Modeling Research of the 27-day Forecast of 10.7 cm Solar Radio Flux (I)

Adopting the autoregressive method for time-series modeling, we have made a study on the medium-term forecast of solar 10.7 cm radio flux (F10.7). The result of forecast experiments and the error analysis indicate that when the solar activity is at a rather low level and the 27-day periodicity of F10.7 is apparent, the autoregressive forecast method has a high accuracy and relatively ideal effectiveness, but when a large active region appears or disappears on the solar dusk, the forecast effectiveness is not ideal. This means that the autoregressive method for the time-series modeling can reflect well the 27-day periodicity of F10.7, and that it has certain applicability for building a mediumterm forecast model of F10.7. By comparing the forecast results in the period from 21th September 2005 to 7th June 2007, it is demonstrated that the accuracy of the autoregressive forecast method is equivalent to that of the forecast made by the American Air Force.     

What do the solar activity indices represent?

Sunspot number, sunspot area, and radio flux at 10.7 cm are the indices which are most frequently used to describe the long‐term solar activity. The data of the daily solar full‐disk magnetograms measured at Mount Wilson Observatory from 19 January 1970 to 31 December 2012 are utilized together with the daily observations of the three indices to probe the relationship of the full‐disk magnetic activity respectively with the indices. Cross correlation analyses of the daily magnetic field measurements at Mount Wilson observatory are taken with the daily observations of the three indices, and the statistical significance of the difference of the obtained correlation coefficients is investigated. The following results are obtained: (1) The sunspot number should be preferred to represent/reflect the full‐disk magnetic activity of the Sun to which the weak magnetic fields (outside of sunspots) mainly contribute, the sunspot area should be recommended to represent the strong magnetic activity of the Sun (in sunspots), and the 10.7 cm radio flux should be preferred to represent the full‐disk magnetic activity of the Sun (both the weak and strong magnetic fields) to which the weak magnetic fields mainly contribute. (2) On the other hand, the most recommendable index that could be used to represent/reflect the weak magnetic activity is the 10.7 cm radio flux, the most recommendable index that could be used to represent the strong magnetic activity is the sunspot area, and the most recommendable index that could be used to represent the full‐disk magnetic activity of the Sun is the 10.7cm radio flux. Additionally, the cycle characteristics of the magnetic field strengths on the solar disk are given. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Prediction of Maximum Amplitudes of Solar Cycles and the Maximum Amplitude of Solar Cycle 24

We present a brief review of predictions of solar cycle maximum amplitude with a lead time of 2 years or more. It is pointed out that a precise prediction of the maximum amplitude with such a lead-time is still an open question despite progress made since the 1960s. A method of prediction using statistical characteristics of solar cycles is developed: the solar cycles are divided into two groups, a high rising velocity (HRV) group and a low rising velocity (LRV) group, depending on the rising velocity in the ascending phase for a given duration of the ascending phase. The amplitude of Solar Cycle 24 can be predicted after the start of the cycle using the formula derived in this paper. Now, about 5 years before the start of the cycle, we can make a preliminary prediction of 83.2-119.4 for its maximum amplitude.     

Solar Cycle Variation of the Interplanetary Forward Shock Drivers Observed at 1 AU

Forecasting space weather more accurately from solar observations requires an understanding of the variations in physical properties of interplanetary (IP) shocks as solar activity changes. We examined the characteristics (occurrence rate, physical parameters, and types of shock driver) of IP shocks. During the period of 1995 – 2001, a total of 249 forward IP shocks were observed. In calculating the shock parameters, we used the solar wind data from Wind at the solar minimum period (1995 – 1997) and from ACE since 1998 including the solar maximum period (1999 – 2001). Most of IP shocks (68%) are concentrated in the solar maximum period. The values of physical quantities of IP shocks, such as the shock speed, the sonic Mach number, and the ratio of plasma density compression, are larger at solar maximum than at solar minimum. However, the ratio of IMF compression is larger at solar minimum. The IP shock drivers are classified into four groups: magnetic clouds (MCs), ejecta, high speed streams (HSSs), and unidentified drivers. The MC is the most dominant and strong shock driver and 150 out of total 249 IP shocks are driven by MCs. The MC is a principal and very effective shock driver not only at solar maximum but also at solar minimum, in contrast to results from previous studies, where the HSS is considered as the dominant IP shock driver.     

Forecast daily indices of solar activity, F10.7, using support vector regression method

The 10.7cm solar radio flux (F10.7), the value of the solar radio emission flux density at a wavelength of 10.7cm, is a useful index of solar activity as a proxy for solar extreme ultraviolet radiation. It is meaningful and important to predict F10.7 values accurately for both long-term (months-years) and short-term (days) forecasting, which are often used as inputs in space weather models. This study applies a novel neural network technique, support vector regression (SVR), to forecasting daily values of F10.7. The aim of this study is to examine the feasibility of SVR in short-term F10.7 forecasting. The approach, based on SVR, reduces the dimension of feature space in the training process by using a kernel-based learning algorithm. Thus, the complexity of the calculation becomes lower and a small amount of training data will be sufficient. The time series of F10.7 from 2002 to 2006 are employed as the data sets. The performance of the approach is estimated by calculating the norm mean square error and mean absolute percentage error. It is shown that our approach can perform well by using fewer training data points than the traditional neural network.     

Verification of a Similar Cycle Prediction for the Ascending and Peak Phases of Solar Cycle 23

Reviews of long-term predictions of solar cycles have shown that a precise prediction with a lead time of 2 years or more of a solar cycle remains an unsolved problem. We used a simple method, the method of similar cycles, to make long-term predictions of not only the maximum amplitude but also the smoothed monthly mean sunspot number for every month of Solar Cycle 23. We verify and compare our prediction with the latest available observational results.     

On the solar rotation and activity

The interaction between differential rotation and magnetic fields in the solar convection zone was recently modelled by Brun (2004). One consequence of that model is that the Maxwell stresses can oppose the Reynolds stresses, and thus contribute to the transport of the angular momentum towards the solar poles, leading to a reduced differential rotation. So, when magnetic fields are weaker, a more pronounced differential rotation can be expected, yielding a higher rotation velocity at low latitudes taken on the average. This hypothesis is consistent with the behaviour of the solar rotation during the Maunder minimum. In this work we search for similar signatures of the relationship between the solar activity and rotation determined tracing sunspot groups and coronal bright points. We use the extended Greenwich data set (1878–1981) and a series of full-disc solar images taken at 28.4 nm with the EIT instrument on the SOHO spacecraft (1998–2000). We investigate the dependence of the solar rotation on the solar activity (described by the relative sunspot number) and the interplanetary magnetic field (calculated from the interdiurnal variability index). Possible rotational signatures of two weak solar activity cycles at the beginning of the 20th century (Gleissberg minimum) are discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Cyclical behavior of solar filaments

The Carte Synoptique catalogue of solar filaments from 1919 March to 1957 July, corresponding to complete cycles 16‐18, is utilized to show the latitudinal migrations of solar filaments at low (≤50°) and high (>50°) latitudes and the latitudinal distributions of solar filaments for all solar filaments, solar filaments whose maximum lengths during solar disk passage are less than or equal to 70° and solar filaments whose maximum lengths during solar disk passage are larger than 70°. The results show the following. (1) The latitudinal migrations of all low‐latitude solar filaments and low‐latitude solar filaments whose maximum lengths during solar disk passage are less than or equal to 70° follow the Spörer sunspot law. However, the latitudinal migration of low‐latitude solar filaments whose maximum lengths during solar disk passage are larger than 70° do not follow the Spörer sunspot law: there is no equatorward and no poleward drift. The latitudinal migration of high‐latitude solar filaments whose maximum lengths during solar disk passage are larger than 70° is more significant than those of all high‐latitude solar filaments and high‐latitude solar filaments whose maximum lengths during solar disk passage are less than or equal to 70°: there is a poleward migration from the latitude of about 50° to 70° and an equatorward migration from the latitude of about 70° to 50° of all high‐latitude solar filaments and high‐latitude solar filaments whose maximum lengths during solar disk passage are less than or equal to 70° and there is a poleward migration from the latitude of about 50° to 80° and an equatorward migration from the latitude of about 80° to 50° of high‐latitude solar filaments whose maximum lengths during solar disk passage are larger than 70°. (2) The statistical characteristics of latitudinal distribution of solar filaments whose maximum lengths during solar disk passage are larger than 70° is different from those of all solar filaments and solar filaments whose maximum lengths during solar disk passage are less than or equal to 70° (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Sunspot groups at high latitude

Data of sunspot groups at high latitude (35°), from the year 1874 to the present (2000 January), are collected to show their evolutional behaviour and to investigate features of the yearly number of sunspot groups at high latitude. Subsequently, an evolutional pattern of sunspot group number at high latitude is given in this paper. Results obtained show that the number of sunspot groups of a solar cycle at high latitude rises to a maximum value about 1 yr earlier than the time of the maximum of sunspot relative numbers of the solar cycle, and then falls to zero more rapidly. The results also show that, at the moment, solar activity described by the sunspot relative numbers has not yet reached its minimum. In general, sunspot groups at high latitude have not appeared on the solar disc during the last 3 yr of a Wolf solar cycle. The asymmetry of the high latitude sunspot group number of a Wolf solar cycle can reflect the asymmetry of solar activity in the Wolf solar cycle, and it is suggested that one could further use the high latitude sunspot group number during the rising time of a Wolf solar cycle, maximum year included, to judge the asymmetry of solar activity over the whole solar cycle.     

Long-Term Sunspot Number Prediction based on EMD Analysis and AR Model

The Empirical Mode Decomposition (EMD) and Auto-Regressive model (AR) are applied to a long-term prediction of sunspot numbers. With the sample data of sunspot numbers from 1848 to 1992, the method is evaluated by examining the measured data of the solar cycle 23 with the prediction: different time scale components are obtained by the EMD method and multi-step predicted values are combined to reconstruct the sunspot number time series. The result is remarkably good in comparison to the predictions made by the solar dynamo and precursor approaches for cycle 23. Sunspot numbers of the coming solar cycle 24 are obtained with the data from 1848 to 2007, the maximum amplitude of the next solar cycle is predicted to be about 112 in 2011-2012.     

伴随CME的微波爆发的特征

分析了与日冕物质抛射(CME)有关的太阳微波爆发(SMB)的特征,包括持 续时间、峰值流量、爆发类型、谱指数等．选取了从1999年11月至2003年9月的136 个事件,包括60个部分晕状CME(120°<宽度<360°)／晕状CME(宽度=360°)和 76个正常CME(20°<宽度<120°)／窄CME(0°<宽度<20°)． 研究发现: (1)与正常CME／窄CME有关的微波爆发持续时间较短,与部分晕状 ／晕状CME有关的微波爆发持续时间有长有短; (2)与慢CME有关的微波爆发持续时 间较短,与快CME有关的微波爆发持续时间可长可短;(3)与正常／窄CME有关的微 波爆发峰值辐射流量比较小,与部分晕状／晕状CME有关的微波爆发峰值辐射流量有大 有小;(4)与慢CME有关的微波爆发峰值辐射流量较小,与快CME有关的微波爆发峰 值辐射流量可长可短; (5)与正常／窄CME有关的微波爆发绝大多数为简单(simple) 型,与晕状CME有关的微波爆发绝大多数为复杂(C)／大爆发(GB)型; (6)与CME 有关的事件在频率,f相似文献   

On the application of information theory to the optimum state-space reconstruction of the short-term solar radio flux (10.7 cm), and its prediction via a neural network

The prediction of a time series using a neural network involves an optimum state-space reconstruction. The state space of the daily 10.7-cm solar radio flux is reconstructed using an information theory approach. A multi-layer feed-forward neural net is used for short-term prediction of the time series. The convergence of the synaptic weights is obtained partially by simulated annealing and partially by the 'quick prop' variation of back-propagation. The result gives a reasonably accurate short-term prediction.     

Dynamics of the solar magnetic field from SOHO/MDI

The investigation of the dynamics of magnetic fields from small scales to the large scales is very important for the understanding of the nature of solar activity. It is also the base for producing adequate models of the solar cycle with the purpose to predict the level of solar activity. Since December 1995 the Michelson Doppler Imager (MDI) on board of the Solar and Heliospheric Observatory (SOHO) provides full disk magnetograms and synoptic maps which cover the period of solar cycle 23 and the current minimum. In this paper, I review the following important topics with a focus on the dynamics of the solar magnetic field. The synoptic structure of the solar cycle; the birth of the solar cycle (overlapping cycles 23 and 24); the relationship of the photospheric magnetic activity and the EUV solar corona, polar magnetic fields and dynamo theory (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Cluster analysis for pattern recognition in solar butterfly diagrams

We investigate to what extent the wings of solar butterfly diagrams can be separated without an explicit usage of Hale's polarity law as well as the location of the solar equator. We apply two algorithms of cluster analysis for this purpose, namely DBSCAN and C‐means, and demonstrate their ability to separate the wings of contemporary butterfly diagrams based on the sunspot group density in the diagram only. Then we apply the method to historical data concerning the solar activity in the 18th century (Staudacher data). The method separates the two wings for Cycle 2, but fails to separate them for Cycle 1. In our opinion, this finding supports the interpretation of the Staudacher data as an indication of the unusual nature of the solar cycle in the 18th century (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

基于深度学习的太阳F_10.7辐射通量的短期预报研究

F_10.7太阳辐射通量作为输入参数被广泛运用于大气经验模型、电离层模型等空间环境模型,其预报精度直接影响航天器轨道预报精度.采用时间序列法统计了太阳辐射通量F10.7指数和太阳黑子数(SSN)的关系,给出了两者之间的线性关系,在此基础上提出了一种基于长短时记忆神经网络(Long and Short Term Memory,LSTM)的预报方法,方法结合了54 d太阳辐射通量指数和SSN历史数据来对F_10.7进行未来7 d短期预报,并与其他预报方法的预报结果进行了比较,结果表明:(1)所建短期预报7 d方法模型的性能优于美国空间天气预报中心(Space Weather Prediction Center, SWPC)的方法,预测值和观测值的相关系数(CC)达到0.96,同时其均方根误差约为11.62个太阳辐射通量单位(sfu),预报结果的均方根误差(RMSE)低于SWPC,下降约11%;(2)对预测的23、24周太阳活动年结果统计表明,太阳活动高年的第7 d F10.7指数预报平均绝对百分比误差(MAPE)最优可达12.9%以内,低年最优可达2...     

Verification of Short-Term Predictions of Solar Soft X-ray Bursts for the Maximum Phase （2000-2001） of Solar Cycle 23

We present a verification of the short-term predictions of solar Xray bursts for the maximum phase (2000-2001) of Solar Cycle 23, issued by two prediction centers. The results are that the rate of correct predictions is about equal for RWC-China and WWA; the rate of too high predictions is greater for RWC-China than for WWA, while the rate of too low predictions is smaller for RWC-China than for WWA.     

太阳活动与太阳自转速率变化关系的分析

研究发现,太阳自转速率的变化与太阳活动之间存在一定的联系,但是不同学者的研究结论存在着矛盾:有的认为两者为正相关,而有的却认为是负相关.究竟两者之间是什么关系,需要做进一步深入的分析.利用EEMD (Ensemble Empirical Mode Decomposition)等方法对太阳自转速率和太阳黑子数据序列进行相关关系以及相位关系的计算和分析,以探讨太阳自转速率变化与太阳活动之间的关系.研究发现:两者的长期趋势项分量呈显著负相关;在11 yr左右周期分量上,观测到的太阳自转速率滞后太阳黑子的变化约2 yr时,呈显著负相关关系,超前3 yr时呈现次显著的正相关;对太阳活动第12–23周各周内部太阳黑子与太阳自转速率的相关分析表明,两者的关系比较复杂,但负相关关系更为显著.这为进一步理解太阳活动变化与太阳自转速率变化之间的成因联系提供了新的依据.     

A New Method to Determine Epochs of Solar Cycle Extrema

A weighted average method is proposed to determine the epochs of solar cycle extrema and hence the solar cycle lengths. Comparing to the previous methods, this method has the advantage that the extremum epochs are easily and uniquely determined.     

Size-Flux Relation in Solar Active Regions

We present a study of the relationship between integral area and corresponding total magnetic flux for solar active regions. It is shown that some of these relationships are satisfied to simple power laws. Fractal examination showed that some of these power laws can not be justified inside the simple models of stationary magnetic flux tube aggregation. All magnetic fluxes and corresponding areas were calculated using the data measured with the Solar Magnetic Field Telescope of the Huairou Solar Observing Station in Beijing.     

Solar Radius Determination from Total Solar Eclipse Observations on 29 March 2006

Solar diameter measurements have been made nearly continuously through different techniques for more than three centuries. They were obtained mainly with ground-based instruments except for some recent estimates deduced from space observations. One of the main problems in such space data analysis is that, up to now, it has been difficult to obtain an absolute value owing to the absence of an internally calibrated system. Eclipse observations provide a unique opportunity to give an absolute angular scale to the measurements, leading to an absolute value of the solar diameter. However, the problem is complicated by the Moon limb, which presents asphericity because of the mountains. We present a determination of the solar diameter derived from the total solar eclipse observation in Turkey and Egypt on 29 March 2006. We found that the solar radius carried back to 1 AU was 959.22±0.04 arcsec at the time of the observations. The inspection of the compiled 19 modern eclipses data, with solar activity, shows that the radius changes are nonhomologous, an effect that may explain the discrepancies found in ground-based measurements and implies the role of the shallow subsurface layers (leptocline) of the Sun.