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1.
We studied the cosmic ray intensity variation due to interplanetary magnetic clouds during an unusual class of low amplitude
anisotropic wave train events. The low amplitude anisotropic wave train events in cosmic ray intensity have been identified
using the data of ground based Deep River neutron monitor and studied during the period 1981–1994. Even though the occurrence
of low amplitude anisotropic wave trains does not depend on the onset of interplanetary magnetic clouds, but the possibility
of occurrence of these events cannot be overlooked during the periods of the interplanetary magnetic cloud events. It is observed
that the solar wind velocity remains higher (> 300) than normal and the interplanetary magnetic field B remains lower than normal on the onset of the interplanetary magnetic cloud during the passage of low amplitude wave trains.
It is also noted that the proton density remains significantly low during high solar wind velocity, which is expected. The
north south component of interplanetary magnetic field Bz turns southward to one day before the arrival of cloud and remains in the southward direction after the arrival of a cloud.
During these events the cosmic ray intensity is found to increase with increase of solar wind velocity. The superposed epoch
analysis of cosmic ray intensity for these events during the onset of interplanetary magnetic clouds reveals that the decrease
in cosmic ray intensity starts not at the onset of the cloud but after a few days. The cosmic ray intensity increases on arrival
of the magnetic cloud and decreases gradually after the passage of the magnetic cloud. 相似文献
2.
S. N. Kuznetsov V. G. Kurt I. N. Myagkova B. Yu. Yushkov K. Kudela 《Solar System Research》2006,40(2):104-110
The SONG instrument onboard the CORONAS-F satellite recorded gamma-ray emission with energy above 500 keV in 28 solar flares over three years of its in-orbit operation. According to the GOES classification, the X-ray importance of these flares lay within the range M1.4-X28. The gamma-ray energy recorded by SONG exceeded 4 MeV in 16 flares. Gamma-ray emission with energy up to 100 MeV was recorded in three events, more specifically, on August 25, 2001, October 28, 2003, and November 4, 2003. Increases in the count rate in the SONG channels that recorded neutrons with energies above 20 MeV were found during these three events. The energies of the recorded neutrons were estimated for the neutron increases. The time dependence of the neutron increases was compared with data from high-altitude ground-based neutron monitors that could, in principle, record the arrival of high-energy neutrons from the Sun. It should be noted that we detected series of flares with gamma-ray emission generated by the same active region (AR). The series in the last decade of August 2002 (AR NOAA 0069), the end of May 2003 (AR NOAA 0365), and the famous period of extreme solar activity in October–November 2003 associated with AR NOAA 0486 and AR NOAA 0501 are quite revealing. The catalog can be of use for future statistical and correlation analyses of solar flares. 相似文献
3.
Cosmic-ray intensity data recorded with the ground-based neutron monitor at Deep River have been investigated taking into
account the associated interplanetary magnetic field and solar-wind plasma data during 1981 – 1994. A large number of days
having abnormally high or low amplitudes for five or more successive days as compared to the annual average amplitude of diurnal
anisotropy have been taken as high- or low-amplitude anisotropic wave-train events. The amplitude of the diurnal anisotropy
of these events is found to increase on days with a magnetic cloud as compared to the days prior to the event, and it is found
to decrease during the later period of the event as the cloud passes the Earth. The high-speed solar-wind streams do not play
any significant role in causing these types of events. However, corotating solar-wind streams produce significant deviations
in cosmic-ray intensity during high- and low-amplitude events. The interplanetary disturbances (magnetic clouds) are also
effective in producing cosmic-ray decreases. Hα solar flares have a good positive correlation with both the amplitude and
direction of the anisotropy for high-amplitude events, while the principal magnetic storms have a good positive correlation
with both amplitude and direction of the anisotropy for low-amplitude events. The source responsible for these unusual anisotropic
wave trains in cosmic rays has been proposed. 相似文献
4.
5.
The cosmic-ray (CR) time series were compared with the green 530.3 nm coronal emission line intensity over the period 1951–2003.
There is a clear asymmetry in the cross-correlation between the cosmic rays and green emission corona for the even- and odd-numbered
solar cycles, where a time lag is ranging between 0 and 380 days. While over the period 1954–1964 and 1978–1985 the time lag
is above 200 days, over the period 1965–1976 and 1986–1995 the time lag is below 130 days. A possible reason for the lag asymmetry
is discussed. The cross-correlations between the cosmic rays and Wolf sunspot number over the period 1951–2003 is also presented. 相似文献
6.
E. Samara A. Smponias I. Lytrosyngounis D. Lingri H. Mavromichalaki C. Sgouropoulos 《Solar physics》2018,293(4):67
Although the current Solar Cycle 24 is characterized by low solar activity, an intense geomagnetic storm (G4) was recorded in June 2015. It was a complex phenomenon that began on 22 June 2015 as the result of intense solar activity, accompanied by several flares and coronal mass ejections that interacted with the Earth’s magnetic field. A Forbush decrease was also recorded at the neutron monitors of the worldwide network, with an amplitude of 8.4%, and in its recovery phase, a second Forbush decrease followed, with an amplitude of 4.0% for cosmic rays of 10 GV obtained with the global survey method. The Dst index reached a minimum value of ?204 nT that was detected on 23 June 2015 at 05:00?–?06:00 UT, while the Kp index reached the value eight. For our analysis, we used hourly cosmic-ray intensity data recorded by polar, mid-, and high-latitude neutron monitor stations obtained from the High Resolution Neutron Monitor Database. The cosmic-ray anisotropy variation at the ecliptic plane was also estimated and was found to be highly complex. We study and discuss the unusual and complex cosmic-ray and geomagnetic response to these solar events. 相似文献
7.
The solar soft X-ray (XUV) radiation is important for upper atmosphere studies as it is one of the primary energy inputs and
is highly variable. The XUV Photometer System (XPS) aboard the Solar Radiation and Climate Experiment (SORCE) has been measuring
the solar XUV irradiance since March 2003 with a time cadence of 10 s and with about 70% duty cycle. The XPS measurements
are between 0.1 and 34 nm and additionally the bright hydrogen emission at 121.6 nm. The XUV radiation varies by a factor
of ∼2 with a period of ∼27 days that is due to the modulation of the active regions on the rotating Sun. The SORCE mission
has observed over 20 solar rotations during the declining phase of solar cycle 23. The solar XUV irradiance also varies by
more than a factor of 10 during the large X-class flares observed during the May–June 2003, October–November 2003, and July
2004 solar storm periods. There were 7 large X-class flares during the May–June 2003 storm period, 11 X-class flares during
the October–November 2003 storm period, and 6 X-class flares during the July 2004 storm period. The X28 flare on 4 November
2003 is the largest flare since GOES began its solar X-ray measurements in 1976. The XUV variations during the X-class flares
are as large as the expected solar cycle variations. 相似文献
8.
Ambika Singh Anil Kumar Tiwari S. P. Agrawal 《Journal of Astrophysics and Astronomy》2010,31(2):89-96
A detailed study has been conducted on the long-term changes in the diurnal variation of cosmic rays in terms of high and
low amplitude wave trains event (HAEs/LAEs) during the period 1996–2008 (solar cycle 23), using the neutron monitor data from
Kiel neutron monitoring station. As such, 17 HAE and 48 LAE cases have been detected and analyzed. These HAEs appear quite
dominantly during the declining phase as well as near the maximum of the solar activity cycle 23. In contrast, the low amplitude
events (LAEs) are inversely correlated with solar activity cycle. In fact, LAEs appear quite dominantly during the minimum
phase of the solar activity. When we compare our results for diurnal phase with that observed on an annual average basis,
we notice no significant diurnal phase shift for HAEs as well as for LAEs. Moreover, we find that the high-speed solar wind
streams (HSSWS) do not play any significant role in causing these variations. These results are discussed on the basis of
that observed in earlier cycles. 相似文献
9.
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
10.
A lead-free neutron monitor operating at High Altitude Research Laboratory (HARL), Gulmarg optimized for detecting 2.45 MeV neutron bursts produced during the atmospheric lightning discharges is also concurrently used for studying background neutron component present in the atmosphere. These background neutrons are produced due to the interaction of primary cosmic rays with the atmospheric constituents. In order to study and extract the information about the yield of the neutron production during transient atmospheric lightning discharges, the system is continuously operated to monitor and record the cosmic ray produced background secondary neutrons in the atmosphere. The data analysis of the background neutrons recorded by Lead-Free Gulmarg Neutron Monitor (LFGNM) has convincingly established that the modulation effects due to solar activity phenomena compare very well with those monitored by the worldwide IGY or NM64 type neutron monitors which have optimum energy response relatively towards the higher energy regime of the cosmic rays. The data has revealed various types of modulation phenomena like diurnal variation, Forbush decrease etc. during its entire operational period. However, a new kind of a periodic/seasonal variation pattern is also revealed in the data from September 2007 to September 2012, which is seen to be significantly consistent with the data recorded by Emilio Segre observatory, Israel (ESOI) Neutron Monitor. Interestingly, both these neutron monitors have comparable latitude and altitude. However, the same type of consistency is not observed in the data recorded by the other conventional neutron monitors operating across the globe. 相似文献
11.
M. S. Potgieter E. E. Vos M. Boezio N. De Simone V. Di Felice V. Formato 《Solar physics》2014,289(1):391-406
The last solar minimum activity period, and the consequent minimum modulation conditions for cosmic rays, was unusual. The highest levels of galactic protons were recorded at Earth in late 2009 in contrast to expectations. Proton spectra observed for 2006 to 2009 from the PAMELA cosmic ray detector on-board the Resurs-DK1 satellite are presented together with the solutions of a comprehensive numerical model for the solar modulation of cosmic rays. The model is used to determine what mechanisms were mainly responsible for the modulation of protons during this period, and why the observed spectrum for 2009 was the highest ever recorded. From mid-2006 until December 2009 we find that the spectra became significantly softer because increasingly more low energy protons had reached Earth. To simulate this effect, the rigidity dependence of the diffusion coefficients had to decrease significantly below ～?3 GeV. The modulation minimum period of 2009 can thus be described as relatively more ‘diffusion dominated’ than previous solar minima. However, we illustrate that drifts still had played a significant role but that the observable modulation effects were not as well correlated with the waviness of the heliospheric current sheet as before. Protons still experienced global gradient and curvature drifts as the heliospheric magnetic field had decreased significantly until the end of 2009, in contrast to the moderate decreases observed during previous minimum periods. We conclude that all modulation processes contributed to the observed increases in the proton spectra for this period, exhibiting an intriguing interplay of these major mechanisms. 相似文献
12.
V. N. Ishkov 《Solar System Research》2005,39(6):453-461
The main properties of the current cycle match almost completely those of average-magnitude solar cycles, and some of the features of the current cycle may indicate a change in the generation mode of magnetic fields in the solar convection zone. In this case, the Sun enters a period of intermediate and weak cycles of solar activity (SA) in terms of the Wolf numbers, which may last for 50 to 100 years. This change may result in further pollution of the Earth's environment (near-Earth space) due to the unfavorable regime of removing cosmic garbage from low-Earth orbit, the substantial increase of the radiation background in near space (the weakening of interplanetary magnetic fields will result in an increased concentration of galactic cosmic rays in the heliosphere), and other, possibly unfavorable, consequences. The main development stages of the 23rd solar-activity cycle are the following: the minimum of the 22nd solar cycle, May 1996 (W*=8.0); the beginning of the growth phase, September 1997; the maximum of the smoothed relative sunspot number, April, 2000; the global polarity reversal of the general solar magnetic field, July to December 2000; the secondary maximum of the relative sunspot number, November 2001; the maximum of the 10.7-cm radio flux, February 2002; the phase of the cycle maximum, October 1999 to June 2002; the beginning of the decrease phase, July 2002; the most powerful flare events of the current cycle, October to November 2003; and the likely point of minimum of the current SA cycle, November to December 2006. 相似文献
13.
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
14.
Galactic cosmic rays (GCRs) encounter an outward-moving solar wind with cyclic magnetic-field fluctuation and turbulence. This causes convection and diffusion in the heliosphere. The GCR counts from the ground-based neutron monitor stations show intensity changes that are anti-correlated with the sunspot numbers with a lag of a few months. GCRs experience various types of modulation from different solar activity features and influence space weather and the terrestrial climate. In this work, we investigate certain aspects of the GCR modulation at low cut-off rigidity (R c≈1 GV) in relation to some solar and geomagnetic indices for the entire solar cycle 23 (1996?–?2008). We separately study the GCR modulation during the ascending phase of cycle 23 including its maximum (1996?–?2002) and the descending phase including its minimum (2003?–?2008). We find that during the descending phase, the GCR recoveries are much faster than those of the solar parameters with negative time-lag. The results are discussed in light of modulation models, including drift effects and previous results. 相似文献
15.
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
16.
17.
C. Plainaki H. Mavromichalaki A. Belov E. Eroshenko M. Andriopoulou V. Yanke 《Solar physics》2010,264(1):239-254
In this work we present a cosmic ray model that couples primary solar cosmic rays at the top of the Earth’s atmosphere with
the secondary ones detected at ground level by neutron monitors during Ground-Level Enhancements (GLEs). The Neutron Monitor
Based Anisotropic GLE Pure Power Law (NMBANGLE PPOLA) model constitutes a new version of the already existing NMBANGLE model,
differing in the solar cosmic ray spectrum assumed. The total output of the model is a multi-dimensional GLE picture that
reveals part of the characteristics of the big solar proton events recorded at ground level. We apply both versions of the
model to the GLE of 15 April 2001 (GLE60) and compare the results. 相似文献
18.
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
19.
Solar circumstances have been evaluated for January 28, 1967, the date of an observed ground level enhancement of cosmic rays
which was not preceded by observation of a suitably great Hα flare. On the visible solar hemisphere, a bright subflare at
S23° E19° occurred in appropriate time association with the cosmic ray event, and was accompanied by weak X-ray enhancement
and radio frequency emission. If this flare, alone, or in combination with other minor flares observed on the visible hemisphere
on January 28 was the source of the energetic cosmic rays recorded on that date, then current thinking regarding the characteristics
of cosmic ray flares must be modified.
An initial study of probable circumstances on the invisible hemisphere did not lead to the immediate recognition of amajor center of activity as the probable source of a cosmic ray flare. Further evaluation of all centers of activity on the invisible
hemisphere identified one region, McMath Plage No. 8687, 64° beyond the west limb, as the most plausible, possible site for
the cosmic ray flare on January 28, 1967. The location of this region is in accord with the source-position deduced in Lockwood's
analysis (1968) of the cosmic ray event. This center of activity could not have been more than 5 days old on January 28, 1967.
The interval of major activity in the region was confined primarily to the invisible hemisphere. The occurrence of an ‘isolated’
major flare in the region on February 13, 1967 is discussed. The present study exemplifies the partial nature of solar observations
which are limited to the visible hemisphere.
The possible role of exceptional geomagnetic calm, 1963–1967, in permitting atypical cosmic ray enhancements, as on January
28, 1967, is mentioned. 相似文献
20.
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