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1.
In this work the galactic cosmic ray modulation in relation to solar activity indices and heliospheric parameters during the years 1996??C?2010 covering solar cycle 23 and the solar minimum between cycles 23 and 24 is studied. A new perspective of this contribution is that cosmic ray data with a rigidity of 10 GV at the top of the atmosphere obtained from many ground-based neutron monitors were used. The proposed empirical relation gave much better results than those in previous works concerning the hysteresis effect. The proposed models obtained from a combination of solar activity indices and heliospheric parameters give a standard deviation <?10?% for all the cases. The correlation coefficient between the cosmic ray variations of 10?GV and the sunspot number reached a value of r=?0.89 with a time lag of 13.6±0.4 months. The best reproduction of the cosmic ray intensity is obtained by taking into account solar and interplanetary indices such as sunspot number, interplanetary magnetic field, CME index, and heliospheric current sheet tilt. The standard deviation between the observed and calculated values is about 7.15?% for all of solar cycle 23; it also works very well during the different phases of the cycle. Moreover, the use of the cosmic ray intensity of 10?GV during the long minimum period between cycles 23 and 24 is of special interest and is discussed in terms of cosmic ray intensity modulation. 相似文献
2.
The existence of the 22-year modulation of cosmic ray intensity is pointed out, using data of the ion chamber at Huancayo and the neutron monitors at Ottawa and Deep River for about four solar cycles. The modulation consists of two discrete states (high and low intensities), corresponding respectively to those of the polarity of the polar magnetic field of the Sun. This can be interpreted on the basis of the following hypothesis; when the polar magnetic field of the Sun is nearly parallel to the galactic magnetic field, they could easily connect with each other, so that galactic cosmic rays could intrude more easily into the heliomagnetosphere along the magnetic line of force, as compared with those in the anti-parallel state of the magnetic fields. The observed intensity difference between two states is about 4.3 ± 0.2% for neutron monitor (Pc = 1.5GV). The abnormal increase in proton (0.28–0.42 GV) and electron (0.41-3.24 GV) fluxes in the 20th solar cycle and the sudden appearance of anomalous components (He+, etc.) since 1972 can be also explained on the basis of the present hypothesis. The transition between the two states has a time lag behind the polarity reversal, depending on the cosmic ray rigidity, such as about 1 year for the neutron monitor (Pc = 1.5 GV) and about 3.5 years for low rigidity components (P < 1 GV). These time lags could be explained on the basis of the generalized Simpson's coasting solar wind model and the general diffusion-convection theory on some assumptions. 相似文献
3.
The diurnal variation of the galactic cosmic ray (GCR) count rates measured by a ground-based neutron monitor (NM) station represents an anisotropic flow of GCR at 1 AU. The variation of the local time of GCR maximum intensity (we call the phase) is thought in general to have a period of two sunspot cycles (22 years). However, other interpretations are also possible. In order to determine the cyclic behavior of GCR anisotropic variation more precisely, we have carried out a statistical study on the diurnal variation of the phase. We examined 54-year data of Huancayo (Haleakala), 40-year data from Rome, and 43-year data from Oulu NM stations using the ‘pile-up’ method and the F-test. We found that the phase variation has two components: of 22-year and 11-year cycles. All NM stations show mainly the 22-year phase variation controlled by the drift effect due to solar polar magnetic field reversal, regardless of their latitudinal location (cut-off rigidity). However, the lower the NM station latitude is (the higher the cut-off rigidity is), the higher is the contribution from the 11-year phase variation controlled by the diffusion effect due to the change in strength of the interplanetary magnetic fields associated with the sunspot cycle. 相似文献
4.
North/south directional telescopes operating at the surface and vertical and inclined telescopes operating at a depth of 60 m.w.e. underground in London have been employed to study changes in the cosmic ray solar diurnal variation over the past few years. In order to extend the study to the low rigidity end of the spectrum, results obtained by the NM64 neutron monitors operating at Deep River and Goose Bay in Canada have also been examined. The surface telescope data require that the full corotation amplitude of 0.59 per cent should have been observed during almost the entire solar cycle with the possible exception of the year 1965 when cosmic ray intensity was a maximum. However, the effective amplitude observed by neutron monitors during most of the solar cycle was only about 0.52 per cent and this reduction has been ascribed to the lower value of the exponent of the energy spectrum which prevails amongst the latitude sensitive primaries. Nevertheless, the upper limiting rigidity was varying during the course of the solar cycle, its value being high when solar activity was high and low when solar activity decreased. During 1965, even though the upper limiting rigidity assumed its lowest value, the free space amplitude was also diminished by a little over 10 per cent. Even though the theory of rigid corotation invoking a purely azimuthal streaming of the cosmic ray gas successfully predicts the free space amplitude, it fails to explain the phase changes observed by both types of monitor and which are quite significant. The underground data require that the component due to atmospheric temperature effects is negligibly small and that throughout the rigidity range covered by the recorder response, there is present an apparent anisotropy due to the orbital motion of the Earth around the Sun. Also the underground data roughly confirm the changes in upper limiting rigidity which were observed by the surface instruments. 相似文献
5.
The pressure-corrected hourly counting rate data of four neutron monitor stations have been employed to study the variation
of cosmic ray diurnal anisotropy for a period of about 50 years (1955–2003). These neutron monitors, at Oulu (
R
c = 0.78 GV), Deep River (
R
c = 1.07 GV), Climax (
R
c = 2.99 GV), and Huancayo (
R
c = 12.91 GV) are well distributed on the earth over different latitudes and their data have been analyzed. The amplitude of
the diurnal anisotropy varies with a period of one solar cycle (∼11 years), while the phase varies with a period of two solar
cycles (∼22 years). In addition to its variation on year-to-year basis, the average diurnal amplitude and phase has also been
calculated by grouping the days for each solar cycle, viz. 19, 20, 21, 22, and 23. As a result of these groupings over solar
cycles, no significant change in the diurnal vectors (amplitude as well as phase) from one cycle to other has been observed.
Data were analyzed by arranging them into groups on the basis of the polarity of the solar polar magnetic field and consequently
on the basis of polarity states of the heliosphere (
A > 0 and
A < 0). Difference in time of maximum of diurnal anisotropy (shift to earlier hours) is observed during
A < 0 (1970s, 1990s) polarity states as compared to anisotropy observed during
A > 0 (1960s, 1980s). This shift in phase of diurnal anisotropy appears to be related to change in preferential entry of cosmic
ray particles (via the helioequatorial plane or via solar poles) into the heliosphere due to switch of the heliosphere from
one physical/magnetic state to another following the solar polar field reversal. 相似文献
6.
Propagation of solar flare-associated interplanetary shock waves in the heliospheric meridional plane 总被引：4，自引：0，他引：4
We have analyzed 149 flare-associated shock wave events based on interplanetary scintillation (IPS) observational data. All of the flare-associated shock waves tend to propagate toward the low latitude region near the solar equator for flares that are located in both the solar northern and southern hemispheres. Also, the fastest propagation directions tend toward the heliospheric current sheet near 1 AU. We suggest that this tendency is caused by the dynamic action of near-Sun magnetic forces on the ejected coronal plasma that traverses the helmet-like magnetic topologies near the Sun outward to the classical topology that is essentially parallel to the heliospheric current sheet. 相似文献
7.
We show that the temporal variations of the integrated galactic cosmic-ray intensity at neutron monitor energies (approximately above 3 GeV) can be reproduced applying a semi-empirical 1-D diffusion-convection model for the cosmic-ray transport in interplanetary space. We divide the interplanetary region into `magnetic shells' and find the relative reduction that each shell causes to the cosmic-ray intensity. Then the cosmic-ray intensity at the Earth is reproduced by the successive influence of all shells between the Earth and the heliospheric termination shock. We find that the position of the termination shock does not significantly affect the cosmic-ray intensity although there are some differences between the results for a constant and a variable termination shock radius. We also reproduce the cosmic-ray intensity applying the analytical solution of the force-field approximation (Perko, 1987) and find that the results cannot fit the observed data. Our results are compared with the Climax (geomagnetic cut-off 3 GV) and Huancayo (geomagnetic cut-off 13 GV) neutron monitor measurements for almost two solar cycles (1976–1996). 相似文献
8.
Variations of the cosmic ray cut-off rigidities have been observed at mid latitudes during the magnetic storm period 16–18 December 1971. In the present paper the cut-off changes over Europe are determined on an hourly basis from the registrations of 10 European neutron monitor stations. As a first order approximation it is assumed that the observed cut-off variations originate from a spherical current sheet concentric with the Earth and with a current density proportional to the cosine of the geomagnetic latitude. Applying results obtained by Treiman (1953), the radii of the current sphere can then be deduced from the dependences of the relative cut-off rigidity variations on geomagnetic latitude. The sphere is found to be located between 4 and 6 Earth radii during the main phase of the magnetic storm on 17 December 1971. A comparison of these results with in situ measurements carried out in the equatorial plane by Explorer 45 shows good agreement. 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.
Using ground-based cosmic-ray (CR) observations on the worldwide network of neutron monitors, we have studied the variations in CR rigidity spectrum, anisotropy, and planetary system of geomagnetic cutoff rigidities during Forbush decreases in March-April 2001 by the global spectrographic method. By jointly analyzing ground-based and satellite measurements, we have determined the parameters of the CR rigidity spectrum that reflect the electromagnetic characteristics of the heliospheric fields in each hour of observations within the framework of the model of CR modulation by the heliosphere’s regular electromagnetic fields. The rigidity spectra of the variations and the relative changes in the intensity of CRs with rigidities of 4 and 10 GV in the solar-ecliptic geocentric coordinate system are presented in specific periods of the investigated events. 相似文献
11.
We have deduced the power-law rigidity spectra, J(P)=AP
–, and the spectral evolution of the solar flare events that occurred in the present solar activity cycle on 6 November 1997, 14 July 2000, and 15 and 18 April 2001. The implications of these results for the acceleration of high-energy protons are discussed. The analysis is based on the ratios of the Mt. Washington to the Durham neutron monitor count-rate increases during the solar flare events. These two neutron monitors are located at different elevations (828 and 1030 g cm–2, respectively) but at approximately the same geographical latitude and longitude. The proton spectra from 1 to 10 GV determined from the ratios of the count rate increases of the two neutron monitors are found to agree with those deduced from the global neutron monitor network or selected neutron monitors in 10 solar flare events from 1960 to 1990 for which comparative results are available. Thus the ratio method is quick, easy and reliable for deducing the spectral shape of solar flare protons at neutron monitor rigidities and for obtaining the spectral evolution as a function of time. 相似文献
12.
The Forbush decrease (Fd) of the Galactic cosmic ray (GCR) intensity and disturbances in the Earth’s magnetic field generally take place simultaneously and are caused by the same phenomenon, namely a coronal mass ejection (CME) or a shock wave created after violent processes in the solar atmosphere. The magnetic cut-off rigidity of the Earth’s magnetic field changes because of the disturbances, leading to additional changes in the GCR intensity observed by neutron monitors and muon telescopes. Therefore, one may expect distortion in the temporal changes in the power-law exponent of the rigidity spectrum calculated from neutron monitor data without correcting for the changes in the cut-off rigidity of the Earth’s magnetic field. We compare temporal changes in the rigidity spectrum of Fds calculated from neutron monitor data corrected and uncorrected for the geomagnetic disturbances. We show some differences in the power-law exponent of the rigidity spectrum of Fds, particularly during large disturbances of the cut-off rigidity of the Earth’s magnetic field. However, the general features of the temporal changes in the rigidity spectrum of Fds remain valid as they were found in our previous study. Namely, at the initial phase of the Fd, the rigidity spectrum is relatively soft and it gradually becomes hard up to the time of the minimum level of the GCR intensity. Then during the recovery phase of the Fd, the rigidity spectrum gradually becomes soft. This confirms that the structural changes of the interplanetary magnetic field turbulence in the range of frequencies of 10?6?–?10?5 Hz are generally responsible for the time variations in the rigidity spectrum we found during the Fds. 相似文献
13.
M. M. Molodensky 《Astronomy Letters》2001,27(9):590-595
The expansion of solar coronal plasma is considered for the model described in Koutchmy et al. (1999). In addition to a spherical solar surface, the initial configuration represents a heliospheric sheet of dense plasma in the dipole equatorial plane. The heliospheric-sheet current decreases with distance as 1/r 2, with its sign being opposite to the sign of the initial-dipole current. The latter follows from the fact that the plasma sheet is denser than the surrounding corona and that the equilibrium condition for the sheet in the gravitational and magnetic fields is satisfied. The field lines of this configuration are nearly straight. We have obtained a general solution of the steady-state MHD equations, which depends not only on distance r but also on latitude θ. Applicability of the solution to interpreting observational data, in particular, those obtained from the Ulysses spacecraft, is discussed. 相似文献
14.
Long-term variations of galactic cosmic rays were compared with the behavior of various solar activity indices and heliospheric
parameters during the current solar cycle. This study continues previous works where the cosmic-ray intensity for the solar
cycles 20, 21, and 22 was well simulated from the linear combination of the sunspot number, the number of grouped solar flares,
and the geomagnetic index A
p. The application of this model to the current solar cycle characterized by many peculiarities and extreme solar events led
us to study more empirical relations between solar-heliospheric variables, such as the interplanetary magnetic field, coronal
mass ejections, and the tilt of the heliospheric current sheet, and cosmic-ray modulation. By analyzing monthly cosmic-ray
data from the Neutron Monitor Stations of Oulu (cutoff rigidity 0.81 GV) and Moscow (2.42 GV) the contribution of these parameters
in the ascending, maximum, and descending phases of the cycle was investigated and it is shown that a combination of these
parameters reproduces the majority of the modulation potential variations during this cycle. The approach applied makes it
possible to better describe the behavior of cosmic rays in the epochs of the solar maxima, which could not be done before.
An extended study of the time profiles, the correlations, and the time lags of the cosmic-ray intensity against these parameters
using the method of minimizing RMS over all the considered period 1996 – 2006 determines characteristic properties of this
cycle as being an odd cycle. Moreover, the obtained hysteresis curves and a correlative analysis during the positive polarity
(qA>0, where q is the particle charge) and during the negative polarity (qA<0) intervals of the cycle result in significantly different behavior between solar and heliospheric parameters. The time
lag and the correlation coefficient of the cosmic-ray intensity are higher for the solar indices in comparison to the heliospheric
ones. A similar behavior also appears in the case of the intervals with positive and negative polarity of the solar magnetic
field. 相似文献
15.
H. S. Ahluwalia M. V. Alania A. Wawrzynczak R. C. Ygbuhay M. M. Fikani 《Solar physics》2014,289(5):1763-1782
The pressure corrected hourly data from the global network of cosmic ray detectors, measurements of the interplanetary magnetic field (IMF) intensity (B) at Earth’s orbit and its components B x , B y , B z (in the geocentric solar ecliptic coordinates) are used to conduct a comprehensive study of the galactic cosmic ray (GCR) intensity fluctuations caused by the halo coronal mass ejection of 13 May 2005. Distinct differences exist in GCR timelines recorded by neutron monitors (NMs) and multidirectional muon telescopes (MTs), the latter respond to the high rigidity portion of the GCR differential rigidity spectrum. The Forbush decrease (FD) onset in MTs is delayed (～5 h) with respect to the onset of a geomagnetic storm sudden commencement (SSC) and a large pre-increase is present in MT data before, during, and after the SSC onset, of unknown origin. The rigidity spectrum, for a range of GCR rigidities (≤200 GV), is a power law in rigidity (R) with a negative exponent (γ=?1.05) at GCR minimum intensity, leading us to infer that the quasi-linear theory of modulation is inconsistent with observations at high rigidities (>1 GV); the results support the force field theory of modulation. At present, we do not have a comprehensive model for the FD explaining quantitatively all the observational features but we present a preliminary model listing physical processes that may contribute to a FD timeline. We explored the connections between different phases of the FD and the power spectra of IMF components but did not find a sustained relationship. 相似文献
16.
The first recorded and analysed cosmic ray event since the Athens 3 NM-64 came into operation, that of 7 November 1970, is presented. The relative amplitude of the Forbush Decrease reached a value of (4.5 ± 0.3)% peak to peak which is comparatively large at a cut-off rigidity of 8.7 GV (Shea et al., 1968).According to the differential method (Amaldi et al., 1963 ; Bachelet et al, 1972) it has been computed that the slope of the primary differential rigidity spectrum varied at the Athens cut-off rigidity during the above mentioned F.D. by (6.3 ± 0.8)%.This information repairs the omission which was in the threshold rigidity region (8 ± 2) GV, which is quite important because the latitude curves change the algebraic sign of their curvatures (Geranios, 1971). 相似文献
17.
Galactic cosmic rays (GCRs) are modulated by the heliospheric magnetic field (HMF) both over decadal time scales (due to long-term, global HMF variations), and over time scales of a few hours (associated with solar wind structures such as coronal mass ejections or the heliospheric current sheet, HCS). Due to the close association between the HCS, the streamer belt, and the band of slow solar wind, HCS crossings are often associated with corotating interaction regions where fast solar wind catches up and compresses slow solar wind ahead of it. However, not all HCS crossings are associated with strong compressions. In this study we categorize HCS crossings in two ways: Firstly, using the change in magnetic polarity, as either away-to-toward (AT) or toward-to-away (TA) magnetic field directions relative to the Sun and, secondly, using the strength of the associated solar wind compression, determined from the observed plasma density enhancement. For each category, we use superposed epoch analyses to show differences in both solar wind parameters and GCR flux inferred from neutron monitors. For strong-compression HCS crossings, we observe a peak in neutron counts preceding the HCS crossing, followed by a large drop after the crossing, attributable to the so-called ‘snow-plough’ effect. For weak-compression HCS crossings, where magnetic field polarity effects are more readily observable, we instead observe that the neutron counts have a tendency to peak in the away magnetic field sector. By splitting the data by the dominant polarity at each solar polar region, we find that the increase in GCR flux prior to the HCS crossing is primarily from strong compressions in cycles with negative north polar fields due to GCR drift effects. Finally, we report on unexpected differences in GCR behavior between TA weak compressions during opposing polarity cycles. 相似文献
18.
We study solar modulation of galactic cosmic rays (GCRs) during the deep solar minimum, including the declining phase, of solar cycle 23 and compare the results of this unusual period with the results obtained during similar phases of the previous solar cycles 20, 21, and 22. These periods consist of two epochs each of negative and positive polarities of the heliospheric magnetic field from the north polar region of the Sun. In addition to cosmic-ray data, we utilize simultaneous solar and interplanetary plasma/field data including the tilt angle of the heliospheric current sheet. We study the relation between simultaneous variations in cosmic ray intensity and solar/interplanetary parameters during the declining and the minimum phases of cycle 23. We compare these relations with those obtained for the same phases in the three previous solar cycles. We observe certain peculiar features in cosmic ray modulation during the minimum of solar cycle 23 including the record high GCR intensity. We find, during this unusual minimum, that the correlation of GCR intensity is poor with sunspot number (correlation coefficient R=?0.41), better with interplanetary magnetic field (R=?0.66), still better with solar wind velocity (R=?0.80) and much better with the tilt angle of the heliospheric current sheet (R=?0.92). In our view, it is not the diffusion or the drift alone, but the solar wind convection that is the most likely additional effect responsible for the record high GCR intensity observed during the deep minimum of solar cycle 23. 相似文献
19.
We analyze the evolution of cosmic ray intensity detected by six neutron monitors located at high altitude from 1990 to 1999,
that includes most of solar cycle 22 and the start of cycle 23. This set of neutron monitors covers a wide range of geomagnetic
cutoff rigidities. We discuss the most significant characteristics of the cosmic ray modulation during the period as: the
extraordinary decreases produced by the events of the first half of 1991, the significant two step evolution of the recovery
phase of solar cycle 22 and the start of cycle 23. We also determine the rigidity dependence of the different phases of the
modulation cycle. Cosmic ray intensity correlations with several solar activity parameters as sunspots, microwave flux at
10.7 cm and solar flares and with the intensity of the interplanetary magnetic field are studied. 相似文献
20.
I. Sabbah 《Solar physics》2007,245(1):207-217
Neutron monitor data observed at Climax (CL) and Huancayo/Haleakala (HU/HAL) have been used to calculate the amplitude A of the 27-day variation of galactic cosmic rays (CRs). The median primary rigidity of response, R
m, for these detectors encompasses the range 18 ≤R
m≤46 GV and the threshold rigidity R
0 covers the range 2.97≤R
0≤12.9 GV. The daily average values of CR counts have been harmonically analyzed for each Bartels solar rotation (SR) during
the period 1953 – 2001. The amplitude of the 27-day CR variation is cross-correlated to solar activity as measured by the
sunspot number R, the interplanetary magnetic field (IMF) strength B, the z-component B
z
of the IMF vector, and the tilt angle ψ of the heliospheric current sheet (HCS). It is anticorrelated to the solar coronal
hole area (CHA) index as well as to the solar wind speed V. The wind speed V leads the amplitude by 24 SRs. The amplitude of the 27-day CR variation is better correlated to each of the these parameters
during positive solar polarity (A>0) than during negative solar polarity (A<0) periods. The CR modulation differs during A>0 from that during A<0 owing to the contribution of the z-component of the IMF. It differs during A
1>0 (1971 – 1980) from that during A
2>0 (1992 – 2001) owing to solar wind speed. 相似文献