Related papers: Does Building a Relative Sunspot Number Make Sense…
Early observations of sunspot were realised by the naked eye. Possible utilization of these records for studying the long-term change in the Sun is discussed here. Other historical sunspot observations with camera obscuras are also…
The long term solar activity dependencies of ionospheric F$_1$ and F$_2$ regions' critical frequencies ($f_0F_1$ and $f_0F_2$) are analyzed for the last four solar cycles (1976--2015). We show that the ionospheric F$_1$ and F$_2$ regions…
Stellar spots may in some cases produce radial velocity (RV) signatures similar to those of exoplanets. To further investigate the impact of spots, we aim at studying the detectability of Earth mass planets in the habitable zone (HZ) of…
Variations of the sunspot number are important indicators of the solar activity cycles. The sunspot formation is a result of a dynamo process inside the Sun, which is far from being understood. We use simple dynamical models of the dynamo…
We report the statistics of the number of active regions (NAR) observed at 17 GHz with the Nobeyama Radioheliograph between 1992, near the maximum of cycle 22, and 2013, that also includes the maximum of cycle 24, and we compare with other…
The sunspot activity is the end result of the cyclic destruction and regeneration of magnetic fields by the dynamo action. We propose a new method to analyze the daily sunspot areas data recorded since 1874. By computing the power spectral…
Sunspot engravings made in the Maunder minimum are used to evaluate the fine structure of sunspots. Based on 78 images of the full solar disk and 77 images of individual sunspots, we have evaluated the ratio of penumbral-to-umbral area…
This research work is based on the study of the longitudinal distribution of the most active sunspot zones on the photosphere. Sunspot data has been analyzed for 12 solar cycles (cycles 12-23) separately for northern and southern…
Context: The evolution of solar active regions is still not fully understood. The growth and decay of active regions have mostly been studied in case-by-case studies. Aims: Instead of studying the evolution of active regions case by case,…
We have analysed the combined Greenwich and Solar Optical Observing Network (SOON) sunspot group data during the period of 1874-2011 and determined variations in the annual numbers (counts) of the small, large and big sunspot groups (these…
How global faculae and network coverage relates to that of sunspots is relevant to the brightness variations of the Sun and Sun-like stars. We extend earlier studies that found the facular-to-sunspot-area ratio diminishes with total sunspot…
In this paper Fourier Transform and Wavelet Transform are applied in case of recent 300 years of sunspot numbers to explain the solar cycles. Here basically parallel study of Fourier and Wavelet analysis are done and we have observed that…
We study the variation in the magnetic field strength and the umbral intensity of sunspots during the declining phase of the solar cycle no.23 and in the beginning of cycle no.24. We analyze a sample of 183 sunspots observed from 1999 until…
Complex network approaches have been recently developed as an alternative framework to study the statistical features of time-series data. We perform a visibility-graph analysis on both the daily and monthly sunspot series. Based on the…
Using neural networks as a prediction method, we attempt to demonstrate that forecasting of the Sun's sunspot time series can be extended to the spatial-temporal case. We employ this machine learning methodology to forecast not only in time…
We have analyzed the full set of SOHO/MDI f- and p-mode oscillation frequencies from 1996 to date in a search for evidence of solar radius evolution during the rising phase of the current activity cycle. Like Antia et al. (2000), we find…
Sunspots are obvious observable manifestations of the toroidal magnetic field generated through the dynamo in the convection zone. They appear in different sizes, having a wide distribution in their area. We analyse the sunspot group area…
We consider the statistical relationship between the growth rate of activity in the early phase of a solar cycle with its subsequent amplitude on the basis of four datasets of global activity indices (Wolf sunspot number, group sunspot…
The historical record of sunspot areas is a valuable and widely used proxy of solar activity and variability. The Royal Greenwich Observatory (RGO) regularly measured this and other parameters between 1874 and 1976. After that time records…
The increased amount of information provided by ongoing missions such as the Solar Dynamics Observatory (SDO) represents a great challenge for the understanding of basic questions such as the internal structure of sunspots and how they…