Dependence of Supergranular Length-Scales on Network Magnetic Fields

In an earlier paper by Raju, Srikanth, and Singh (1998), the average size of chromospheric network cells has been shown to have a dependence on the solar latitude. This was presumed to be due to the reduction of supergranular length-scales by network magnetic field enhancements. It has been found that the network brightness enhancements over solar latitude support this finding. Significant negative correlations have been found between the average cell size and the network brightness enhancements. Since the brightness enhancements are essentially due to the magnetic field concentrations, it is suggested that the network magnetic fields reduce the network cell sizes. We have also obtained the variations of skewness of network brightness distributions over solar latitude, which follow the network field variations. This complements the findings of Caccin et al. (1998) that skewness of brightness distribution follows the solar cycle. The findings suggest that the dependence of supergranular sizes, network brightness, and skewness of network brightness distribution on solar latitude or on the phase of the solar cycle is due to the associated variation of network magnetic fields.     

第22和23太阳周太阳活动预测

本文首先分析指出第22太阳周前半周的太阳活动所具有的特点:(1)有最高的起始极小值;(2)上升速度快;(3)升段时间最短;(4)峰期长,可能有双峰;(5)个别时段活动水平极高.然后对第22周后半周的活动情况做了预计:在后半周将可能观测到大约2800个活动区,28000个耀斑,210个X级X射线爆发和大约80次太阳质子事件.最后,应用本文给出的太阳周参量关系式.预报第23周太阳黑子数月均平滑值的峰值为119,位于2001.6年.     

Instantaneous Phase and Amplitude Correlation in the Solar Cycle

In the present study we address the issue of discerning between deterministic and stochastic paradigms in order to understand the behavior of the solar cycle. To this end we show the degree of correlation between the instantaneous amplitude and frequency in the sunspot number time series by the use of the Gabor analytic signal. We compare this correlation with those arising from two theoretical models: (a) the Barnes model of widespread use in the literature and (b) a spatial truncation of the MHD equations. We show that comparisons between the correlation observed in the sunspot time series with those arising from theoretical models can be used to refute one of the models.     

Magnetic Clouds: Solar Cycle Dependence,Sources, and Geomagnetic Impacts

Magnetic clouds (MCs) are transient magnetic structures giving the strongest southward magnetic field (Bz south) in the solar wind. The sheath regions of MCs may also carry a southward magnetic field. The southward magnetic field is responsible for space-weather disturbances. We report a comprehensive analysis of MCs and Bz components in their sheath regions for 1995 to 2017. 85% of 303 MCs contain a south Bz up to 50 nT. Sheath Bz during the 23 years may reach as high as 40 nT. MCs of the strongest magnetic magnitude and Bz south occur in the declining phase of the solar cycle. Bipolar MCs depend on the solar cycle in their polarity, but not in the occurrence frequency. Unipolar MCs show solar-cycle dependence in their occurrence frequency, but not in their polarity. MCs with the highest speeds, the largest total-\(B\) magnitudes, and sheath Bz south originate from source regions closer to the solar disk center. About 80% of large Dst storms are caused by MC events. Combinations of a south Bz in the sheath and south-first MCs in close succession have caused the largest storms. The solar-cycle dependence of bipolar MCs is extended to 2017 and now spans 42 years. We find that the bipolar MC Bz polarity solar-cycle dependence is given by MCs that originated from quiescent filaments in decayed active regions and a group of weak MCs of unclear sources, while the polarity of bipolar MCs with active-region flares always has a mixed Bz polarity without solar-cycle dependence and is therefore the least predictable for Bz forecasting.     

Solar and Heliospheric Causes of Geomagnetic Perturbations during the Growth Phase of Solar Cycle 23

A database is compiled for the study of solar and heliospheric causes of geomagnetic perturbations with the daily average index A > 20 that were observed in the period 1997–2000. The number of such events (more than 200) progressively increased and fluctuated as the current solar cycle developed. It is established that geomagnetic storms are generated by dynamical processes and structures near the center of the solar disk in a zone of several tens of degrees, and these processes are responsible for the appearance in the Earth's region, within several tens of hours, of quasistationary and transient solar wind streams with a sufficiently strong southward component of the heliospheric magnetic field. These streams lasted more than a few hours. The following structures can serve as morphological indicators for the prediction of the appearance of such streams: (1) active and disappearing filaments derived from synoptic -maps of the Sun, (2) solar flares, (3) coronal holes and evolving active regions, and (4) the heliospheric current sheet. The geometry of coronal mass ejections needs further observational study.     

Prediction of Solar Cycle Maximum Using Solar Cycle Lengths

If the rise time RT, fall time FT, and total time TT (i.e., RT+FT) of a solar cycle are compared against the maximum amplitude Rz(max ) for the following cycle, then only the association between TT and Rz(max ) is inferred to be well anticorrelated, inferring that the larger (smaller) the value of Rz(max ) for the following cycle, the shorter (longer) the TT of the preceding cycle. Although the inferred correlation (−0.68) is statistically significant, the inferred standard error of estimate is quite large, so predictions using the inferred correlation are not very precise. Removal of cycle pairs 15/16, 19/20, and 20/21 (statistical outliers) yields a regression that is highly statistically significant (−0.85) and reduces the standard error of estimate by 18%. On the basis of the adjusted regression and presuming TT=140 months for cycle 23, the present ongoing cycle, cycle 24’s 90% prediction interval for Rz(max ) is estimated to be about 94±44, inferring only a 5% probability that its Rz(max ) will be larger than about 140, unless of course cycle pair 23/24 is a statistical outlier.     

Formation of a Switchback During the Rising Phase of Solar Cycle 21

The customary notion that high-latitude filaments arise from magnetic flux originating in the active-region belts finds its modern expression in numerical models that generate filament channels from flux patterns migrating from active latitudes to the polar caps. Polarity inversions underlying high-latitude filament channels are swept into distinct patterns called `switchbacks' under the joint influence of differential rotation, supergranular diffusion, and meridional flow. The numerical model of Mackay and van Ballegooijen (2001) predicts a heretofore unsuspected solar-cycle dependence to the hemispheric pattern of filament magnetic fields. Observations presented here of a switchback formed early in cycle 21 confirm some key aspects of their model. In this remarkable example the flux diffusing out of the source region migrates to the opposite side of the Sun before it encounters another active region with which to create the quadrupolar field configuration wherein a return arm forms to complete the switchback.     

Three Super Active Regions in the Descending Phase of Solar Cycle 23

We analyze the magnetic configurations of three super active regions, NOAA 10484, 10486 and 10488, observed by the Huairou Multi-Channel Solar Telescope (MCST) from 2003 October 18 to November 4. Many energetic phenomena, such as flares (including a X-28 flare) and coronal mass ejections (CMEs), occurred during this period. We think that strong shear and fast emergence of magnetic flux are the main causes of these events. The question is also of great interest why these dramatic eruptions occurred so close together in the descending phase of the solar cycle.     

太阳活动23周上升阶段质子事件的 预报分析

以２２周太阳活动低年（１９９３－１９９５）质子事件及其对应活动区的综合分析结果为判据,预报２３周太阳活动上升阶段的质子事件．从１９９７年１１月开始到１９９８年１２月,用该方法预报的质子事件共６个,报准３个,不确定一个,虚报１个,漏报１个（太阳背面产生的事件）．本文对用该方法预报的结果进行了分析讨论,并与世界警报中心的预报结果进行了比对,结果表明,该方法对于质子事件的短期预报是有效的．     

Solar Cycle Workshop

Conclusion Clearly there is no concensus or agreement at present about the nature and mechanism of the solar cycle or, indeed, about many of its observed features. However, by highlighting these areas of agreement and disagreement through the presentations and discussions during this meeting, it is hoped that the work of the Workshop Groups will be directed to resolving at least some of these questions at or before the next meeting (planned for August, 1987). In particular, it is hoped that Group V (The Sun as a Star) will be able to contribute through studies of the sun in relation to stellar cycles and activity.     

Solar Cycle Workshop

The presentations and discussions which took place during the second meeting of the Solar Cycle Workshop are summarized under the headings: sunspot minimum, the extended cycle, the large-scale photospheric motions, the large-scale magnetic fields and the polar reversal, the small-scale fields, global cyclic phenomena and the fundamental processes. The progress achieved so far is assessed and the directions for future observational and theoretical work are suggested.     

Fluctuations of Solar Activity during the Declining Phase of the 11-Year Sunspot Cycle

The number of coronal mass ejections (CMEs) erupting from the Sun follows a trend similar to that of sunspot numbers during the rising and maximum phase of the solar cycle. In the declining phase, the CME number has large fluctuations, dissimilar to those of sunspot numbers. In several studies of solar – interplanetary and solar – terrestrial relationships, the sunspot numbers and the 2800-MHz flux (F10) are used as representative of solar activity. In the rising phase, this may be adequate, but in the declining phase, solar parameters such as CMEs may have a different behaviour. Cosmic-ray Forbush decreases may occur even when sunspot activity is low. Therefore, when studying the solar influence on the Earth, one has to consider that although geomagnetic conditions at solar maximum will be disturbed, conditions at solar minimum may not be necessarily quiet.     

Propagation of Coronal Mass Ejections Observed During the Rising Phase of Solar Cycle 24

In this study, we investigate the interplanetary consequences and travel time details of 58 coronal mass ejections (CMEs) in the Sun–Earth distance. The CMEs considered are halo and partial halo events of width \({>}\,120\)°. These CMEs occurred during 2009?–?2013, in the ascending phase of the Solar Cycle 24. Moreover, they are Earth-directed events that originated close to the centre of the solar disk (within about \(\pm30\)° from the Sun’s centre) and propagated approximately along the Sun–Earth line. For each CME, the onset time and the initial speed have been estimated from the white-light images observed by the LASCO coronagraphs onboard the SOHO space mission. These CMEs cover an initial speed range of \({\sim}\,260\,\mbox{--}\,2700~\mbox{km}\,\mbox{s}^{-1}\). For these CMEs, the associated interplanetary shocks (IP shocks) and interplanetary CMEs (ICMEs) at the near-Earth environment have been identified from in-situ solar wind measurements available at the OMNI data base. Most of these events have been associated with moderate to intense IP shocks. However, these events have caused only weak to moderate geomagnetic storms in the Earth’s magnetosphere. The relationship of the travel time with the initial speed of the CME has been compared with the observations made in the previous Cycle 23, during 1996?–?2004. In the present study, for a given initial speed of the CME, the travel time and the speed at 1 AU suggest that the CME was most likely not much affected by the drag caused by the slow-speed dominated heliosphere. Additionally, the weak geomagnetic storms and moderate IP shocks associated with the current set of Earth-directed CMEs indicate magnetically weak CME events of Cycle 24. The magnetic energy that is available to propagate CME and cause geomagnetic storm could be significantly low.     

The Solar Cycle Workshop

The contributions to the third meeting of the Solar Cycle Workshop are briefly summarized. The topics discussed at the meeting included (i) predictions and precursors, (ii) large and small-scale magnetic fields, (iii) photospheric velocity fields, (iv) coronal phenomena, (v) the Sun as a star, (vi) limb temperature measurements and helioseismic data, (vii) theoretical modelling of the cycle, (viii) cyclic activity in stars, and (ix) the interpretation of the Elatina Sandstone Layers.This paper was presented at the third meeting of the Solar Cycle Workshop, held in Sydney, Australia, January 9–13, 1989.     

Predictions of Solar Cycle 24

A summary and analysis of more than 50 predictions of the amplitude of the upcoming Solar Cycle 24 is presented. All of the predictions were published before solar minimum and represent our efforts to anticipate solar maximum at ever-earlier epochs. The consistency of the predictions within their assigned categories is discussed. Estimates of the significance of the predictions, compared to the climatological average, are presented.     

Solar Rotation Rate during Solar Activity Cycle 23

We studied the solar rotation rate and its temporal change, using the sunspot data obtained during activity cycle 23 (1996 – 2006). The equatorial rotation rate is nearly the same as in the former cycle 22, while the latitudinal gradient of differential rotation considerably increased. Comparison of our results with others indicates the existence of a long-term periodicity of about eight cycles in differential rotation. In addition, no significant asymmetry in differential rotation between the northern and southern hemispheres during cycle 23 was found. The equatorial rotation rate and the latitudinal gradient of the differential rotation in the period of cycle 23 are approximately constant, except for the initial and final phases in the cycle.     

Solar Rotation And Cycle Length

A positive correlation is suggested between solar rotation rate and solar cycle length for cycles 12 to 20. This result seems to be opposite to recent observations in solar-type stars and the Sun and yields inverse correlations between cycle lengths and chromospheric activity, but it agrees with previous work with solar-type stars and the Sun suggesting a positive correlation between cycle length and rotation rate. Estimates of solar cycle length for the Maunder minimum suggest a length 17 yr.