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1.
Recently, Juckett and Wolff (Solar Phys.
252, 247, 2008) showed that the timing and longitude of sunspot patterns has some correspondence with a model based on coupled g modes. The model maximizes the nonlinear coupling of those g modes sharing harmonic degree ℓ to generate a “set(ℓ)” that assists its own excitation by locally enhancing nuclear burning. Each set(ℓ) has oscillatory power concentrated at two longitudes, on opposite sides of the Sun and drifts slowly retrograde within the
radiative zone (RZ) at a rate that depends on ℓ. When the strong longitudes of two or more sets overlap, wave dissipation adds extra energy to that locality at the base
of the convective envelope increasing convection and then sunspot activity. We compare the main subdecadal sunspot frequencies
with the intersections of sets derived from ℓ=2 – 11 and G, where G represents unresolvable high-ℓ modes that rotate similarly to the RZ. After determining the set(ℓ) spatial phases, we show that 17 subdecadal oscillations with periods in the range 0.6 to 7.0 years (4.5 to 50 nHz), generated
by 23 unique intersections of the 11 sets, are synchronous with 17 corresponding frequencies in the sunspot time series. After
optimizing parameters, we find a mean correlation of 0.96 for synchrony among the 17 waveform pairs. These 17 frequencies
constitute the bulk of the non-noise subdecadal frequency domain of the sunspot variation. We conclude that the sunspot series
contains oscillatory components with the same temporal phases and frequencies as various set(ℓ) intersections spanning the past ≈ 100 years. This additional evidence for the role of coupled g modes in sunspot dynamics suggests that more of sunspot variability can be understood with nonmagnetic fluid mechanics than
popularly thought. 相似文献
2.
Solar g-modes are global oscillations that would exist primarily in the radiative zone (RZ) and would be excited by either
convective overshoot or nuclear burning in the core. Wolff and O’Donovan (Astrophys. J.
661, 568, 2007) proposed a non-linear coupling of g-modes into groups that share the same harmonic degree ℓ. Each group (denoted set(ℓ)) exhibits a unique retrograde rotation rate with respect to the RZ that depends mainly on ℓ. The coupling yields a standing wave (nearly stationary in longitude) that has two angularly defined hot spots offset from
the equator on opposite sides of the Sun that would deposit energy asymmetrically in the lower convective envelope (CE). It
is anticipated that when two or more groups overlap in longitude, an increase in local heating would influence the distribution
of sunspots. In this paper, we scanned a multitude of rotational reference frames for sunspot clustering to test for frames
that are concordant with the rotation of these g-modes sets. To achieve this, spherical harmonic filtering of sunspot synoptic
maps was used to extract patterns consistent with coalesced g-modes. The latitude band, with minimal differential rotation,
was sampled from each filtered synoptic map and layered into a stackplot. This was progressively shifted, line-by-line, into
different rotational reference frames. We have detected long-lived longitudinal alignments, spanning 90 years of solar cycles,
which are consistent with the rotation rate of the deep solar interior as well as other rotational frames predicted by the
coupled g-mode model. Their sidereal rotation rates of 370.0, 398.8, 412.7, 418.3, 421.0, 424.2 and 430.0 nHz correspond,
respectively, to coupled g-modes for ℓ = 2 through 7 and G, where G is a set with high ℓ values or a group of such sets (unresolved) that rotate almost as fast as the RZ. While the clustering in these reference
frames offers new approaches for studying the longitudinal behavior of solar activity, it tentatively leads to the more profound
conclusion that a portion of the driving force for sunspot occurrence is linked to energy extracted from the solar core and
deposited at the top of the RZ by solar g-modes. 相似文献
3.
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
4.
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
5.
R. P. Kane 《Solar physics》2007,245(2):415-421
The occurrence of double peaks near the maximum of sunspot activity was first emphasized by Gnevyshev (Solar Phys.
1, 107, 1967) for the peak years of solar cycle 19 (1954 – 1964). In the present analysis, it is shown that double peaks in sunspot numbers
were clearly visible in solar latitudes 10 – 30° N but almost absent in the southern latitudes, where some single peaks were
observed out of phase by several months from any of the peaks in the northern latitudes. The spacing between the double peaks
increased from higher to lower northern latitudes, hinting at latitudinal migration. In the next cycle 20 (1965 – 1976), which
was of about half the strength of cycle 19, no clear-cut double peaks were seen, and the prominent peak in the early part
of 1967 in the northern latitudes was seen a few months later in the southern latitudes. A direct relationship of Gnevyshev
peaks with changes in the solar polar magnetic fields seems to be dubious. The commencements do not match. 相似文献
6.
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
7.
Based on the extended Greenwich – NOAA/USAF catalogue of sunspot groups, it is demonstrated that the parameters describing
the latitudinal width of the sunspot generating zone (SGZ) are closely related to the current level of solar activity, and
the growth of the activity leads to the expansion of the SGZ. The ratio of the sunspot number to the width of the SGZ shows
saturation at a certain level of the sunspot number, and above this level the increase of the activity takes place mostly
due to the expansion of the SGZ. It is shown that the mean latitudes of sunspots can be reconstructed from the amplitudes
of solar activity. Using the obtained relations and the group sunspot numbers by Hoyt and Schatten (Solar Phys.
179, 189, 1998), the latitude distribution of sunspot groups (“the Maunder butterfly diagram”) for the eighteenth and the first half of
the nineteenth centuries is reconstructed and compared with historical sunspot observations. 相似文献
8.
In the present study, the short-term periodicities in the daily data of the sunspot numbers and areas are investigated separately
for the full disk, northern, and southern hemispheres during Solar Cycle 23 for a time interval from 1 January 2003 to 30
November 2007 corresponding to the descending and minimum phase of the cycle. The wavelet power spectrum technique exhibited
a number of quasi-periodic oscillations in all the datasets. In the high frequency range, we find a prominent period of 22 – 35
days in both sunspot indicators. Other quasi-periods in the range of 40 – 60, 70 – 90, 110 – 130, 140 – 160, and 220 – 240
days are detected in the sunspot number time series in different hemispheres at different time intervals. In the sunspot area
data, quasi-periods in the range of 50 – 80, 90 – 110, 115 – 130, 140 – 155, 160 – 190, and about 230 days were noted in different
hemispheres within the time period of analysis. The present investigation shows that the well-known “Rieger periodicity” of
150 – 160 days reappears during the descending phase of Solar Cycle 23, but this is prominent mainly in the southern part
of the Sun. Possible explanations of these observed periodicities are delivered on the basis of earlier results detected in
photospheric magnetic field time series (Knaack, Stenflo, and Berdyugina in Astron. Astrophys.
438, 1067, 2005) and solar r-mode oscillations. 相似文献
9.
We study variations of the lifetimes of high-ℓ solar p modes in the quiet and active Sun with the solar activity cycle. The lifetimes in the degree range ℓ=300 – 600 and ν=2.5 – 4.5 mHz were computed from SOHO/MDI data in an area including active regions and quiet Sun using the time – distance
technique. We applied our analysis to the data in four different phases of solar activity: 1996 (at minimum), 1998 (rising
phase), 2000 (at maximum), and 2003 (declining phase). The results from the area with active regions show that the lifetime
decreases as activity increases. The maximal lifetime variations are between solar minimum in 1996 and maximum in 2000; the
relative variation averaged over all ℓ values and frequencies is a decrease of about 13%. The lifetime reductions relative to 1996 are about 7% in 1998 and about
10% in 2003. The lifetime computed in the quiet region still decreases with solar activity, although the decrease is smaller.
On average, relative to 1996, the lifetime decrease is about 4% in 1998, 10% in 2000, and 8% in 2003. Thus, measured lifetime
increases when regions of high magnetic activity are avoided. Moreover, the lifetime computed in quiet regions also shows
variations with the activity cycle. 相似文献
10.
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
11.
We study the evolution of the longitudinal asymmetry in solar activity through the wave packet technique applied to the period
domain of 25 – 31 days (centered at the 27-day solar rotation period) for the sunspot number and geomagnetic aa index. We observe the occurrence of alternating smaller and larger amplitudes of the 11-year cycle, resulting in a 22-year
periodicity in the 27-day signal. The evolution of the 22-year cycle shows a change of regime around the year 1912 when the
22-year period disappears from the sunspot number series and appears in the aa index. Other changes, such as a change in the correlation between solar and geomagnetic activity, took place at the same
time. Splitting the 27-day frequency domain of aa index shows an 11-year cycle for higher frequencies and a pure22-year cycle for lower frequencies, which we attribute to
higher latitude coronal holes. This evidence is particularly clear after 1940, which is another benchmark in the evolution
of the aa index. We discuss briefly the mechanisms that could account for the observed features of the 22-year cycle evolution. 相似文献
12.
One goal of helioseismology is to determine the subsurface structure of sunspots. In order to do so, it is important to understand
first the near-surface effects of sunspots on solar waves, which are dominant. Here we construct simplified, cylindrically-symmetric
sunspot models that are designed to capture the magnetic and thermodynamics effects coming from about 500 km below the quiet-Sun
τ
5000=1 level to the lower chromosphere. We use a combination of existing semi-empirical models of sunspot thermodynamic structure
(density, temperature, pressure): the umbral model of Maltby et al. (1986, Astrophys. J. 306, 284) and the penumbral model of Ding and Fang (1989, Astron. Astrophys. 225, 204). The OPAL equation-of-state tables are used to derive the sound-speed profile. We smoothly merge the near-surface properties
to the quiet-Sun values about 1 Mm below the surface. The umbral and penumbral radii are free parameters. The magnetic field
is added to the thermodynamic structure, without requiring magnetostatic equilibrium. The vertical component of the magnetic
field is assumed to have a Gaussian horizontal profile, with a maximum surface field strength fixed by surface observations.
The full magnetic-field vector is solenoidal and determined by the on-axis vertical field, which, at the surface, is chosen
such that the field inclination is 45° at the umbral – penumbral boundary. We construct a particular sunspot model based on
SOHO/MDI observations of the sunspot in active region NOAA 9787. The helioseismic signature of the model sunspot is studied
using numerical simulations of the propagation of f, p
1, and p
2 wave packets. These simulations are compared against cross-covariances of the observed wave field. We find that the sunspot
model gives a helioseismic signature that is similar to the observations. 相似文献
13.
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
14.
The comparison of the brightness and area of coronal holes (CH) to the solar wind speed, which was started by Obridko et al. (Solar Phys.
260, 191, 2009a) has been continued. While the previous work was dealing with a relatively short time interval 2000 – 2006, here we have
analyzed the data on coronal holes observed in the Sun throughout activity Cycle 23. A catalog of equatorial coronal holes
has been compiled, and their brightness and area variations during the cycle have been analyzed. It is shown that CH is not
merely an undisturbed zone between the active regions. The corona heating mechanism in CH seems to be essentially the same
as in the regions of higher activity. The reduced brightness is the result of a specific structure with the magnetic field
being quasi-radial at as low an altitude as 1.1R
⊙ or a bit higher. The plasma outflow decreases the measure of emission from CH. With an adequate choice of the photometric
boundaries, the CH area and brightness indices display a fairly high correlation (0.6 – 0.8) with the solar wind velocity
throughout the cycle, except for two years, which deviate dramatically – 2001 and 2007, i.e., the maximum and the minimum of the cycle. The mean brightness of the darkest part of CH, where the field lines are nearly
radial at low altitudes, is of the order of 18 – 20% of the solar brightness, while the brightness of the other parts of the
CH is 30 – 40%. The solar wind streams originate at the base of the coronal hole, which acts as an ejecting nozzle. The solar
wind parameters in CH are determined at the level where the field lines are radial. 相似文献
15.
R. P. Kane 《Solar physics》2008,248(1):177-190
From the LASCO CME (Coronal Mass Ejection) catalog, the occurrence frequencies of all CMEs (all strong and weak CMEs, irrespective
of their widths) were calculated for 3-month intervals and their 12-month running means determined for cycle 23 (1996 – 2007)
and were compared with those of other solar parameters. The annual values of all-CME frequency were very well correlated (+ 0.97)
with sunspot numbers, but several other parameters also had similarly high correlations. Comparisons of 12-month running means
indicated that the sunspot numbers were very well correlated with solar electromagnetic radiations (Lyman-α, 2800-MHz flux,
coronal green line index, solar flare indices, and X-ray background); but for corpuscular radiations [proton fluxes, solar
energetic particles (SEP), CMEs, interplanetary CMEs (ICMEs), and stream interaction regions (SIR)] and solar open magnetic
fields, the correlations were lower. A notable feature was the appearance of two peaks during 2000 – 2002, and those double
peaks in different parameters matched approximately except for proton fluxes and SEP and SIR frequencies. When hemispheric
intensities were considered, north – south asymmetries appeared, more in some parameters than in others. When intensities
in smaller latitude belts (10°) were compared, sunspot group numbers (SGN) were found to be confined mostly to latitudes within
± 30° of the solar equator, showing two peaks in all latitude belts, and during the course of the 11-year cycle, the double peaks shifted from middle to equatorial
solar latitudes, just as seen in the Maunder butterfly diagrams. In contrast, CME frequency was comparable at all latitude
belts (including high, near-polar latitudes), having more than two peaks in almost all latitude belts, and the peaks were
almost simultaneous in all latitude belts. Thus, the matching of SGN peaks with those of CME peaks was poor. Incidentally,
the CME frequency data for all events (all widths) after 2003 are not comparable to earlier data, owing to inclusion of very
weak (narrow) CMEs in later years. The frequencies are comparable with earlier data only for widths exceeding about 70°. 相似文献
16.
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
17.
P. Rudawy K. J. H. Phillips A. Buczylko D. R. Williams F. P. Keenan 《Solar physics》2010,267(2):305-327
Some 8000 images obtained with the Solar Eclipse Coronal Imaging System (SECIS) fast-frame CCD camera instrument located at Lusaka, Zambia, during the total eclipse of 21 June 2001 have been analysed
to search for short-period oscillations in intensity that could be a signature of solar coronal heating mechanisms by MHD
wave dissipation. Images were taken in white-light and Fe xiv green-line (5303 ?) channels over 205 seconds (frame rate 39 s−1), approximately the length of eclipse totality at this location, with a pixel size of four arcseconds square. The data are
of considerably better quality than those that we obtained during the 11 August 1999 total eclipse (Rudawy et al.: Astron. Astrophys. 416, 1179, 2004), in that the images are much better exposed and enhancements in the drive system of the heliostat used gave a much improved
image stability. Classical Fourier and wavelet techniques have been used to analyse the emission at 29 518 locations, of which
10 714 had emission at reasonably high levels, searching for periodic fluctuations with periods in the range 0.1 – 17 seconds
(frequencies 0.06 – 10 Hz). While a number of possible periodicities were apparent in the wavelet analysis, none of the spatially
and time-limited periodicities in the local brightness curves was found to be physically important. This implies that the
pervasive Alfvén wave-like phenomena (Tomczyk et al.: Science
317, 1192, 2007) using polarimetric observations with the Coronal Multi-Channel Polarimeter (CoMP) instrument do not give rise to significant oscillatory intensity fluctuations. 相似文献
18.
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
19.
Results are presented from a study of various sunspot contrast parameters in broadband red (672.3 nm) Cartesian full-disk
digital images taken at the San Fernando Observatory (SFO) over eight years, 1997 – 2004, of the twenty-third sunspot cycle.
A subset of over 2700 red sunspots was analyzed and values of average and maximum sunspot contrast as well as maximum umbral
contrast were compared to various sunspot parameters. Average and maximum sunspot contrasts were found to be significantly
correlated with sunspot area (r
s=− 0.623 and r
s=− 0.714, respectively). Maximum umbral contrast was found to be significantly correlated with umbral area (r
s=− 0.535). These results are in agreement with the works of numerous other authors. No significant dependence was detected
between average contrast, maximum contrast, or maximum umbral contrast during the rising phase of the solar cycle (r
s=0.024, r
s=0.033, and r
s=0.064, respectively). During the decay phase, no significant correlation was found between average contrast or maximum contrast
and time (r
s=− 0.057 and r
s=0.009, respectively), with a weak dependence seen between maximum umbral contrast and cycle (r
s=0.102). 相似文献
20.
Using nine years of solar wind plasma and magnetic field data from the Wind mission, we investigated the characteristics of both magnetic clouds (MCs) and magnetic cloud-like structures (MCLs) during
1995 – 2003. A MCL structure is an event that is identified by an automatic scheme (Lepping, Wu, and Berdichevsky, Ann. Geophys.
23, 2687, 2005) with the same criteria as for a MC, but it is not usually identifiable as a flux rope by using the MC (Burlaga et al., J. Geophys. Res.
86, 6673, 1981) fitting model developed by Lepping, Jones, and Burlaga (Geophys. Res. Lett.
95(11), 957, 1990). The average occurrence rate is 9.5 for MCs and 13.6 for MCLs per year for the overall period of interest, and there were
82 MCs and 122 MCLs identified during this period. The characteristics of MCs and MCL structures are as follows: (1) The average
duration, Δt, of MCs is 21.1 h, which is 40% longer than that for MCLs (Δt=15 h); (2) the average
(minimum B
z
found in MC/MCL measured in geocentric solar ecliptic coordinates) is −10.2 nT for MCs and −6 nT for MCLs; (3) the average
Dstmin (minimum Dst caused by MCs/MCLs) is −82 nT for MCs and −37 nT for MCLs; (4) the average solar wind velocity is 453 km s−1 for MCs and 413 km s−1 for MCLs; (5) the average thermal speed is 24.6 km s−1 for MCs and 27.7 km s−1 for MCLs; (6) the average magnetic field intensity is 12.7 nT for MCs and 9.8 nT for MCLs; (7) the average solar wind density
is 9.4 cm−3 for MCs and 6.3 cm−3 for MCLs; and (8) a MC is one of the most important interplanetary structures capable of causing severe geomagnetic storms.
The longer duration, more intense magnetic field and higher solar wind speed of MCs, compared to those properties of the MCLs,
are very likely the major reasons for MCs generally causing more severe geomagnetic storms than MCLs. But the fact that a
MC is an important interplanetary structure with respect to geomagnetic storms is not new (e.g., Zhang and Burlaga, J. Geophys. Res.
93, 2511, 1988; Bothmer, ESA SP-535, 419, 2003). 相似文献