NonThermal Continuum Radiation Observed from the CLUSTER Fleet

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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 of

magnetosphere, 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 Plasmapause

5th anniversary of Cluster 19-23 Sept. 2005 ESTEC

7

2.

Advances with Cluster observations

Ray path from multipoint observatory

2 examples

8

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 source

200 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 element

is illuminated by the direct path

•

A large orbit element

is 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}-1_Hz -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

_GSE

Receiving antenna

Spin plane

X

GSE

Y

_GSE

Sun

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 ( R_E) 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 sector

14

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 equator

16

NTC Sources

•

Intense ES emissions at plasmapause surface are often associated with LF broadband emissions

•

More analysis is needed to interpret these observations

5th anniversary of Cluster 19-23 Sept. 2005 ESTEC

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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 event

EM 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’ NTC

structures

•

Different spectral characteristics when viewed from different SC

•

Local sources (off equator) are illuminating short orbit elements

5th anniversary of Cluster 19-23 Sept. 2005 ESTEC

23

5. Summary and conclusion

Various types of ES emissions observed in the Ppause boundary layer (a) Intense emissions in F_pe - F_q band

(b) ‘Micro’ sources, in density holes, some at n F_ce

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)