共查询到20条相似文献，搜索用时 31 毫秒
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Asok K. Sen 《Solar physics》2007,241(1):67-76
In this paper we use the notion of multifractality to describe the complexity in Hα flare activity during the solar cycles 21, 22, and 23. Both northern and southern hemisphere flare indices are analyzed. Multifractal behavior of the flare activity is characterized by calculating the singularity spectrum of the daily flare index time series in terms of the Hölder exponent. The broadness of the singularity spectrum gives a measure of the degree of multifractality or complexity in the flare index data. The broader the spectrum, the richer and more complex is the structure with a higher degree of multifractality. Using this broadness measure, complexity in the flare index data is compared between the northern and southern hemispheres in each of the three cycles, and among the three cycles in each of the two hemispheres. Other parameters of the singularity spectrum can also provide information about the fractal properties of the flare index data. For instance, an asymmetry to the left or right in the singularity spectrum indicates a dominance of high or low fractal exponents, respectively, reflecting a relative abundance of large or small fluctuations in the total energy emitted by the flares. Our results reveal that in the even (22nd) cycle the singularity spectra are very similar for the northern and southern hemispheres, whereas in the odd cycles (21st and 23rd) they differ significantly. In particular, we find that in cycle 21, the northern hemisphere flare index data have higher complexity than its southern counterpart, with an opposite pattern prevailing in cycle 23. Furthermore, small-scale fluctuations in the flare index time series are predominant in the northern hemisphere in the 21st cycle and are predominant in the southern hemisphere in the 23rd cycle. Based on these findings one might suggest that, from cycle to cycle, there exists a smooth switching between the northern and southern hemispheres in the multifractality of the flaring process. This new observational result may bring an insight into the mechanisms of the solar dynamo operation and may also be useful for forecasting solar cycles. 相似文献
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X. L. Yan L. H. Deng Z. Q. Qu C. L. Xu D. F. Kong 《Journal of Astrophysics and Astronomy》2012,33(4):387-397
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. 相似文献
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Using the smoothed time series of maximum CME speed index for solar cycle 23, it is found that this index, analyzed jointly with six other solar activity indicators, shows a hysteresis phenomenon. The total solar irradiance, coronal index, solar radio flux (10.7?cm), Mg?ii core-to-wing ratio, sunspot area, and H?? flare index follow different paths for the ascending and the descending phases of solar cycle?23, while a saturation effect exists at the maximum phase of the cycle. However, the separations between the paths are not the same for the different solar activity indicators used: the H?? flare index and total solar irradiance depict broad loops, while the Mg?ii core-to-wing ratio and sunspot area depict narrow hysteresis loops. The lag times of these indices with respect to the maximum CME speed index are discussed, confirming that the hysteresis represents a clue in the search for physical processes responsible for changing solar emission. 相似文献
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This paper reports the results of a study of the N-S asymmetry in the flare index using the results of Knoka (1985) combined with our results for the solar cycles 17 to the current cycle 22. By comparing the time-variation of the asymmetry curve with the solar activity variation of the 11-year cycle, we have found that the flare index asymmetry curve is not in phase with the solar cycle and that the asymmetry peaks during solar minimum. A periodic behaviour in the N-S asymmetry appears: the activity in one hemisphere is more important during the ascending part of the cycle whereas during the descending part the activity becomes more important in the other hemisphere. The dominance of flare activity in the southern hemisphere continues during cycle 22 and, according to our findings, this dominance will increase gradually during the following cycle 23. 相似文献
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In this paper, the monthly counts of flare index in the northern and southern hemispheres are used to investigate the hemispheric variation of the flare index in each of solar cycles 20–23. It is found that, (1) the flare index is asymmetrically distributed in each solar cycle and its asymmetry is a real phenomenon; (2) the flare index in the northern hemisphere begins earlier than that in the southern hemisphere in each of solar cycles 20–23, and the phase shifts between the two hemispheres show an odd‐even pattern; (3) although the flare index dominating in a hemisphere does not mean that it leads in phase in this hemisphere in individual solar cycle, these two features have an intrinsic relationship. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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In this paper, we investigate the spatial distribution of solar flares in the northern and southern hemispheres of the Sun
that occurred during the period 1996 to 2003. This period of investigation includes the ascending phase, the maximum and part
of the descending phase of solar cycle 23. It is revealed that the flare activity during this cycle is low compared to the
previous solar cycle, indicating the violation of Gnevyshev-Ohl rule. The distribution of flares with respect to heliographic
latitudes shows a significant asymmetry between northern and southern hemisphere which is maximum during the minimum phase
of the solar cycle. The present study indicates that the activity dominates the northern hemisphere in general during the
rising phase of the cycle (1997–2000). The dominance of northern hemisphere shifted towards the southern hemisphere after
the solar maximum in 2000 and remained there in the successive years. Although the annual variations in the asymmetry time
series during cycle 23 are quite different from cycle 22, they are comparable to cycle 21. 相似文献
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Magnetic fields give rise to distinctive features in different solar atmospheric regimes. To study this, time variations of
the flare index, sunspot number and sunspot area, each index arising from different physical conditions, were compared with
the solar composite irradiance throughout cycle 23. Rieger-type periodicities in these time series were calculated using Fourier
and wavelet transforms (WTs). The peaks of the wavelet power of these periodicities appeared between the years 1999 and 2002.
We found that the solar irradiance oscillations are less significant than those in the other indices during this cycle. The
irradiance shows non-periodic fluctuations during this time interval. The peaks of the flare index, sunspot number and sunspot
total area were seen around 2000.4, 1999.9 and 2001.0, respectively. These periodicities appeared intermittently and were
not simultaneous in different solar activity indices during the three years of the maximum phase of solar cycle 23. 相似文献
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H. Kiliç 《Solar physics》2009,255(1):155-162
The short-term periodicities in sunspot numbers, sunspot areas, and flare index data are investigated in detail using the
Date Compensated Discrete Fourier Transform (DCDFT) for the full disk of the Sun separately over the rising, the maximum,
and the declining portions of solar cycle 23 (1996 – 2006). While sunspot numbers and areas show several significant periodicities
in a wide range between 23.1 and 36.4 days, the flare index data do not exhibit any significant periodicity. The earlier conclusion
of Pap, Tobiska, and Bouwer (1990, Solar Phys.
129, 165) and Kane (2003, J. Atmos. Solar-Terr. Phys.
65, 1169), that the 27-day periodicity is more pronounced in the declining portion of a solar cycle than in the rising and maximum
ones, seems to be true for sunspot numbers and sunspot area data analyzed here during solar cycle 23. 相似文献
11.
V. K. Verma 《Journal of Astrophysics and Astronomy》2000,21(3-4):173-176
We report here a study of various solar activity phenomena occurring in both north and south hemispheres of the Sun during
solar cycles 8–23. In the study we have used sunspot data for the period 1832–1976, flare index data
for the period 1936-1993, Hα flare data 1993–1998 and solar active prominences data for the period 1957–1998.
Earlier Verma reported long-term cyclic period in N-S asymmetry and also that the N-S asymmetry of solar activity phenomena
during solar cycles 21, 22, 23 and 24 will be south dominated and the N-S asymmetry will shift to north hemisphere in solar
cycle 25. The present study shows that the N-S asymmetry during solar cycles 22 and 23 are southern dominated as suggested
by Verma. 相似文献
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We have analyzed the intermediate-term periodicities in soft X-ray flare index (FISXR) during solar cycles 21, 22 and 23. Power-spectral analysis of daily FISXR reveals a significant period of 161 days in cycle 21 which is absent during cycles 22 and 23. We have found that in cycle 22 periodicities of 74 and 83 days are in operation. A 123-day periodicity has been found to be statistically significant during part of the current solar cycle 23. The existence of these periodicities has been discussed in the light of earlier results. 相似文献
13.
Taeil Bai 《Solar physics》2006,234(2):409-419
In the declining phase of the current solar cycle (23), a large number of major flares were produced. In this cycle, the monthly
sunspot number continuously remained below 100 since October 2002. However, during four epochs since then, flare activity
became very high. Compared to this, each of cycles 21 and 22 produced only one epoch of high activity in the declining phase.
In the declining phase of cycle 20, similarly to this cycle, there were four epochs of high flare activity. During 2003 and
2004, the distribution of flare sizes measured in GOES classes was much harder (i.e., proportionately more energetic flares) than during the maximum years. Such pronounced hardening of the size distribution
was not observed in the previous cycles. It is of theoretical interest to understand why some cycles are very active in the
declining phase, and the high level of activity in the declining phase has practical implications for planning solar observations
and forecasting space weather. 相似文献
14.
Asymmetry, a well established fact, can be extracted from various solar atmospheric activity indices. Although asymmetry is being localized within short time scale, it also persists at different time scales. In the present study we examine the character and nature of asymmetry at various time scales by optimizing the data set, in units of Carrington Rotations (CRs), for Sunspot Area (SA) and soft X-ray flare index (FI SXR). We find from three solar cycles (21-23) that at a small time scale (viz., daily, CRs and monthly) activity appears to be asymmetric with less significance. At larger time scales (≥01 CRs) strength of asymmetry enhances. Number of significant asymmetry points probably depends upon the solar heights. For different combination of data, asymmetry strength appears to be lowered at certain periods ～06, ～12, ～18 CRs (164, 327 and 492 days i.e., harmonics of ～1.3 years. Owing to similar behavior of emergence of magnetic flux, it is conjectured that emergence of flux on the surface probably contributes to the asymmetry of the solar activity. 相似文献
15.
Although solar ultraviolet (UV) irradiance measurements have been made regularly from satellite instruments for almost 20 years, only one complete solar cycle minimum has been observed during this period. Solar activity is currently moving through the minimum phase between cycles 22 and 23, so it is of interest to compare recent data taken from the NOAA-9 SBUV/2 instrument with data taken by the same instrument during the previous solar minimum in 1985–1986. NOAA-9 SBUV/2 is the first instrument to make continuous solar UV measurements for a complete solar cycle. Direct irradiance measurements (e.g., 205 nm) from NOAA-9 are currently useful for examining short-term variations, but have not been corrected for long-term instrument sensitivity changes. We use the Mgii proxy index to illustrate variability on solar cycle time scales, and to provide complementary information on short-term variability. Comparisons with contemporaneous data from Nimbus-7 SBUV (1985–1986) and UARS SUSIM (1994–1995) are used to validate the results obtained from the NOAA-9 data. Current short-term UV activity differs from the cycle 21–22 minimum. Continuous 13-day periodicity was observed from September 1994 to March 1995, a condition which has only been seen previously for shorter intervals during rising or maximum activity levels. The 205 nm irradiance and Mgii index are expected to track very closely on short time scales, but show differences in behavior during the minimum between cycles 22 and 23. 相似文献
16.
In order to investigate the relationship between magnetic-flux emergence, solar flares, and coronal mass ejections (CMEs), we study the periodicity in the time series of these quantities. It has been known that solar flares, sunspot area, and photospheric magnetic flux have a dominant periodicity of about 155 days, which is confined to a part of the phase of the solar cycle. These periodicities occur at different phases of the solar cycle during successive phases. We present a time-series analysis of sunspot area, flare and CME occurrence during Cycle 23 and the rising phase of Cycle 24 from 1996 to 2011. We find that the flux emergence, represented by sunspot area, has multiple periodicities. Flares and CMEs, however, do not occur with the same period as the flux emergence. Using the results of this study, we discuss the possible activity sources producing emerging flux. 相似文献
17.
The short-term periodicities of the flare index are investigated in detail using Fourier and wavelet transforms for the full disc and for the northern and the southern hemispheres of the Sun separately over the epoch of almost 4 cycles (1966–2002). The most pronounced power peaks were found by the Fourier transform to be present at 25.6, 27.0, 30.2, and 33.8 days. The wavelet transform results show that the occurrence of periodicities of flare index power is highly intermittent in time. A comparison of the results of the Fourier transform and the time-period wavelet transform of the flare index time series has clarified the importance of different periodicities, whether they are or are not the harmonics of the basic ones, as well as the temporal location of their occurrence. We found that the modulation of the flare index due to the 27-day solar rotation is more pronounced during the declining portion of solar cycle than during the rising portion. 相似文献
18.
The short-term periodicities of the flare index are investigated in detail using Fourier and wavelet transforms for the full disc and for the northern and the southern hemispheres of the Sun separately over the epoch of almost 4 cycles (1966–2002). The most pronounced power peaks were found by the Fourier transform to be present at 25.6, 27.0, 30.2, and 33.8 days. The wavelet transform results show that the occurrence of periodicities of flare index power is highly intermittent in time. A comparison of the results of the Fourier transform and the time-period wavelet transform of the flare index time series has clarified the importance of different periodicities, whether they are or are not the harmonics of the basic ones, as well as the temporal location of their occurrence. We found that the modulation of the flare index due to the 27-day solar rotation is more pronounced during the declining portion of solar cycle than during the rising portion. 相似文献
19.
We study the hysteresis effect between the solar flare index and cosmic ray intensity for the past 37 years from January 1, 1965 to December 31, 2001 on a daily basis. We show that smoothed time series of flare index and the daily Calgary Galactic Cosmic Ray intensity values exhibit significant solar cycle dependent differences in their relative variations during the studied period. The shapes of these differences vary from cycle to cycle. So we investigate the momentary time lags between the two time series for the odd and even cycles. 相似文献
20.
The periodic analyses of solar flare data have been carried out by different authors for about three decades. Controversial
results appear as depending on the analysis techniques and investigated time periods. Considering that different authors applied
different methods to different data sets, it seems necessary to reanalyze the periodicity of solar flare index with a unified
method. In this study we used two new methods to investigate the periodic behavior of solar flare index data, first for individual
cycles 21, 22 and 23, and then for all of them. We used i) the multi taper method with red- and white-noise approximations, and ii) the Morlet wavelet transform for periodicity analysis. Apart from the solar rotation periodicity of about 27 days which
is of obvious significance and is found in all examined cycles with at least a 90% significance level, we obtained the following
prominent periods: 152 days for cycle 21, 73 days for cycle 22, and 62 days for cycle 23. Finally, we compare our results
with the ones previously found. We emphasize the fact that a lesser number of periodicities is found in the range of low frequencies
(long periods) while the higher frequencies show a greater number of periodicities. This result might be useful for better
predictions of the solar cycles. 相似文献