Characteristics of the source region of chorus.

With multisatellite data from the Cluster project we succeeded to determine the dimensions of sources of the electromagnetic waves called "chorus". This result is important for further development of theories on the origin of these very intense emissions. Figure shows an example of observations of chorus.
Source region of chorus: Detailed time-frequency power spectrograms of electric field fluctuations in the source region recorded by the WBD instruments on board the four Cluster spacecraft on April 18, 2002. Panels (a - d) show data from Cluster 1 - 4, respectively. Arrows indicate one half of the local electron cyclotron frequency for each spacecraft. Magnetic dipole latitude is given on the bottom for Cluster 1. Radial distance is 4.37 Earth radii, and magnetic local time is 21.01 h during this interval. (From Santolik and Gurnett, 2003.)

Polarization properties of waves at the proton cyclotron frequency and its lowest harmonics in the auroral region.

We have analyzed measurements of the Polar spacecraft showing that the waves at the proton cyclotron frequency and its lowest harmonics are often observed with a significant magnetic component. The polarization of the wave magnetic field was recorded in both right-hand and left-hand senses. We proposed a statistical model to explain the polarization of the magetic component of these bursty waves. Figure shows an example of observations.
Waves at the proton cyclotron frequency and its harmonics: Time-frequency spectrogram of the magnetic field measured by the loop antenna, and recorded by the wide-band receiver of the University of Iowa plasma wave instrument on 5 June 1996. Universal time (UT), radial geocentric distance (R) in Earth radii, the magnetic dipole latitude (MLAT) in degrees, the magnetic local time (MLT) in hours, and McIlwain's parameter (L) are given on the bottom. Local proton cyclotron frequency and its harmonics are displayed on the spectrogram as white dashed lines. (From Santolik et al., 2002a.)

Detection of radial propagation of the equatorial noise below the local lower hybrid frequency.

We found a significant radial component of the wave vectors of equatorial noise below the local lower hybrid frequency. The implication is that these electromagnetic waves propagate from source regions at different radial distances compared to the point of observation. This analysis of the data from the Cluster spacecraft is important for explanation of the origin of the fine structure in power spectra of equatorial noise. Figure shows this fine structure.
Equatorial noise below the local lower hybrid frequency: Time-frequency spectrograms of electric field data recorded by the University of Iowa wide-band (WBD) instruments on 4 December 2000. Data from three Cluster spacecraft were simultaneously transmitted through the Deep Space Network (DSN). The fourth Cluster spacecraft was not recorded during that event. Common power scale is on the right. Position of the three Cluster satellites is given below the spectrograms: R is radial distance; MLat is magnetic dipole latitude; MLT is magnetic local time. Arrows show the positions of the dipole equator and calculated minima of the magnetic field strength. (From Santolik et al., 2002b.)

Experimental verification of the propagation pattern of auroral hiss at high altitudes over the active region.

Multicomponent measurement of the University of Iowa plasma wave instrument (PWI) onboard the Polar spacecraft allowed us to determine Poynting flux and wave vector directions of the auroral hiss. We found that the results are consistent with previous explanations of the funnel shaped forms on the power spectrograms. Figure shows an example of this analysis.
Propagation pattern of auroral hiss: Detailed analysis of multicomponent data received by the Polar PWI high frequency waveform receiver on March 6, 1997. (a) Spectrogram of the electric components; (b) spectrogram of the magnetic components; (c) parallel component of the Poynting vector normalized by its standard deviation; (d) the same for the component in the meridian plane; (e) angle deviation of the wave vector from the ambient magnetic field; (f) azimuth of the wave vector measured from the meridian plane; (g) 2D degree of coherence in the magnetic polarization plane. Universal time (UT), radial geocentric distance (R) in Earth radii, the magnetic dipole latitude (MLAT) in degrees, the magnetic local time (MLT) in hours, and McIlwain's parameter (L) are on the bottom. Local electron cyclotron frequency is displayed on the spectrograms. Analysis results are shown only for sufficiently strong electromagnetic signals. (From Santolik and Gurnett, 2002.)

New analysis methods for wave propagation analysis.

We developed new wave propagation analysis methods based on the Singular value decomposition (SVD) algorithm, and on analysis of the Poynting flux. These methods are now implemented in processing procedures for the data of the Cluster project of the European Space Agency.

Wave distribution function analysis of plasmaspheric hiss emissions observed by the Polar satellite.

Using multicomponent measurements we succeeded to distinguish waves propagating in antiparallel directions. This lead us to estimates of amplification rates connected to wave particle interactions in the equatorial plasmasphere.