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1.
Extreme-ultraviolet data from EIT/SOHO (1996–2002), soft X-ray data from Yohkoh (1991–2001), and magnetic field data from MDI/SOHO (1996–2002) and Kitt Peak Observatory, NSO/NOAO (1991–2002) are analyzed
together in the form of synoptic maps for the investigation of solar cycle variations of the corona and their relation to
the magnetic field. These results show new interesting relations between the evolution of the topological structure of the
corona, coronal heating and the large-scale magnetic field. The long-lived coronal structures are related to complexes of
solar activity and display quasi-periodic behavior (in the form of impulses of coronal activity) with periods of 1.0–1.5 year,
in the axisymmetric distribution of EUV and X-ray fluxes during the current solar cycle 23. In particular, during the second
maximum of this cycle the solar corona became somewhat hotter than it was in the period of the first maximum. 相似文献
2.
The north – south (N – S) asymmetry of solar activity is investigated by using the data on coronal green-line brightness and
total number and total area of sunspots over the period of 1939 – 2001. Typical time variations of the N – S asymmetry are
found to be consonant in these indices. Quasi-biennial oscillations (QBO) of solar activity are well recognizable in the N – S
asymmetry of the examined indices. Moreover, the QBO are much better manifested in the N – S asymmetry of the individual indices
than in the original (N plus S) indices. The time variations of relative QBO power are synchronous for the N – S asymmetry
of various solar activity indices whereas such a synchronization is weaker for the indices themselves. It is revealed that
the relative QBO power found in the N – S asymmetry of the studied indices has a negative correlation with the value of the
N – S asymmetry itself. The findings indicate that the N – S asymmetry should be regarded as a fundamental phenomenon of solar
activity similarly manifested in different activity indices. These findings should be taken into account when any dynamo theory
of solar activity is constructed. 相似文献
3.
We study variations of the lifetimes of high-ℓ solar p modes in the quiet and active Sun with the solar activity cycle. The lifetimes in the degree range ℓ=300 – 600 and ν=2.5 – 4.5 mHz were computed from SOHO/MDI data in an area including active regions and quiet Sun using the time – distance
technique. We applied our analysis to the data in four different phases of solar activity: 1996 (at minimum), 1998 (rising
phase), 2000 (at maximum), and 2003 (declining phase). The results from the area with active regions show that the lifetime
decreases as activity increases. The maximal lifetime variations are between solar minimum in 1996 and maximum in 2000; the
relative variation averaged over all ℓ values and frequencies is a decrease of about 13%. The lifetime reductions relative to 1996 are about 7% in 1998 and about
10% in 2003. The lifetime computed in the quiet region still decreases with solar activity, although the decrease is smaller.
On average, relative to 1996, the lifetime decrease is about 4% in 1998, 10% in 2000, and 8% in 2003. Thus, measured lifetime
increases when regions of high magnetic activity are avoided. Moreover, the lifetime computed in quiet regions also shows
variations with the activity cycle. 相似文献
4.
Mykola I. Pishkalo 《Solar physics》2006,233(2):277-290
We have investigated the correlation between the relative sunspot number and tilt of the heliospheric current sheet (HCS)
in solar cycles 21–23. Strong and highly significant positive correlation (r > 0.8, P < 0.001) was found for corresponding data in the time interval from May 1976 through December 2004. Cross-correlation analysis
does not reveal any time shift between the data sets. Reconstructed values of the HCS tilt, for the time interval before 1976,
are found using sunspot numbers. To take different amplitude of solar cycles into account they were then normalized to zero
in the minima of the solar activity and to average in solar cycles 21–23 maximal calculated HCS tilt in the maxima. These
normalized reconstructed HCS data are compared with the angular positions of the brightest coronal streamers observed during
total solar eclipses in 1870–2002, and their agreement is better for the minima of the solar activity than for the maxima. 相似文献
5.
We analyze the high-frequency drift radio structures observed by the spectrometer at Purple Mountain Observatory (PMO) over
the frequency range of 4.5 – 7.5 GHz during the 18 March 2003 solar flare. The drifting structures take place before the soft
X-ray maximum, almost at the maximum of hard X-ray flux at 25 – 50 keV. For the first time, the positive drift in this kind
of radio structures is detected in such a high frequency range. Their global drifting rate is roughly estimated as 3.6 GHz s−1. They appear in four groups, lasting in total for less than 6 s, and have a broad bandwidth of more than 2 GHz but a smaller
ratio of the bandwidth of the drifting structures to mean frequency than that of the lower frequency range. The lifetime of
each individual burst in this event can be derived by using the high temporal resolution of the spectrometer at PMO and has
an average value of 36.3 ms. Since the negative drifting structures observed in the 0.6 – 4.5 GHz frequency range were interpreted
to be a radio signature of a plasmoid ejected upward (moving out of the Sun), the present observation may imply that it is
possible for a plasmoid to move downward during a solar flare. However, for a confirmation of this suggestion direct radio
imaging observation would be needed. 相似文献
6.
R. P. Kane 《Solar physics》2006,233(1):107-115
This paper examines the variations of coronal mass ejections (CMEs) and interplanetary CMEs (ICMEs) during solar cycle 23
and compares these with those of several other indices. During cycle 23, solar and interplanetary parameters had an increase
from 1996 (sunspot minimum) to ∼2000, but the interval 1998–2002 had short-term fluctuations. Sunspot numbers had peaks in
1998, 1999, 2000 (largest), 2001 (second largest), and 2002. Other solar indices had matching peaks, but the peak in 2000
was larger than the peak in 2001 only for a few indices, and smaller or equal for other solar indices. The solar open magnetic
flux had very different characteristics for different solar latitudes. The high solar latitudes (45∘–90∘) in both N and S hemispheres had flux evolutions anti-parallel to sunspot activity. Fluxes in low solar latitudes (0∘–45∘) evolved roughly parallel to sunspot activity, but the finer structures (peaks etc. during sunspot maximum years) did not
match with sunspot peaks. Also, the low latitude fluxes had considerable N–S asymmetry. For CMEs and ICMEs, there were increases
similar to sunspots during 1996–2000, and during 2000–2002, there was good matching of peaks. But the peaks in 2000 and 2001
for CMEs and ICMEs had similar sizes, in contrast to the 2000 peak being greater than the 2001 peak for sunspots. Whereas
ICMEs started decreasing from 2001 onwards, CMEs continued to remain high in 2002, probably due to extra contribution from
high-latitude prominences, which had no equivalent interplanetary ICMEs or shocks. Cosmic ray intensity had features matching
with those of sunspots during 2000–2001, with the 2000 peak (on a reverse scale, actually a cosmic ray decrease or trough)
larger than the 2001 peak. However, cosmic ray decreases started with a delay and ended with a delay with respect to sunspot
activity. 相似文献
7.
Arvind Bhatnagar 《Journal of Astrophysics and Astronomy》2006,27(2-3):59-78
In this presentation we briefly describe the Sun through large number of illustrations and pictures of the Sun taken from
early times to the present day space missions. The importance of the study of the Sun is emphasized as it is the nearest star
which presents unparallelled views of surface details and numerous phenomena. Our Sun offers a unique celestial laboratory
where a large variety of phenomena take place, ranging in temporal domain from a few milliseconds to several decades, in spatial
domain from a few hundred kilometers to thousands of kilometers, and in the temperature domain from a few thousand degrees
to several million degrees. Its mass motion ranges from thousandths to thousands of kilometers per second. Such an object
provides us with a unique laboratory to study the state of matter in the Universe.
The existing solar ground-based and space missions have already revealed several mysteries of the outer environment of our
Sun and much more is going to come in the near future from planned new sophisticated ground-based solar telescopes and Space
missions.
The new technique of helioseismology has unravelled many secrets of the solar interior and has put the Standard Solar Model
(SSM) on firm footing. The long-standing problem of solar neutrinos has been recently sorted out, and even the ‘back side’
view of the Sun can be seen using the technique of holographic helioseismology. 相似文献
8.
Baolin Tan 《Astrophysics and Space Science》2011,332(1):65-72
Based on analysis of the annual averaged relative sunspot number (ASN) during 1700–2009, 3 kinds of solar cycles are confirmed:
the well-known 11-yr cycle (Schwabe cycle), 103-yr secular cycle (numbered as G1, G2, G3, and G4, respectively since 1700);
and 51.5-yr Cycle. From similarities, an extrapolation of forthcoming solar cycles is made, and found that the solar cycle
24 will be a relative long and weak Schwabe cycle, which may reach to its apex around 2012–2014 in the vale between G3 and
G4. Additionally, most Schwabe cycles are asymmetric with rapidly rising-phases and slowly decay-phases. The comparisons between
ASN and the annual flare numbers with different GOES classes (C-class, M-class, X-class, and super-flare, here super-flare
is defined as ≥ X10.0) and the annal averaged radio flux at frequency of 2.84 GHz indicate that solar flares have a tendency:
the more powerful of the flare, the later it takes place after the onset of the Schwabe cycle, and most powerful flares take
place in the decay phase of Schwabe cycle. Some discussions on the origin of solar cycles are presented. 相似文献
9.
In an earlier research the employment of a radiation transport model with angle-dependent partial frequency redistribution,
self-absorption by interplanetary hydrogen, realistic solar HLyαemission profile, and a time dependent `hot' hydrogen model to analyze 5 interplanetary HLyα glow spectra obtained with theHubble–Space–Telescope–GHRS spectrometer, has not resulted in unequivocal determination of
a set of thermodynamical parameters of the interstellar hydrogen The residual discrepancies between the model and the data
concern the observations performed within an interval of 1 year close to the solar minimum from very similar lines of sight.
In this paper we investigate by calculating interplanetary HLyα lines with the use of a one hydrogen distribution and several solar HLyα line profiles whether this residual may be caused by possible variations in time of the shape of the solar HLyα emission line profile which cause variable illuminations of the interplanetary gas. These variations of illuminations cause
variations in Doppler shift of the resonant interplanetary HLyα line that can amount to ≃ 4 km s-1in the line peak. Consequently we conclude that without adequate knowledge of the solar HLyα emission line profile during spectral observations of the interplanetary hydrogen gas it is impossible to obtain an agreement
between models and observations better than by this value.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
This contribution is a follow-up to the recent paper of Kuznetsov et al. (Contrib. Astron. Obs. Skalnaté Pleso
36, 85, 2006) on the ground level enhancement (GLE) on 20 January 2005. We focused on a study of Forbush decrease (FD) of 17 – 18 and
21 – 22 January 2005, respectively. The data from the neutron monitor at Lomnicky Štít (1 min counts) and from the Geomagnetic
Observatory in Hurbanovo, both in Slovakia, were used as the basis for our investigation. The data on magnetic field and solar
wind from GOES 10 and 12, SOHO-CELIAS, ACE and WIND satellites were used for better understanding of the global evolution
of the event. The magnetic field is transformed to the RTN (Radial – Tangential – Normal) system where only the disturbed
part of the field is compared, i.e., daily variations and a constant part are subtracted. The field reduction method is described. Our results are temporal vector
diagrams of variation of all parameters at all positions from where we used the data. The amplitudes of |B| exceed 100 nT and variations during the arrival of the wavefront of CME take place simultaneously at the ground-based station
and at GOES satellites. The character of the variations is as if there would be regions with the dominant electric charge
of opposite signs, or electric currents with different orientations in the CME. On the basis of the values v
p and n
p and using certain assumptions we determined the mass of CME on 17 January and 21 January, respectively, of 1012 kg. A decrease of the cosmic ray level runs suddenly (during 10 minutes), starting, however, about two hours after a sudden
change of the magnetic field. 相似文献
11.
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
12.
Forecasting space weather more accurately from solar observations requires an understanding of the variations in physical
properties of interplanetary (IP) shocks as solar activity changes. We examined the characteristics (occurrence rate, physical
parameters, and types of shock driver) of IP shocks. During the period of 1995 – 2001, a total of 249 forward IP shocks were
observed. In calculating the shock parameters, we used the solar wind data from Wind at the solar minimum period (1995 – 1997) and from ACE since 1998 including the solar maximum period (1999 – 2001). Most
of IP shocks (68%) are concentrated in the solar maximum period. The values of physical quantities of IP shocks, such as the
shock speed, the sonic Mach number, and the ratio of plasma density compression, are larger at solar maximum than at solar
minimum. However, the ratio of IMF compression is larger at solar minimum. The IP shock drivers are classified into four groups:
magnetic clouds (MCs), ejecta, high speed streams (HSSs), and unidentified drivers. The MC is the most dominant and strong
shock driver and 150 out of total 249 IP shocks are driven by MCs. The MC is a principal and very effective shock driver not
only at solar maximum but also at solar minimum, in contrast to results from previous studies, where the HSS is considered
as the dominant IP shock driver. 相似文献
13.
A one-dimensional numerical model with a size distribution of aerosol particles in Martian atmosphere is developed. The model
incorporates detailed microphysics and turbulent transport. Dust particles suspended in the Martian atmosphere play a role
of cloud condensation nuclei. Diurnal cycle of condensational processes is obtained on the basis of GCM temperature profiles.
An effective radius of ice particles is 1–2 μm near the lower boundary of cloud layer and 0.2–0.3 μm at the altitude of 50–60
km. These results are consistent with solar infrared occultations by SPICAM experiment on Mars-Express. Near-surface fogs
may form under specific conditions. The connections of condensational processes and cloud macroscopic parameters on microphysical
properties of aerosol particles are main focus of this paper. In particular, the dependence on variations of cloud condensation
nuclei contact parameter is analyzed, taking into account new experimental data of adsorption properties of minerals at low
temperatures. 相似文献
14.
The periodicity of climatic processes along the Russian Arctic Ocean coast has been studied by analyzing the tree-ring chronologies
for the regions close to the northern timberline. The wavelet analysis of annual series of conifer tree rings for the period
1458–1975 has revealed climatic oscillations with periods of 20–25 years. The amplitudes and periods of climatic oscillations
in the region of Russian Arctic Ocean proved to exhibit appreciable changes. Especially strong climatic variations in comparison
with the recent ones were found to occur during the Maunder minimum epoch when the period of oscillations increased from 22–23
years to 24–29 years, and oscillations with periods of 15 years appeared. After the Maunder minimum, the periods of oscillations
and their amplitudes again decreased, and the 15–16-year maximum disappeared. Analysis of solar activity based on of radiocarbon
(14C) concentration in annual tree rings has revealed a similar pattern in changes of periodicity before, during, and after the
Maunder minimum. This suggests that quasi-bidecadal climatic oscillations and variations in solar activity can be connected
with each other. A possible solar forcing of periodic climatic processes and its nonlinear influence on the atmosphere-ocean-continental
system are discussed. The intense quasi-bidecadal climatic oscillations can be, in all probability, interpreted as resulting
from amplification of a weak solar signal in the atmosphere-ocean system that has its own noises whose frequencies are close
to the 22–23-year solar cycles. 相似文献
15.
Orbital parameters of several artificial satellites of the Earth were analyzed for 1964–2007 and secular variations of the
atmospheric density were estimated for the last 30–40 years. The analysis was based on the information about orbital parameters
of 17 satellites and high-precision numerical integrations of the equations of motion with allowance for basic perturbing
factors and spatiotemporal density variations, calculated from measured solar activity indices using the NRLMSISE-00 atmosphere
model. The results demonstrate the presence of long-term variations in the atmospheric density not presented in modern atmosphere
models. During solar-activity cycle 21, the atmospheric density became 0.4 to 19% higher (depending on height) than in cycle
20. It decreased by 1.0 to 11% (depending on height) in cycle 22 as compared to cycle 21. Both decreases and increases were
observed in the atmospheric density during cycle 23, but with much smaller gradients. The results cannot be explained only
by the growing concentration of greenhouse gases. Possible causes of the density variations and possible ways to take them
into account in modern empirical and semiempirical atmospheric models are discussed. 相似文献
16.
The solar UV continuum has been derived from intensity-calibrated observations with the High-Resolution Telescope and Spectrograph
- HRTS - on its second rocket flight in 1978. A database has been constructed using the spatially-resolved solar spectrum
1180–1700 Å along a slit extending from near disk center to the solar limb and crossing a sunspot and two active regions.
The angular resolution is approximately 1.8″.
The data consist of 1772 spectral scans in the full center-to-limb range, including both quiet and active solar regions. The
distribution of solar UV intensities has been derived and the center-to-limb variations of the continuum intensities in the
quiet Sun are studied. Both quantities show spectral variations, particularly across the Sii continuum edge at 1521 Å. The spectra have been fitted to curves of constant color temperature above and below the Sii edge.
The derived center-to-limb variations have been compared to the values of Samain (1979) which are frequently referred to in
the literature. A relatively large discrepancy may be explained by the higher spectral and angular resolution of the HRTS
as compared to the rocket instrument used by Samain. Comparisons with the VAL III model calculations by Vernazza, Avrett,
and Loeser (1981) show discrepancies between the observations and the model predictions, particularly with regard to the sign
and amount of the intensity change across the Sii continuum edge.
It is noted that some of the results presented, i.e., absolute intensities and brightness temperatures may change, pending
confirmation of the SUSIM Spacelab 2 irradiance results (VanHoosieret al., 1988). 相似文献
17.
The north – south asymmetries (NSA) of three solar activity indices are derived and mutually compared over a period of more
than five solar cycles (1945 – 2001). A catalogue of the hemispheric sunspot numbers, the data set of the coronal green line
brightness developed by us, and the magnetic flux derived from the NSO/KP data (1975 – 2001) are treated separately within
the discrete low- and mid-latitude zones (5° – 30°, 35° – 60°). The calculated autocorrelations, cross-correlations, and regressions
between the long-term NSA data sets reveal regularities in the solar activity phenomenon. Namely, the appearance of a distinct
quasi-biennial oscillation (QBO) is evident in all selected activity indices. Nevertheless, a smooth behavior of QBO is derived
only when sufficient temporal averaging is performed over solar cycles. The variation in the significance and periodicity
of QBO allows us to conclude that the QBO is not persistent over the whole solar cycle. A similarity in the photospheric and
coronal manifestations of the NSA implies that their mutual relation will also show the QBO. A roughly two-year periodicity
is actually obtained, but again only after significant averaging over solar cycles. The derived cross-correlations are in
fact variable in degree of correlation as well as in changing periodicity. A clear and significant temporal shift of 1 – 2
months in the coronal manifestation of the magnetic flux asymmetry relative to the photospheric manifestation is revealed
as a main property of their mutual correlation. This shift can be explained by the delayed large-scale coronal manifestation
in responding to the emergence of the magnetic flux in the photosphere. The reliability of the derived results was confirmed
by numerical tests performed by selecting different numerical values of the used parameters. 相似文献
18.
Plasma and magnetic field parameter variations across fast forward interplanetary shocks are analyzed during the last solar
cycle minimum (1995–1996, 15 shocks), and maximum year 2000 (50 shocks). It was observed that the solar wind velocity and
magnetic field strength variation across the shocks were the parameters better correlated with Dst. Superposed epoch analysis centered on the shock showed that, during solar minimum, B
z
profiles had a southward, long-duration variation superposed with fluctuations, whereas in solar maximum the B
z
profile presented 2 peaks. The first peak occurred 4 hr after the shock, and seems to be associated with the magnetic field
disturbed by the shock in the sheath region. The second peak occurred 19 hr after the shock, and seems to be associated with
the ejecta fields. The difference in shape and peak in solar maximum (Dst peak =−50 nT, moderate activity) and minimum (Dst peak =−30 nT, weak activity) in average Dst profiles after shocks are, probably, a consequence of the energy injection in the magnetosphere being driven by different
interplanetary southward magnetic structures. A statistical distribution of geomagnetic activity levels following interplanetary
shocks was also obtained. It was observed that during solar maximum, 36% of interplanetary shocks were followed by intense
(Dst≤−100 nT) and 28% by moderate (−50≤Dst <−100 nT) geomagnetic activity. During solar minimum, 13% and 33% of the shocks were followed by intense and moderate geomagnetic
activity, respectively. Thus, during solar maximum a higher relative number of interplanetary shocks might be followed by
intense geomagnetic activity than during solar minimum. One can extrapolate, for forecasting goals, that during a whole solar
cycle a shock has a probability of around 50–60% to be followed by intense/moderate geomagnetic activity. 相似文献
19.
The Theory of Alfven drag (Drell et al. in J Geophys Res 70: 3131–3145 1965; Anselmo and Farinella in Icarus, 58, 182–185 1983) is applied here to show that the existence of a possible solar ring structure at a radial distance of 0.02 AU (~4R
⊙
, R
⊙
= radius of the sun) predicted by earlier authors (Brecher et al. in Nature 282, 50–52 1979; Rawal in Bull. Astr. Soc. India 6, 92–95 1978, Moon Planets 24, 407–414 1981, Moon Planets 31, 175–182 1984, J Astrophys Astr 10, 257–259 1989) may not survive Alfven drag produced during even moderate solar magnetic storms which take place from time to time through
the age of the sun, but a possible solar ring structure at a radial distance of 0.13 AU (~27R
⊙
) (Brecher et al. in Nature 282, 50–52 1979; Rawal in Bull. Astr. Soc. India 6, 92–95 1978, Moon Planets 24, 407–414 1981, Moon Planets 31, 175–182 1984, J Astrophys Astr 10, 257–259 1989) may survive intense Alfven drag produced during even strong magnetic storms of magnetic field value up to 1,000 G. 相似文献
20.
V. A. Kotov 《Bulletin of the Crimean Astrophysical Observatory》2010,106(1):137-151
The prolonged 2007–2009 minimum is a big surprise for solar physics. In order to reveal the causes, we analyze the variability
of the general magnetic field (GMF) of the Sun as a star measured by CrAO and five other observatories since 1968 (more than
19000 daily field strengths B were obtained in 41 years). Sharp yearly mean extrema of the negative (S) field took place in 1969, 1990, and 2008, with
the third extremum, in contrast to the two previous ones, having coincided with the sunspot minimum. This explains both the
long duration of the minimum and the record (over the last 100 years) increase in the length of the Wolf cycle (no. 23) to
12 or more years. The S-field extrema followed with a period of 19.5 ± 1.1 yr—some mean between the 22.1 ± 0.3-yr sunspot
cycle, the 18.6-yr saros, and the 19.9-yr Jupiter-Saturn conjunction period. It is pointed out that, for some unclear reason,
the negative polarity dominated on the Sun in 1968–2008: the overall mean B = −0.021 ± 0.015 G. The existence of a second Sun that obeys the laws of quantum mechanics is hypothesized. The “quantum”
model of the Sun-2 explains many properties of the “classical” Sun-1, including the coronal heating, cyclic activity, periodic
variations in GMF, and its sector structure. 相似文献