共查询到20条相似文献，搜索用时 31 毫秒
1.
R. W. Komm 《Solar physics》1994,149(2):417-420
Meridional flow and rotation are studied using high-resolution magnetograms taken during the year 1988 with the NSO Vacuum Telescope on Kitt Peak. Motions are determined by a two-dimensional crosscorrelation analysis of 107 pairs of consecutive daily observations. The analysis was done first with active regions included and repeated with active regions excluded. The difference between the two analyses provides an estimate of the motions of active regions. I find that active regions rotate slower than small magnetic features and that active regions show a meridional flow toward the mean latitude of activity.Operated by the Association of Universities for Research in Astronomy, Inc. under cooperative agreement with the National Science Foundation. 相似文献
2.
Robert F. Howard 《Solar physics》1990,126(2):299-309
The Mount Wilson coarse array data set is used to define active regions in the interval 1967 to August, 1988. From the positions of these active regions on consecutive days, rotation rates are derived. The differential rotation of the active regions is calculated and compared with previous magnetic field and plage rates. The agreement is good except for the variation with time. The active region rates are slower by a few percent than the magnetic field or facular rates. The differential rotation rate of active regions with reversed magnetic polarity orientations is calculated. These regions show little or no evidence for differential rotation, although uncertainties in this determination are large. A correlation is found between rotation rate and region size in the sense that larger regions rotate more slowly. A correlation between rotation rate and cycle phase is suggested which is in agreement with earlier sunspot results. Leading and following portions of active regions, unlike leading and following spots, show little or no difference in their rotation rates. The regions with polarity orientations nearest the normal configuration tend to show rotation rates that are nearest the average values. Most of these results generally support the conclusion that old, weaker magnetic fields have evolved different subsurface connections from the time they were a part of sunspots or plages. It seems possible that they are connected at a shallower layer than are sunspot or plage fields.Operated by the Association of Universities for Research in Astronomy, Inc., under Contract with the National Science Foundation. 相似文献
3.
W. C. Livingston 《Solar physics》1969,9(2):448-451
Spectroscopic measurements of solar rotation having good height discrimination show no change in angular velocity through
the photosphere layers but an increase of 8% for the Hα chromosphere (epoch 1968.9). Spectroscopic results in general are
compared with measures made with tracers, i.e. sunspots, filaments, etc., and it is seen that the spectroscopic method always
shows increased differential rotation with height, while tracers indicate none. A westward flowing wind is proposed that increases
in velocity with height, but produces negligible movement to magnetic regions associated with tracers.
Kitt Peak National Observatory Contribution No. 450.
Operated by The Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. 相似文献
4.
In a previous paper, we suggested that the twisting of coronal magnetic fiels by photospheric motions produces the steady heating of an active region, while braiding of these fields stores energy which is eventually released in an avalanche process, as sporadic large flares. We explore these ideas with numerical simulations. Our results indicate that the combined effect of twisting and braiding can account for the observed power input and the flare frequency spectrum of typical active regions.Operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under coooperative agreement with the National Science Foundation. 相似文献
5.
We have previously studied large-scale motions using high-resolution magnetograms taken from 1978 to 1990 with the NSO Vacuum Telescope on Kitt Peak. Latitudinal and longitudinal motions were determined by a two-dimensional crosscorrelation analysis of pairs of consecutive daily observations using small magnetic features as tracers. Here we examine the shape and amplitude of the crosscorrelation functions. We find a characteristic length scale as indicated by the FWHM of the crosscorrelation functions of 16.6 ± 0.2 Mm. The length scale is constant within ±45° latitude and decreases by about 5% at 52.5° latitude; i.e., the characteristic size is almost latitude independent. The characteristic scale is within 3% of the average value during most times of the solar cycle, but it increases during cycle maximum at latitudes where active regions are present. For the time period 1978–1981 (solar cycle maximum), the length scale increases up to 1.7 Mm or 10% at 30° latitude. In addition, we derive the average amplitude of the crosscorrelation functions, which reflects the diffusion of magnetic elements and their evolutionary changes (including formation and decay). We find an average value of 0.091 ± 0.003 for the crosscorrelation amplitude at a time lag of one day, which we interpret as being caused by the combined effect of the lifetime of magnetic features and a diffusion process. Assuming a lifetime of one day, we find a value of 120 km2 s–1 for the diffusion constant, while a lifetime of two days leads to 230 km2 s–1.Operated by the Association of Universities for Research in Astronomy, Inc. under cooperative agreement with the National Science Foundation. 相似文献
6.
Howard (1993) finds a relationship between the tilt angles of BMRs (Bipolar Magnetic Regions) and the separation between their leading and following polarities; the tilt angle increases with polarity separation. Here we present a more detailed analysis of this relationship and show that this effect constrains the strength of the magnetic field at the bottom of the convection zone to a value between 40 and 150 kG, which confirms the constraints put by D'Silva and Choudhuri (1993) based on Joy's law (the tilt-latitude relationship), through an entirely different approach.Operated by the Association of Universities for Research in Astronomy, Inc., under CooperativeOperated by the Association of Universities for Research in Astronomy, Inc., under Cooperative 相似文献
7.
Donald F. Neidig Jr. 《Solar physics》1977,54(1):165-168
Microwave burst spectra are compared with the position, within the active region, of their associated flares observed in H. The magnetic fields predicted by Takakura's burst model (1972) are found to be in reasonable agreement with the fields expected at the flare locations.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. 相似文献
8.
First observations of the full Stokes vector in the upper chromosphere are presented. The He I 10830 Å line, which has been shown to give reliable measurements of the line-of-sight component of the magnetic field vector, has been used for this purpose. It is shown that the difference between the appearance of chromospheric and photospheric magnetic structures observed close to the solar limb is largely due to the difference in height to which they refer and projection effects. The observations do suggest, however, that the magnetic field above sunspot penumbrae is somewhat more vertical in the chromosphere than in the photosphere.The National Optical Astronomy Obervatories are operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation 相似文献
9.
Robert F. Howard 《Solar physics》1992,142(1):47-65
Mount Wilson synoptic data of both plages and sunspots are examined in an effort to determine in some detail the manner of the appearance and disappearance of the magnetic flux of active regions at the solar surface. Separating regions into leading and following portions by magnetic polarity in the case of the plages and by position in the case of sunspots (for which there is no magnetic information available in this data set), various characteristics of these features are studied, namely their rotation, their relative longitudinal motions, and the east-west inclinations of their magnetic fields. The evidence, taken together, suggests that the magnetic flux loops which comprise a region rise to the surface at the time of its formation, and (at least some of them) sink back below the surface at the time of the decay of the region. It is likely that not all the magnetic flux that arises sinks again below the surface.Operated by the Association of Universities for Research in Astronomy, Inc., under Cooperative Agreement with the National Science Foundation. 相似文献
10.
Harrison P. Jones Thomas L. Duvall Jr. John W. Harvey Charles T. Mahaffey Jan D. Schwitters Jorge E. Simmons 《Solar physics》1992,139(2):211-232
The NASA/NSO Spectromagnetograph is a new focal plane instrument for the National Solar Observatory/Kitt Peak Vacuum Telescope which features real-time digital analysis of long-slit spectra formed on a two-dimensional CCD detector. The instrument is placed at an exit port of a Littrow spectrograph and uses an existing modulator of circular polarization. The new instrument replaces the 512-channel Diode Array Magnetograph first used in 1973. Commercial video processing boards are used to digitize the spectral images at video rates and to separate, accumulate, and buffer the spectra in the two polarization states. An attached processor removes fixed-pattern bias and gain from the spectra in cadence with spatial scanning of the image across the entrance slit. The data control computer performs position and width analysis of the line profiles as they are acquired and records line-of-sight magnetic field, Doppler shift, and other computed parameters. The observer controls the instrument through windowed processes on a data control console using a keyboard and mouse. Early observations made with the spectromagnetograph are presented and plans for future development are discussed.The National Solar Observatory is a Division of the National Optical Astronomy Observatories which is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation. 相似文献
11.
Robert F. Howard 《Solar physics》1993,145(1):105-109
Sunspot group and magnetic (plage) data are examined to search for a relationship between the tilt angles of active regions and the separations of their leading and following portions. A relationship is found in the sense that larger positive tilt angles are associated with larger polarity separations. This is the direction predicted by recent theoretical work (D'Silva and Choudhuri, 1992). The explanation for this appears to be that smaller surface polarity separations lead to larger magnetic tension forces, which diminish the effect of the Coriolis force that acts to twist rising flux tubes.Operated by the Association of Universities for Research in Astronomy, Inc., under Cooperative Agreement with the National Science Foundation. 相似文献
12.
Richard C. Altrock Laurence J. November George W. Simon Robert W. Milkey Simon P. Worden 《Solar physics》1975,43(1):33-37
Heights of formation of lines that do not exhibit Zeeman splitting are calculated using an LTE, partial non-LTE, and full
non-LTE approach. Non-magnetic (g=0) lines are valuable for velocity investigations in quiet-Sun magnetic field regions, and a knowledge of their formation
heights is useful for obtaining three dimensional velocity profiles in these regions.
Presently at Sacramento Peak Observatory.
Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. 相似文献
13.
During sunspot cycles 20 and 21, the maximum in smoothed 10.7-cm solar radio flux occurred about 1.5 yr after the maximum smoothed sunspot number, whereas during cycles 18 and 19 no lag was observed. Thus, although 10.7-cm radio flux and Zürich suspot number are highly correlated, they are not interchangeable, especially near solar maximum. The 10.7-cm flux more closely follows the number of sunspots visible on the solar disk, while the Zürich sunspot number more closely follows the number of sunspot groups. The number of sunspots in an active region is one measure of the complexity of the magnetic structure of the region, and the coincidence in the maxima of radio flux and number of sunspots apparently reflects higher radio emission from active regions of greater magnetic complexity. The presence of a lag between sunspot-number maximum and radio-flux maximum in some cycles but not in others argues that some aspect of the average magnetic complexity near solar maximum must vary from cycle to cycle. A speculative possibility is that the radio-flux lag discriminates between long-period and short-period cycles, being another indicator that the solar cycle switches between long-period and short-period modes.Operated by the Association of Universities for Research in Astronomy, Inc. under contract with the National Science Foundation. 相似文献
14.
We study the covariance of longitudinal and latitudinal motions of small magnetic features after subtracting long-term averages
of differential rotation and meridional flow. The covariance is generally interpreted as Reynolds stress and linked to the
equatorward transport of angular momentum. Using high-resolution magnetograms taken daily with the NSO Vacuum Telescope on
Kitt Peak, we determine large-scale motions by a two-dimensional crosscorrelation analysis of pairs of consecutive daily observations
from which active regions are excluded, i.e., we analyze the motions of small magnetic features. In the present work, we focus
on 107 day pairs obtained during the year 1988 and on 472 day pairs taken in selected intervals from 1978 to 1990. We find
that all covariance values are very small (below 250 m2 s−2), which is about one to two orders of magnitude smaller than the values from sunspot measurements derived by other authors.
At active region latitudes, the masking process increases the noise, which increases the chance that the covariances at these
latitudes are not significantly different from zero. We find that the results depend strongly on the temporal averaging involved.
Daily unaveraged crosscorrelations lead to no apparent correlation between the residual velocities, while in the monthly averages
of the 1988 data, we find a covariance of −37 ± 15 m2 s−2 at 45° with a linear correlation of −0.59, which is significantly different from zero and has the right sign for an equatorial
transport of angular momentum. When we average over longer time periods, the covariance values decrease again. The annual
averages of the 1978–1990 data show both no significant covariances and the smallest errors. These small covariances imply
that the motions of small magnetic features do not reflect the transport of angular momentum via the mechanism of Reynolds
stress.
Operated by the Association of Universities for Research in Astronomy, Inc. under cooperative agreement with the National
Science Foundation. 相似文献
15.
The commonly used magnetograph line of Fe 5250.2 Å is found to be weakly blended by telluric water vapor. This circumstance could bias solar rotation measurements.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. 相似文献
16.
Robert F. Howard 《Solar physics》1991,132(2):257-270
Magnetogram data are analyzed to study east-west magnetic flux differences interpreted as the component of magnetic field line inclination at the photospheric level in a plane parallel to the solar equator. This component is determined by comparing average east-west pairs of flux values at equal distances from the central meridian. The average inclination of a whole region is such as to trail the rotation (incline toward the east) by about 1.9 deg. Leading and following polarities tilt toward each other by about 16 deg. Growing regions are strongly inclined to the west (to lead the rotation) with large differences between leading and following portions. Decaying regions are slightly inclined to the east with more normal differences between leading and following portions. These results concerning growing and decaying regions are seen with greater amplitude for reversed polarity regions. As the activity cycle progresses, the average inclination of the field lines of the following portions of regions varies from about 10 to about 3 deg (leading the rotation), and the average difference in inclination of the leading and following portions of regions decreases monotonically during the cycle from nearly 20 to about 11 deg. A slight difference is seen between the average east-west inclination angles of regions that are rotating faster than average and those that are rotating slower than average in the sense that slower regions are slightly inclined toward the east and faster regions toward the west. Some of these results may be related to the location or nature of the subsurface flux tubes to which the active regions fields are connected and also, perhaps, to the nature of this connection.Operated by the Association of Universities for Research in Astronomy, Inc., under Cooperative Agreement with the National Science Foundation. 相似文献
17.
Daily measurements for 18 months made at Tucson of the Ca K-index in integrated sunlight have been used to derive solar rotation rates. Power spectral analysis shows that one can obtain a well defined value of solar rotation rate in a period of six months, provided the data are fairly continuous. One might suppose it is possible to study the variation of solar (or stellar) rotation rate with time, a variation arising from a combination of differential rotation and shifts in the active latitude. A comparison between our observed rates and the prevailing dominant activity zones does not support this supposition, at least for the interval studied. Rather, our rates seem to depend on the circumstances of sampling and active region birth and decay.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. 相似文献
18.
J. B. Zirker 《Solar physics》1993,148(1):43-60
The prospects for observational tests of coronal heating theories are examined. Three heating mechanisms (Alfvén waves, D.C. electric currents, and MHD turbulence) are reviewed from this point of view. Some suggestions are offered for future tests but none, so far, would give unambiguous critical results.Operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation. 相似文献
19.
The response function defines the response of line profiles to a depth variation of such atmospheric parameters as velocity, magnetic field and turbulence. The properties of this function are derived and compared with the so-called contribution function.Operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. 相似文献
20.
The rotation of the magnetic axes of sunspot groups is studied as a function of the expansion and contraction of the groups along their magnetic axes. In general, except for the extreme values of tilt-angle change, slow rates of rotation of the magnetic axes are associated with low values of expansion or contraction, and faster rotation of the magnetic axes is associated with rapid expansion or contraction. The direction of rotation of the magnetic axes is related to expansion or contraction in the sense that would be predicted by the Coriolis force. A comparison of the effect at high and low latitudes shows a difference that further supports the Coriolis force hypothesis, and an examination of the amplitude of the effect also suggests that the Coriolis force may be a factor in the tilt-angle rotation of spot groups.Operated by the Association of Universities for Research in Astronomy, Inc., under Cooperative Agreement with the National Science Foundation. 相似文献