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Solar activity, such as sunspots and flares, has a great impact on humans, living beings, and technologies in the whole world. Changes in sunspots will influence high-frequency and space-navigation radio communications. Based on the full-disk, southern and northern hemispheres sunspot areas (SAs) data in 1874–2023 from the Royal Observatory, Greenwich (RGO) USAF/NOAA, extreme value theory (EVT) is applied to predict the trend of the 25th and 26th solar cycles (SCs) in this work. Two methods with EVT, the block maxima (BM) approach and the peaks-over-threshold (POT) approach, are employed to research solar extreme events. The former method focuses on each block's maximum sunspot areas value and is applied for the generalized extreme value (GEV) distribution. The latter method aims to select the extreme values exceeding a threshold value and is used to obtain the generalized Pareto (GP) distribution. It is the first time that the EVT is applied on the sunspot areas data from the Royal Observatory, Greenwich (RGO) USAF/NOAA. The analysis indicates that the estimated 8-year return levels for sunspot areas are 5701 and 6258 using the two methods, while the estimated 19-year return levels are all 7165. This suggests that the trends of the 25th and 26th solar cycles will be stronger than that of the 24th solar cycle. [ABSTRACT FROM AUTHOR]

Hα flare index is one of the solar activity indicators to describe the physical properties of the active regions in the solar atmosphere. Sunspot number is a representative indicator of the magnetic activity in the photosphere, which is associated with the energy supply rate to the corona. Thus, it is significant to investigate the phase relationship between Hα flare activity and sunspot activity. In the present work, monthly Hα flare index (FIm), monthly sunspot activity (sunspot numbers (Rs) and group sunspot numbers (Rg)) compiled from the Purple Mountain Observatory are used to find their phase relationship using the cross-correlation analysis. For solar cycles 20–23, there is a very pronounced time lag of about 9, 4, 4.5 and 10 months between the monthly FIm and Rs, respectively. Furthermore, there is a noticeable time lag of about 7, 8, 4.5 and 9 months between FIm and Rg for the same cycles, respectively. If we take the whole time series together, we notice that FIm has a time lag of about 4 months with regard to both Rs and Rg. The possible physical mechanisms for their observed phase lag are discussed. [ABSTRACT FROM AUTHOR]

Studying solar filaments can help in understanding the distribution of large-scale field in the solar atmosphere and provide useful insights into the nature of the solar magnetic field. Recently, the National Astronomical Observatory of the Chinese Academy of Sciences has collected huge volumes of data about solar filaments from several international observing stations for nearly 100 years. Designing a database, as well as establishing a networked tool for making the best of it, are necessary to provide efficient and convenient access to the data for researchers. In this study, we introduce a solar filament database, involving digital image data of nearly 45 terabytes, based on MySQL and a data management platform named database management system of hundred years of solar filament archives (http://faste.ctgu.edu.cn) that adopts Browser/Server mode and is written in the Java programming language. From this data system, users can realise multi-property query on the basis of demands, download data under multiple conditions, perform visual query for information on one single filament, view long-term data statistics of filament properties, and implement extensions and management of the database. [ABSTRACT FROM AUTHOR]

It is necessary to better understand the dynamic process of solar differential rotation. Here the hand-drawing sunspot group records from 1958 to 2015 of Yunnan Observatories (YNAO) are used to study the solar rotation profile. Firstly, the rotation profile in each solar cycle 19-23 is calculated. Secondly, the rotation parameters (equatorial rotation velocity A and differential gradient B) of YNAO are compared with the well-known earlier results. Finally, the rotation parameters in the northern and southern hemispheres during each solar cycle 19-23 are summarized. The main conclusions we reached are as follows: (1) The average difference of the equatorial rotation velocity and differential gradient, between YNAO sunspot and other sunspot datasets, are 0.09 and 0.4, respectively. (2) The magnitudes of the gradient B in the northern hemisphere are larger than that in the southern hemisphere at even-number cycles, and it will approximately reverse at odd-number cycles. [ABSTRACT FROM AUTHOR]

Based on the daily sunspot number (SN) data (1954–2011) from the Purple Mountain Observatory, the extreme value theory (EVT) is employed for the research of the long-term solar activity. It is the first time that the EVT is applied on the Chinese SN. Two methods are used for the research of the extreme events with EVT. One method is the block maxima (BM) approach, which picks the maximum SN value of each block. Another one is the peaks-over-threshold (POT) approach. After a declustering process, a threshold value (here it is 300) is set to pick the extreme values. The negative shape parameters are obtained by the two methods, respectively, indicating that there is an upper bound for the extreme SN value. Only one value of the N -year return level (RL) is estimated: N = 19 years. For N = 19 years, the RL values of SN obtained by two methods are similar with each other. The RL values are found to be 420 for the POT method and the BM method. Here, the trend of 25th solar cycle is predicted to be stronger, indicating that the length of meridional forms of atmospheric circulation will be increased. [ABSTRACT FROM AUTHOR]