We explore the latitudinal distribution of sunspots and pursue to establish a correlation between the statistical parameters of the latitudinal distribution of sunspots and characteristics of solar activity. For this purpose, we have statistically analyzed the daily sunspot areas and latitudes observed from May in 1874 to September in 2016. As results, we confirm that the maximum of the monthly averaged International Sunspot Number (ISN) strongly correlates with the mean number of sunspots per day, while the maximum ISN strongly anti-correlates with the number of spotless days. We find that both the maximum ISN and the mean number of sunspots per day strongly correlate with the the average latitude, the standard deviation, the skewness of the the latitudinal distribution of sunspots, while they appears to marginally correlate with the kurtosis. It is also found that the northern and southern hemispheres seem to show a correlated behavior in a different way when sunspots appearing in the northern and southern hemispheres are examined separately.

We study an association between the duration of solar activity and characteristics of the latitude distribution of sunspots by means of center-of-latitude (COL) of sunspots observed during the period from 1878 to 2008 spanning solar cycles 12 to 23. We first calculate COL by taking the area- weighted mean latitude of sunspots for each calendar month to determine the latitudinal distribution of COL of sunspots appearing in the long and short cycles separately. The data set for the long solar cycles consists of the solar cycles 12, 13, 14, 20, and 23. The short solar cycles include the solar cycles 15, 16, 17, 18, 19, 21, and 22. We then fit a double Gaussian function to compare properties of the latitudinal distribution resulting from the two data sets. Our main findings are as follows: (1) The main component of the double Gaussian function does not show any significant change in the central position and in the full-width-at-half-maximum (FWHM), except in the amplitude. They are all centered at  11◦ with FWHM of  5◦. (2) The secondary component of the double Gaussian function at higher latitudes seems to differ in that even though their width remains fixed at  4◦, their central position peaks at  22.1◦ for the short cycles and at  20.7◦ for the long cycles with quite small errors. (3) No significant correlation could be established between the duration of an individual cycle and the parameters of the double Gaussian. Finally, we conclude by briefly discussing the implications of these findings on the issue of the cycle 4 concerning a lost cycle.

We have analyzed vector magnetograms and Hβ filtergrams of two sunspot groups, one in a growing phase and the other in a decaying phase. In this study, the temporal evolution of their magnetic morphology has been investigated in association with solar activity. The morphological variations of the growing and decaying phase of these sunspots revealed in detail the coalescence of small spots into a large spot and the fragmentation of a large spot into many small spots, respectively. Numerous small flares were detected in the spot group during the decaying phase. This seems to be intimately associated with the shearing motions of many spots with different polarities created by fragmentation of a large sunspot. The magnetic flux and the average shear angle are found to be substantially reduced during the decaying phase, especially in the course of the flarings. This implies that the decaying phase of the sunspot is, to some degree, involved with magnetic field cancellation. The growing spot group has not shown any large activities, but numerous small spots have grown into a typical bipolar sunspot.

An attempt has been made to analyze time series of Hα, Hβ, and Hɤ line profiles taken from a 3B/X6.1 flare which occurred on Oct. 27, 1991 in an active region, NOAA 6891. A total of 22 sets of Hα, Hβ, and Hɤ taken with a low and non-uniform time resolution of 10-40 seconds were scanned by PDS with absolute intensity calibration to derive the physical characteristics of the material in the flare chromosphere. Our . results are as follows: (1) The lower Balmer lines observed during the flare activity are broadened by Stark effect. (2) At the peak of the flare activity, the electron temperature of the Balmer line emitting region reaches up to 35000K and its geometrical thickness increases to a scale of ~104km, suggesting that high energy particles penetrate deep into the photospheric level.

The reduced profiles of C 2 5150.56, CN 3864.32, MgH 5150.20 and FeI 5150.84 lines, representing the penumbra, the penumbra-umbra boundary and the umbra of spa 6403 have been analyzed by comparing them with the synthetic profiles computed from a set of umbral and penumbral models. The results are presented and discussed. It is suggested that there may be a significant lateral flow of pbotospheric radiation into the umbral and penumbral regions of the sunspots.

High spatial and spectral resolution observations have been made over a sunspot (SPO 6403) with the Echelle Spectrograph at the Vacuum Tower Telescope, Sacramento Peak Observatory. Our observed spectra, scanned with SPO's fast microdensitometer, clearly show strengthening of C 2 lines in the penumbra relative to the photosphere and much weakening in the umbra in agreement with the predictions made by our molecular equilibrium calculations (Lee et al. 1981).

Theoretical profiles of selected rotational lines of C 2 CH, CN, TiO and MgH are computed by using the current models of sunspot unbrae and penumbrae. It is found that the lines of the diatomic carbides are enhanced in penumbrae relative to umbrae, while MgH lines are more strongly enhanced in umbrae than in penumbrae and the quiet photosphere. The results are discussed with respect to selecting lines suitable for studying the structure of sunspots.

Calculations of molecular number densities as a function of optical depth in selected umbral, penumbral and photospheric models predict penumbral enhancement of diatomic molecules containing carbon atoms, strong umbral enhancement of oxides, and moderate umbral enhancement of hydrides. The role of CO formation in an oxygen rich atmosphere is discussed.

A hydrostatic model atmosphere of a typical umbral core is constructed on the basis of both Na I D 2 line profile and umbral core-to disk continuum intensity ratio. The observations were obtained by Mullan and Wyller with photoelectric means over the range from 4000 |AA a n d 6500 |AA . The computed line profile of Na I D 2 and the emergent continuum intensity distribution are compared with the observations. The temperature of umbral cores is found to be lower by 300 ˚ K t o 500 ˚ K than that of their ambient umbral region. The detailed physical structure of a working model of umbral cores is proposed.

Observational implication for a possible presence of a magnetic monopole-like field in the visible layers of sunspots is examined by constructing a magnetostatic model of sunspots with a monopole-like field configuration. The resulting monopole approximation for a magnetic structure of spots is found to be compatible with the observations within a certain limited range of optical depth, which happens to lie mostly in its visible range.

The earlier findings on the radiative heating through the umbral walls in large sunspots are further investigated. No significant evidence for the umbra! heating has been found in small-sized sunspot umbrae.