排序方式： 共有50条查询结果，搜索用时 968 毫秒
1.
Global Heliospheric Parameters and Cosmic-Ray Modulation: An Empirical Relation for the Last Decades
We study empirical relations between the modulation of galactic cosmic rays quantified in terms of the modulation potential
and the following global heliospheric parameters: the open solar magnetic flux, the tilt angle of the heliospheric current
sheet, and the polarity of the heliospheric magnetic field. We show that a combination of these parameters explains the majority
of the modulation potential variations during the neutron monitor era 1951 – 2005. Two empirical models are discussed: a quasi-linear
model and a model assuming a power-law relation between the modulation potential and the magnetic flux. Both models describe
the data fairly well. These empirical models provide a simple tool for evaluating various cosmic-ray related effects on different
time scales. The models can be extended backwards in time or used for predictions, if the corresponding global heliospheric
variables can be independently estimated. 相似文献
2.
Persistent 22-year cycle in sunspot activity: Evidence for a relic solar magnetic field 总被引：1，自引：0，他引：1
We use the recently presented group sunspot number series to show that a persistent 22-year cyclicity exists in sunspot activity throughout the entire period of about 400 years of direct sunspot observations. The amplitude of this cyclicity is about 10% of the present sunspot activity level. A 22-year cyclicity in sunspot activity is naturally produced by the 22-year magnetic polarity cycle in the presence of a relic dipole magnetic field. Accordingly, a persistent 22-year cyclicity in sunspot activity gives an evidence for the existence of such a relic magnetic field in the Sun. The stable phase and the roughly constant amplitude of this cyclicity during times of very different sunspot activity level strongly support this interpretation. 相似文献
3.
We have estimated the upper and lower limits of sunspot activity, in terms of active day fraction during the Maunder minimum
(1645–1710), using raw information on individual daily observations (Hoyt and Schatten, 1998). Establishing the relation between
the sunspot activity and active day fraction after 1850, we evaluate the upper limit of annual group sunspot number during
the deep Maunder minimum (1645–1700) which does not exceed 4. The earlier finding of a dominant 22-year periodicity during
the Maunder minimum is verified and shown to be robust. Also we confirm that the start of the Maunder minimum was very abrupt. 相似文献
4.
G. A. Kovaltsov I. G. Usoskin L. G. Kocharov H. Kananen P. J. Tanskanen 《Solar physics》1995,158(2):395-398
Response of Alma-Ata neutron monitor for solar neutrons from the 15 June 1991 was studied. We considered this response as a test for various scenarios of proton acceleration during the flare. The analysis of neutron monitor is an evidence in favour of the assumption of two acts of proton acceleration at impulsive and post-impulsive phases of the flare. 相似文献
5.
We demonstrate that a simple solar dynamo model, in the form of a Parker migratory dynamo with random fluctuations of the
dynamo governing parameters and algebraic saturation of dynamo action, can at least qualitatively reproduce all the basic
features of solar Grand Minima as they are known from direct and indirect data. In particular, the model successfully reproduces
such features as an abrupt transition into a Grand Minimum and the subsequent gradual recovery of solar activity, as well
as mixed-parity butterfly diagrams during the epoch of the Grand Minimum. The model predicts that the cycle survives in some
form during a Grand Minimum, as well as the relative stability of the cycle inside and outside of a Grand Minimum. The long-term
statistics of simulated Grand Minima appears compatible with the phenomenology of the Grand Minima inferred from the cosmogenic
isotope data. We demonstrate that such ability to reproduce the Grand Minima phenomenology is not a general feature of the
dynamo models but requires some specific assumption, such as random fluctuations in dynamo governing parameters. In general,
we conclude that a relatively simple and straightforward model is able to reproduce the Grand Minima phenomenology remarkably
well, in principle providing us with a possibility of studying the physical nature of Grand Minima. 相似文献
6.
The solar wind modulates the flux of galactic cosmic rays impinging on Earth inversely with solar activity. Cosmic ray ionisation is the major source of air's electrical conductivity over the oceans and well above the continents. Differential solar modulation of the cosmic ray energy spectrum modifies the cosmic ray ionisation at different latitudes, varying the total atmospheric columnar conductance. This redistributes current flow in the global atmospheric electrical circuit, including the local vertical current density and the related surface potential gradient. Surface vertical current density and potential gradient measurements made independently at Lerwick Observatory, Shetland, from 1978 to 1985 are compared with modelled changes in cosmic ray ionisation arising from solar activity changes. Both the lower troposphere atmospheric electricity quantities are significantly increased at cosmic ray maximum (solar minimum), with a proportional change greater than that of the cosmic ray change. 相似文献
7.
8.
The method of active-day fraction (ADF) was proposed recently to calibrate different solar observers to standard observational conditions. The result of the calibration may depend on the overall level of solar activity during the observational period. This dependency is studied quantitatively using data of the Royal Greenwich Observatory by formally calibrating synthetic pseudo-observers to the full reference dataset. It is shown that the sunspot group number is precisely estimated by the ADF method for periods of moderate activity, may be slightly underestimated by 0.5?–?1.5 groups (\({\leq}\,10\%\)) for strong and very strong activity, and is strongly overestimated by up to 2.5 groups (\({\leq}\,30\%\)) for weak-to-moderate activity. The ADF method becomes inapplicable for the periods of grand minima of activity. In general, the ADF method tends to overestimate the overall level of activity and to reduce the long-term trends. 相似文献
9.
Agnieszka Gil Gennady A. Kovaltsov Vladimir V. Mikhailov Alexander Mishev Stepan Poluianov Ilya G. Usoskin 《Solar physics》2018,293(11):154
A usual event, called anisotropic cosmic-ray enhancement (ACRE), was observed as a small increase (\({\leq}\,5\%\)) in the count rates of polar neutron monitors during 12?–?19 UT on 07 June 2015. The enhancement was highly anisotropic, as detected only by neutron monitors with asymptotic directions in the southwest quadrant in geocentric solar ecliptic (GSE) coordinates. The estimated rigidity of the corresponding particles is \({\leq}\,1\) GV. No associated detectable increase was found in the space-borne data from the Geostationary Operational Environmental Satellite (GOES), the Energetic and Relativistic Nuclei and Electron (ERNE) on board the Solar and Heliospheric Observatory (SOHO), or the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) instruments, whose sensitivity was not sufficient to detect the event. No solar energetic particles were present during that time interval. The heliospheric conditions were slightly disturbed, so that the interplanetary magnetic field strength gradually increased during the event, followed by an increase of the solar wind speed after the event. It is proposed that the event was related to a crossing of the boundary layer between two regions with different heliospheric parameters, with a strong gradient of low-rigidity (\({<}\,1\) GV) particles. It was apparently similar to another cosmic-ray enhancement (e.g., on 22 June 2015) that is thought to have been caused by the local anisotropy of Forbush decreases, with the difference that in our case, the interplanetary disturbance was not observed at Earth, but passed by southward for this event. 相似文献
10.
We present the results of our studies of the cosmic-ray fluctuations in the frequency range 10−4−1.67 × 10−3 Hz based on energetic particle flux measurements on spacecraft in the solar wind, in the magnetosphere, and at Earth in the
11-year solar cycle. The cosmic-ray fluctuation spectrum is shown to have an 11-year modulation related to the solar cycle.
A different behavior of the level of energetic particle fluctuations measured in different regions of space is observed for
cosmic rays of different origins. We conclude that the new, previously unknown phenomenon of 11-year modulation of the cosmic-ray
fluctuation spectrum has been established. A possible explanation of this phenomenon is given. 相似文献