X. M. Gu

Regularity of the north-south asymmetry of solar activity

In the present work, the dominant hemisphere of solar activity in each of solar cycles 12 to 22 has been clarified by calculating the actual probability of the hemispheric distribution of several solar activity phenomena using long-term observational records. An attempt is made to demonstrate that a long characteristic time scale, about 12-cycle length, is inferred to occur in solar activity.

On long-term predictions of the maximum sunspot numbers of solar cycles 21 to 23

We have collected a set of predicted values of maximum sunspot numbers of solar cycles 22 and 23 published in the literature and examined the characteristics of predictions made by various methods. The precursor methods are found to be always superior to other prediction methods. The maximum sunspot number of solar cycle 23 is here inferred to be about 162.

Hemispheric variation in solar activity

Hemispheric solar activity is usually found to be asymmetric within each solar cycle, and this behavior is also found in its extended cycle. In addition to the familiar Il yr individual cyclic variation, a long-term hemispheric variation of at least 12-cycle length is inferred to exist.

On the Latitudinal Distribution of Sunspot Groups over a Solar Cycle

The latitudinal distribution of sunspot groups over a solar cycle is investigated. Although individual sunspot groups of a solar cycle emerge randomly at any middle and low latitude, the whole latitudinal distribution of sunspot groups of the cycle is not stochastic and, in fact, can be represented by a probability density function of the Γ distribution having maximum probability at about 15.5°. The maximum amplitude of a solar cycle is found to be positively correlated against the number of sunspot groups at high latitude (≥35°) over the cycle, as well as the mean latitude. Also, the relation between the asymmetry of sunspot groups and its latitude is investigated, and a pattern of the N-S asymmetry in solar activity is suggested.

Latitude Migration of Sunspot Groups

Characteristics of latitude migration of sunspot groups in the northern and southern hemispheres are investigated by using the Royal Greenwich Observatory data set from the years 1874 through 1999. Latitude migration of sunspot groups is found to be represented by a binomial formula, which quantitatively describes the law. Latitude migration velocity of sunspot groups is largest at the beginning of a Sporer solar cycle, and as the solar cycle progresses, it decreases with time, with an average of about 1-degrees6 yr(1) during a solar cycle. Two different methods have been employed to confirm that latitude migration in both hemispheres is statistically the same.

STATISTICAL BEHAVIOR OF SUNSPOT GROUPS ON THE SOLAR DISK

In the present study we have produced a diagram of the latitude distribution of sunspot groups from the year 1874 through 1999 and examined statistical characteristics of the mean latitude of sunspot groups. The reliability of the observed data set prior to solar cycle 19 is found quite low as compared with that of the data set observed after cycle 19. A correlation is found between maximum latitude at which first sunspot groups of a new cycle appear and the maximum solar activity of the cycle. It is inferred that solar magnetic activity during the early part of an extended solar cycle may contain some information about the strength of forthcoming solar cycle. A formula is given to describe latitude change of sunspot groups with time during an extended solar cycle. The latitude-migration velocity is found to be largest at the beginning of solar cycle and decreases with time as the cycle progresses with a mean migration velocity of about 1.61° per year.

A solar Stokes spectrum telescope

A solar Stokes spectrum telescope has been built and is routinely used to measure full Stokes spectra of solar surface features. Its optical and electronic systems are outlined while the polarization analyzer is described in detail. The observations carried out by this telescope are sampled and the performance parameters are given. The measured Stokes spectra during solar cycle 23 show that the measurement accuracy of Stokes polarization components can reach an r.m.s. noise level of less than 9.0×10−4 with short time integration for an active region and 5.0×10−4 with long time integration for a weak field region without smoothing.