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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.
Hourly interplanetary proton plasma data, measured by Helios-1 and Helios-2 heliocentric satellites over the period extending between the sunspot minimum and maximum of the 21rst solar cycle are analysed. This analysis gives an emphasis in the presence of a third type solar wind (intermediate) at 450 km s–1, appearing at solar minimum, during which large coronal holes are dominating in the Sun. This type of solar wind is hardly to be observed during the solar maximum period.Both Helios-1 and Helios-2 data give an average speed of the slow solar wind of 350 km s–1 for the period between these two extremes of solar activities.After correlation of the plasma temperature with its speed in different heliocentric distances, it comes out the stronger heating which takes place in distances shorter than 0.6 AU than in distances between 0.6 and 1.0 AU.A different behaviour of the radial proton temperature gradient in different solar activities appears after the calculation of the gradients as a function of solar wind speed and radial distance. 相似文献
3.
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.
4.
A study of the green corona rotation rate, during the period 1970–1974, confirms that the differential rotation degree varies systematically through a solar cycle and that the corona rotates in an almost rigid manner before sunspot minimum. During the first two years, 1970–1971, the differential rotation degree, characteristic of high solar activity periods is detected. While during the years of declining activity, 1972–1974, a drastic decrease of the differential rotation degree occurs and the green corona rotates almost rigidly, as the coronal holes observed in the same period. These conclusions are valid only for the rotation of coronal features with lifetime of at least one solar rotation. 相似文献
5.
We describe the decay phase of one of the largest active regions of solar cycle 22 that developed by the end of June 1987. The center of both polarities of the magnetic fields of the region systematically shifted north and poleward throughout the decay phase. In addition, a substantial fraction of the trailing magnetic fields migrated equatorward and south of the leading, negative fields. The result of this migration was the apparent rotation of the magnetic axis of the region such that a majority of the leading polarity advanced poleward at a faster rate than the trailing polarity. As a consequence, this region could not contribute to the anticipated reversal of the polar field.The relative motions of the sunspots in this active region were also noteworthy. The largest, leading, negative polarity sunspot at N24 exhibited a slightly slower-than-average solar rotation rate equivalent to the mean differential rotation rate at N25. In contrast, the westernmost, leading, negative polarity sunspot at N21 consistently advanced further westward at a mean rate of 0.13 km s–1 with respect to the mean differential rotation rate at its latitude. These sunspot motions and the pattern of evolution of the magnetic fields of the whole region constitute evidence of the existence of a large-scale velocity field within the active region.Solar Cycle Workshop Paper. 相似文献
6.
The rotation of the corona can be determined either directly by using Doppler methods or indirectly by using tracers, i.e., structures within the corona. In this study the rotational characteristics of the corona are determined using coronal holes as tracers, for the period 1978–1991. The coronal data used here are from an atlas of coronal holes mapped in Hei 10830 data. A comparison is made between our results and previous determinations of the coronal rotation rate, e.g., by Sime (1986), using white-light K-coronameter observations, by Timothy, Krieger, and Vaiana (1975), using soft X-ray observations, and by Shelke and Pande (1985) and Navarro-Peralta and Sanchez-Ibarra (1994), using Hei 10830 data. For the atlas of coronal holes used in this study the nature of the coronal hole distributions in number and latitude, in yearly averages, has been determined. These distributions show that at solar minimum the polar coronal holes dominate and the few non-polar holes are confined to a narrow band near the equator. At solar maximum, however, mid-latitude coronal holes dominate, with a large spread in latitudes. Given these distributions we consider the differential rotation data only as an average over a solar cycle. This removes spurious effects caused by having only a small number of coronal holes contributing to the results, or by having a narrow latitude band for the observations, thus limiting the results to that narrow latitude band. By considering these coronal holes as tracers of the differential rotation we show that the mid-latitude corona rotates more rigidly than the photosphere, but still exhibits significant differential rotation, with an equatorial rate of 13.30 ± 0.04° day–1, and at 45° latitude a rate of 12.57 ± 0.13° day–1. These results are comparable, within errors, to the Sime (1986) results which have an equatorial rate of approximately 13.2 ± 0.2° day–1 and a rate of approximately 12.9 ± 0.3° day–1 at 45° latitude. 相似文献
7.
Observations of interplanetary magnetic field polarity, solar wind speed, and geomagnetic disturbance index (C9) during the years 1962–1975 are compared in a 27-day pictorial format that emphasizes their associated variations during the sunspot cycle. This display accentuates graphically several recently reported features of solar wind streams including the fact that the streams were faster, wider, and longer-lived during 1962–1964 and 1973–1975 in the declining phase of the sunspot cycle than during intervening years (Bame et al., 1976; Gosling et al., 1976). The display reveals strikingly that these high-speed streams were associated with the major, recurrent patterns of geomagnetic activity that are characteristic of the declining phase of the sunspot cycle. Finally, the display shows that during 1962–1975 the association between long-lived solar wind streams and recurrent geomagnetic disturbances was modulated by the annual variation (Burch, 1973) of the response of the geomagnetic field to solar wind conditions. The phase of this annual variation depends on the polarity of the interplanetary magnetic field in the sense that negative sectors of the interplanetary field have their greatest geomagnetic effect in northern hemisphere spring, and positive sectors have their greatest effect in the fall. During 1965–1972 when the solar wind streams were relatively slow (500 km s-1), the annual variation strongly influenced the visibility of the corresponding geomagnetic disturbance patterns.Visiting Scientist, Kitt Peak National Observatory, Tucson, Arizona.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. 相似文献
8.
A. I. Poland R. A. Howard M. J. Koomen D. J. Michels N. R. Sheeley Jr. 《Solar physics》1981,69(1):169-175
The Naval Research Laboratory's most recent Earth-orbiting coronagraph, called Solwind, has been observing the Sun's outer corona (2.6–10.0 R
) at 10-min intervals since March 28, 1979. These observations provide the first comprehensive view of coronal transients near the peak of a sunspot cycle. Six, well-defined transients in our quick-look data have masses ranging from 7 × 1014 g to 2 × 1016 g and outward speeds ranging from 150 km s–1 to 900 km s–1. These values are comparable to the ones that were obtained with the OSO-7 and Skylab observations during the declining phase of the last sunspot cycle. Although the amount of quick-look data is not sufficient to provide meaningful statistics, the coronal transients near sunspot maximum seem to occur with a greater frequency and a wider latitude range than the transients during the declining phase of the cycle. In both eras, there is a good, but imperfect, association between the occurrence of coronal transients and surface phenomena such as eruptive prominences and flares.On leave from the High Altitude Observatory, National Center for Atmospheric Research, Boulder, Colo. 80307, U.S.A. Now at Goddard Space Flight Center; Greenbelt, Md. 20771, U.S.A. 相似文献
9.
J. Hirshberg 《Astrophysics and Space Science》1973,20(2):473-481
Recent theories of the solar cycle and of coronal heating strongly suggest that solar cycle variations of different quantities (i.e. sunspots, coronal green line, etc.) ought not to be expected to be in phase with one another. In agreement with this notion we note that the shape of the corona typical of a maximum eclipse occurs 1.5yr before sunspot maximum, compared with 2 yr as might be expected from Leighton's standard model. Further, we argue that the phase of the solar wind cycle can be determined from geomagnetic observations. Using this phase, a solar cycle variation of 100 km s–1 in the solar wind velocity and 1 in the magnetic field intensity becomes apparent. In general, the solar wind cycle lags the coronal-eclipse-form cycle by 3 yr, compared with the 2 yr that might be expected from model calculations. 相似文献
10.
Plasma data from Pioneers 6–7 and from a variety of satellites operating near the Earth are used to investigate the heliographic latitude dependence of the solar wind bulk speed near the sunspot maximum. No evidence is found for a latitude effect: the latitudinal gradient, if any, turns out to be 2 km (sec degree)–1, to be compared with the gradient of 10 km (sec degree)–1 observed in periods of low or moderate solar activity. 相似文献
11.
Daily calcium plage areas for the period 1951–1981 (which include the solar cycle 19 and 20) have been used to derive the rotation period of the Sun at latitude belts 10–15 ° N, 15–20 ° N, 10–15 ° S, and 15–20 ° S and also for the entire visible solar disk. The mean rotation periods derived from 10–20 ° S and N, total active area and sunspot numbers were 27.5, 27.9, and 27.8 days (synodic), respectively. A power spectral analysis of the derived rotation rate as a function of time indicates that the rotation rate in each latitude belt varies over time scales ranging from the solar activity cycle, down to about 2 years. Variations in adjacent latitude belts are in phase, whereas those in different hemispheres are not correlated. The rotation rates derived from sunspot numbers also behave similarly though the dependence over the solar cycle are not very apparent. The total plage areas, integrated over the entire visible hemisphere of the Sun shows a dominant periodicity of 7 years in rotation rate, while the other time scales are also discernible. 相似文献
12.
G. D. Parker 《Solar physics》1987,108(1):77-87
Long-lived brightness structures in the solar electron corona persist over many solar rotation periods and permit an observational determination of coronal magnetic tracer rotation as a function of latitude and height in the solar atmosphere. For observations over 1964–1976 spanning solar cycle 20, we compare the latitude dependence of rotation at two heights in the corona. Comparison of rotation rates from East and West limbs and from independent computational procedures is used to estimate uncertainty. Time-averaged rotation rates based on three methods of analysis demonstrate that, on average, coronal differential rotation decreases with height from 1.125 to 1.5 R
S. The observed radial variation of differential rotation implies a scale height of approximately 0.7 R
S for coronal differential rotation.Model calculations for a simple MHD loop show that magnetic connections between high and low latitudes may produce the observed radial variations of magnetic tracer rotation. If the observed tracer rotation represents the rotation of open magnetic field lines as well as that of closed loops, the small scale height for differential rotation suggests that the rotation of solar magnetic fields at the base of the solar wind may be only weakly latitude dependent. If, instead, closed loops account completely for the radial gradients of rotation, outward extrapolation of electron coronal rotation may not describe magnetic field rotation at the solar wind source. Inward extrapolations of observed rotation rates suggest that magnetic field and plasma are coupled a few hundredths of a solar radius beneath the photosphere. 相似文献
13.
The rotational behaviour of the chromosphere, observed in the Ca ii K3 line, is studied during 1972–1973, years of decreasing solar activity. Daily chromospheric filtergrams, detected at the Anacapri Observatory, are digitized by means of a flying-spot photometer, controlled by computer. The time series of the daily chromospheric data detected at central meridian, relative to 30 consecutive latitude zones, are analyzed to determine the recurrence tendency due to the rotation of long-lived chromospheric features. The computed rotation rate is independent of latitude, in agreement with the results obtained for the green corona during the years before sunspot minimum. Namely both chromospheric and coronal features, with lifetime exceeding one solar rotation, are almost not affected by differential rotation before sunspot minimum. 相似文献
14.
J. D. Bohlin 《Solar physics》1977,51(2):377-398
The disk boundaries of coronal holes have been systematically determined from XUV observations taken during the manned Skylab missions (June 1973–January 1974). The resulting Atlas was used to find the sizes, global distributions, differential rotation rates, growth/decay rates and lifetimes of holes during this period. The polar cap holes together covered 15% of the Sun's total surface area, a number which remained surprisingly constant throughout Skylab despite the fact that each pole was independently evolving in time. Lower latitude holes contributed another 2 to 5%. The anomalous differential rotation law derived for a large north-south hole by Timothy et al. (1975) has been confirmed. However, other Skylab holes were too low in latitude to demonstrate the generality of this result. The average growth/decay rate for holes was 1.5 × 104 km2 s-1, in excellent agreement with the value used by Leighton (1964) for his successful treatment of the surface transport of solar magnetic fields. The lifetimes of lower-latitude holes are found to regularly exceed 5 solar rotations, in good agreement with the lifetimes of recurrent geomagnetic storms with which holes are now known to be associated. 相似文献
15.
The sidereal rotation rate of the high-latitude solar regions is examined using long-lived photospheric polar faculae. The observations were carried out with the photoheliograph of Kislovodsk Mountain Station of the Pulkovo Observatory from 1982 to 1986. The following facts have been established: (a) There is a differential rotation of the polar faculae close to the maximum of solar activity, while the amount of latitude gradient of solar rotation decreases towards the sunspot minimum; (b) small differences of rotation in the northern and southern hemispheres of the Sun are observed; (c) some deviations of differential rotation curves constructed for each Carrington rotation from the mean curve of differential rotation are revealed. The total amplitude of the maximum positive and negative excesses is about 40–50 m s–1. The positive surplus velocities of solar rotation (the amplitude of which is about 20–25 m s–1) move in the form of a wave from heliographic latitudes 40° with a velocity of 1.6 m s–1. The latitude width of this flow is B 15°. This wave of abnormally high velocity starts in the year of minimum solar activity and reaches the pole 11 years later. The picture is symmetrical relative to the equator. 相似文献
16.
This study deals with the short-term variations of cosmic ray intensity during the interval 1973–78. Daily means of high latitude neutron and meson monitors from the same station and those of a low latitude neutron monitor have been analysed using the Chree method of superposed epochs. The zero epoch for the Chree analyses corresponds to the day of a substantial increase (V 200 km s–1) in the solar wind speed to values of 550 km s–1 and which persists at such high values for an interval of at least three days. The investigation reveals the existence of two types of cosmic ray intensity variations with distinctly different spectral characteristics. During the interval 1973–76, relative changes in the neutron and meson monitor rates are nearly equal indicating an almost flat rigidity spectrum of variation. During 1977–78, however, the spectrum acquires a negative spectral character similar to that observed for Forbush decreases. We suggest that events of the interval 1973–76 are essentially due to high speed streams associated with solar coronal holes and that events of the interval 1977–78 are due to fast streams from solar active regions with flare activity. 相似文献
17.
We measured the average soft X-ray emission from coronal holes observed on images obtained during AS & E rocket flights from 1974 to 1981. The variation of this emission over the solar cycle was then compared with photospheric magnetic flux measurements within coronal holes over the same period. We found that coronal hole soft X-ray emission could be detected and that this emission appeared to increase with the rise of the sunspot cycle from activity minimum to maximum. Our quantitative results confirmed previous suggestions that the coronal brightness contrast between holes and large-scale structure decreased during this period of the cycle. Gas pressures at the hole base were estimated for assumed temperatures and found to vary from about 0.03 dyne cm–2 in 1974 to 0.35 dyne cm–2 in 1981. The increase in coronal hole X-ray emission was accompanied by a similar trend in the surface magnetic flux of near-equatorial holes between 1975 and 1980 (Harvey et al., 1982). 相似文献
18.
This paper presents the results of a comparison between observations of coronal holes in UV (SOHO EIT) and radio emission (17, 5.7 GHz, 327 and 150.9 MHz, from NoRH, SSRT and Nançay radioheliographs), and solar wind parameters, from ACE spacecraft data over the period 12 March?–?31 May 2007. The increase in the solar wind velocity up to ～?600 km?s?1 was found to correlate with a decrease in the UV flux in the central parts of the solar disk. A connection between the parameters of the radio emission from three different layers of the solar atmosphere and the solar wind velocity near the Earth’s orbit was discovered. Such a connection is suggestive of a common mechanism of solar wind acceleration from chromospheric heights to the upper corona. 相似文献
19.
From high precision computer controlled tracings of bright Ca+-mottles we investigated differential rotation, meridional and random motions of these chromospheric fine structures. The equatorial angular velocity of the Ca+-mottles agrees well with that of sunspots (14°.50 per day, sidereal) and is 5 % higher than for the photosphere. The slowing down with increasing latitude is larger than for sunspots. Hence in higher latitudes Ca+-mottles rotate as fast as the photospheric plasma. A systematic meridional motion of about 0.1 km s–1 for latitudes around 10° was found. The Ca+-mottles show horizontal random motions due to the supergranular flow pattern with an rms velocity of about 0.15 km s–1. We finally investigated the correctness of the solar rotation elements i and derived by Carrington (1863). 相似文献
20.
We devised a new method, which we call the running-segment method, to achieve high-resolution time series of indices of solar rotation for determining the latitude dependence of the differential rotation by a least-squares fitting of the daily translation of positions of sunspot groups during a fixed time segment of 11 years. The segment is moved by an amount of one year to determine the differential profile of the next point of time. Time of the determined rotation data is defined by an arithmetic mean of the beginning and ending years of the segment. The rotation underwent an acceleration from 1948 to 1974 and a deceleration from 1974 to 1987. We found that the time profile of the indexM, the angular momentum surface layer density defined by integration of the angular momentum volume density over the whole surface, follows almost exactly the time profile of the 11-year running mean of the yearly mean of the sunspot relative number with a delay time of about 20 years. The acceleration (deceleration) phase corresponds to the ascending (descending) phase of amplitude of the 11-year solar cycle of cycle 16 (19) to cycle 19 (20) with a delay time of about 20 years. The cycles 15–20 correspond to the 55-year grand cycle V of the 11-year cycle. The delay time of about 20 years agrees well with the delay time predicted by a nonlinear dynamo theory of the solar cycle for driving the 55-year modulation of the 11-year solar cycle. The agreement suggests that the Lorentz force of the magnetic field of the solar cycle during grand cycle V drives the solar rotation modulation from 1948 to 1987 and that the force needed about 20 years to modify the rotation during 1943–1992. 相似文献