Journal cover Journal topic
Annales Geophysicae An interactive open-access journal of the European Geosciences Union
Journal topic

Journal metrics

Journal metrics

  • IF value: 1.621 IF 1.621
  • IF 5-year value: 1.614 IF 5-year
    1.614
  • CiteScore value: 1.61 CiteScore
    1.61
  • SNIP value: 0.900 SNIP 0.900
  • IPP value: 1.58 IPP 1.58
  • SJR value: 0.910 SJR 0.910
  • Scimago H <br class='hide-on-tablet hide-on-mobile'>index value: 80 Scimago H
    index 80
  • h5-index value: 24 h5-index 24
Volume 19, issue 10/12
Ann. Geophys., 19, 1241-1258, 2001
https://doi.org/10.5194/angeo-19-1241-2001
© Author(s) 2001. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: CLUSTER

Ann. Geophys., 19, 1241-1258, 2001
https://doi.org/10.5194/angeo-19-1241-2001
© Author(s) 2001. This work is distributed under
the Creative Commons Attribution 3.0 License.

  30 Sep 2001

30 Sep 2001

Early results from the Whisper instrument on Cluster: an overview

P. M. E. Décréau1, P. Fergeau1, V. Krasnoselskikh1, E. Le Guirriec1, M. Lévêque1, Ph. Martin1, O. Randriamboarison1, J. L. Rauch1, F. X. Sené1, H. C. Séran1, J. G. Trotignon1, P. Canu2, N. Cornilleau2, H. de Féraudy2, H. Alleyne3, K. Yearby3, P. B. Mögensen4, G. Gustafsson5, M. André5, D. C. Gurnett6, F. Darrouzet7, J. Lemaire7, C. C. Harvey8, P. Travnicek9, and Whisper experimenters (Table 1)* P. M. E. Décréau et al.
  • 1LPCE/CNRS and Université d’Orléans, Orléans, France
  • 2CETP/CNRS and VSQP University, Vélizy, France
  • 3University of Sheffield, Sheffield, UK
  • 4DSRI, Copenhaguen, Denmark
  • 5I. R. F. U., Uppsala, Sweden
  • 6University of Iowa, Iowa, USA
  • 7Institut d’Aéronomie Spatiale de Belgique, Bruxelles, Belgium
  • 8CESR, Toulouse, France
  • 9Czech Academy of Science, Prague, Czech Republic
  • *The Whisper team deeply regrets the untimely demise of Les Woolliscroft, PI of the DWP instrument and Co-I of Whisper. He played a key role in the Whisper instrument’s capabilities.

Abstract. The Whisper instrument yields two data sets: (i) the electron density determined via the relaxation sounder, and (ii) the spectrum of natural plasma emissions in the frequency band 2–80 kHz. Both data sets allow for the three-dimensional exploration of the magnetosphere by the Cluster mission. The total electron density can be derived unambiguously by the sounder in most magnetospheric regions, provided it is in the range of 0.25 to 80 cm-3 . The natural emissions already observed by earlier spacecraft are fairly well measured by the Whisper instrument, thanks to the digital technology which largely overcomes the limited telemetry allocation. The natural emissions are usually related to the plasma frequency, as identified by the sounder, and the combination of an active sounding operation and a passive survey operation provides a time resolution for the total density determination of 2.2 s in normal telemetry mode and 0.3 s in burst mode telemetry, respectively. Recorded on board the four spacecraft, the Whisper density data set forms a reference for other techniques measuring the electron population. We give examples of Whisper density data used to derive the vector gradient, and estimate the drift velocity of density structures. Wave observations are also of crucial interest for studying small-scale structures, as demonstrated in an example in the fore-shock region. Early results from the Whisper instrument are very encouraging, and demonstrate that the four-point Cluster measurements indeed bring a unique and completely novel view of the regions explored.

Key words. Space plasma physics (instruments and techniques; discontinuities, general or miscellaneous)

Publications Copernicus
Special issue
Download
Citation
Share