排序方式： 共有4条查询结果，搜索用时 15 毫秒
1
1.
C. Caroubalos D. Maroulis N. Patavalis J.-L. Bougeret G. Dumas C. Perche C. Alissandrakis A. Hillaris X. Moussas P. Preka-Papadema A. Kontogeorgos P. Tsitsipis G. Kanelakis 《Experimental Astronomy》2001,11(1):23-32
We present the new solar radiospectrograph of the University of Athensoperating at the Thermopylae Station since 1996. Observations cover thefrequency range from 110 to 688 MHz. The radiospectrograph has a 7-meterparabolic antenna and two receivers operating in parallel. One is a sweepfrequency receiver and the other a multichannel acousto-optical receiver.The data acquisition system consists of a front-end VME based subsystem anda Sun Sparc-5 workstation connected through Ethernet. The two subsystems areoperated using the VxWorks real-time package. The daily operation is fullyautomated: pointing of the antenna to the sun, starting and stopping theobservations at pre-set times, data acquisition, data compression by`silence suppression', and archiving on DAT tapes. The instrument can beused either by itself to study the onset and evolution of solar radio bursts or in conjunction with other instruments including theNançay Decametric Array and the WIND/WAVES RAD1 and RAD2 low frequencyreceivers to study associated interplanetary phenomena. 相似文献
2.
From the analysis of 119 low-frequency (LF) burst spectra observed onboard the Wind spacecraft, we propose an interpretation of the frequency-time characteristics including the low frequency cutoff of the LF burst spectra, and we use these characteristics to sound the bow shock structure at large tailward distances from Earth. When observed from within the solar wind, LF bursts appear to be made of two spectral components. The high frequency one is bursty and observed above twice the solar wind plasma frequency fpsw. The low frequency one is diffuse (ITKR) and its spectrum extends from about 2fpsw to a cutoff frequency fc not much higher than fpsw; its onset time δt(f) increases as the frequency f decreases. For each of the 119 events observed from near the Lagrange point L1, the solar wind density variations were measured and the variations of the density jump across the shock calculated from plasma data all along a shock model over more than 2000RE. But, except for a few events, neither the solar wind overdensities nor the shock density barrier can prevent waves with frequencies below fc from reaching the spacecraft. Scattering on plasma density inhomogeneities was then introduced to account for the propagation of the LF burst waves in the magnetosheath, from near Earth to their escape point through the bow shock at a frequency-dependent distance |Xesc(f)| (GSE), and then in the solar wind to the spacecraft. In such media, at frequencies between 2fpsw and fpsw, the bulk speed of the scattered waves decreases rapidly as f decreases, and this accounts for the observed variations of the onset time δt(f). Angular scattering can also account for the observed cutoff at fc if the distance |Xesc(f)| increases exponentially when f/fpsw decreases. As the shock model we used meets that requirement, we consider that this model is valid, which implies that the bow shock still exists beyond 1000RE from the Earth. The observed decrease of the average spectral intensity of the LF burst between about 1.5fpsw and 2fpsw can also be explained by the scattering in the solar wind if we take into account the angular distribution of the rays when they leave the bow shock. 相似文献
3.
Caroubalos C. Alissandrakis C.E. Hillaris A. Nindos A. Tsitsipis P. Moussas X. Bougeret J.-L. Bouratzis K. Dumas G. Kanellakis G. Kontogeorgos A. Maroulis D. Patavalis N. Perche C. Polygiannakis J. Preka-Papadema P. 《Solar physics》2001,204(1-2):165-177
In this report we present a complex metric burst, associated with the 14 July 2000 major solar event, recorded by the ARTEMIS-IV
radio spectrograph at Thermopylae. Additional space-borne and Earth-bound observational data are used, in order to identify
and analyze the diverse, yet associated, processes during this event. The emission at metric wavelengths consisted of broad-band
continua including a moving and a stationary type IV, impulsive bursts and pulsating structures. The principal release of
energetic electrons in the corona was 15–20 min after the start of the flare, in a period when the flare emission spread rapidly
eastwards and a hard X-ray peak occurred. Backward extrapolation of the CME also puts its origin in the same time interval,
however, the uncertainty of the extrapolation does not allow us to associate the CME with any particular radio or X-ray signature.
Finally, we present high time and spectral resolution observations of pulsations and fiber bursts, together with a preliminary
statistical analysis. 相似文献
4.
A. Mangeney C. Salem C. Lacombe J.-L. Bougeret C. Perche R. Manning P. J. Kellogg K. Goetz S. J. Monson J.-M. Bosqued 《Annales Geophysicae》1999,17(3):307-320
The time domain sampler (TDS) experiment on WIND measures electric and magnetic wave forms with a sampling rate which reaches 120 000 points per second. We analyse here observations made in the solar wind near the Lagrange point L1. In the range of frequencies above the proton plasma frequency fpi and smaller than or of the order of the electron plasma frequency fpe, TDS observed three kinds of electrostatic (e.s.) waves: coherent wave packets of Langmuir waves with frequencies f ≃ fpe, coherent wave packets with frequencies in the ion acoustic range fpi ≥ f ≥ fpe, and more or less isolated non-sinusoidal spikes lasting less than 1 ms. We confirm that the observed frequency of the low frequency (LF) ion acoustic wave packets is dominated by the Doppler effect: the wavelengths are short, 10 to 50 electron Debye lengths λD. The electric field in the isolated electrostatic structures (IES) and in the LF wave packets is more or less aligned with the solar wind magnetic field. Across the IES, which have a spatial width of the order of ≃25D, there is a small but finite electric potential drop, implying an average electric field generally directed away from the Sun. The IES wave forms, which have not been previously reported in the solar wind, are similar, although with a smaller amplitude, to the weak double layers observed in the auroral regions, and to the electrostatic solitary waves observed in other regions in the magnetosphere. We have also studied the solar wind conditions which favour the occurrence of the three kinds of waves: all these e.s. waves are observed more or less continuously in the whole solar wind (except in the densest regions where a parasite prevents the TDS observations). The type (wave packet or IES) of the observed LF waves is mainly determined by the proton temperature and by the direction of the magnetic field, which themselves depend on the latitude of WIND with respect to the heliospheric current sheet. 相似文献
1