Mid-Term Periodicities in the Solar Magnetic Flux

In this paper we report an analysis of the solar magnetic fluxes estimated in the period 1971–1998. We applied the wavelet technique to find the significant periodicities of these series. We concentrate particularly in the mid-term quasi-periodicities (1–2 years). The mid-term periodicity of 1.7 year is the dominant fluctuation for all the types of fluxes analyzed (total, closed, open, low and high latitude open fluxes) and has a strong tendency to appear during the descending phase of solar activity. The mid-term fluctuation of 1 year is significantly present in total and closed fluxes, but it is less important in open fluxes. It is recognizable in the high latitude open flux, but it is absent in the low latitude open flux. Due to the uncertainties involved in estimating the exact period of the quasi-annual peak, this component may not be different from the previously-reported 1.3 year periodicity. The high frequency fluctuations of all the fluxes but the high latitude open flux are in phase with the 11 years solar cycle. The high latitude flux tends to be present all the time, showing that along the cycle both the low latitude bipolar active regions and the polar coronal holes regulate this flux. These findings rule out the possibility of a more basic periodicity different from the 11 years cycle.     

Historical Dataset Reconstruction and a Prediction Method of Solar 10.7 cm Radio Flux

We reconstruct the developing history of solar 10.7 cm radio flux (F10.7) since 1848, based on the yearly sunspot number and the variations. A relationship between the maximum and the linear regression slope of the first 3 years starting from minimum of the solar cycle is considered. We put forward a method of predicting the maximum of F10.7 by means of the slope-maximum relationship. Running tests for cycles 19 to 23 indicate that the method can properly predict the peak of F10.7.     

Multi-technique Analysis of the Solar 10.7 cm Radio Flux Time-Series in Relation to Predictability

We studied the predictability of the 10.7 cm solar radio flux by using stationary and non-stationary time-series analysis techniques of fractal theory to find the correlation exponent, the spectral exponent, the Hurst exponent, and the fluctuation exponent of the time series. The Hurst exponent was determined, from which the fractal dimension and consequently the predictability was evaluated. The results suggest that stationary methods of analysis yield inconsistent result, that is, amongst the four techniques used, the values of the exponents show great disparity. While two of the techniques, namely the auto-correlation function analysis and the spectral analysis, indicate long-term positive correlation, the other two methods, specifically the Hurst rescaled range-analysis and the fluctuation analysis, clearly exhibit the anti-correlated nature of the time series. The two non-stationary methods, that is, the discrete wavelet transform and the centered moving-average analysis, yielded values of the Hurst exponent that are indicative of positive correlation, of persistent behavior, and also showed that the time series is predictable to a certain extent.     

Short-Term Periodicities in the Time Series of Solar Radio Emissions at Different Solar Altitudes

A spectral analysis of the time series of daily values of 12 parameters, namely, ten solar radio emissions in the range 275–1755 MHz, 2800 MHz solar radio flux, and sunspot numbers for six continuous intervals of 132 values each during June 1997–July 1999 showed considerable differences from one interval to the next, indicating a nonstationary nature. A 27-day periodicity was noticed in Interval 2 (26.8 days), 3 (27.0 days), 5 (25.5 days), 6 (27.0 days). Other periodicities were near 11.4, 12.3, 13.3, 14.5, 15.5, 16.5, 35, 40, 50–70 days. Periodicities were very similar in a large vertical span of the coronal region corresponding to 670–1755 MHz. Above this region, the homogeneity disappeared. Below this region, there were complications and distortions due to localized solar surface phenomena.     

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.     

A Comparison of the 10.7-cm Radio Flux Values and the International Sunspot Numbers for Solar Activity Cycles 19, 20, and 21

A nonlinear analysis of the daily 10.7-cm radio flux values for each of Solar Cycles 19, 20, and 21 is used to determine if the results match those of the International Sunspot Numbers for each of these cycles. Fractals and chaos are described and a brief review of utilizing fractals and chaos is given. The origin of the 10.7-cm radio flux is discussed and a short review of recent work discussing its measurement and its relation to the international sunspot number and other proxies for solar activity cycles given. The parameters used to describe chaos for the 10.7-cm radio flux are discussed. The length of the data sets for either statistical analysis or nonlinear analysis of the 10.7-cm radio flux values is considered. These results indicate that the 10.7-cm radio flux values appear to be stochastic for Cycle 19 and chaotic for Cycles 20 and 21. The International Sunspot Numbers show similar behavior for these three cycles. A day-by-day comparison of the dimensionless 10.7-cm radio flux values and the dimensionless International Sunspot Numbers differences shows a linear trend. The results remain consistent in that the 10.7-cm radio flux values indicate, as did the International Sunspot Numbers, that there is a transition from stochastic behavior for Cycle 19 to chaotic behavior in Cycles 20 and 21. The day-by-day comparison of the 10.7-cm radio flux values and the International Sunspot Numbers emphasizes that the 10.7?cm radio flux values are responding to the magnetic field associated with the sunspots.     

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...     

Short-Term Periodicities in Solar Indices

The purpose of the present communication is to identify the short-term (few tens of months) periodicities of several solar indices (sunspot number, Caii area and K index, Lyman , 2800 MHz radio emission, coronal green-line index, solar magnetic field). The procedure used was: from the 3-month running means (3m) the 37-month running means (37m) were subtracted, and the factor (3m – 37m) was examined for several parameters. For solar indices, considerable fluctuations were seen during the ± 4 years around sunspot maxima of cycles 18–23, and virtually no fluctuations were seen in the ± 2 years around sunspot minima. The spacings between successive peaks were irregular but common for various solar indices. Assuming that there are stationary periodicities, a spectral analysis was carried out which indicated periodicities of months: 5.1–5.7, 6.2–7.0, 7.6–7.9, 8.9–9.6, 10.4–12.0, 12.8–13.4, 14.5–17.5, 22–25, 28 (QBO), 31–36 (QBO), 41–47 (QTO). The periodicities of 1.3 year (15.6 months) and 1.7 years (20.4 months) often mentioned in the literature were seen neither often nor prominently. Other periodicities occurred more often and more prominently. For the open magnetic flux estimated by Wang, Lean, and Sheeley (2000) and Wang and Sheeley (2002), it was noticed that the variations were radically different at different solar latitudes. The open flux for < 45 solar latitudes had variations very similar (parallel) to the sunspot cycle, while open flux for > 45 solar latitudes had variations anti-parallel to the sunspot cycle. The open fluxes, interplanetary magnetic field and cosmic rays, all showed periodicities similar to those of solar indices. Many peaks (but not all) matched, indicating that the open flux for < 45 solar latitudes was at least partially an adequate carrier of the solar characteristics to the interplanetary space and thence for galactic cosmic ray modulation.     

10.7cm射电流量月平均变化的动力行为和可预报性研究

本文用非线性动力系统理论探讨了10.7cm射电流量月平均变化的动力行为和可预报性,计算了该过程的分维数(D=3.1±0.1)和最大Lyapunov指数(λ_1=0.045±0.003 bit/月).结果表明,这是一个具有有限自由度的复杂的浑沌系统,可用有限个参数描述,所需的变量最少是4个,最多为6个.从10.7cm射电流量月平均变化说明了太阳活动的浑沌行为.本文还讨论了10.7cm射电流量月均值的可预报时间尺度,平均可预报时间尺度为8个月,最大可预报时间尺度是22个月,     

太阳暗条活动的周期性研究

运用法国巴黎默东天文台记录的暗条目录资料构造了一个时间精度为每天的暗条数目序列,选用Scargle周期图和Morlet小波变换两种周期方法研究了这个序列的周期性,发现其存在4个显著的周期,它们分别是1557天、1141天、795天和367天,详细分析了这些周期的时变特征,并简单讨论了其中个别典型周期的相位、物理机制和相互关系．     

Periodicities in the Time Series of Solar Coronal Radio Emissions and Chromospheric uv Emission Lines

A spectral analysis of the time series of daily values of ten solar coronal radio emissions in the range 275–1755 MHz, the 2800 MHz radio flux, several UV emission lines in the chromosphere and in the transition region, and sunspot number, for six successive intervals of 132 days each, during June 1997–July 1999 (26 months) showed that the spectral characteristics were not the same for all intervals. Details are presented for Interval 1, where there was no 27-day oscillation, and Interval 2, where there was a strong 27-day oscillation. In every interval, periodicities were remarkably similar in most of these indices, indicating that the solar atmosphere (chromosphere and corona) rotated as one block, up to a height of 150000 km. Above this height, the periodicities became obscure. Near the solar surface, sunspots showed extra or different periodicities, some of which vanished at low altitudes. For the 27-day feature as also for the long-term rise during 1996–1998, the maximum percentage changes were for radio emissions near 1350–1620 MHz.     

Density Depletion in a Coronal Flux Tube Associated With Solar Radio Emission

A discussion, which is motivated by recent study of solar radio emission, is presented to address the issue under what conditions the depletion of plasma density in a flux tube in the corona may take place. Two particular situations are of interest: One is that density is depleted due to the presence of beams of energetic particles, and the other is attributed to magnetic compression. The scenario discussed appears to be consistent with the occurrence type III solar radio bursts.     

The Search for Solar Gravity-Mode Oscillations in the Solar Wind Using it Ulysses Plasma Data

A recent report that energetic particles measured in the solar wind may be influenced by solar gravity-mode ( -mode) oscillations motivated the search for -mode signatures in the Ulysses solar wind plasma data. Ulysses solar wind plasma data from 1 March 1992 through the 12 April 1996 were examined in this study for signs of possible solar oscillations. The multi-taper method for spectral analysis was used to look for significant spectral peaks in the entire four-year data set, as well as in the smaller, more heliographically homogenous data set over the solar poles. Several frequencies satisfying certain significance requirements were found in the -mode frequency range in both data sets that also agree with the previously published findings. However, these identifications are shown to be false detections, and hence the frequencies found cannot be identified as solar modes.     

Phase Relationship Between Sunspot Number, Flare Index and Solar Radio Flux

To understand better the variation of solar activity indicators originated at different layers of the solar atmosphere with respect to sunspot cycles, we carried out a study of phase relationship between sunspot number, flare index and solar radio flux at 2800 MHz from January 1966 to May 2008 by using cross-correlation analysis. The main results are as follows: (1) The flare index and sunspot number have synchronous phase for cycles 21 and 22 in the northern hemisphere and for cycle 20 in the southern hemisphere. (2) The flare index has a noticeable time lead with respect to sunspot number for cycles 20 and 23 in the northern hemisphere and for cycles 22 and 23 in the southern hemisphere. (3) For the entire Sun, the flare index has a noticeable time lead for cycles 20 and 23, a time lag for cycle 21, and no time lag or time lead for cycle 22 with respect to sunspot number. (4) The solar radio flux has a time lag for cycles 22 and 23 and no time lag or time lead for cycles 20 and 21 with respect to sunspot number. (5) For the four cycles, the sunspot number and flare index in the northern hemisphere are all leading to the ones in the southern hemisphere. These results may be instructive to the physical processes of flare energy storage and dissipation.     

太阳射电频谱观测数据分析系统方案设计

中国太阳射电宽带动态频谱仪(solar Broadband Radio Spectrometer)在太阳物理研究和国际合作交流中发挥了重要作用.为进一步扩大该设备观测数据的国际交流和共享、挖掘数据的深层信息、加快科学产出,有必要开发一套与SSW(Solar Soft Ware)兼容的数据分析系统.该系统具有以下主要特点:(1)按SSW规范设计编写,既可以在SSW环境下运行也可以独立安装使用;(2)新界面设计更易于用户上手,也可以进行复杂深层的数值分析;(3)规范明晰的功能模块和流程设计减少了漏洞和排错时间,定标和特征信息提取等多种亟需功能的完善为科学研究开拓了空间,节省了时间;(4)利用MySQL关系数据库管理系统建设一个安全稳定、易于升级管理的数据库,便于浏览搜索和批量下载.此外,该数据分析系统的开发将为正在研制的中国太阳射电频谱日像仪积累经验和储备技术,并为国内其它台站提供模式和经验.     

A Simple Model to Describe Solar Cycle Periodicities below 11 Years

Together with the main 11-year cycle, solar activity also displays intracycle periodicities. A simple nonlinear model that describes the 11-year solar cycle with subperiodicities can be derived from the usual α – ω dynamo theory in the form of a Van der Pol equation with a forcing term. In this paper the results obtained from the Van der Pol oscillator describing the amplitude modulations and periodicities observed from the data set of the global daily coronal emission of the Fe xiv line at 530.3 nm are presented.     

Estimating Solar Flux Density at Low Radio Frequencies Using a Sky Brightness Model

Sky models have been used in the past to calibrate individual low radio frequency telescopes. In this article we generalize this approach from a single antenna to a two element interferometer, and formulate the problem in a way that allows us to estimate the flux density of the Sun using the normalized cross-correlations (visibilities) measured on a low resolution interferometric baseline. For wide field-of-view instruments, typically the case at low radio frequencies, this approach can provide robust absolute solar flux calibration for well characterized antennas and receiver systems. It can provide a reliable and computationally lean method for extracting parameters of physical interest using a small fraction of the voluminous interferometric data, which can be computationally prohibitively expensive to calibrate and image using conventional approaches. We demonstrate this technique by applying it to data from the Murchison Widefield Array and assess its reliability.