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1.
To gain insight into the relationships between solar activity, the occurrence and variability of coronal holes, and the association of such holes with solar wind features such as high-velocity streams, a study of the period 1963–1974 was made. This period corresponds approximately with sunspot cycle 20. The primary data used for this work consisted of X-ray and XUV solar images obtained from rockets. The investigation revealed that:
- The polar coronal holes prominent at solar minimum, decreased in area as solar activity increased and were small or absent at maximum phase. This evolution exhibited the same phase difference between the two hemispheres that was observed in other indicators of activity.
- During maximum, coronal holes occurred poleward of the sunspot belts and in the equatorial region between them. The observed equatorial holes were small and persisted for one or two solar rotations only; some high latitude holes had lifetimes exceeding two solar rotations.
- During 1963–74 whenever XUV or X-ray images were available, nearly all recurrent solar wind streams of speed ?500 km s?1 were found associated with coronal holes at less than 40° latitude; however some coronal holes appeared to have no associated wind streams at the Earth.
2.
Coordinates of polar faculae have been measured and processed using daily photoheliograms of the Kislovodsk Station of the Pulkovo observatory with the final goal of studying their latitude distribution during the solar cycles 20–21. The results obtained are as follows:
- The first polar faculae emerge immediately after the polarity inversion of the solar magnetic field at the latitudes from 40° to 70° with the average ?-55°.
- The zone of the emergence of polar faculae migrates poleward during the period between the neighbouring polarity inversions of the solar magnetic field. This migration is about 20° for 8 years, which corresponds to a velocity of 0.5 m s-1.
- The maximum number of polar faculae was reached at the activity minimum (1975–1976).
- The last polar faculae were observed in the second half of 1978 at the latitudes from 70° to 80°.
3.
Correlation and spectral analysis of solar radio flux density and sunspot number near the maximum of the sunspot cycle has indicated the existence of
- long period amplitude modulation of the slowly varying component (SVC) of radio emission
- coronal storage over a period of the order of three solar rotations
- fast decay (one solar rotation period or less) of gyromagnetic emissions from radio sources
- shift in location of chromospheric sources compared to those of either the upper corona or the photosphere.
4.
A study of ephemeral active regions (ER) identified on good quality full-disk magnetograms reveals:
- On the average 373 and 179 ER were present on the Sun in 1970 and 1973 respectively. The number varies with the solar cycle.
- The median lifetime of ER depends on observation quality and selection rules but is estimated as about 12 hr for our data.
- The latitude distribution is very broad but not uniform. The distribution peaks near the equator and shows variations similar to distributions of large active regions.
- The longitude distribution is essentially homogeneous.
- The spatial orientation of ER is almost random. In 1973 there is a hint of an excess of new cycle orientations at high latitudes.
5.
We have extended our previous study of coronal holes, solar wind streams, and geomagnetic disturbances from the declining phase (1973–1975) of sunspot cycle 20 through sunspot minimum (1976) into the rising phase (1977) of cycle 21. Using daily He I 10830 Å spectroheliograms and photospheric magnetograms, we found the following results:
- As the magnetic field patterns changed, the solar atmosphere evolved from a structure having a few, large, long-lived, low-latitude coronal holes to one having numerous small, short-lived, high-latitude holes (in addition to the polar holes which persisted throughout this 5-year interval).
- The high-latitude holes recurred with a synodic rotation period of 28–29 days instead of the 27-day period already known to be characteristic of low-latitude holes.
- During 1976–1977 many coronal holes were intrinsically ‘weak’ in the sense that their average intensities did not differ greatly from the intensity of their surroundings. Such low-contrast holes were rare during 1973–1975.
6.
Maurizio Ternullo 《Solar physics》1987,112(1):153-163
An analysis of Ca ii spectroheliograms obtained at Catania Astrophysical Observatory throughout the years 1967–1977 has been carried out, to throw light on the complex relationship linking (Ternullo, 1986) the angular rotation rate of Ca plages with their age, as well as with solar cycle phase, and with latitude. Given the rotation law w =, a + b sin2
I, solar-cycle-related oscillatory properties both of a and b coefficients are described, both for young and old Ca plages.The aging-dependent rate-increments vary, for each epoch, both in module and sign with latitude; that results in deep distortions of the differential rotation latitudinal profile, which exhibits, when old plages are taken into account, a fine structure (Ternullo, 1987). Such a fine structure is absent in the young plage differential rotation profile.Throughout the time interval under examination, the torsional waves observed by Howard and LaBonte (1980) have appeared to be in close spatial relationship with the latitude bands where aging-dependent rate increments occur.
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7.
We define for observational study two subsets of all polar zone filaments, which we call polemost filaments and polar filament bands. The behavior of the mean latitude of both the polemost filaments and the polar filament bands is examined and compared with the evolution of the polar magnetic field over an activity cycle as recently distilled by Howard and LaBonte (1981) from the past 13 years of Mt. Wilson full-disk magnetograms. The magnetic data reveal that the polar magnetic fields are built up and maintained by the episodic arrival of discrete f-polarity regions that originate in active region latitudes and subsequently drift to the poles. After leaving the active-region latitudes, these unipolar f-polarity regions do not spread equatorward even though there is less net flux equatorward; this indicates that the f-polarity regions are carried poleward by a meridional flow, rather than by diffusion. The polar zone filaments are an independent tracer which confirms both the episodic polar field formation and the meridional flow. We find:
- The mean latitude of the polemost filaments tracks the boundary of the polar field cap and undergoes an equatorward dip during each arrival of additional polar field.
- Polar filament bands track the boundary latitudes of the unipolar regions, drifting poleward with the regions at about 10 m s-1.
- The Mt. Wilson magnetic data, combined with a simple model calculation, show that the filament drift expected from diffusion alone would be slower than observed, and in some cases would be equatorward rather than poleward.
- The observation that filaments drift poleward along with the magnetic regions shows that fields of both polarities are carried by the meridional flow, as would be expected, rather than only the f-polarity flux which dominates the strength. This leads to the prediction that in the mid-latitudes during intervals between the passage of f-polarity regions, both polarities are present in nearly equal amounts. This prediction is confirmed by the magnetic data.
8.
Markus J. Aschwanden 《Journal of Astrophysics and Astronomy》2008,29(1-2):3-16
Celebrating the diamond jubilee of the Physics Research Laboratory (PRL) in Ahmedabad, India, we look back over the last six decades in solar physics and contemplate on the ten outstanding problems (or research foci) in solar physics:
- The solar neutrino problem
- Structure of the solar interior (helioseismology)
- The solar magnetic field (dynamo, solar cycle, corona)
- Hydrodynamics of coronal loops
- MHD oscillations and waves (coronal seismology)
- The coronal heating problem
- Self-organized criticality (from nanoflares to giant flares)
- Magnetic reconnection processes
- Particle acceleration processes
- Coronal mass ejections and coronal dimming
9.
E. I. Tetruashvili 《Solar physics》1977,54(1):135-138
In order to establish some regularities or variations in the distribution of widths and intensities of the coronal line profiles λ 5303 and λ 6374 depending upon the solar activity, a statistical analysis was made for more than 3000 profiles (the data covering the period 1966–1972). The following results obtained:
- The distribution of coronal line profile widths changes depending upon the solar activity phase.
- The character of the relation between the intensities and widths varies with variation of the solar activity phase.
10.
The Ca II K filtergrams from Kodaikanal Solar Observatory have been used to study solar activity.The images are dominated by the chromospheric network and plages.Programs have been developed to obtain the network and plage indices from the daily images as functions of solar latitude and time.Preliminary results from the analysis are reported here.The network and plage indices were found to follow the sunspot cycle.A secondary peak is found during the period of declining activity in both the indices.A comparison of network indices from the northern and the southern hemispheres shows that the former is more active than the latter.However such an asymmetry is not clearly seen in the plage index. 相似文献
11.
He i 10830 Å images show that early in sunspot cycles 21 and 22, large bipolar magnetic regions strongly affected the boundaries of the nearby polar coronal holes. East of each eruption, the hole boundary immediately contracted poleward, leaving a band of enhanced helium network. West of the eruption, the boundary remained diffuse and gradually expanded equatorward into the leading, like-polarity part of the bipolar magnetic region. Comparisons between these observations and simulations based on a current-free coronal model suggest that:
- The Sun's polar magnetic fields are confined to relatively small caps of high average field strength, apparently by a poleward meridional flow.
- The enhanced helium network at high latitude marks the location of relatively strong polar fields that have become linked to the newly erupted bipolar region in that hemisphere.
- The distortion of the polar-hole boundary is accompanied by a corresponding distortion of the equatorial neutral sheet in the outer corona, in which the amount of warping depends on the magnitude of the erupted flux relative to the strength of the Sun's polar magnetic fields.
12.
Yu. A. Nagovitsyn 《Astrophysical Bulletin》2008,63(1):43-55
We report the results of the application of our approach to study the behavior of solar activity in the past, where: When reconstructing the variations of solar activity, geomagnetic parameters, and the interplanetary magnetic field in the past we select a sequence of increasing time scales, which can be naturally represented by the potentials of available observational data. We select a total of four time scales: 150–200 years, 400 years, 1000 years, and 10000 years. When constructing the series of each successive (in terms of length) time scale we use the data of the previous time scale as reference data. We abandon, where possible, the series of traditional statistical parameters in favor of the series of physical parameters. When deriving the relations between any parameters of solar activity, geomagnetic disturbance, and the interplanetary magnetic field, we take into account the differential nature of relations on different time scales. To this end, we use the earlier proposed MSR and DPS methods. To verify the resulting reconstructions, we use the “principle of witnesses”, which uses independent (in some cases, indirect) information as initial data. 相似文献
13.
Robert F. Howard 《Solar physics》1992,137(1):51-65
Digitized Mount Wilson sunspot data from 1917 to 1985 are analyzed to examine the growth and decay rates of sunspot group umbral areas. These rates are distributed roughly symmetrically about a median rate of decay of a few hemisphere day-1. Percentage area change rates average 502% day-1 for growing groups and -45% day-1 for decaying groups. These values are significantly higher than the comparable rates for plage magnetic fields because spot groups have shorter lifetimes than do plages. The distribution of percentage decay rates also differs from that of plage magnetic fields. Small spot groups grow at faster rates on average than they decay, and large spot groups decay on average at faster rates than they grow. Near solar minimum there is a marked decrease in daily percentage spot area growth rates. This decrease is not related to group area, nor is it due to latitude effects. Sunspot groups with rotation rates close to the average (for each latitude) have markedly slower average rates of daily group growth and decay than do those groups with rotation rates faster or slower than the average. Similarly, sunspot groups with latitude drift rates near zero have markedly slower average rates of daily group growth and decay than do groups with significant latitude drifts in either direction. Both of these findings are similar to results for plage magnetic fields. These various correlations are discussed in the light of our views of the connection of the magnetic fields of spot groups to subsurface magnetic flux tubes. It is suggested that a factor in the rates of growth or decay of spot groups and plages may be the inclination angle to the vertical of the magnetic fields of the spots or plages. Larger inclination angles may result in faster growth and decay rates.Operated by the Association of Universities for Research in Astronomy, Inc., under Cooperative Agreement with the National Science Foundation. 相似文献
14.
Preliminary results are presented of observations of the solar Na D lines obtained with high space and time resolution (2.4″ × 2.4″), (6 s). The following conclusions may be drawn.
- The line profiles vary strongly with space and time implying that time averaging over a long period and large area will not produce the ‘true’ profile.
- The centre-limb increase in apparent Doppler width in the D lines is intrinsic. It is not due to space or time averaging.
- The amplitude of the 300-s oscillation may range up to 1.5 km/s in the region of formation of the D lines. Large line asymmetries are associated with this motion. Observations which do not resolve this motion can not be considered adequate.
- The variation of the D line profile caused by the 300-s oscillation may be described as follows: (a) The core is raised and lowered without change of shape, (b) The wings broaden as the central intensity rises and narrow as it falls. These variations are qualitatively explained by the scanning of the line formation region through the solar atmosphere.
- Doppler width values derived from pairs of D line profiles are strongly correlated with the motion of the element observed. Hotter elements move upward, cooler downward.
- Indications of running waves have been found in the time variation of the core line bisectors.
15.
After adding the data observed in the years from 1979 to 1982 to those obtained earlier (Ding et al., 1981), we re-examine the previous results and conclude:
- The longitudinal distribution of spiral spots on the solar disc is generally the same as that of sunspot groups with areas of S p ≥ 400, but their active longitudes seem to be more concentrated.
- The distribution of spiral patterns in the southern and northern hemispheres shows that the differential rotation may be a fundamental solar dynamo for the formation of the spiral spots.
- The statistical directions of the emerging twisted magnetic vectors in the active regions in the southern and northern hemispheres are synchronously inverse with a period of about two years. This period seems to be detected in other solar observations.
16.
W. Stanek 《Solar physics》1972,27(1):89-106
It is well known to the observer of sunspots that the spots seem not to be randomly distributed on the solar surface but rather occur at an increased rate at distances of 180° of each other on the same hemisphere while northern and southern hemispheres are independent. The following investigation - based on observational data of rotations No. 1457–1568 (1962–1970) shows four main results:
- Northern and southern hemisphere behave independently.
- Each hemisphere can be divided in longitude into sections of 45° so that successive sections alternatively show higher and lower spot occurrence. In other words: maximum spot occurrence is found in intervals of about 90° and 180°.
- Second-order peaks can be found in intervals of 30° and multiples of it. The spot maxima explained above coincide with some of these second-order peaks.
- Areas of minimal spot occurrence can be traced over a long period of time. These areas can be understood as the center of long-living magnetic areas along the borders of which we find the so-called ‘streets of prominences’ with its spots. This theory of Stanek (1971) explains the occurrence of prominences. Because of the steep magnetic gradient along these streets the theory is expected to hold true even for spots. This leads to a better understanding of the pattern already known and now being generalized to ‘streets of activity’.
17.
We present observations of the extended solar cycle activity in white-light coronagraphs, and compare them with the more familiar features seen in the Fe?xiv green-line corona. We show that the coronal activity zones seen in the emission corona can be tracked high into the corona. The peak latitude of the activity, which occurs near solar maximum, is found to be very similar at all heights. But we find that the equatorward drift of the activity zones is faster at greater heights, and that during the declining phase of the solar cycle, the lower branch of activity (that associated with the current cycle) disappears at about 3R ??. This implies that during the declining phase of the cycle, the solar wind detected near Earth is likely to be dominated by the next cycle. The so-called ??rush to the poles?? is also seen in the higher corona. In the higher corona it is found to start at a similar time but at lower latitudes than in the green-line corona. The structure is found to be similar to that of the equatorward drift. 相似文献
18.
A. Vidal-Madjar 《Solar physics》1975,40(1):69-86
Four consecutive years of a quasi-continuous survey of the solar Lα line are presented. Absolute calibration and aging correction are evaluated producing higher quality measurements which are: -the total Lα flux, -the central Lα flux, -the blue wing flux at 0.33 Å from the center, -the slope of the blue wing at the same location. Empirical laws are deduced from this large amount of data giving a relation between these different parameters and the flux integrated over the whole line. Furthermore, other empirical laws are obtained between the total Lα flux and two solar activity indices. These relations give a possibility of evaluating the solar Lα flux even when no observation is available and, as previously found by Prinz (1974), show that to a first approximation the solar Lα flux is composed of a quiet and of an active component. The active component changes with the 27 days period; the quiet one with the 11 yr solar cycle. 相似文献
19.
T. M. L. Wigley 《Solar physics》1981,74(2):435-471
The Earth's climate is not constant, and has experienced major changes in the past on all timescales. The causes of these changes, although still incompletely understood, vary according to the timescale considered. Some of the most important causal mechanisms include continental drift, changes in the Earth's orbital parameters, volcanic activity and solar variations. Solar variations have been invoked to explain climatic change on almost all timescales from 1 to 109 yr. Unfortunately, even though the Sun is a prime candidate for explaining many changes in past climate, the use of past climate as a proxy for solar luminosity changes is fraught with difficulty. For example:
- In many cases observed changes in climate can be adequately explained without recourse to solar variations as a causal factor. In fact, on the longest timescales the Earth's climate was remarkably similar to today in spite of a considerably lower solar output.
- For most timescales of climatic change there are, as yet, no plausible theories giving similar timescale variations in solar activity, so that a vital link between cause and effect is missing.
- There are considerable uncertainties in the record of past climates.
- On short timescales many proposed solar activity-climate links have failed to stand up to rigorous statistical analysis.
20.
The purpose of this paper is to present the correlation of seasonal variation of 5893 Å line intensity with relative sunspot numbers, solar flare numbers and the variable component of 10.7 cm solar flux. A study has been made and the following important results have been obtained.
- The intensity of 5893 Å line at Calcutta shows periodic variation with different solar parameters during descending part of secondary peak of 21st solar cycle (1984–1985).
- 5893 Å line intensity of Mt. Abu also shows periodic variation with solar parameters during the period 1965–1968 when there was a peak phase of 20th solar cycle.
- A possible explanation for such type of variation is also presented.