Evidence of Solar Variation in Tree-Ring-Based Climate Reconstructions

Analyses of the summer temperature anomalies in northern Fennoscandia for A.D. –1991 and mean annual temperature in the northern hemisphere for A.D. 1000–1990 (both reconstructed by means of dendrochronological methods) are performed using Fourier and wavelet approaches. It is revealed that the century-type (65–140 yr) periodicity is present in both series during most of the full time range. A comparison of the northern Fennoscandian temperature record with a variety of indicators of solar activity (direct measurements and proxies) shows that this century-scale periodicity most probably was forced by a centennial cycle of solar activity (Gleissberg cycle). Despite the fact that the connection between the centennial variation of global northern hemispheric temperature and that of the Sun's activity is weaker, a link between the two can also not be excluded. The results obtained give us new evidence of the reality of the solar–climate link over a record long-time scale (at least during the last millennium). Variable length of the century-long temperature periodicity may reflect the corresponding changes in the length of the Gleissberg solar cycle. The effects, which can obscure the Sun's influence on the global hemispheric climate, are discussed.     

Wavelet Spectrum Analysis Of Eit/Soho Images

The extreme ultraviolet imaging telescope (EIT) of SOHO offers a unique record of the solar atmosphere for its sampling in temperature, field of view, resolution, duration, and cadence. To investigate globally and locally its topology and evolution during the solar cycle, we consider a multi-scale approach, and more precisely we use the wavelet spectrum. We present three results among the applications of such a procedure. First, we estimate the typical dimension of the supergranules as seen in the 30.4 nm passband, and we show that the evolution of the characteristic network scale is almost in phase with the solar cycle. Second, we build pertinent time series that give the evolution of the signal energy present in the corona at different scales. We propose a method that detects eruptions and post-flaring activity in EUV image sequences. Third, we introduce a new way to extract active regions in EIT images, with perspectives in, e.g., long-term irradiance analysis.     

Possible solar modulation of pacific decadal oscillation

The Pacific Decadal Oscillation (PDO) is an El Niño-like pattern of Pacific climate variability, oscillating between its warm and cool phase about every 20–30 years as defined by oceanic temperature anomalies in the northeast and tropical Pacific Ocean. In this work, the authors investigate the possible connection between the PDO and solar activity by means of wavelet technique. The study shows obvious fluctuation characteristics in the PDO series. The modulation action from solar activity plays an important role in the oscillation of the Pacific, and there is a possible association existing in the PDO and solar activity on decade time scales.     

Wavelet Analysis of solar,solar wind and geomagnetic parameters

The sunspot number, solar wind plasma, interplanetary magnetic field, and geomagnetic activity index A _p have been analyzed using a wavelet technique to look for the presence of periods and the temporal evolution of these periods. The global wavelet spectra of these parameters, which provide information about the temporal average strength of quasi periods, exhibit the presence of a variety of prominent quasi periods around 16 years, 10.6 years, 9.6 years, 5.5 years, 1.3 years, 180 days, 154 days, 27 days, and 14 days. The wavelet spectra of sunspot number during 1873–2000, geomagnetic activity index A _p during 1932–2000, and solar wind velocity and interplanetary magnetic field during 1964–2000 indicate that their spectral power evolves with time. In general, the power of the oscillations with a period of less than one year evolves rapidly with the phase of the solar cycle with their peak values changing from one cycle to the next. The temporal evolution of wavelet power in R _z, v _sw, n, B _y, B _z, |B|, and A _p for each of the prominent quasi periods is studied in detail.     

Hierarchy of Cyclic Solar Activity Changes

A hierarchy of cyclic changes in solar activity is studied based on energetic and phase wavelet analyses. The phase wavelet spectrum of yearly number of sunspot groups shows fork-like bifurcations. Separate 11-yr cycles are combined in pairs and wave trains to make up complete magnetic cycles with complex synergies. The phase spectrum also indicates the existence of different regimes in solar activity cyclic changes. This variability seems to be controlled by changes in the solar dynamo regime.     

Statistical Properties of Extreme Solar Activity Intervals

A study of long-term solar variability reflected in indirect indices of past solar activity leads to stimulating results. We compare the statistics of intervals of very low and very high solar activity derived from two cosmogenic radionuclide records and look for consistency in their timing and physical interpretation. According to the applied criteria, the numbers of minima and of maxima are 61 and 68, respectively, from the ¹⁰Be record, and 42 and 46 from the ¹⁴C record. The difference between the enhanced and depressed states of solar activity becomes apparent in the difference in their statistical distributions. We find no correlation between the level or type (minimum or maximum) of an extremum and the level or type of the predecessor. The hypothesis of solar activity as a periodic process on the millennial time scale is not supported by the existing proxies. A new homogeneous series of ¹⁰Be measurements in polar ice covering the Holocene would be of great value for eliminating the existing discrepancy in the available solar activity reconstructions.     

Activity cycle of solar filaments

Long-term variation in the distribution of the solar filaments observed at the Observatorie de Paris, Section de Meudon from March 1919 to December 1989 is presented to compare with sunspot cycle and to study the periodicity in the filament activity, namely the periods of the coronal activity with the Morlet wavelet used. It is inferred that the activity cycle of solar filaments should have the same cycle length as sunspot cycle, but the cycle behavior of solar filaments is globally similar in profile with, but different in detail from, that of sunspot cycles. The amplitude of solar magnetic activity should not keep in phase with the complexity of solar magnetic activity. The possible periods in the filament activity are about 10.44 and 19.20 years. The wavelet local power spectrum of the period 10.44 years is statistically significant during the whole consideration time. The wavelet local power spectrum of the period 19.20 years is under the 95% confidence spectrum during the whole consideration time, but over the mean red-noise spectrum of α = 0.72 before approximate Carrington rotation number 1500, and after that the filament activity does not statistically show the period. Wavelet reconstruction indicates that the early data of the filament archive (in and before cycle 16) are more noiseful than the later (in and after cycle 17).     

Solar Magnetic Activity and Total Irradiance Since the Maunder Minimum

We develop a model for estimating solar total irradiance since 1600 AD using the sunspot number record as input, since this is the only intrinsic record of solar activity extending back far enough in time. Sunspot number is strongly correlated, albeit nonlinearly with the 10.7-cm radio flux (F _10.7), which forms a continuous record back to 1947. This enables the nonlinear relationship to be estimated with usable accuracy and shows that relationship to be consistent over multiple solar activity cycles. From the sunspot number record we estimate F _10.7 values back to 1600 AD. F _10.7 is linearly correlated with the total amount of magnetic flux in active regions, and we use it as input to a simple cascade model for the other magnetic flux components. The irradiance record is estimated by using these magnetic flux components plus a very rudimentary model for the modulation of energy flow to the photosphere by the subphotospheric magnetic flux reservoir feeding the photospheric magnetic structures. Including a Monte Carlo analysis of the consequences of measurement and fitting errors, the model indicates the mean irradiance during the Maunder Minimum was about 1 ± 0.4 W m⁻² lower than the mean irradiance over the last solar activity cycle.     

On the relationship of cosmic ray intensity with solar,interplanetary, and geophysical parameters

The flux rate of cosmic rays incident on the Earth’s upper atmosphere is modulated by the solar wind and the Earth’s magnetic field. The amount of solar wind is not constant due to changes in solar activity in each solar cycle, and hence the level of cosmic ray modulation varies with solar activity. In this context, we have investigated the variability and the relationship of cosmic ray intensity with solar, interplanetary, and geophysical parameters from January 1982 through December 2008. Simultaneous observations have been made to quantify the exact relationship between the cosmic ray intensity and those parameters during the solar maxima and minima, respectively. It is found that the stronger the interplanetary magnetic field, solar wind plasma velocity, and solar wind plasma temperature, the weaker the cosmic ray intensity. Hence, the lowest cosmic ray intensity has good correlations with simultaneous solar parameters, while the highest cosmic ray intensity does not. Our results show that higher solar activity is responsible for a higher geomagnetic effect and vice versa.     

Thousand-Year Cycle Signals in Solar Activity

Long-term variations of solar activity closely relate to terrestrial phenomena. More and more people attach importance to studies of long-term fluctuations of solar variation. However, because direct observations of solar activity are available only for the past four centuries, such studies are few. In this work, using the wavelet technique, the author investigates long-term fluctuations of reconstructed sunspot number series covering the past 11 400 years, with emphasis on the thousand-year cycle signals of solar variation. The results show a thousand-year cycle in solar activity.     

太阳黑子数的子波分析

本文讨论了子波变换用于信号突变检测的原理，用它分析了１７００－１９９３年间的太阳黑子数的年均值．精确地检测到了太阳活动的突变点，用相邻两个突变点的时间长度求得了不同尺度下太阳黑子变化的周期．结果表明：利用子波变换检测太阳黑子周期与传统方法相比具有独到之处．     

On the Relation Between Solar Activity and Clear-Sky Terrestrial Irradiance

The Mauna Loa Observatory record of direct-beam solar irradiance measurements for the years 1958?–?2010 is analysed to investigate the variation of clear-sky terrestrial insolation with solar activity over more than four solar cycles. The raw irradiance data exhibit a marked seasonal cycle, extended periods of lower irradiance due to emissions of volcanic aerosols, and a long-term decrease in atmospheric transmission independent of solar activity. After correcting for these effects, it is found that clear-sky terrestrial irradiance typically varies by ≈?0.2±0.1 % over the course of the solar cycle, a change of the same order of magnitude as the variations of the total solar irradiance above the atmosphere. An investigation of changes in the clear-sky atmospheric transmission fails to find a significant trend with sunspot number. Hence there is no evidence for a yet unknown effect amplifying variations of clear-sky irradiance with solar activity.     

Wavelet entropy and the multi-peaked structure of solar cycle maximum

Wavelet analysis of different solar activity indices—sunspot numbers, sunspot areas and flare index—allows us to investigate the time evolution of some frequency dependent functionals, like wavelet entropy, which gives useful information about the complexity level of the related signals. The main aim of this work is the analysis of the time behavior of wavelet entropy near the maximum phases of solar cycles 21–22–23 in order to further contribute to the characterization of the multi-peaked structure of solar cycle maxima and to support the current interpretation of the so-called Gnevyshev gap.     

Maximum and minimum temperatures at armagh observatory, 1844–1992, and the length of the sunspot cycle

The question of whether or not the Earth's climate is influenced by solar activity has received considerable attention since the mid-nineteenth century. Most investigations have adopted the sunspot number as the parameter of solar activity. Recently, however, it has been shown by Friis-Christensen and Lassen (1991) that the mean northern hemisphere temperature, from 1861–1990, follows a strikingly similar trend to thelength of the sunspot cycle, suggesting that the recent global warming could, at least in part, arise from changes in solar activity. In view of the importance of this result, we have examined a set of continuous meteorological records, maintained at Armagh Observatory since 1844, to assess, first, whether data from a single site can give meaningful information on global trends, and second, whether the data from this particular site for the period 1844–1866 can be used to extend the baseline of the comparison with solar activity. We find that both are indeed the case and that there is a strong correlation between the solar cycle length and the mean temperature at Armagh over the past 149 years.     

Possible Influence of the 11-year Solar Cycle on Precipitation in Huashan Mountain of China over the Last 300 Years

Taking into account reconstructed precipitation time series in Huashan mountain area of China on the one hand and sunspot numbers observations on the other hand, the authors used here continuous wavelet transform and cross wavelet transform to investigate possible connection between the two sets of indicators. The analysis was performed over the last 300 years: it is found that solar activity influences precipitation in that geographical area of China to some extent, with an excess of 5% statistical significance level red noise over the 11-year solar activity cycle.     

Critical Analysis of a Hypothesis of the Planetary Tidal Influence on Solar Activity

The present work is a critical revision of the hypothesis of the planetary tidal influence on solar activity published by Abreu et al. (Astron. Astrophys. 548, A88, 2012; called A12 here). A12 describes the hypothesis that planets can have an impact on the solar tachocline and therefore on solar activity. We checked the procedure and results of A12, namely the algorithm of planetary tidal torque calculation and the wavelet coherence between torque and heliospheric modulation potential. We found that the claimed peaks in long-period range of the torque spectrum are artefacts caused by the calculation algorithm (viz. aliasing effect). Also the statistical significance of the results of the wavelet coherence is found to be overestimated by an incorrect choice of the background assumption of red noise. Using a more conservative non-parametric random-phase method, we found that the long-period coherence between planetary torque and heliospheric modulation potential becomes insignificant. Thus we conclude that the considered hypothesis of planetary tidal influence on solar activity is not based on a solid ground.     

太阳光球磁通量南北不对称性研究

运用统计方法系统研究了1978-2002年太阳光球磁通量南北不对称性变化特征，发现其与太阳活动周有关．不对称值在太阳活动极小年要明显高于太阳活动极大年，并且磁通量变化总是由上升段的北半球占优逐渐过渡到下降段的南半球占优．另外运用小波变换方法详细讨论了这种不对称性变化可能存在的周期信息．     

太阳活动周期的小波分析

运用小波技术对太阳射电流量2800 MHz,太阳黑子数和太阳黑子面积数周期进行分析．其结果表明: (1)这3个系列的数据显示最显著的周期是10．69年,其他周期并不明显．(2)小波功率谱给出了全部时间-周期范围的功率谱变化,它显示了在某个周期处于某个时段的局部功率的变化,小波功率谱分析表明,小于1年的周期仅仅在太阳活动最大期附近比较明显．(3)太阳射电2800 MHz,太阳黑子数和太阳黑子面积数的几个周期(10．69年,5．11年, 155．5天)的小波功率谱比较相似,出现峰值的时间相同;曲线的起伏相似,周期越小,曲线起伏的频率越大．     

Effect of Large-Scale Magnetic Fields on Total Solar Irradiance

The effect of large-scale magnetic fields on total solar irradiance (TSI) was studied both in time–frequency and in time–longitude aspects. A continuous wavelet analysis revealed that the energy of thermomagnetic disturbances due to sunspots and faculae cascades into the magnetic network and facular macrostructure. A numerical technique of time–longitude analysis was developed to study the fine structure of temporal changes in the TSI caused by longitudinal brightness inhomogeneities and rotation of the Sun. The analysis facilitates mapping large-scale thermal inhomogeneities of the Sun and reveals patterns of radiative excesses and deficits relative to the undisturbed solar photosphere. These patterns are organized into 2- and 4-sector structures that exhibit the effects of both activity complexes and magnetically active longitudes. Large-scale patterns with radiative excess display a facular macrostructure and bright patterns in the magnetic network caused by the dissipation of large-scale thermomagnetic disturbances. Similar global-scale temperature patterns were found in the upper solar atmosphere. These temperature patterns are also causally related to long-lived magnetic fields of the Sun. During activity cycles 21–23 the patterns with radiative excess tend to be concentrated around the active longitudes which are centered at about 60° and 230° in the Carrington system.     

Decoupling Solar Variability and Instrument Trends Using the Multiple Same-Irradiance-Level (MuSIL) Analysis Technique

The solar spectral irradiance (SSI) dataset is a key record for studying and understanding the energetics and radiation balance in Earth’s environment. Understanding the long-term variations of the SSI over timescales of the 11-year solar activity cycle and longer is critical for many Sun–Earth research topics. Satellite measurements of the SSI have been made since the 1970s, most of them in the ultraviolet, but recently also in the visible and near-infrared. A limiting factor for the accuracy of previous solar variability results is the uncertainties for the instrument degradation corrections, which need fairly large corrections relative to the amount of solar cycle variability at some wavelengths. The primary objective of this investigation has been to separate out solar cycle variability and any residual uncorrected instrumental trends in the SSI measurements from the Solar Radiation and Climate Experiment (SORCE) mission and the Thermosphere, Mesosphere, Ionosphere, Energetic, and Dynamics (TIMED) mission. A new technique called the Multiple Same-Irradiance-Level (MuSIL) analysis has been developed, which examines an SSI time series at different levels of solar activity to provide long-term trends in an SSI record, and the most common result is a downward trend that most likely stems from uncorrected instrument degradation. This technique has been applied to each wavelength in the SSI records from SORCE (2003?–?present) and TIMED (2002?–?present) to provide new solar cycle variability results between 27 nm and 1600 nm with a resolution of about 1 nm at most wavelengths. This technique, which was validated with the highly accurate total solar irradiance (TSI) record, has an estimated relative uncertainty of about 5% of the measured solar cycle variability. The MuSIL results are further validated with the comparison of the new solar cycle variability results from different solar cycles.