[show abstract][hide abstract] ABSTRACT: Identifying the magnetic structure in the region where the magnetic field lines break and how reconnection happens is crucial to improving our understanding of three-dimensional reconnection. Here we show the in situ observation of magnetic null structures in the diffusion region, the dynamics, and the associated waves. Possible spiral null pair has been identified near the diffusion region. There is a close relation among the null points, the bipolar signature of the Z component of the magnetic field, and enhancement of the flux of energetic electrons up to 100 keV. Near the null structures, whistler-mode waves were identified by both the polarity and the power law of the spectrum of electric and magnetic fields. It is found that the angle between the fans of the nulls is quite close to the theoretically estimated maximum value of the group-velocity cone angle for the whistler wave regime of reconnection.
Journal of Geophysical Research 01/2009; · 3.17 Impact Factor
[show abstract][hide abstract] ABSTRACT: The Venus Express mission is scheduled for launch in 2005. Among many other instruments, it carries a magnetometer to investigate the Venus plasma environment. Although Venus has no intrinsic magnetic moment, magnetic field measurements are essential in studying the solar wind interaction with Venus. Our current understanding of the solar wind interaction with Venus is mainly from the long lasting Pioneer Venus Orbiter (PVO) observations. In this paper, we briefly describe the magnetic field experiment of the Venus Express mission. We compare Venus Express mission with PVO mission with respect to the solar wind interaction with Venus. Then we discuss what we will achieve with the upcoming Venus Express mission.
Planetary and Space Science 01/2006; · 2.11 Impact Factor
[show abstract][hide abstract] ABSTRACT: The spacecraft potential of Double Star TC-1 is positive in large parts of the orbits due to the photo-effect from solar EUV irradiation. These positive potentials typically disturb low energy plasma measurements on board. The potential can be reduced, and thereby the particle measurements improved, by emitting a positive ion beam. This method has successfully been applied on several other spacecraft and it has also been chosen for TC-1. The instrument TC-1/ASPOC is a derivative of the Cluster/ASPOC instruments, from which it has inherited many features. The paper describes the adaptations and further developments made for the ion emitters and the electronics. The instrument performs very well and can support higher beam currents than on Cluster. The expected significant improvement of the low energy particle measurements on board was indeed observed. The modifications of the electron distributions are analysed for a one-time interval when the spacecraft was located in the magnetosheath. The change in the potential due to the ion beam was determined, and first studies of the 3-D electron distributions in response to the spacecraft potential control have been performed, which indicate that the method works as expected.
[show abstract][hide abstract] ABSTRACT: An ion emitter instrument ASPOC (Active Spacecraft Potential Control)
belongs to the payload of the Chinese-European Double Star mission
(TC-1) launched in December 2003. The instrument is a further
development to the ones flown in the Cluster mission. Its objective is a
reduction of the spacecraft potential in order to minimise the
perturbations to the plasma measurements on board. The operation of the
scientific payload began after commissioning in February 2004.
Comparisons to Cluster are being made based on data from the first half
year of the Double Star mission. The enhanced capabilities of the
instrument allow to achieve even lower potentials than on Cluster.
Differences to Cluster can also be expected because of the plasma
environment at the equatorial orbit of TC-1. The effects of spacecraft
potential control on the electron measurements by the instrument PEACE
as observed during the first months of science operations are discussed.
[show abstract][hide abstract] ABSTRACT: On June 14, 1998, a Pi 2 pulsation of unusually large amplitude was observed simultaneously by ground stations located in both of dayside and nightside local time sectors and with 145-degree latitude span (from 70.6°N to 74.7° S). The geomagnetic field observed by stations in nightside clearly showed substrom signatures at the event time and it appeared that the dayside Pi 2 signature is also associated with the substorm. We analyzed the polarization of the dayside Pi 2 wave in the horizontal plane and found that the longitudinal variation of the polarization agreed with that generated by a current wedge. This has previously been reported for nighttime Pi 2 but is unexpected for daytime events.
Advances in Space Research 01/2002; 30(10):2339-2343. · 1.18 Impact Factor
[show abstract][hide abstract] ABSTRACT: Electrostatic charging of a spacecraft modifies the distribution of electrons and ions before the particles enter the sensors mounted on the spacecraft body. The floating potential of magnetospheric satellites in sunlight very often reaches several tens of volts, making measurements of the cold (several eV) component of the ambient ions impossible. The plasma electron data become contaminated by large fluxes of photoelectrons attracted back into the sensors. The Cluster spacecraft are equipped with emitters of the liquid metal ion source type, producing indium ions at 5 to 9 keV energy at currents of some tens of microampere. This current shifts the equilibrium potential of the spacecraft to moderately positive values. The design and principles of the operation of the instrument for active spacecraft potential control (ASPOC) are presented in detail. Experience with spacecraft potential control from the commissioning phase and the first two months of the operational phase are now available. The instrument is operated with constant ion current for most of the time, but tests have been carried out with varying currents and a "feedback" mode with the instrument EFW, which measures the spacecraft potential . That has been reduced to values according to expectations. In addition, the low energy electron measurements show substantially reduced fluxes of photoelectrons as expected. The flux decrease in photoelectrons returning to the spacecraft, however, occurs at the expense of an enlarged sheath around the spacecraft which causes problems for boom-mounted probes.
[show abstract][hide abstract] ABSTRACT: The northward and southward orientation of the interplanetary magnetic field (IMF) is usually considered as providing the external boundary conditions in the solar wind interaction with the Earth's magnetopause but it is the magnetic field in the magnetosheath that interacts with the Earth's magnetic field. In this paper, we consider the possibility that the wave activity in the foreshock region may affect the magnetic field orientation in the magnetosheath with time scales that might be geomagnetically effective. If magnetosheath magnetic field becomes disturbed on plasma streamlines which are connected to the quasi-parallel bow shock and foreshock, the magnetic field orientation on the inner magnetosheath may differ significantly from the undisturbed IMF. We present a model of dayside reconnection which may occur when the IMF northward and illustrate its effects on the erosion of the magnetopause.
Advances in Space Research 01/1997; 19(12):1943-1946. · 1.18 Impact Factor
[show abstract][hide abstract] ABSTRACT: Large amplitude Pc5 event was observed on ground and in the space on August 3, 2001, about two hours after contact of the strong discontinuity in the solar wind with the magnetosphere due to data from ACE and WIND satellites. The Pc5 amplitude was as high as 15 nT in the tail of magnetosphere and about 5 nT at the ground based stations. Pc5 waves were observed in the magnetosphere by Cluster and Polar satellites, which occupied positions in the morning part of the near tail at the close field lines but were parted by distance of 11.5 RE, mainly along the X-axis of the GSM coordinate system. Both compressional and transverse components of the Pc5 wave activity were observed in the space, with the transverse component having the larger amplitude. Time delay between the Cluster and Polar satellites was about 8 minutes, which can be witness of wave propagation from the geomagnetic tail to the Earth with the 150 km/s group velocity. The ground-based Pc5 activity was analyzed by using data from the IMAGE magnetometer network. Some demonstrations of a field line resonant structure were found in variations of amplitude and polarization with latitude. Finnish chain of search coil magnetometers observed modulated Pc1 emission simultaneously with the Pc5 wave train. A possibility of non-linear impact of Pc5 wave energy on the plasma and waves in the magnetosphere is discussed. The work was supported by INTAS 01-0013 and RFBR 03-05-64361 grants.