A higher correlation tends to yield a more accurate prediction,so that a correlation as high as possible has been searched for and employed in the prediction of solar activity.Instead of using geomagnetic activity during the descending phase of the solar cycle,the minimum annual aa index (aa min) is used as an indicator for the ensuing maximum amplitude (R m) of the sunspot cycle.A four-cycle periodicity is roughly shown in the correlation between R m and aa min.The widely accepted Ohl's precursor prediction method often fails due to the prediction error relative to its estimated uncertainty.An accurate prediction depends on the positive variation of the correlation rather than a higher correlation.Previous experiences by using this method indicate that a prediction for the next cycle,R m (24)=80 ± 17,is likely to fail,implying that the sunspot maximum of Cycle 24 may be either smaller than 63 or greater than 97.
The maximum amplitude (Rm) of a solar cycle,in the term of mean sunspot numbers,is well-known to be positively correlated with the preceding minimum (Rmin).So far as the long term trend is concerned,a low level of R min tends to be followed by a weak R m,and vice versa.We found that the evidence is insufficient to infer a very weak Cycle 24 from the very low R min in the preceding cycle.This is concluded by analyzing the correlation in the temporal variations of parameters for two successive cycles.
The growth rate of solar activity in the early phase of a solar cycle has been known to be well correlated with the subsequent amplitude (solar maximum).It provides very useful information for a new solar cycle as its variation reflects the temporal evolution of the dynamic process of solar magnetic activities from the initial phase to the peak phase of the cycle.The correlation coefficient between the solar maximum (R max) and the rising rate (β a) at Δm months after the solarminimum (Rmin) is studied and shown to increase as the cycle progresses with an inflection point (r=0.83) at about Δm=20 months.The prediction error of R max based on β a is found within estimation at the 90% level of confidence and the relative prediction error will be less than 20% when Δm 20.From the above relationship,the current cycle (24) is preliminarily predicted to peak around October,2013 with a size of R max=84±33 at the 90% level of confidence.
From the observed vector magnetic fields by the Solar Optical Telescope/ Spectro-Polarimeter aboard the satellite Hinode, we have examined whether or not the quiet Sun magnetic fields are non-potential, and how the G-band filigrees and Ca II network bright points (NBPs) are associated with the magnetic non-potentiality. A sizable quiet region in the disk center is selected for this study. The new findings by the study are as follows. (1) The magnetic fields of the quiet region are obviously non-potential. The region-average shear angle is 40-, the average vertical current is 0.016A m-2, and the average free magnetic energy density, 2.7×102 erg cm-3. The magnitude of these non-potential quantities is comparable to that in solar active regions. (2) There are over- all correlations among current helicity, free magnetic energy and longitudinal fields. The magnetic non-potentiality is mostly concentrated in the close vicinity of network elements which have stronger longitudinal fields. (3) The filigrees and NBPs are magnetically characterized by strong longitudinal fields, large electric helicity, and high free energy density. Because the selected region is away from any enhanced network, these new results can generally be applied to the quiet Sun. The findings imply that stronger network elements play a role in high magnetic non-potentiality in heating the solar atmosphere and in conducting the solar wind.
Meng Zhao Jing-Xiu Wang Chun-Lan Jin Gui-Ping Zhou
The temperature curve in the solar chromosphere has puzzled astronomers for a long time.Referring to the structure of supergranular cells,we propose an inductive heating model.It mainly includes the following three steps.(1) A small-scale dynamo exists in the supergranulation and produces alternating small-scale magnetic fluxes;(2) The supergranular flow distributes these small-scale fluxes according to a regular pattern;(3) A skin effect occurs in the alternating and regularly-distributed magnetic fields.The induced current is concentrated near the transition region and heats it by resistive dissipation.
During the total solar eclipse of July 22, 2009, we carried out a white-light observation in Anji, Zhejiang, China. The aim wasto observe the polar plumes (PPs) with high spatial and temporal resolutions in white-light. With the observational data, weinvestigate the properties and evolution of the PPs and compare them with those of the low-latitude plumes (LPs). We find thatboth the PPs and the LPs have comparable lengths and widths, and the mean length and width are 300 Mm and 16 Mm, re-spectively. The average inclination angle (13 degree) of the PPs is smaller than that (32 degree) of the LPs. Generally, theplumes which are closer to the coronal hole center are more vertical. We trace the PPs and the LPs in the sequence of imagesand find that none of them disappears and no new one is created. Additionally, neither plasma outflow nor transverse oscilla-tion is observed. These imply that the evolution process of plumes is much longer than the timescale of eclipse.
Ever since the magnetohydrodynamic(MHD)method for extrapolation of the solar coronal magnetic field was first developed to study the dynamic evolution of twisted magnetic flux tubes,it has proven to be efficient in the reconstruction of the solar coronal magnetic field.A recent example is the so-called data-driven simulation method(DDSM),which has been demonstrated to be valid by an application to model analytic solutions such as a force-free equilibrium given by Low and Lou.We use DDSM for the observed magnetograms to reconstruct the magnetic field above an active region.To avoid an unnecessary sensitivity to boundary conditions,we use a classical total variation diminishing Lax-Friedrichs formulation to iteratively compute the full MHD equations.In order to incorporate a magnetogram consistently and stably,the bottom boundary conditions are derived from the characteristic method.In our simulation,we change the tangential fields continually from an initial potential field to the vector magnetogram.In the relaxation,the initial potential field is changed to a nonlinear magnetic field until the MHD equilibrium state is reached.Such a stable equilibrium is expected to be able to represent the solar atmosphere at a specified time. By inputting the magnetograms before and after the X3.4 flare that occurred on 2006 December 13,we find a topological change after comparing the magnetic field before and after the flare.Some discussions are given regarding the change of magnetic configuration and current distribution.Furthermore,we compare the reconstructed field line configuration with the coronal loop observations by XRT onboard Hinode.The comparison shows a relatively good correlation.
Using the multi-wavelength data from the Atmospheric Imaging Assembly (AIA)onboard the Solar Dynamics Observatory(SDO)spacecraft,we study a jet occurring in a coronal hole near the northern pole of the Sun.The jet presented distinct upward helical motion during ejection.By tracking six identified moving features (MFs)in the jet,we found that the plasma moved at an approximately constant speed along the jet's axis.Meanwhile,the MFs made a circular motion in the plane transverse to the axis.Inferred from linear and trigonometric fittings to the axial and transverse heights of the six tracks,the mean values of the axial velocities,transverse velocities,angular speeds,rotation periods,and rotation radii of the jet are 114 km s-1, 136 km s-1,0.81-s-1,452 s and 9.8×103 km respectively.As the MFs rose,the jet width at the corresponding height increased.For the first time,we derived the height variation of the longitudinal magnetic field strength in the jet from the assumption of magnetic flux conservation.Our results indicate that at heights of 1×104～7× 104 km from the base of the jet,the flux density in the jet decreases from about 15 to 3 G as a function of B=0.5(R/R⊙-1)-0.84(G).A comparison was made with other results in previous studies.
With the observations of the Solar-Terrestrial Relations Observatory(STEREO) and the Solar Dynamics Observatory(SDO),we analyze in detail the kinematics of global coronal waves together with their intensity amplitudes(so-called "perturbation profiles").We use a semi-automatic method to investigate the perturbation profiles of coronal waves.The location and amplitude of the coronal waves are calculated over a 30? sector on the sphere,where the wave signal is strongest.The position with the strongest perturbation at each time is considered as the location of the wave front.In all four events,the wave velocities vary with time for most of their lifetime,up to 15 min,while in the event observed by the Atmospheric Imaging Assembly there is an additional early phase with a much higher velocity.The velocity varies greatly between different waves from 216 to 440 km s-1.The velocity of the two waves initially increases,subsequently decreases,and then increases again.Two other waves show a deceleration followed by an acceleration.Three categories of amplitude evolution of global coronal waves are found for the four events.The first is that the amplitude only shows a decrease.The second is that the amplitude initially increases and then decreases,and the third is that the amplitude shows an orderly increase,a decrease,an increase again and then a decrease.All the extreme ultraviolet waves show a decrease in amplitude while propagating farther away,probably because the driver of the global coronal wave(coronal mass ejection) is moving farther away from the solar surface.
With the polarimetric observations obtained by the Spectro-Polarimeter on board Hinode, we study the relationship between granular development and magnetic field evolution in the quiet Sun. Six typical cases are displayed to exhibit interaction between granules and magnetic elements, and we have obtained the following results. (1) A granule develops centrosymmetrically when no magnetic flux emerges within the granular cell. (2) A granule develops and splits noncentrosymmetrically while flux emerges at an outer part of the granular cell. (3) Magnetic flux emergence in a cluster of mixed polarities is detected at the position of a granule as soon as the granule breaks up. (4) A dipole emerges accompanied by the development of a granule, and the two elements of the dipole are rooted in the adjacent intergranular lanes and face each other across the granule. Advected by the horizontal granular motion, the positive element of the dipole then cancels with the pre-existing negative flux. (5) Flux cancellation also takes place between a positive element, which is advected by granular flow, and its surrounding negative flux. (6) While magnetic flux cancellation takes place in a granular cell, the granule shrinks and then disappears. (7) Horizontal magnetic fields are enhanced at the places where dipoles emerge and where opposite polarities cancel each other, but only the horizontal fields between the dipolar elements point in an orderly way from the positive elements to the negative ones. Our results reveal that granules and small-scale magnetic fluxes influence each other. Granular flow advects magnetic flux, and magnetic flux evolution suppresses granular development. There exist extremely large Doppler blue-shifts at the site of one canceling magnetic element. This phenomenon may be caused by the upward flow produced by magnetic reconnection below the photosphere.
