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1.
Kinetic theory is used to calculate the power dissipated by obliquely propagating Alfvén waves to heat the solar wind protons,
using the Generalized (r, q) distribution function. The evolution of power dissipation of protons with increasing heliocentric distance is subsequently
determined. Comparison between theoretical and observational results with data shows good agreement, especially for the slow
solar wind streams. Previous results where a Maxwellian distribution function was used to calculate the power dissipated did
not match well with observations. 相似文献
2.
The aim of the present study is to investigate the short-term periodicity in the solar radius measurements and to compare
with the short periods in sunspot numbers, sunspot areas and flare index data. The spectral analysis of data sets covering
a time interval from 26 February 2000 to 26 October 2007 during Solar Cycle 23 were made by using the Date Compensated Discrete
Fourier Transform (DCDFT). The power spectrum of solar radius data corrected for the seeing effect gives an evident peak at
25.7 days with the amplitude of 0.034 arcsec, which is slightly different from the peaks of 26.2 and 26.7 days produced by
sunspot numbers and sunspot areas data, respectively. Besides, the main peak of 25.7 days detected in the power spectrum of
solar radius data is in agreement with the period of 25.5 days, suggested to be the fundamental period of the Sun by Bai and
Sturrock (in Nature
350, 141, 1991). 相似文献
3.
The aim of the present work is the detection of solar g-modes, by means of a new observational strategy based on the exploitation of their spatial and temporal properties. The basic data, obtained at the Observatorio del Teide in 1993, consists of daily solar velocity measurements taken continuously and sequentially at six different and symmetric positions on the solar disk. By correlating the time series resulting from the reduction process, from different solar disk positions and considering the geometrical properties of different modes (l,m) on the Sun's surface, some of these can be selectively eliminated or enhanced. Moreover, the main spectral features present in the resulting power spectra must have precise phase relations if they correspond to global solar g-modes. The severe constraints established by the above properties have been applied to the best observed series (summer 1993). As a result, a discrete series of peaks have been selected that fulfill all the imposed conditions and which can therefore be interpreted as being of solar origin. 相似文献
4.
Solar wind isotropic proton temperatures as measured out to 12.2 AU heliocentric distance by the Ames plasma analyzer aboard Pioneer-10 are presented as consecutive averages over three Carrington solar rotations and discussed. The weighted least-squares fit of average temperature to heliocentric radial distance, R, yields the power law R
-0.52. These average proton temperatures are not correlated as well with Pioneer-10's heliocentric radial distance (-0.85) as are the corresponding average Zürich sunspot numbers R
z (-0.95). Consequently, it is difficult to isolate the spatial gradient in the Pioneer-10 solar wind proton temperatures using that data alone. 相似文献
5.
Periodicities in the occurrence rate of solar proton events 总被引：1，自引：0，他引：1
Power spectral analyses of the time series of solar proton events during the past three solar cycles reveal a periodicity around 154 days. This feature is prominent in all of the cycles combined, cycles 19 and 21 individually but is only weak in cycle 20. These results are consistent with the presence of similar periodicities between 152 and 155 days in the occurrence rate of major solar flares, the sunspot blocking function (P
s
), the 10.7 cm radio flux (F
10.7) and the sunspot number (R
z
). This suggests that the circa 154-days periodicity may be a fundamental characteristic of the Sun. Periods around 50–52 days are also found in the combined data set and in the three individual cycles in general agreement with the detection of this periodicity in major flares in cycle 19 and inP
s
,F
10.7, andR
z
in cycle 21. The cause of the 155 day period remains unknown. The spectra contain lines (or show power at frequencies) consistent with a model in which the periodicity is caused by differential rotation of active zones and a model in which it is related to beat frequencies between solar oscillations, as proposed by Wolff. 相似文献
6.
A brief summary is given of a program which is currently being carried out with the McMath telescope of the Kitt Peak National Observatory in order to study high-degree (l ≳ 150) solar p-mode oscillations. This program uses a 244 × 248 pixel CID camera and the main spectrograph of the McMath telescope to obtain velocity-time maps of the oscillations which can be converted into two-dimensional (k h - ω) power spectra of the oscillations. Several different regions of the solar spectrum have been used in order to study the oscillations at different elevations in the solar atmosphere. The program concentrates on eastward- and westward-propagating sectoral harmonic waves so that measurements can be made of the absolute rotational velocities of the solar photospheric and shallow sub-photospheric layers. Some preliminary results from this program are now available. First, we have been unable to confirm the existence of a radial gradient in the equatorial rotational velocity as was previously suggested. Second, we have indeed been able to confirm the presence of p-mode waves in the solar chromosphere as was first suggested by Rhodes et al. (1977). Third, we have been able to demonstrate differences in photospheric and chromospheric power spectra.
相似文献7.
More than 20 real periodicities ranging from 20 days to 2 years modulate the solar irradiance data accumulated since November 1978 by Nimbus 7. Many are quite strong during the first three years (solar maximum) and weak after that. There is a high correspondence between periods in irradiance and 28 periods predicted from the rotation and beating of global solar oscillations (r-modes and g-modes). Angular states = 1, 2, and 3 are detected as well as some unresolved r-mode power at higher . The prominence of beat periods implies a nonlinear system whose effective nonlinear power was measured to be about 2. This analysis constitutes a detection of r-modes in the Sun and determines from them a mean sidereal rotation rate for the convective envelope of 459 ± 4 nHz which converts to a period of 25.2 days (27.ld, synodic). 相似文献
8.
R. Caimmi 《Astronomische Nachrichten》2001,322(4):241-263
The oxygen abundance distribution in solar neighbourhood halo subdwarfs is deduced, using two alternative, known empirical relationships, involving the presence or the absence of [O/Fe] plateau for low [Fe/H] values, from a sample of 372 kinematically selected halo stars, for which the iron abundance distribution has been determined by Ryan & Norris (1991). The data are interpreted by a simple, either homogeneous or inhomogeneous model of chemical evolution, using an updated value of the solar oxygen abundance. The effect of changing the solar oxygen abundance, the power‐law exponent in the initial mass function, and the rate of oxygen nucleosyntesis, keeping the remaining input parameters unchanged, is investigated, and a theorem is stated. In all cases, part of the gas must necessarily be inhibited from forming stars, and no disk contamination has to be advocated for fitting the empirical oxygen abundance distribution in halo subdwarfs of the solar neighbourhood (EGD). Then a theorem is stated, which allows a one‐to‐one correspondence between simple, homogeneous models with and without inhibited gas, related to same independent parameters of chemical evolution, except lower stellar mass limit, real yield, and inhibition parameter. The mutual correlations between the latter parameters are also specified. In addition the starting point, and the point related to the first step, of the theoretical distribution of oxygen abundance (TGD) predicted by simple, inhomogeneous models, is calculated analytically. The mean oxygen abundance of the total and only inhibited gas, respectively, are also determined. Following the idea of a universal, initial mass function (IMF), a power‐law with both an exponent p = 2.9, which is acceptably close to Scalo IMF for m ≳ m⊙, and an exponent p = 2.35, i.e. Salpeter IMF, have been considered. In general, both the age‐metallicity relationship and the empirical distribution of oxygen abundance in G dwarfs of the disk solar neighbourhood, are fitted by power‐law IMF exponents in the range 2.35 ≤ p ≤ 2.9. Acceptable models predict about 15% of the total mass in form of long‐lived stars and remnants, at the end of halo evolution, with a mean gas oxygen abundance which is substantially lower than the mean bulge and initial disk oxygen abundance. To avoid this discrepancy, either the existence of a still undetected, baryonic dark halo with about 15% of the total mass, or an equal amount of gas loss during bulge and disk formation, is necessary. The latter alternative implies a lower stellar mass limit close to 0.2 m⊙, which is related to a power‐law IMF exponent close to 2.77. Acceptable models also imply a rapid halo formation, mainly during the first step, Δt = 0.5 Gyr, followed by a period (three steps) where small changes occur. Accordingly, statistical fluctuations are found to produce only minor effects on the evolution. 相似文献
9.
We experiment with a method of measuring the frequency of solar p modes, intended to extend the passband for the variations of the frequency spectrum as high as possible. So far this passband is limited to a fraction of μ Hz for the classical analysis based on numerical fits of a theoretical line profile to a power spectrum averaged over periods lasting at least several weeks. This limit for the present analysis can be shifted to the mHz range, corresponding to some of the “5 min” oscillations, but in this range we use a lower resolution which allows us to separate odd and even p modes. We show an example of the results for long term variations and apply this analysis to search for a modulation of the p‐mode frequency spectrum by asymptotic series of solar g modes. A faint signal is found in the analysis of 10 years of GOLF data. This very preliminary result possibly indicates the detection of a small number of g modes of degree l = 1. A tentative determination of an observational value of the parameter P0 follows. P0 is the scaling factor of the asymptotic series of g modes and is a key data for solar core physics. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
10.
Power spectral analysis of cosmic-ray intensity recorded by eight stations was carried out over a wide range of frequencies from 2.3 × 10–8 Hz to 5.8 × 10–6 Hz (2–500 days) during the period 1964–1995. Spectrum results of large-scale fluctuations have revealed the existence of a broad peak near 250–285 days and a narrower peak at 45–50 days during the studied epochs as a stable feature in all neutron monitors covering a wide rigidity range. The cosmic-ray power spectrum displayed significant peaks of varying amplitude with the solar rotation period (changed inversely with the particle rigidities) and its harmonics. The amplitudes of 27-day and 13.5-day fluctuations are greater during the positive-polarity epochs of the interplanetary magnetic field (qA>0) than during the qA<0 epochs. The comparison of cosmic-ray power spectra during the four successive solar activity minima have indicated that at the low-rigidity particles the spectrum differences between the qA>0 and qA<0 epochs are significantly large. Furthermore, the spectrum for even solar maximum years are higher and much harder than the odd years. There are significant differences in the individual spectra of solar maxima for different cycles. 相似文献
11.
S.R. Prabhakaran Nayar V. Sanalkumaran Nair V.N. Radhika K. Revathy 《Solar physics》2001,201(2):405-417
The solar wind plasma exhibits many features of the solar surface passed on to the interplanetary medium as temporal variations
due to the solar rotation. The yearly average values of solar wind velocity, and geomagnetic index A
p during 1965–1999 were found to exhibit long period evolution. They were found to peak around the declining phase of each
solar cycle. While the solar wind velocity peaks around the second half of the declining phase, the IMF field strength increases
around the first half of the declining phase of each solar cycle. The power spectrum of these parameters shows peaks around
37-day, 30-day, 27-day, 13.5-day, 9-day, and 7-day periods. The temporal evolution of the power spectrum of the solar wind
plasma parameters and the geomagnetic activity index A
p are also studied in detail and presented with the help of contour graphs. These studies indicate that the strength of the
quasi-periodicities in the interplanetary medium evolves with time. 相似文献
12.
Results are presented from a study of solar radius measurements taken with the solar astrolabe at the TUBITAK National Observatory
(TUG) over seven years, 2001–2007. The data series with standard deviation of 0.35 arcsec shows the long-term variational
trend with 0.04 arcsec/year. On the other hand, the data series of solar radius are compared with the data of sunspot activity
and H-α flare index for the same period. Over the seven year trend, we have found significant linear anti-correlations between the
solar radius and other indicators such as sunspot numbers, sunspot areas, and H-α flare index. While the solar radius displays the strongest anti-correlation (−0.7676) with sunspot numbers, it shows a significant
anti-correlation of −0.6365 with sunspot areas. But, the anti-correlation between the solar radius and H-α flare index is found to be −0.4975, slightly lower than others. In addition, we computed Hurst exponent of the data sets
ranging between 0.7214 and 0.7996, exhibiting the persistent behavior for the long term trend. In the light of the strong
correlations with high significance, we may suggest that there are a causal relationship between the solar radius and solar
time series such as sunspot activity and H-α flare index. 相似文献
13.
Thirteen synoptic maps of expansion rate of the coronal magnetic field (CMF; RBR) calculated by the so-called ‘potential model’ are constructed for 13 Carrington rotations from the maximum phase of solar activity cycle 22 through the maximum phase of cycle 23. Similar 13 synoptic maps of solar wind speed (SWS) estimated by interplanetary scintillation observations are constructed for the same 13 Carrington rotations as the ones for the RBR. The correlation diagrams between the RBR and the SWS are plotted with the data of these 13 synoptic maps. It is found that the correlation is negative and high in this time period. It is further found that the linear correlation is improved if the data are classified into two groups by the magnitude of radial component of photospheric magnetic field, |Bphor|; group 1, 0.0 G ≦ |Brpho| < 17.8 G and group 2, 17.8 G ≦ |Brpho|. There exists a strong negative correlation between the RBR and the SWS for the group 1 in contrast with a weak negative correlation for the group 2. Group 1 has a double peak in the density distribution of data points in the correlation diagram; a sharp peak for high-speed solar wind and a low peak for low-speed solar wind. These two peaks are located just on the axis of maximum variance of data points in the correlation diagram. This result suggests that the solar wind consists of two major components and both the high-speed and the low-speed winds emanating from weak photospheric magnetic regions are accelerated by the same mechanism in the course of solar activity cycle. It is also pointed out that the SWS can be estimated by the RBR of group 1 with an empirical formula obtained in this paper during the entire solar activity cycle. 相似文献
14.
Using data from the Global Oscillation Network Group (GONG) covering the period from 1995 to 1998, we study the change with solar activity in solar f-mode frequencies. The results are compared with similar changes detected from the Michelson Doppler Imager (MDI) data. We find variations in f-mode frequencies which are correlated with solar activity indices. If these changes are due to variation in solar radius then the implications are that the solar radius decreases by about 5 km from minimum to maximum activity. 相似文献
15.
A. Claverie G. R. Isaak C. P. McLeod H. B. Van Der Raay T. Roca Cortès 《Solar physics》1981,74(1):51-57
The discrete structure in the 5 min velocity oscillations of the solar surface has been confirmed by a re-analysis of data obtained between 1976 and 1979, and in addition a preliminary analysis of 1980 data show excellent consistency of the determined frequencies over the five year period. It is further shown that atmospheric transparency, as measured by the power in the solar intensity fluctuations, shows no correlation with the measured amplitude of the velocity fluctuations, over 2 orders of magnitude.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands. 相似文献
16.
Periodic Appearance of Coronal Holes and the Related Variation of Solar Wind Parameters 总被引：1，自引：0，他引：1
We compared the variability of coronal hole (CH) areas (determined from daily GOES/SXI images) with solar wind (daily ACE
data) and geomagnetic parameters for the time span 25 January 2005 until 11 September 2005 (late declining phase of solar
cycle 23). Applying wavelet spectral analysis, a clear 9-day period is found in the CH time series. The GOES/SXI image sequence
suggests that this periodic variation is caused by a mutual triangular distribution of CHs ∼120° apart in longitude. From
solar wind parameters a 9-day periodicity was obtained as well, simultaneously with the 9-day period in the CH area time series.
These findings provide strong evidence that the 9-day period in solar wind parameters, showing up as higher harmonic of the
solar rotation frequency, is caused by the “periodic” longitudinal distribution of CHs on the Sun recurring for several solar
rotations. The shape of the wavelet spectrum from the Dst index matches only weakly with that from the CH areas and is more similar to the wavelet spectrum of the solar wind magnetic
field magnitude. The distinct 9-day period does not show up in sunspot group areas which gives further evidence that the solar
wind modulation is strongly related to CH areas but not to active region complexes. The wavelet power spectra for the whole
ACE data range (∼1998 – 2006) suggest that the 9-day period is not a singular phenomenon occurring only during a specific
time range close to solar minimum but is occasionally also present during the maximum and decay phase of solar cycle 23. The
main periods correspond to the solar rotation (27d) as well as to the second (13.5d) and third (9d) harmonic.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
17.
Several candidates for low-order p modes (n 5) and possibly g modes were found by applying mode-detection techniques such as multivariate spectral regression analysis and time-frequency analysis to the VIRGO full-disc solar irradiance data. Three out of the candidates for low-order p modes could be confirmed by significant peaks in the un-treated power spectra in good agreement with theoretical predictions. The frequency of a fourth candidate for a low-order p mode lies some 2.8 Hz below the predicted frequency. The candidates found for g modes are less reliable, since none of them could be confirmed neither by significant peaks in the un-treated power spectra nor by the detection of multiplets. 相似文献
18.
Data series for the same time interval of characteristic solar parameters (sunspot number R; flux at 2.8 GHz), ionospheric parameters (critical frequency of the E-region) and atmospheric parameters (stratospheric and tropospheric temperatures T) have been analysed by the maximum-entropy method, in order to study the occurrence of periodicities in those parameters in the range from 12 to 150 days. Digital filtering of the most pronounced of the detected periods (mainly in the range between 19 to 33 days) shows a similar but not identical feature in the time interval 1974–1978. It is demonstrated that sunspot number and solar radio flux at 2.8 GHz behave in a similar way on the average, and at periods greater than 20 days. Although a number of similar periods occurred in solar, ionospheric and atmospheric parameters, cross-correlation estimations only show a relationship between periods in solar and ionospheric data, but none between solar data and stratospheric and tropospheric temperatures; exception: T (35 km) correlates with R at 12.3 days. The most obvious correlation was found between the critical frequency of the E layer and the solar flux at 2.8 GHz at a frequency of approximately 1/23 days–1.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands. 相似文献
19.
R. Simoniello S.J. Jimnez‐Reyes R.A. García P.L. Pall 《Astronomische Nachrichten》2008,329(5):494-497
In this work we investigate p‐mode power variation with solar atmosphere. To this aim, we use THÉMIS observations of the Na D1 (λ 5896 Å) and K (λ 7699 Å) spectral lines. While the formation heights of the K spectral line are essentially located in the photospheric layer, the formation heights of the Na D1 line span a much wider region: from photosphere up to chromosphere. Hence, we had the opportunity to infer p‐mode power variation up to the chromospheric layer. By analyzing power spectra obtained by temporal series at different points of the Na D1 and K spectral lines, we confirm and quantify the increase in p‐mode power towards higher atmospheric layers. Furthermore, the large span in formation heights of the Na D1 line induces a larger enhancement of p‐mode power with solar atmosphere compared to the K spectral line. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
20.
Wavelet Analysis of solar,solar wind and geomagnetic parameters 总被引：3，自引：0，他引：3
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. 相似文献