XVII CLUSTER Workshop, Uppsala, 14 May 2009

Fan and horseshoe instabilities -relation to the low frequency waves registered by

Cluster in the polar cusp

J.Błęcki (1), M.Parrot (2), S.Savin (3), R.Wronowski (1), N.Cornilleau-Wehrlin (4), E. Amata (5).

(1) Space Research Centre PAS 00-716 Warsaw, Bartycka 18A, Poland, (4) LPCE/CNRS, Orléans, France(3) Space Research Institute RAS, Moscow, Russia(4) CETP/Velizy, France(5) IFSI/INAF, Rome, Italy

XVII CLUSTER Workshop, Uppsala, 14 May 2009

Main modes of the plasma waves in the cusp

XVII CLUSTER Workshop, Uppsala, 14 May 2009

Magion 4 observations in the polar cusp

Blecki et al. ASR, 1997

XVII CLUSTER Workshop, Uppsala, 14 May 2009

Savin et al. 2004

04:03:36 UT

XVII CLUSTER Workshop, Uppsala, 14 May 2009

XVII CLUSTER Workshop, Uppsala, 14 May 2009

Fan Instability• First studies by Kadomtsev and Pogutse (1967),

discussed in relation to auroral region by Omelchenko et al. (JGR 1994) and Vaivads et al. (1997), solar wind and auroral region by Krafft and Volokitin (2003and 2004) and magnetopause by Savin (2004).

• Fan instability is driven by a particle beam along the magnetic field lines but in contrast to the usual beam-plasma instabilities it does not require a threshold in the relative velocity and positive slope in the distribution function

• Long superthermal tail in the distribution function is needed for developing of this instability

• The electron tail that forms drives the anomalous Doppler resonance instability–which results in pitch angle scattering of the electrons and the generation of cyclotron radiation.

XVII CLUSTER Workshop, Uppsala, 14 May 2009

Electrostatic aproximation Vaivads et al.. 1997

Kraft and Volokitin 2003 extended the model on so-called electromagnetic lower hybrid waves

They applied their model to study emissions in solar wind, where

The same condition is applicable for the polar cusp

It gives dispersion relation

Kraft and Volokitin 2003

XVII CLUSTER Workshop, Uppsala, 14 May 2009

For auroral magnetosphere they obtained

Next paper by Kraft and Volokitin 2004 brings the nonlinear analysis of the wave – particle and wave-wave interactions. They shown importance of these processes for the lower hybrid branch of electromagnetic waves

XVII CLUSTER Workshop, Uppsala, 14 May 2009

XVII CLUSTER Workshop, Uppsala, 14 May 2009

• For polar cusp one can assume simplification

• Frequency• Oblique propagation• Maximum of the spectral density

for 0.2<cosΘ<0.4• For the outer cusp• 0.19ωce<ω<0.38 ωce

ceLH

k

k z

pe

ce

ce

cos

1

1

cos

2

2

XVII CLUSTER Workshop, Uppsala, 14 May 2009

Fan instability

13.03.2003

XVII CLUSTER Workshop, Uppsala, 14 May 2009

XVII CLUSTER Workshop, Uppsala, 14 May 2009

XVII CLUSTER Workshop, Uppsala, 14 May 2009

XVII CLUSTER Workshop, Uppsala, 14 May 2009

XVII CLUSTER Workshop, Uppsala, 14 May 2009

Plasma waves in the polar cusp at the ionospheric altitude - registrations by DEMETER DEMETER is a low-altitude satellite (710 km) launched in June 2004 onto a polar and circular orbit which measures electromagnetic waves all around the Earth except in the auroral zones (Parrot, 2006). In December 2005, the altitude of the satellite was decreased to 660 km. The ELF/VLF range for the electric field is from DC up to 20 kHz. There are two scientific modes: a survey mode where spectra of one electric and one magnetic component are onboard computed up to 20 kHz and a burst mode where, in addition to the onboard computed spectra, waveforms of one electric and one magnetic field component are recorded up to 20 kHz. The burst mode allows performing a spectral analysis with higher time and frequency resolution. During the burst mode, the waveforms of the six components of the electromagnetic field are also recorded up to 1.25 kHz. This allows performing a detailed wave propagation analysis .

XVII CLUSTER Workshop, Uppsala, 14 May 2009

XVII CLUSTER Workshop, Uppsala, 14 May 2009

Polar cusp at the ionospheric level

• Kilometric continuum emission cone corotates with plasmasphere mergring with the AKR emission cone on the night side

• No AKR cusp source found !!!!

Green 2003

XVII CLUSTER Workshop, Uppsala, 14 May 2009

XVII CLUSTER Workshop, Uppsala, 14 May 2009

10.03.2006

KR

XVII CLUSTER Workshop, Uppsala, 14 May 2009

XVII CLUSTER Workshop, Uppsala, 14 May 2009

SUMMARY and CONCLUSIONS• Broad emissions as the typical feature of the cusp, but

characteristic emissions around electron cyclotro frequency

• Localized fluxes of energetic electrons and sources of the waves below electron cyclotron frequency

• Subtle structure of the sources• Fan instability as an effective source of the waves below

electron gyrofrequency• Lower hybrid waves as a accelerator of particles • Measurements at the ionospheric altitude (~700km)

done by DEMETER show presence of the energetic electrons together with low frequency waves.

• Presence of the kilometric radiation at the boundary of the cusp together with energetic electron fluxes