摘要 :
Recurrent Forbush decreases and recurrent geomagnetic disturbances have been attributed to the solar M-regions, which are sources of high velocity solar plasma streams. A study of recurrent Forbush decreases for the period 1966-75...
展开
Recurrent Forbush decreases and recurrent geomagnetic disturbances have been attributed to the solar M-regions, which are sources of high velocity solar plasma streams. A study of recurrent Forbush decreases for the period 1966-75 has been made to examine any possible relationship of M-regions with solar active regions. It is shown that at the onset of the recurrent Forbush decrease at earth, there is a high probability of encountering a class of active regions at central meridian of the sun which give rise to flares of importance >= 28/3N. These active regions are found to be long-lasting and to have large areas as well as high Hsub( alpha )-intensities. Other active regions, producing flares of only lower importance, are distributed randomly on the sun with respect to the onset of a recurrent Forbush decrease. Using the quasiradial hypervelocity approximation, the base of the leading edge of the high velocity stream, at the onset of a recurrent Forbush decrease at earth, is traced to the solar longitude about 40 deg West of the central meridian. From these results, it is deduced that M-regions are located preferentially to the West of long-lasting, magnetically complex active regions. Earlier studies of the identification of the M-regions on the sun have been re-examined and shown to conform to this positional relationship. A possible mechanism of the development of an M-region to the West of the long-lasting magnetically complex active region is also discussed. (Atomindex citation 09:372264)
收起
摘要 :
We have continued our previous efforts in studies of fourier imaging methods applied to hard X-ray flares. We have performed physical and theoretical analysis of rotating collimator grids submitted to GSFC for future space or subo...
展开
We have continued our previous efforts in studies of fourier imaging methods applied to hard X-ray flares. We have performed physical and theoretical analysis of rotating collimator grids submitted to GSFC for future space or suborbital missions involving the imaging of solar flares in hard X-rays. In particular, we have simulated the performance of the High Energy Solar Spectroscopic Imager (HESSI), using pseudo-flare images provided. We have computed count rates that HESSI would record for these simulated flares, and reconstructed images from the count rates.
收起
摘要 :
During the Forbush decrease of February 14, 1978 a huge cosmic ray decrease lasting 10 hours was observed by neutron monitoring stations. A detailed analysis, performed on data of numerous neutron monitors, shows that this event w...
展开
During the Forbush decrease of February 14, 1978 a huge cosmic ray decrease lasting 10 hours was observed by neutron monitoring stations. A detailed analysis, performed on data of numerous neutron monitors, shows that this event was a bidirectional anisotropy with a cosmic ray density gradient rising from a plane tilted 30 deg with respect to the Earth equator; the interplanetary magnetic field should be perpendicular to that plane.
收起
摘要 :
Two intense heliospheric 2-3 kHz radio emission events have been observed byVoyager 1 and 2, the first in 1983-84 and the second in 1992-93. These radio emission events occurred about 400 days after large Forbush decreases in mid-...
展开
Two intense heliospheric 2-3 kHz radio emission events have been observed byVoyager 1 and 2, the first in 1983-84 and the second in 1992-93. These radio emission events occurred about 400 days after large Forbush decreases in mid-1982 and mid-1991. Since Forbush decreases are indicative of a strong interplanetary shock propagating outward through the heliosphere, this temporal relationship provides strong evidence that the radio emissions are triggered by the interaction of a shock with one of the outer boundaries of the heliosphere. From the travel time and the known speed of the shock, the distance to the interaction region can be estimated and is well beyond 100 AU. At this great distance the plasma frequency at the terminal shock (100 to 200 Hz) is believed to be too small to explain the observed emission frequencies, which extend up to 3.6 kHz. For this reason, we have proposed that the interaction takes place at or near the heliopause, where remote sensing measurements show that the plasma frequency is in a suitable range (approximately 3 kHz) for explaining the radio emission. From the travel time and shock propagation speed, the radial distance to the heliopause has been calculated for various candidate solar events. After taking into account the likely deceleration of the shock, the heliopause is estimated to be in the range from about 110 to 160 AU.
收起
摘要 :
Observational evidence for a Forbush decrease (Fd) model in which a strong perturbation, originating from an energetic type 4 solar flare and propagating into the interplanetary space is the origin of Fds is discussed. This pertur...
展开
Observational evidence for a Forbush decrease (Fd) model in which a strong perturbation, originating from an energetic type 4 solar flare and propagating into the interplanetary space is the origin of Fds is discussed. This perturbation is bordered ahead by a shock which marks the front boundary of the modulated region. The lateral boundaries of the modulated region are located close to two perturbations which recur for several solar rotations. As the frontal perturbation propagates into interplanetary space, the modulated region between the two boundary streams rotates westward with the Sun; so the Fd effect is also observed in interplanetary regions not swept by the frontal perturbation. Flares not associated with Fd are produced by type 4 activity on the back side of the Sun.
收起
摘要 :
Interplanetary perturbations associated with Forbush decreases from 1965 to 1974 are studied. The systematic appearance of the results confirms that type 4 solar flares are the origin of these perturbations. The perturbation front...
展开
Interplanetary perturbations associated with Forbush decreases from 1965 to 1974 are studied. The systematic appearance of the results confirms that type 4 solar flares are the origin of these perturbations. The perturbation front is a wide (100 deg in longitude) driven shock followed by a magnetic blob and high speed plasma cloud of 0.5 AU average radial dimension at the Earth orbit, emitted in a short time interval (10 hr average) immediately following the type 4 solar flare. The Forbush decrease amplitude is correlated with an empirical parameter which caters for the importance of the shock and magnetic blob at the perturbation front. In the interplanetary regions in which the galactic cosmic ray intensity is depressed, low energy cosmic ray fluxes are observed.
收起
摘要 :
The two dimensional pattern of interplanetary shock waves is deduced by taking into account the solar longitude depen-dence of the time intervals between SSC geomagnetic storms and responsible flares. This pattern near the earth's...
展开
The two dimensional pattern of interplanetary shock waves is deduced by taking into account the solar longitude depen-dence of the time intervals between SSC geomagnetic storms and responsible flares. This pattern near the earth's orbit is not symmetric with respect to the meridian plane which crosses the position of the flare, and the highest speed of this wave propagation is observed in the direction about 30 degrees east of this meridian plane. The magnitude of the Forbush decreases of galactic cosmic rays also varies with the longitude positions of those flares. This is used to estimate the distribution of magnetic fields behind the shock waves. (Author)
收起
