共查询到20条相似文献，搜索用时 31 毫秒
1.
Y. C. Whang 《Solar physics》1977,53(2):507-517
A statistical study of microscale magnetic fluctuations in the interplanetary and magnetosheath region during quiet conditions is approached from the concept of probability distribution function. Magnetic field data from Explorer 34 were used to reconstruct the distribution functions and to calculate some of their moments. The distribution functions are found to be nearly tri-Maxwellian as the background field is relatively quiet. The direction of maximum fluctuations is found to be nearly perpendicular to that of the background magnetic field, but the fluctuations are rarely circularly polarized. Across the Earth's bow shock, the degree of fluctuation anisotropy increases, but no noticeable change in relative fluctuation intensity has been observed. 相似文献
2.
We examine the interpretation of plasma parameters derived by quantitative analysis of solar X-ray photographs obtained through broad band filters. We find some of the recent criticisms of the filter ratio method to be unfounded. Using active region and quiet Sun emission measures derived mostly from spectroscopic observations we find that effective emission measures and temperatures derived from S-054 data by filter ratio analysis are within better than 20% of the total emission measure and average temperature, respectively. The uncertainties associated with filtered flux determination are found to produce an error of about 10% in the derived effective temperature. We thus conclusively demonstrate that parameters derived from S-054 data by filter ratio analysis are representative of the observed active region and quiet Sun material. 相似文献
3.
Binod Adhikari Nirakar Sapkota Prashrit Baruwal Narayan P. Chapagain Carlos Roberto Braga 《Solar physics》2017,292(10):149
Geomagnetic disturbances are the results of interplanetary causes such as high-speed streamers (HSSs), interplanetary coronal mass ejections (ICMEs), corotating interaction regions (CIRs), and magnetic clouds. During different forms of geomagnetic disturbances, we observed changes in the count rate at neutron monitors that are kept at various locations. We studied the count rates measured by neutron monitors at four stations at various latitudes during different categories of geomagnetic events and compared them. We analysed five events: a geomagnetically quiet event, a non-storm high-intensity long-duration continuous AE activity (HILDCAA) event, a storm-preceded HILDCAA event, a geomagnetic substorm event, and a geomagnetic moderate storm event. We based our analysis on geomagnetic indices, solar wind parameters, and interplanetary magnetic field (IMF) parameters. We found that the strength of the modulation was least during the quiet event and highest during the storm-preceded HILDCAA. By analysing the cause of these geomagnetic disturbances, we related each decrease in the neutron monitor data with the corresponding solar cause. For the ICME-driven storm, we observed a decrease in neutron monitor data ranging from 6% to 12% in all stations. On the other hand, we observed a decrease ranging from 2% to 5% for the HSS-driven storm. For the non-storm HILDCAA, we observed a decrease in neutron monitor data of about 1% to 1.5%. For the quiet event, the neutron monitor data fluctuated such that there was no overall decrease in all stations. 相似文献
4.
P. Romano F. Berrilli S. Criscuoli D. Del Moro I. Ermolli F. Giorgi B. Viticchié F. Zuccarello 《Solar physics》2012,280(2):407-416
We present a comparative study of photometric and dynamic properties of photospheric bright points (BPs) observed at the disk centre in the active region (AR) NOAA 10912 and in the quiet Sun. We found that the average concentration of BPs is 54% larger in the AR than in the quiet Sun. We also measure a decrease of the BP concentration and an increase of their size moving away from the AR centre. However, these variations can be ascribed to the variation of the spatial resolution and image quality in the field of view of the AR dataset. We also found that BPs in the quiet Sun are associated with larger downflow motions than those measured within the AR. Finally, from our measurements of contrast and velocity along the line of sight, we deduced that BPs are less bright in high magnetic flux density regions than in quiet regions, due to a lower efficiency of convection in the former regions. 相似文献
5.
Sensitive observations of the quiet Sun observed by EIT on the SOHO satellite in high-temperature iron-line emission originating in the corona are presented. The thermal radiation of the quiet corona is found to fluctutate significantly, even on the shortest time scale of 2 min and in the faintest pixels. The power spectrum of the emission measure time variations is approximately a power law with an exponent of 1.79±0.08 for the brightest pixels and 1.69±0.08 for the average and the faintest pixels. The more prominent enhancements are identified with previously reported X-ray network flares (Krucker et al., 1997) above the magnetic network of the quiet chromosphere. In coronal EUV iron lines they are amenable to detailed analysis suggesting that the brightenings are caused by additional plasma injected from below and heated to slightly higher temperature than the preexisting corona. Statistical investigations are consistent with the hypothesis that the weaker emission measure enhancements originate from the same parent population. The power input derived from the impulsive brightenings is linearly proportional to the radiative loss in the observed part of the corona. The absolute amount of impulsive input is model-dependent. It cannot be excluded that it can satisfy the total requirement for heating. These observations give strong evidence that a significant fraction of the heating in quiet coronal regions is impulsive. 相似文献
6.
D. J. McEwen 《Planetary and Space Science》1977,25(12):1161-1166
Energy spectra of electrons between 30 eV and 18 keV were obtained with a spectrometer on a Black Brant rocket launched from Cape Parry, N.W.T. (Λ = 75.2°) on December 6, 1974 to study the dayside magnetospheric cleft. The rocket flew to an apogee of 236 km and travelled poleward to 80° invariant latitude. The cleft was observed to extend from 76.9 to 78.4° invariant latitude. Equatorward of this electrons of a few keV energy were observed with a total energy flux of up to 2 erg/cm2 sec ster. Variable fluxes of electrons with a spectrum fitted by a Maxwellian distribution of 150 eV characteristic energy were observed through most of the cleft. One inverted V structure was crossed. In that region, the electron energy increased to 650 eV and a total energy flux of 8 erg/cm2 sec ster was measured. The event was a temporal one and only a few km in width, as deduced from optical data. Fluxes of about 10−2 erg/cm2 sec ster were recorded poleward of the cleft. 相似文献
7.
V.A. Sergeev E.M. Sazhina N.A. Tsyganenko J.Å. Lundblad F. Søraas 《Planetary and Space Science》1983,31(10):1147-1155
Characteristics of the nightside isotropic precipitation of energetic protons during a period of 4 quiet days has been studied using data from the ESRO 1A satellite. The observed features of the equatorward precipitation boundary (its thickness, energy dependence, dynamics, dependence of its latitudinal position on the magnetic field at the geosynchronous orbit, etc.) were found to be in good agreement with calculations based on recent magnetospheric magnetic field models. We argue that the mechanism of non-adiabatic pitchangle scattering in the equatorial current sheet is a dominant source of isotropic precipitation of energetic protons observed in the nightside auroral zone. Observations of the isotropic precipitation boundary can be used for monitoring the changes in the magnetotail current intensity. 相似文献
8.
High-resolution white-light pictures are analyzed to study the differences between the granular size near sunspot penumbrae and in light-bridges presenting granular structure and that of the quiet photosphere. No difference is found between the mean granular diameter in light-bridges and the quiet photosphere. The dispersion found in the results corresponding to different zones around the sunspots indicates that the size of the granulation may vary from place to place near the sunspots, its mean value not differing significantly from that of the quiet photosphere. A possible systematic bias in the selection of the granules by Macris (1979) is found. 相似文献
9.
C. Jordan K.P. Macpherson G.R. Smith 《Monthly notices of the Royal Astronomical Society》2001,328(4):1098-1114
Observations made at the quiet Sun-centre with the Coronal Diagnostic Spectrometer (CDS) and Solar Ultraviolet Measurements of Emitted Radiation (SUMER) instruments on the Solar and Heliospheric Observatory ( SOHO ) have shown that the intensities of the resonance lines of He i and He ii are significantly larger than predicted by emission measure distributions found from other transition region lines. The intensities of the helium lines are observed to be lower in coronal holes than in the quiet Sun. Any theory proposed to account for the behaviour of the helium lines must explain the observations of both the quiet Sun and coronal holes. We use observations made with SOHO to find the physical conditions in a polar coronal hole. The electron pressure is found using the C iii 1175-Å and N iii 991.5-Å lines, as the C iii line at 977.0 Å becomes optically thick in some regions at high latitudes. The mean electron pressure is a factor of ≃2 lower than that at the quiet Sun-centre. The mean coronal electron temperature is . The helium lines are enhanced with respect to other transition region lines but by factors which are ≃ 30 per cent smaller than at the quiet Sun-centre. The mean ratios of the intensities of the He i 537.0- and 584.3-Å lines and of the He i and He ii 303.8-Å lines vary little with the type of region studied. These ratios are compared with those predicted by models of the transition region, taking into account the radiative transfer in the helium lines. No significant variation is found in the relative abundances of carbon and silicon. 相似文献
10.
The predictions of a time-dependent, three-dimensional model of the high-latitude ionosphere have been compared with the diurnal variations of plasma convection velocities and electron densities observed at Chatanika on geomagnetically quiet and disturbed days near equinox. The model predictions for the quiet day are in good agreement, both qualitatively and quantitatively, with the measurements. The model predictions for the disturbed day are in qualitative agreement with the measurements, but at certain local times there are significant quantitative differences. Also, the model cannot produce the detailed fine structure in the electron density that was observed on the disturbed day owing to the lack of fine structure in the model convection pattern and auroral precipitation fluxes. For the quiet day, the gross features of plasma convection are consistent with a symmetric two-cell pattern with a cross-polar cap potential of 52 kV. For the disturbed day, on the other hand, the observed plasma convection is consistent with an asymmetric two-cell pattern with enhanced plasma flow in the dusk sector and a cross-polar cap potential of 90 kV. For both the quiet and disturbed days, the lower latitude region of the high-latitude ionosphere was found to be sensitive to the competition between the vertical components of the electrodynamic and wind-induced ion drifts. For both days, horizontal plasma transport was found to be very important. One consequence of transport is that on the dayside the peak density at a given altitude occurs at a later local time as altitude increases. Another consequence of transport is that high electron densities are maintained in regions devoid of ionization sources, particularly on the disturbed day. 相似文献
11.
K. R. Nicolas G. E. Brueckner R. Tousey D. A. Tripp O. R. White R. G. Athay 《Solar physics》1977,55(2):305-319
Spectral line profiles of Si ii and Si iii are presented which were observed both at solar center and near the quiet solar limb with the Naval Research Laboratory EUV spectrograph of ATM/SKYLAB. Absolute intensities and line profiles are derived from the photographic data. A brief discussion is given of their center-to-limb variations and of the optical thickness of the chromosphere in these lines. Nonthermal broadening velocities are found for the optically thin lines from their full width at half maximum intensity (FWHM).Also at High Altitude Observatory for part of this work.The National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
12.
The locations of coronal holes are usually based on equivalent-width images in the He i 1083 nm line. However, it is difficult to differentiate coronal holes from the centers of quiet chromospheric network without complementary data and the skill of an experienced observer. Analysis of imaging spectroscopy shows that line half-width and central intensity are correlated differently in coronal holes and a quiet Sun. This fact can be used to form linear combinations of these images in which coronal holes are better separated from the quiet Sun. Coronal hole borders agree well with SOHO/EIT data but can show significant differences from National Solar Observatory maps. 相似文献
13.
Data from a low altitude polar orbiting satellite, on auroral protons >115 keV in the evening and forenoon sectors, are presented.In the forenoon sector there is a weak but fairly steady precipitation at Λ ≈ 75° during quiet conditions. This precipitation is situated at higher invariant latitudes at local noon than at local dawn and can probably be ascribed to the high energy tail of the polar cleft protons. During moderately disturbed conditions, especially during the recovery phase of geomagnetic storms, there are some seemingly more “impulsive” precipitation events at Λ ≈ 65°. During very disturbed conditions these two precipitation zones in the forenoon sector seem to merge.In the evening sector a rather sharp equatorward boundary of the main precipitation, at Λ ≈ 69° during quiet conditions, varies fairly smoothly from pass to pass. South of this boundary, at invariant latitudes around 62°, there is a steady weak drizzle from the radiation belt. Due to a longitudinal effect this drizzle, as recorded by the satellite, shows a diurnal variation.The equatorward boundaries of the main precipitation at both local times move equatorward with increasing ring current strength. When Dst gets less than about — 100nT, the poleward boundaries are found to move equatorward too. From an attempt to reveal some of the substorm-dependent changes of the precipitation it is found that an equatorward shift of the precipitation areas takes place during, or just prior to, the substorm expansive phase, accompanied by a large intensity increase in the evening sector, whereas the recovery phase is linked with a poleward expansion of the precipitation at both local times. 相似文献
14.
R. A. Gulyaev 《Solar physics》1975,44(1):25-40
Slitless spectra of the chromosphere, observed cinematographically at the total solar eclipse of 10 July 1972, were reduced. The surface brightness distribution of the helium D3 line in the undisturbed chromosphere was obtained in agreement with results by other observers. The available eclipse data on the D3 absolute brightness was analysed by means of theoretical curves of growth. Intensity data by some observers were found to be certainly too high. A trend was found that the D3 absolute brightness in the quiet chromosphere decreases with the increasing solar activity (sunspot number). This perhaps indicates a variation of the spicule number over the solar surface during a sunspot cycle. 相似文献
15.
Steven G. Wallenhorst 《Solar physics》1982,79(2):333-341
Models of the solar corona which include the effects of hot downflowing material are considered. Temperature-height profiles of the quiet and flaring corona are derived, under the assumptions of hydrostatic equilibrium and that the dominant cause of transition region heating is due to the enthalpy of the downflowing matter. In addition, scaling laws for the lengths of coronal loops are derived. It is found that inclusion of the downward enthalpy flux leads to a loop scaling law for quiet Sun loops which does not differ appreciably from that of Rosner et al. (1978). However, inclusion of the effects of enthalpy flux lead to a scaling law for compact flare loops of L = (3.6 × 109)T
infc
sup0.55
cm, which predicts much smaller loop sizes than expected from the quiet Sun loop law; these predicted lengths, however, are in agreement with the observed small sizes of compact flare loops. 相似文献
16.
Michael Turmon Harrison P. Jones Olena V. Malanushenko Judit M. Pap 《Solar physics》2010,262(2):277-298
A maximum a posteriori (MAP) technique is developed to identify solar features in cotemporal and cospatial images of line-of-sight magnetic flux, continuum intensity, and equivalent width observed with the NASA/National Solar Observatory (NSO) Spectromagnetograph (SPM). The technique facilitates human understanding of patterns in large data sets and enables systematic studies of feature characteristics for comparison with models and observations of long-term solar activity and variability. The method uses Bayes’ rule to compute the posterior probability of any feature segmentation of a trio of observed images from per-pixel, class-conditional probabilities derived from independently-segmented training images. Simulated annealing is used to find the most likely segmentation. New algorithms for computing class-conditional probabilities from three-dimensional Gaussian mixture models and interpolated histogram densities are described and compared. A new extension to the spatial smoothing in the Bayesian prior model is introduced, which can incorporate a spatial dependence such as center-to-limb variation. How the spatial scale of training segmentations affects the results is discussed, and a new method for statistical separation of quiet Sun and quiet network is presented. 相似文献
17.
High-resolution magnetograph observations of the polar magnetic fields have been obtained at intervals of time since the end of 1986 at Big Bear Solar Observatory. The Big Bear data differ from the low-resolution, full-disk magnetograph observations in that the 2 arc sec resolution makes it possible to resolve concentrated field upward of 100 G. The purpose of this ongoing observation is to examine the evolution of polar fields during the expected polarity reversal as cycle 22 passes its maximum phase, and secondly, to study the polar magnetic field: its true field strength, distribution, and how it compares to other parts of the quiet Sun.We find that the >70° net polar flux of both poles has not reversed as of the end of 1989. However, in the lower latitudes of both poles, 50° to 70°, there are signs reminiscent of those preceding the reversals in cycles 19 and 20. These include: decreasing field intensity in the old polarity fluctuations in net flux between the old and new polarities.We find that the net average longitudinal polar fields (above 50°) are 1–2 G, in agreement with results found in cycles 19 and 20. For individual elements, however, the strongest observed field strength poleward of 70° is over 100 G.We compare the polar fields with the equatorial limb as a function of latitute and longitude, respectively, and find the polar fields are comparable to (or stronger than) the quiet equatorial limb. When the observed mean flux density of the polar field as a function of latitude is corrected for limb-darkening and projection effects (assuming the field is radial), the result is nearly constant. These results suggest that despite the high latitudes, the polar fields have field strength and distribution similar to other parts of the quiet Sun. 相似文献
18.
V. A. Sergeev A. G. Yahnin R. A. Rakhmatulin S. I. Solovjev F. S. Mozer D. J. Williams C. T. Russell 《Planetary and Space Science》1986,34(12):1169-1188
Auroral, magnetic variation and pulsation data from the dense network in the nearmidnight portion of the auroral zone are used together with the measurements of suprathermal particles and electromagnetic fields by the IMP-8 and ISEE-1 spacecraft within the plasma sheet to study the characteristics of activity during two magnetically quiet periods on 3 March 1976 and 23 March 1979. Contrary to existing beliefs, we found clear signatures of numerous (5–10 events per hour) transient events, characterized by plasma flows, energetic particle bursts and E−B field variations. A close association of these events in the plasma sheet with the local auroral flares (LAFs) in the conjugate sector of the auroral zone is established for many events. We conclude that LAF (local auroral arc activation with associated Pi pulsations but extremely weak magnetic bays) have the same plasma sheet manifestations (apparently, the same physics) as the individual substorm intensifications during strong substorm expansion events, which differ from the studied quiet periods mainly by the strength and number of these intensifications. These transient phenomena seem to play an important role in the energetics of the quiet time magnetotail. 相似文献
19.
Eike Guenther 《Astrophysics and Space Science》1990,170(1-2):17-22
Photographic spectra of three photospheric lines with an approximate resolution of 0
.
8 were used to evaluate average line profiles of granules and the intergranular space in quiet and plage regions. The bisectors of the profiles of the quiet regions were compared with numerical calculations from the literature. The calculated bisectors resemble the observed ones. The corresponding bisectors of the plage regions were found to be very different from those of the quiet regions. An increase of the FWHM may indicate a concentration of magnetic flux in the plage regions.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain. 相似文献
20.
Position of the mid-latitude trough in the topside ionosphere as deduced from ESRO 4 observations 总被引：1，自引：0，他引：1
The position of the mid-latitude trough in the topside ionosphere is determined from electron density data of ESRO 4 during quiet solar conditions. An analysis of about 300 trough observations in the northern and southern hemispheres showed that the trough was generally seen only during the night from 19 to 05 hr LT. During this period, the invariant latitude of the minimum of the trough was found to decrease both with increasing geomagnetic disturbance represented by Kp and with increasing LT after sunset. 相似文献