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1.
In the previous study (Dabas et al. in Solar Phys.
250, 171, 2008), to predict the maximum sunspot number of the current solar cycle 24 based on the geomagnetic activity of the preceding
sunspot minimum, the Ap index was used which is available from the last six to seven solar cycles. Since a longer series of the aa index is available for more than the last 10 – 12 cycles, the present study utilizes aa to validate the earlier prediction. Based on the same methodology, the disturbance index (DI), which is the 12-month moving
average of the number of disturbed days (aa≥50), is computed at thirteen selected times (called variate blocks 1,2,…,13; each of them in six-month duration) during the
declining portion of the ongoing sunspot cycle. Then its correlation with the maximum sunspot number of the following cycle
is evaluated. As in the case of Ap, variate block 9, which occurs exactly 48 months after the current cycle maximum, gives the best correlation (R=0.96) with a minimum standard error of estimation (SEE) of ± 9. As applied to cycle 24, the aa index as precursor yields the maximum sunspot number of about 120±16 (the 90% prediction interval), which is within the 90%
prediction interval of the earlier prediction (124±23 using Ap). Furthermore, the same method is applied to an expanded range of cycles 11 – 23, and once again variate block 9 gives the
best correlation (R=0.95) with a minimum SEE of ± 13. The relation yields the modified maximum amplitude for cycle 24 of about 131±20, which
is also close to our earlier prediction and is likely to occur at about 43±4 months after its minimum (December 2008), probably
in July 2012 (± 4 months). 相似文献
2.
Precursor techniques, in particular those using geomagnetic indices, often are used in the prediction of the maximum amplitude
for a sunspot cycle. Here, the year 2008 is taken as being the sunspot minimum year for cycle 24. Based on the average aa index value for the year of the sunspot minimum and the preceding four years, we estimate the expected annual maximum amplitude
for cycle 24 to be about 92.8±19.6 (1-sigma accuracy), indicating a somewhat weaker cycle 24 as compared to cycles 21 – 23.
Presuming a smoothed monthly mean sunspot number minimum in August 2008, a smoothed monthly mean sunspot number maximum is
expected about October 2012±4 months (1-sigma accuracy). 相似文献
3.
Spotless days (i.e., days when no sunspots are observed on the Sun) occur during the interval between the declining phase of the old sunspot
cycle and the rising phase of the new sunspot cycle, being greatest in number and of longest continuous length near a new
cycle minimum. In this paper, we introduce the concept of the longest spotless segment (LSS) and examine its statistical relation
to selected characteristic points in the sunspot time series (STS), such as the occurrences of first spotless day and sunspot
maximum. The analysis has revealed statistically significant relations that appear to be of predictive value. For example,
for Cycle 24 the last spotless day during its rising phase should be about August 2012 (± 9.1 months), the daily maximum sunspot
number should be about 227 (± 50; occurring about January 2014±9.5 months), and the maximum Gaussian smoothed sunspot number
should be about 87 (± 25; occurring about July 2014). Using the Gaussian-filtered values, slightly earlier dates of August
2011 and March 2013 are indicated for the last spotless day and sunspot maximum for Cycle 24, respectively. 相似文献
4.
J. Javaraiah 《Solar physics》2008,252(2):419-439
Recently, using Greenwich and Solar Optical Observing Network sunspot group data during the period 1874 – 2006, Javaraiah
(Mon. Not. Roy. Astron. Soc.
377, L34, 2007: Paper I), has found that: (1) the sum of the areas of the sunspot groups in 0° – 10° latitude interval of the Sun’s northern
hemisphere and in the time-interval of −1.35 year to +2.15 year from the time of the preceding minimum of a solar cycle n correlates well (corr. coeff. r=0.947) with the amplitude (maximum of the smoothed monthly sunspot number) of the next cycle n+1. (2) The sum of the areas of the spot groups in 0° – 10° latitude interval of the southern hemisphere and in the time-interval
of 1.0 year to 1.75 year just after the time of the maximum of the cycle n correlates very well (r=0.966) with the amplitude of cycle n+1. Using these relations, (1) and (2), the values 112±13 and 74±10, respectively, were predicted in Paper I for the amplitude
of the upcoming cycle 24. Here we found that the north – south asymmetries in the aforementioned area sums have a strong ≈44-year
periodicity and from this we can infer that the upcoming cycle 24 will be weaker than cycle 23. In case of (1), the north – south
asymmetry in the area sum of a cycle n also has a relationship, say (3), with the amplitude of cycle n+1, which is similar to (1) but more statistically significant (r=0.968) like (2). By using (3) it is possible to predict the amplitude of a cycle with a better accuracy by about 13 years
in advance, and we get 103±10 for the amplitude of the upcoming cycle 24. However, we found a similar but a more statistically
significant (r=0.983) relationship, say (4), by using the sum of the area sum used in (2) and the north – south difference used in (3).
By using (4) it is possible to predict the amplitude of a cycle by about 9 years in advance with a high accuracy and we get
87±7 for the amplitude of cycle 24, which is about 28% less than the amplitude of cycle 23. Our results also indicate that
cycle 25 will be stronger than cycle 24. The variations in the mean meridional motions of the spot groups during odd and even
numbered cycles suggest that the solar meridional flows may transport magnetic flux across the solar equator and potentially
responsible for all the above relationships.
The author did a major part of this work at the Department of Physics and Astronomy, UCLA, 430 Portola Plaza, Los Angeles,
CA 90095-1547, USA. 相似文献
5.
R. P. Kane 《Solar physics》2007,246(2):471-485
Many methods of predictions of sunspot maximum number use data before or at the preceding sunspot minimum to correlate with
the following sunspot maximum of the same cycle, which occurs a few years later. Kane and Trivedi (Solar Phys. 68, 135, 1980) found that correlations of R
z(max) (the maximum in the 12-month running means of sunspot number R
z) with R
z(min) (the minimum in the 12-month running means of sunspot number R
z) in the solar latitude belt 20° – 40°, particularly in the southern hemisphere, exceeded 0.6 and was still higher (0.86)
for the narrower belt > 30° S. Recently, Javaraiah (Mon. Not. Roy. Astron. Soc.
377, L34, 2007) studied the relationship of sunspot areas at different solar latitudes and reported correlations 0.95 – 0.97 between minima and maxima of sunspot areas at low latitudes
and sunspot maxima of the next cycle, and predictions could be made with an antecedence of more than 11 years. For the present
study, we selected another parameter, namely, SGN, the sunspot group number (irrespective of their areas) and found that SGN(min) during a sunspot minimum year at latitudes > 30° S had a correlation
+0.78±0.11 with the sunspot number R
z(max) of the same cycle. Also, the SGN during a sunspot minimum year in the latitude belt (10° – 30° N) had a correlation +0.87±0.07 with the
sunspot number R
z(max) of the next cycle. We obtain an appropriate regression equation, from which our prediction for the coming cycle 24 is R
z(max )=129.7±16.3. 相似文献
6.
Robert M. Wilson 《Solar physics》1990,125(1):143-155
Precursor prediction techniques have generally performed well in predicting the maximum amplitude of sunspot cycles, based on cycles 10–21. Single variate methods based on minimum sunspot amplitude have reliably predicted the size of the sunspot cycle 9 out of 12 times, where a reliable prediction is defined as one having an observed maximum amplitude within the prediction interval (determined from the average error). On the other hand, single variate methods based on the size of the geomagnetic minimum have reliably predicted the size of the sunspot cycle 8 of 10 times (geomagnetic data are only available since about cycle 12). Bivariate prediction methods have, thus far, performed flawlessly, giving reliable predictions 10 out of 10 times (bivariate methods are based on sunspot and geomagnetic data). For cycle 22, single variate methods (based on geomagnetic data) suggest a maximum amplitude of about 170 ± 25, while bivariate methods suggest a maximum amplitude of about 140 ± 15; thus, both techniques suggest that cycle 22 will be of smaller maximum amplitude than that observed during cycle 19, and possibly even smaller than that observed for cycle 21. Compared to the mean cycle, cycle 22 is presently behaving as if it is a + 2.6 cycle (maximum amplitude about 225). It appears then that either cycle 22 will be the first cycle not to be reliably predicted by the combined precursor techniques (i.e., cycle 22 is an anomaly, a statistical outlier) or the deviation of cycle 22 relative to the mean cycle will substantially decrease over the next 18 months. Because cycle 22 is a large amplitude cycle, maximum smoothed sunspot number is expected to occur early in 1990 (between December 1989 and May 1990). 相似文献
7.
R. P. Kane 《Solar physics》2007,243(2):205-217
For many purposes (e.g., satellite drag, operation of power grids on Earth, and satellite communication systems), predictions of the strength of
a solar cycle are needed. Predictions are made by using different methods, depending upon the characteristics of sunspot cycles.
However, the method most successful seems to be the precursor method by Ohl and his group, in which the geomagnetic activity
in the declining phase of a sunspot cycle is found to be well correlated with the sunspot maximum of the next cycle. In the
present communication, the method is illustrated by plotting the 12-month running means aa(min ) of the geomagnetic disturbance index aa near sunspot minimum versus the 12-month running means of the sunspot number Rz near sunspot maximum [aa(min ) versus Rz(max )], using data for sunspot cycles 9 – 18 to predict the Rz(max ) of cycle 19, using data for cycles 9 – 19 to predict Rz(max ) of cycle 20, and so on, and finally using data for cycles 9 – 23 to predict Rz(max ) of cycle 24, which is expected to occur in 2011 – 2012. The correlations were good (∼+0.90) and our preliminary predicted
Rz(max ) for cycle 24 is 142±24, though this can be regarded as an upper limit, since there are indications that solar minimum
may occur as late as March 2008. (Some workers have reported that the aa values before 1957 would have an error of 3 nT; if true, the revised estimate would be 124±26.) This result of the precursor
method is compared with several other predictions of cycle 24, which are in a very wide range (50 – 200), so that whatever
may be the final observed value, some method or other will be discredited, as happened in the case of cycle 23. 相似文献
8.
What the Sunspot Record Tells Us About Space Climate 总被引:1,自引:0,他引:1
The records concerning the number, sizes, and positions of sunspots provide a direct means of characterizing solar activity
over nearly 400 years. Sunspot numbers are strongly correlated with modern measures of solar activity including: 10.7-cm radio
flux, total irradiance, X-ray flares, sunspot area, the baseline level of geomagnetic activity, and the flux of galactic cosmic
rays. The Group Sunspot Number provides information on 27 sunspot cycles, far more than any of the modern measures of solar
activity, and enough to provide important details about long-term variations in solar activity or “Space Climate.” The sunspot
record shows: 1) sunspot cycles have periods of 131± 14 months with a normal distribution; 2) sunspot cycles are asymmetric
with a fast rise and slow decline; 3) the rise time from minimum to maximum decreases with cycle amplitude; 4) large amplitude
cycles are preceded by short period cycles; 5) large amplitude cycles are preceded by high minima; 6) although the two hemispheres
remain linked in phase, there are significant asymmetries in the activity in each hemisphere; 7) the rate at which the active
latitudes drift toward the equator is anti-correlated with the cycle period; 8) the rate at which the active latitudes drift
toward the equator is positively correlated with the amplitude of the cycle after the next; 9) there has been a significant
secular increase in the amplitudes of the sunspot cycles since the end of the Maunder Minimum (1715); and 10) there is weak
evidence for a quasi-periodic variation in the sunspot cycle amplitudes with a period of about 90 years. These characteristics
indicate that the next solar cycle should have a maximum smoothed sunspot number of about 145 ± 30 in 2010 while the following
cycle should have a maximum of about 70 ± 30 in 2023. 相似文献
9.
R. P. Kane 《Solar physics》2008,249(2):369-380
The sunspot number series at the peak of sunspot activity often has two or three peaks (Gnevyshev peaks; Gnevyshev, Solar Phys.
1, 107, 1967; Solar Phys.
51, 175, 1977). The sunspot group number (SGN) data were examined for 1997 – 2003 (part of cycle 23) and compared with data for coronal
mass ejection (CME) events. It was noticed that they exhibited mostly two Gnevyshev peaks in each of the four latitude belts
0° – 10°, 10° – 20°, 20 ° – 30°, and > 30°, in both N (northern) and S (southern) solar hemispheres. The SGN were confined
to within latitudes ± 50° around the Equator, mostly around ± 35°, and seemed to occur later in lower latitudes, indicating
possible latitudinal migration as in the Maunder butterfly diagrams. In CMEs, less energetic CMEs (of widths < 71°) showed
prominent Gnevyshev peaks during sunspot maximum years in almost all latitude belts, including near the poles. The CME activity
lasted longer than the SGN activity. However, the CME peaks did not match the SGN peaks and were almost simultaneous at different
latitudes, indicating no latitudinal migration. In energetic CMEs including halo CMEs, the Gnevyshev peaks were obscure and
ill-defined. The solar polar magnetic fields show polarity reversal during sunspot maximum years, first at the North Pole
and, a few months later, at the South Pole. However, the CME peaks and gaps did not match with the magnetic field reversal
times, preceding them by several months, rendering any cause – effect relationship doubtful. 相似文献
10.
An Estimate for the Size of Sunspot Cycle 24 总被引:1,自引:0,他引:1
R. P. Kane 《Solar physics》2013,282(1):87-90
For the sunspot cycles in the modern era (cycle?10 to the present), the ratio of R Z(max)/R Z(36th month) equals 1.26±0.22, where R Z(max) is the maximum amplitude of the sunspot cycle?using smoothed monthly mean sunspot number and R Z(36th month) is the smoothed monthly mean sunspot number 36 months after cycle?minimum. For the current sunspot cycle?24, the 36th month following the cycle?minimum occurred in November 2011, measuring?61.1. Hence, cycle?24 likely will have a maximum amplitude of about 77.0±13.4 (the one-sigma prediction interval), a value well below the average R Z(max) for the modern era sunspot cycles (about 119.7±39.5). 相似文献
11.
K. M. Hiremath 《Astrophysics and Space Science》2008,314(1-3):45-49
In the previous study (Hiremath, Astron. Astrophys. 452:591, 2006a), the solar cycle is modeled as a forced and damped harmonic oscillator and from all the 22 cycles (1755–1996), long-term
amplitudes, frequencies, phases and decay factor are obtained. Using these physical parameters of the previous 22 solar cycles
and by an autoregressive model, we predict the amplitude and period of the present cycle 23 and future fifteen solar cycles. The period of present solar
cycle 23 is estimated to be 11.73 years and it is expected that onset of next sunspot activity cycle 24 might starts during
the period 2008.57±0.17 (i.e., around May–September 2008). The predicted period and amplitude of the present cycle 23 are almost similar to the period
and amplitude of the observed cycle. With these encouraging results, we also predict the profiles of future 15 solar cycles.
Important predictions are: (i) the period and amplitude of the cycle 24 are 9.34 years and 110 (±11), (ii) the period and
amplitude of the cycle 25 are 12.49 years and 110 (±11), (iii) during the cycles 26 (2030–2042 AD), 27 (2042–2054 AD), 34
(2118–2127 AD), 37 (2152–2163 AD) and 38 (2163–2176 AD), the sun might experience a very high sunspot activity, (iv) the sun
might also experience a very low (around 60) sunspot activity during cycle 31 (2089–2100 AD) and, (v) length of the solar
cycles vary from 8.65 years for the cycle 33 to maximum of 13.07 years for the cycle 35. 相似文献
12.
According to research results from solar-dynamo models, the northern and southern hemispheres may evolve separately throughout
the solar cycle. The observed phase lag between the northern and southern hemispheres provides information regarding how strongly
the hemispheres are coupled. Using hemispheric sunspot-area and sunspot-number data from Cycles 12 – 23, we determine how
out of phase the separate hemispheres are during the rising, maximum, and declining period of each solar cycle. Hemispheric
phase differences range from 0 – 11, 0 – 14, and 2 – 19 months for the rising, maximum, and declining periods, respectively.
The phases appear randomly distributed between zero months (in phase) and half of the rise (or decline) time of the solar
cycle. An analysis of the sunspot cycle double peak, or Gnevyshev gap, is conducted to determine if the double-peak is caused
by the averaging of two hemispheres that are out of phase. We confirm previous findings that the Gnevyshev gap is a phenomenon
that occurs in the separate hemispheres and is not due to a superposition of sunspot indices from hemispheres slightly out
of phase. Cross hemispheric coupling could be strongest at solar minimum, when there are large quantities of magnetic flux
at the Equator. We search for a correlation between the hemispheric phase difference near the end of the solar cycle and the
length of solar-cycle minimum, but found none. Because magnetic flux diffusion across the Equator is a mechanism by which
the hemispheres couple, we measured the magnetic flux crossing the Equator by examining Kitt Peak Vacuum Telescope and SOLIS
magnetograms for Solar Cycles 21 – 23. We find, on average, a surplus of northern hemisphere magnetic flux crossing during
the mid-declining phase of each solar cycle. However, we find no correlation between magnitude of magnetic flux crossing the
Equator, length of solar minima, and phase lag between the hemispheres. 相似文献
13.
Samuel Heinrich Schwabe, the discoverer of the sunspot cycle, observed the Sun routinely from Dessau, Germany during the interval
of 1826–1868, averaging about 290 observing days per year. His yearly counts of ‘clusters of spots’ (or, more correctly, the
yearly number of newly appearing sunspot groups) provided a simple means for describing the overt features of the sunspot
cycle (i.e., the timing and relative strengths of cycle minimum and maximum). In 1848, Rudolf Wolf, a Swiss astronomer, having
become aware of Schwabe's discovery, introduced his now familiar ‘relative sunspot number’ and established an international
cadre of observers for monitoring the future behavior of the sunspot cycle and for reconstructing its past behavior (backwards
in time to 1818, based on daily sunspot number estimates). While Wolf's reconstruction is complete (without gaps) only from
1849 (hence, the beginning of the modern era), the immediately preceding interval of 1818–1848 is incomplete, being based
on an average of 260 observing days per year. In this investigation, Wolf's reconstructed record of annual sunspot number
is compared against Schwabe's actual observing record of yearly counts of clusters of spots. The comparison suggests that
Wolf may have misplaced (by about 1–2 yr) and underestimated (by about 16 units of sunspot number) the maximum amplitude for
cycle 7. If true, then, cycle 7's ascent and descent durations should measure about 5 years each instead of 7 and 3 years,
respectively, the extremes of the distributions, and its maximum amplitude should measure about 86 instead of 70. This study
also indicates that cycle 9's maximum amplitude is more reliably determined than cycle 8's and that both appear to be of comparable
size (about 130 units of sunspot number) rather than being significantly different. Therefore, caution is urged against the
indiscriminate use of the pre-modern era sunspot numbers in long-term studies of the sunspot cycle, since such use may lead
to specious results. 相似文献
14.
《New Astronomy》2007,12(1):29-32
A weak 5-cycle periodicity (r = −0.64) is found in the maximum amplitudes of the modern era sunspot cycles (11–23), slightly stronger than the 8-cycle (Gleissberg) periodicity (r = 0.60).We propose a new parameter called ‘effective duration’, defined as the total sunspot numbers in a cycle divided by the maximum amplitude. This parameter has two advantages: one is that it is almost independent of the exact definition of minimum timing; another is that the maximum amplitude is found to be highly correlated (r = 0.86) with this parameter five cycles before, when applied to the smoothed monthly mean sunspot numbers in modern era.Implied is that this parameter carries some information of the amplitude five cycles later, and may become one of the parameters to study solar activity and the theory of solar dynamo. With the relationship above, the amplitude of cycle 24 is estimated to be 115.7 ± 19.7, where the error is the standard error. 相似文献
15.
We present the sunspot ideas and observations of the 18th century Portuguese scholar Teodoro de Almeida (1722 – 1804) and
Mexican scientist José Antonio Alzate (1737 – 1799). We describe the implications of dating a single sunspot observation performed
by Almeida in the early 1760s, during the maximum of cycle number 1. A possible solar cycle peak in 1760 (instead of 1761)
is investigated. We present several observations of sunspots obtained by Alzate during 1769 (partially associated with the
Venus and Mercury transits) and also on 20 July 1786. We estimate 100±34 as the Group Sunspot Number for this date. These
records were unknown and, therefore, not included in the database compiled by Hoyt and Schatten (1998). 相似文献
16.
J. Javaraiah 《Solar physics》2011,270(2):463-483
Using the combined Greenwich (1874 – 1976) and Solar Optical Observatories Network (1977 – 2009) data on sunspot groups, we
study the long-term variations in the mean daily rates of growth and decay of sunspot groups. We find that the minimum and
the maximum values of the annually averaged daily mean growth rates are ≈ 52% day−1 and ≈ 183% day−1, respectively, whereas the corresponding values of the annually averaged daily mean decay rates are ≈ 21% day−1 and ≈ 44% day−1, respectively. The average value (over the period 1874 – 2009) of the growth rate is about 70% more than that of the decay
rate. The growth and the decay rates vary by about 35% and 13%, respectively, on a 60-year time scale. From the beginning
of Cycle 23 the growth rate is substantially decreased and near the end (2007 – 2008) the growth rate is lowest in the past
about 100 years. In the extended part of the declining phase of this cycle, the decay rate steeply increased and it is largest
in the beginning of the current Cycle 24. These unusual properties of the growth and the decay rates during Cycle 23 may be
related to cause of the very long declining phase of this cycle with the unusually deep and prolonged current minimum. A ≈ 11-year
periodicity in the growth and the decay rates is found to be highly latitude and time dependent and seems to exist mainly
in the 0° – 10° latitude interval of the southern hemisphere. The strength of the known approximate 33 – 44-year modulation
in the solar activity seems to be related to the north-south asymmetry in the growth rate. Decreasing and increasing trends
in the growth and the decay rates indicate that the next 2 – 3 solar cycles will be relatively weak. 相似文献
17.
An improved correlation between maximum sunspot number (SSNM) and the preceding minimum (SSNm) is reported when the monthly mean sunspot numbers are smoothed with a 13-month running window. This relation allows prediction of the amplitude of a sunspot cycle by making use of the sunspot data alone. The estimated smoothed maximum sunspot number (126±26) and time of maximum epoch (second half of 2000) of cycle 23 are in good agreement with the predictions made by some of the precursor methods. 相似文献
18.
We examine daily records of sunspot group areas (measured in millionths of a solar hemisphere or μHem) for the last 130 years
to determine the rate of decay of sunspot group areas. We exclude observations of groups when they are more than 60° in longitude
from the central meridian and only include data when at least three days of observations are available following the date
of maximum area for a group’s disk passage. This leaves data for over 18 000 measurements of sunspot group decay. We find
that the decay rate increases linearly from 28 μHem day−1 to about 140 μHem day−1 for groups with areas increasing from 35 μHem to 1000 μHem. The decay rate tends to level off for groups with areas larger
than 1000 μHem. This behavior is very similar to the increase in the number of sunspots per group as the area of the group
increases. Calculating the decay rate per individual sunspot gives a decay rate of about 3.65 μHem day−1 with little dependence upon the area of the group. This suggests that sunspots decay by a Fickian diffusion process with
a diffusion coefficient of about 10 km2 s−1. Although the 18 000 decay rate measurements are lognormally distributed, this can be attributed to the lognormal distribution
of sunspot group areas and the linear relationship between area and decay rate for the vast majority of groups. We find weak
evidence for variations in decay rates from one solar cycle to another and for different phases of each sunspot cycle. However,
the strongest evidence for variations is with latitude and the variations with cycle and phase of each cycle can be attributed
to this variation. High latitude spots tend to decay faster than low latitude spots. 相似文献
19.
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
20.
Fluctuations of Solar Activity during the Declining Phase of the 11-Year Sunspot Cycle 总被引:1,自引:0,他引:1
R. P. Kane 《Solar physics》2009,255(1):163-168
The number of coronal mass ejections (CMEs) erupting from the Sun follows a trend similar to that of sunspot numbers during
the rising and maximum phase of the solar cycle. In the declining phase, the CME number has large fluctuations, dissimilar
to those of sunspot numbers. In several studies of solar – interplanetary and solar – terrestrial relationships, the sunspot
numbers and the 2800-MHz flux (F10) are used as representative of solar activity. In the rising phase, this may be adequate,
but in the declining phase, solar parameters such as CMEs may have a different behaviour. Cosmic-ray Forbush decreases may
occur even when sunspot activity is low. Therefore, when studying the solar influence on the Earth, one has to consider that
although geomagnetic conditions at solar maximum will be disturbed, conditions at solar minimum may not be necessarily quiet. 相似文献