 40 49 dB above 10 -7 V rms .Hz -1/2 2 20 40 60 80 Frequency (kHz) C4
CLUSTER-WHISPER Spectrogram / JUL 16, 2005 (Day 197) Method: Average UT 04:00:00 05:00:00 06:00:00 07:00:00 08:00:00 09:00:00 10:00:00 11:00:00 X_gse(Re) -0.82 0.42 1.62 2.60 3.12 3.09 2.61 1.88 Y_gse(Re) 4.04 4.50 4.57 4.04 2.81 1.08 -0.82 -2.66 Z_gse(Re) -5.78 -4.18 -2.23 -0.00 2.21 4.04 5.31 6.09 Lat_sm(deg) -62.41 -50.30 -31.75 -5.89 24.54 53.39 76.84 84.15 LT_sm(h) 17.52 16.66 16.05 15.64 15.39 15.30 15.59 1.61
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Interpretation
•
A small orbit elementis illuminated by the direct path
•
A large orbit elementis illuminated by the reflected radiation
5th anniversary of Cluster 19-23 Sept. 2005 ESTEC
11
Spin modulation as a clue to ray path orientation
1
2
Phase angle (0-180°) E field
(10 -7 V m-1Hz -1/2) m ~ 25%
The spin modulation gives an estimation of the inclination of the ray wrt the spin plane
It allows to find out if the ray reaches the
observatory directly (1) or after a reflection (2)
Z
GSEReceiving antenna
Spin plane
X
GSEY
GSESun
k
12 11 20 30 40 49 dB above 10 -7 V rms .Hz -1/2 35 40 45 50 55 60 65 70 Frequency (kHz) C1 10 20 30 40 50 dB above 10 -7 V rms .Hz -1/2 35 40 45 50 55 60 65 70 Frequency (kHz) C2 10 15 20 25 30 dB above 10 -7 V rms .Hz -1/2 35 40 45 50 55 60 65 70 Frequency (kHz) C3 15 20 25 30 dB above 10 -7 V rms .Hz -1/2 35 40 45 50 55 60 65 70 Frequency (kHz) C4
CLUSTER-WHISPER Spectrogram / JUL 16, 2005 (Day 197)
Method: AvgNat UT 04:40:00 04:55:00 05:10:00 05:25:00 05:40:00 X_gse(Re) 0.01 0.32 0.63 0.94 1.24 Y_gse(Re) 4.38 4.48 4.54 4.59 4.60 Z_gse(Re) -4.75 -4.32 -3.88 -3.41 -2.91 Lat_sm(deg) -54.97 -51.53 -47.70 -43.45 -38.75 LT_sm(h) 16.92 16.72 16.54 16.38 16.23
Compared spin modulations
Modulation values indicate that beams have been reflected
Directivity angles complete the information 1 2 m ~ 25% m ~ 10% m ~ 30% m ~25%
5th anniversary of Cluster 19-23 Sept. 2005 ESTEC
13 MPause
Triangulation points toward high X value, it is compatible with the proposed scenario
0 2 4 6 X ( RE) 0 2 4 Y ( R E ) Dusk Dawn
•
Conclusion: the origin of beams observed in the dusk sector is probably a source placed in the dawn sector14
2.
Advances with Cluster observations
Ray path from multipoint observatory
5th anniversary of Cluster 19-23 Sept. 2005 ESTEC
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NTC Sources: Which candidate Electrostatic Emissions ?
•
Equatorial n+1/2?Too far from density gradient (inside plasmasphere)
•
Intense (saturating) emissions at PPause density gradient ? Observed just above Fp (in the band Fp - Fq), close to equator16
NTC Sources
•
Intense ES emissions at plasmapause surface are often associated with LF broadband emissions•
More analysis is needed to interpret these observations5th anniversary of Cluster 19-23 Sept. 2005 ESTEC
17
Role of Bernstein waves
Several examples show convincing evidence of a link between ES
emission at local Fqs (Bernstein mode) and simultaneously observed NTC Canu et al., 2005
18
Possibly linked with small density cavities
5th anniversary of Cluster 19-23 Sept. 2005 ESTEC 19 10 20 30 40 50 dB above 10 -7 V rms .Hz -1/2 35 40 45 50 55 60 65 70 Frequency (kHz) C2 35 UT 04:40:00 04:55:00 05:10:00 05:25:00 05:40:00 X_gse(Re) 0.01 0.32 0.63 0.94 1.24
NTC observed at sources
More from the 16 July 2005 eventEM emissions near density cavities
1
2
20
B (1)
(2)
Ripples in the PPause boundary (rays aligned with density gradient) could explain different beam orientations
(1)
(2)
(1)
(2)
Analysis of directivity properties
High modulation indices
Beam orientations at about 80°
Study in the spin plane (parallel to XY GSE) F re q u e n c y Time (1) (1) (2) (2)
5th anniversary of Cluster 19-23 Sept. 2005 ESTEC
21
22
Other large scale findings
•
Simultaneous observations of harmonic ‘large band’ NTCstructures
•
Different spectral characteristics when viewed from different SC•
Local sources (off equator) are illuminating short orbit elements5th anniversary of Cluster 19-23 Sept. 2005 ESTEC
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5. Summary and conclusion
Various types of ES emissions observed in the Ppause boundary layer (a) Intense emissions in Fpe - Fq band
(b) ‘Micro’ sources, in density holes, some at n Fce
Two main types of structured EM radiations observed in magnetosphere: (a) multiple narrow spectral lines, radiating over a long range, having
undergone one reflection at Msheath in many cases
(b) ‘harmonic wide bands’, structured according to local magnetic field conditions.
Both forms could result from many small size sources. Respective source spatial distribution might be different.
Challenging question: how to conciliate numerous, micro sources, with well established beams of large aperture ?
Perspectives
Close analysis of ES sources (PEACE, WBD, WHISPER) plus simulation, toward a better understanding of source behavior (stability, power)