首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Periodic variations in Davis' experimental data concerning the solar neutrino capture rate are derived on the basis of a Fourier spectrum analysis. Variations in the 37Ar production rate are obtained for a series of randomly spaced observations in the period 1970–1985 (runs 18–89). The harmonic analysis of runs 18–89 has determined solar neutrino capture rate variations with periods of 8.33, 5.00, 2.13, 1.61, 0.83, 0.61, 0.54, and 0.51 yr, thereby confirming earlier calculations performed for the set of runs 18–69 (1983), 18–74 (1985a), and 18–80 (1985b). The results also confirm those of Sakurai (1979) who showed that there is strong evidence that the observed solar neutrino flux has a tendency to vary with quasi-biennial periodicity. We show that the results of the Fourier spectrum analysis do not depend upon certain high or low values in Davis' experimental data.  相似文献   

2.
Makarov  V.I.  Filippov  B.P. 《Solar physics》2003,214(1):55-63
We have studied the variations of the height of polar crown prominences according to daily observations of the Sun at the Kodaikanal Observatory (India) during 1905–1975. Polar ring filaments at latitudes 60°–80° are related to the polar magnetic field reversal. A double decrease of the height of polar ring filaments was found in the course of their migration from 40°to the poles. We estimated the limiting height of the equilibrium of polar ring filaments from the stability condition of a strong electric current. We found that the transition from large-scale to small-scale ring filaments reduces the critical height of the stability for the prominences. A model of an inverse-polarity filament was used.  相似文献   

3.
In this article we investigate the short-term characteristics of the sodium layer and their implications for laser guide star systems. We report measurements of sodium density andcentroid-height variations on timescales of 100 ms upwards. Significant centroid-height variations on short timescales may necessitate frequent refocussing of the beam and wavefront sensor system.We present results from observations of the mesospheric sodium layer taken at the Max Planck observatory in Calar Alto, Spain in September 1997 and August 1998. We describe our experiment which uses the resonant optical backscatter of 589.2 nm laser light from the upper atmosphere as a measure of sodium abundance.Short-term variations are dominated by the formation of dense sporadic layers in the normal sodium layer. Measurements were made on 3 nights in 1997 and on 2 nights in 1998. Somewhat unexpectedly for a mid-latitude site, sporadic sodium layers were seen on 4 of these 5 nights. One of the sporadic layers was observed for its duration. The 2 km wide layer reached a maximum intensity of approximately two and a half times that of the background layer and could be distinguished from the background for over five hours. Centroid height variations of up to 400 m were observed on timescales of 1–2 min. In 1998 we were sensitive to variations of 5% or more in total sodium abundance on timescales of 100 ms upwards. We found no evidencefor variations of this level on these short timescales.  相似文献   

4.
The Atmospheric Model Intercomparison Project (AMIP) conducted simulations by 30 different atmospheric general circulation models forced by observed sea surface temperatures for the 10-year period, 1979–1988. These models include a variety of different soil moisture parameterizations which influence their simulations of the entire land surface hydrology, including evaporation, soil moisture, and runoff, and their simulations of the energy balance at the surface. Here we compare these parameterizations, and evaluate their simulations of soil moisture by comparing them with actual observations of soil moisture, literally ground truth. We compared model-generated ‘data sets' and simulations of soil moisture with observations from 150 stations in the former Soviet Union for 1979–1985 and Illinois for 1981–1988. The spatial patterns, mean annual cycles, and interannual variations were compared to plant-available soil moisture in the upper 1 m of soil. The model-generated ‘data sets' are quite different from the observations, and from each other in many regions, even though they use the same bucket model calculation method. The AMIP model simulations are also quite different from each other, especially in the tropics. Models with 15-cm field capacities do not capture the observed large high latitude values of soil moisture. In addition, none of the models properly simulate winter soil moisture variations in high latitudes, keeping soil moisture constant, while observations show that soil moisture varies in the winter as much as in other seasons. The observed interannual variations of soil moisture were not captured by any of the AMIP models. Several models have large soil moisture trends during the first year or two of the AMIP simulations, with potentially large impacts on global hydrological cycle trends and on other climate elements. This is because the simulations were begun without spinning up the soil moisture to the model climatology. The length of time it took for each to reach equilibrium depended on the particular parameterization. Although observed temporal autocorrelation time scales are a few months, some models had much longer time scales than that. In particular, the three parameterizations based on the Simple Biosphere model (SiB) had trends in some regions for virtually the entire AMIP simulation period.  相似文献   

5.
Microwave maps of solar active region NOAA 8365 are used to derive the coronal magnetograms of this region. The technique is based on the fact that the circular polarization of a radio source is modified when microwaves pass through the coronal magnetic field transverse to the line of sight. The observations were taken with the Siberian Solar Radio Telescope (SSRT) on October 21 – 23 and with the Nobeyama Radio Heliograph (NoRH) on October 22 – 24, 1998. The known theory of wave mode coupling in quasi-transverse (QT) region is employed to evaluate the coronal magnetograms in the range of 10 – 30 G at the wavelength 5.2 cm and 50 – 110 G at 1.76 cm, taking the product of electron density and the scale of coronal field divergence to be constant of 1018 cm–2. The height of the QT-region is estimated from the force-free field extrapolations as 6.2 × 109 cm for the 20 G and 2.3 × 109 cm for 85 G levels. We find that on large spatial scale, the coronal magnetograms derived from the radio observations show similarity with the magnetic fields extrapolated from the photosphere.  相似文献   

6.
We present new near-infrared observations of Sakurai's Object obtainedduring 1998–99 when this final helium shell flash object was in the dustcondensation phase. The infrared colours have reddened compared to earlierepochs, indicating increased dust condensation. The infrared spectrareveal all the features of a carbon star superposed on a dust continuum.  相似文献   

7.
J. P. Rozelot 《Solar physics》1998,177(1-2):321-327
The objective of this paper is to present some results deduced from the analysis of (space-based) solar irradiance observations used jointly with (ground-based) solar diameter variations. The idea which is explored consists in searching a possible influence of the variability of the Sun's whole shape on the luminosity. It is shown that such an effect, albeit small, may occur. Thus, the global geometry of the Sun – which is not a perfect static ellipsoid – would have to be taken into account when attempting to model the irradiance. Our very preliminary results may help to construct empirical models that can be used, in turn to force any model of the thermal structure of the ocean and atmosphere to deduce climate variations, if any.  相似文献   

8.
Based on long-term spectrophotometric observations of Jupiter in the wavelength range 320–1100 nm, we investigate the variations of aerosol extinction (at 320–600 nm) and methane–ammonia absorption (at 600–1100 nm) over Jupiter's disk. We give estimates of the optical parameters for the upper cloud layer of the planet, the overlying stratospheric haze, and a Rayleigh atmosphere.  相似文献   

9.
The O–C diagrams of EE Aquarii have been presented for the first time, the period variations present in the system have been analysed, and tentative results have been presented. In all, four period decreases and three period increases are noted in the time interval 1940 to 1985. The strongest period change is noted in the time interval 1957 to 1959. Sufficiently strong period changes have also been noted in the time intervals, 1948 to 1950 and 1970 to 1976. Besides four period decreases and three period increases, eleven period fluctuations are also seen in the O–C diagram (II) of EE Aqr. The total period change in different portions of the O–C diagram (II) ranges from 1.7×10–7 d to 8.2×10–6 d. The period increases are stronger than the period decreases. An overall picture of the period variations suggests that weak period variations are present in the system EE Aqr.  相似文献   

10.
On the basis of the data from ground-based polarimetric, photometric, and other observations, as well as from space measurements (Mariner 10), we survey the investigations of the properties and peculiarities of Mercury's regolith in detail. We also present the results of our own observations performed during three apparitions of the planet in 2000–2002. An analysis of the published data points to essentially more intensive maturation processes in the Hermean surface regolith compared to that on the lunar surface. In addition, the orbital characteristics of Mercury allow us to suppose that the intensity of its regolith maturation and, therefore, the optical properties of its surface can noticeably depend on the planetocentric longitude. Polarimetric observations of Mercury's surface (the planetocentric longitude range was 265°–330°) carried out in 2000–2002 with a 70-cm reflector actually detected a polarization degree varying with an amplitude of about 1.5%. To ascertain the nature of these variations, additional observations of Mercury in a maximally wide range of planetocentric longitudes of the viewed surface are required.  相似文献   

11.
We present new interferometric observations of the molecular gas distribution and kinematics in the nuclei of different active galaxies at high angular resolution and high sensitivity carried out with the IRAM Plateau de Bure interferometer (PdBI). The observations cover galaxies in a redshift range of 0.03–1.4. We have so far observed five different active galaxies: NGC3718, NGC1068, HE1029–1831, 3C48 and Q0957+561. The first two objects belong to the NUGA (NUclei of GAlaxies) project – an international collaboration mainly between Spain, France and Germany – containing about 30 Seyfert and LINER galaxies. Both are at the same distance of 14Mpc and show a warped gas and dust disk. The new mosaic map of NGC3718 corrected for short-spacing effects with IRAM 30 m observations well demonstrates the existence of the warped gas disk with several secondary maxima in the projected gas distribution caused by orbit crowding effects. Based on these new data we have improved recent simulations of the warped disk in NGC3718. HE1029–1831 and 3C48 are nearby QSOs. HE1029–1831 is taken out of the Cologne nearby QSO sample. The maps of the integrated CO(1–0) and CO(2–1) emission clearly show that the molecular gas is mostly related to the central bulge with a non-negligible fraction distributed along the bar known from optical observations. Our new CO data of 3C48 unveil new information about the kinematics of its molecular gas complementing and improving further studies based on previous infrared observations and detailed multi-particle simulations. Finally, new measurements of the CO(1–0) line in Q0957+561 – a highly-red-shifted, gravitationally lensed quasar – will be presented as a link to earlier evolutionary stages of active galaxies and their hosts.  相似文献   

12.
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   

13.
Unexpected asymmetries and variations, which showed up in the first, preliminary reductions of new limb-darkening observations made in June 1986, near the present minimum of solar activity, stimulated a re-analysis of our limb-darkening observations made in April 1981 at Kitt Peak (Neckel and Labs, 1984). The results seem to indicate rather definitely that the intensity distribution across the disk varies at all observed wavelengths between 3300 and 6600 Å with amplitudes in the order of 1–2 % and time-scales from minutes to hours. Asymmetries in the intensity distribution with respect to the disk center are a frequent phenomenon. There can be no doubt, that also the absolute disk center intensity undergoes variations with comparable size and modulation, as they were in fact recently observed by Koutchmy and Lebecq (1986). Presumably, the solar oscillations contribute a significant part to the observed effects. However, due to the 5–7 min periodicity of our observations no definite conclusions can be drawn.Examples for widely differing limb darkening curves - at the same wavelength! - are given in Figure 7. Figure 8 illustrates the variations in time by exhibiting the differences between (north-) western and (south-) eastern radius for a larger number of selected, successive scans, regardless of wavelength. Figure 9 displays some differences between observed limb-to-limb distributions and special, symmetric reference curves.  相似文献   

14.
Twenty-five coudé spectrograms (22 with dispersion 12 Å mm–1 and three 7 Å mm–1) of 6 Cassiopeiae (A3 Ia) have been studied. The observations were made at the Haute Provence Observatory. The results of the analysis suggest a correlation between the variations of the equivalent widths, the microturbulence and the radial velocity. The radial velocity and turbulent velocity present a rapid variation with time, even in intervals as short as about an hour. The hydrogen lines are slightly asymmetric but the strongest Feii lines are clearly asymmetric. We found that the amount of asymmetry of the strongest Feii lines (I>6) correlates with the loggf value, with the estimated laboratory intensityI, and with the equivalent widthW .The observations have been made at the Astronomical Observatory of Haute Provence (CNRS). This work has been supported by TUBITAK (Scientific and Technical Research Council of Turkey), and partially by CNR (Consiglio Nazionale delle Ricerche) of Italy.  相似文献   

15.
V. Letfus 《Solar physics》2002,205(1):189-200
We derived daily relative sunspot numbers and their monthly and annual means in the first half of the seventeenth century. The series of observations collected by Wolf were recorded in the years 1611–1613 and 1642–1644. We used a nonlinear two-step interpolation method derived earlier (Letfus, 1996, 1999) to enlarge the number of daily data. Before interpolation the relative monthly frequency of observations in 24 months of the first time interval 1611–1613 was 49.4% and in 22 months of the second interval 1642–1644 was 49.9%. After interpolation the relative frequency increased in the first time interval to 91.3%, in the second time interval to 82.6%. Most data series in the years 1611–1613 overlap one another and also overlap with a series, for which Wolf estimated a scaling factor converting relative sunspot numbers on the Zürich scale. We derived the scaling factors of all individual series of observations also from the ratios of observed numbers of sunspots to the numbers of sunspot groups (Letfus, 2000). The differences between almost all scaling factors derived in one and the other way are not substantial. All data series were homogenized by application of scaling factors and parallel data in the overlapping parts of data series were averaged. Resulting daily relative sunspot numbers and their monthly and annual means in the years l61l–1613 are given in Table I and those in the years 1642–1644 in Table II. The annual means of these data are compared with analogous data obtained otherwise.  相似文献   

16.
A zonal spottedness model proposed and developed by us to represent periodic brightness variations of dwarfs of the BY Dra type is applied to a sample of stars with long sequences of BVRI observations.Translated fromAstrofizika, Vol. 39, No. 1, pp. 67–89, January–March, 1995.  相似文献   

17.
UBVRI observations of the eclipsing symbiotic star CI Cyg made during 1991–1995 are analyzed, the results of which indicate that the system is in the same quiescent state as during 1985–1990. Variations in the "extra-eclipse" color index U-B with an amplitude of about 0m.3–0m.4 and a characteristic time of about 9–10 yr have been detected for the first time. A more thorough analysis of all available data in the UBVRI bands of the spectrum will be required to investigate the existence of possible long-period variations in the other color indices and brightness of the system.Translated fromAstrofizika, Vol. 39, No. 2, pp. 211–216, April–June, 1996.  相似文献   

18.
Results of rocket observations of SCO X-1 over the spectral range of 220 keV are presented. The observations have been performed partly in India and partly in Japan under the collaboration of the three groups. The present results are compared with results of similar observations carried out by the LRL (Lawrence Radiation Laboratory) group. Some of these X-ray observations were accompanied by simultaneous optical observations. Relationships between the hardness of the X-ray spectrum and the X-ray intensity and between the hardness and the optical luminosity are compiled. The relationships among the parameters (temperature, density and size) which characterize the postulated isothermal cloud model of SCO X-1 are given. They indicate that SCO X-1 is characterized by a temperature of about 107–108K, a density of about 1016–1017 cm–3 and a radius of about 108–109 cm respectively. We further show that the temperature is inversely correlated with the size of the source; an increase in temperature corresponds to a decrease in the radius and an increase in density.  相似文献   

19.
Experimental results on the intensity, energy spectrum and time variations in hard X-ray emission from Cyg X-1 based on a balloon observation made on 1971, April 6 from Hyderabad (India) are described. The average energy spectrum of Cyg X-1 in the 22–154 keV interval on 1971 April 6 is best represented by a power law dN/dE=(5.41±1.53)E –(1.92±0.10) photons cm–2s–1 keV–1 which is in very good agreement with the spectrum of Cyg X-1 derived from an earlier observation made by us on 1969 April 16 in the 25–151 keV band and given by dN/dE=(3.54±2.44)E –(1.89±0.22) photons cm–2s–1 keV–1. A thermal bremsstrahlung spectrum fails to give a good fit over the entire energy range for both the observations. Comparison with the observations of other investigators shows that almost all balloon experiments consistently give a spectrum of E –2, while below 20 keV the spectrum varies fromE –1.7 toE –5. There is some indication of a break in the Cyg X-1 spectrum around 20 keV. Spectral analysis of data in different time intervals for the 1971 April 6 flight demonstrates that while the source intensity varies over time scales of a few minutes, there is no appreciable variation in the spectral slope. Analysis of various hard X-ray observations for long term variations shows that over a period of about a week the intensity of Cyg X-1 varies upto a factor of four. The binary model proposed by Dolan is examined and the difficulties in explaining the observed features of Cyg X-1 by this model are pointed out.  相似文献   

20.
MARTIN  RENATO  MACCARI  LISA  NOCI  GIANCARLO 《Solar physics》1997,172(1-2):215-223
We investigate the expected emission from coronal transients in the following spectral lines observable with the Ultraviolet Coronagraph Spectrometer (UVCS) on board SOHO: Hi L 1216 Å, Ovi 1032–1037 Å, Nv 1239–1243 Å, Mgx 610–625 Å, Sixii 499–521 Å, and Fexii 1242 Å. We calculate line intensities and profiles for typical CME conditions, and we analyse their relation with the properties of the perturbed coronal region. We find that significant changes in UV line intensities are produced during a coronal transient. An overall decrease of the Hi L intensity is found, which is mainly due to the Doppler dimming produced by the increase in plasma outflow velocity. The emission from heavy ions is instead mainly affected by variations in plasma density and temperature. We expect to compare these results with the future UVCS observations of coronal transients.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号