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1.
Ashutosh K. Singh K. K. Singh A. K. Singh Lalmani 《Astrophysics and Space Science》2011,331(2):459-468
A unique night-time natural electromagnetic disturbances in the VLF/ELF range received during a magnetically quite period
at a low latitude Indian ground station, Jammu (geomag. lat. 19°26′ N, L=1.17) has been reported. During the routine observation
of VLF waves at Jammu, whistlers and different types of VLF/ELF emissions such as whistlers of varying dispersion confined
to a small band limited frequency range, hisslers, pulsing hiss, discrete chorus emissions of rising and falling tones with
multiple bands, oscillating tone discrete emission, whistler-triggered hook and discrete chorus risers emissions, etc. have
been observed simultaneously during the quiet period on a single night. Such type of unique simultaneous observations has
never been reported from any of the low latitude ground stations and this is the first observation of its kind. The results
are discussed in the light of recorded features of whistlers and emissions. Generation and propagation mechanism are discussed
briefly. Plasma parameters are further derived from the dispersion analysis of nighttime whistlers and emissions recorded
simultaneously during magnetically quiet periods. 相似文献
2.
R. P. Kane 《Solar physics》2008,249(2):355-367
The 12-month running means of the conventional sunspot number Rz, the sunspot group numbers (SGN) and the frequency of occurrence of Coronal Mass Ejections (CMEs) were examined for cycle
23 (1996 – 2006). For the whole disc, the SGN and Rz plots were almost identical. Hence, SGN could be used as a proxy for Rz, for which latitude data are not available. SGN values were used for 5° latitude belts 0° – 5°, 5° – 10°, 10° – 15°, 15° – 20°,
20° – 25°, 25° – 30° and > 30°, separately in each hemisphere north and south. Roughly, from latitudes 25° – 30° N to 20° – 25°
N, the peaks seem to have occurred later for lower latitudes, from latitudes 20° – 25° N to 15° – 20° N, the peaks are stagnant or occur slightly earlier, and then from latitudes 15° – 20° N to 0° – 5° N, the peaks seem to have occurred again later for lower latitudes. Thus, some latitudinal migration is suggested, clearly in the northern hemisphere, not very clearly
in the southern hemisphere, first to the equator in 1998, stagnant or slightly poleward in 1999, and then to the equator again
from 2000 onwards, the latter reminiscent of the Maunder butterfly diagrams. Similar plots for CME occurrence frequency also
showed multiple peaks (two or three) in almost all latitude belts, but the peaks were almost simultaneous at all latitudes,
indicating no latitudinal migration. For similar latitude belts, SGN and CME plots were dissimilar in almost all latitude
belts except 10° – 20° S. The CME plots had in general more peaks than the SGN plots, and the peaks of SGN often did not match
with those of CME. In the CME data, it was noticed that whereas the values declined from 2002 to 2003, there was no further
decline during 2003 – 2006 as one would have expected to occur during the declining phase of sunspots, where 2007 is almost
a year of sunspot minimum. An inquiry at GSFC-NASA revealed that the person who creates the preliminary list was changed in
2004 and the new person picks out more weak CMEs. Thus a subjectivity (overestimates after 2002) seems to be involved and
hence, values obtained before and during 2002 are not directly comparable to values recorded after 2002, except for CMEs with
widths exceeding 60°. 相似文献
3.
A transistorized wide-band (0.5–11 kHz) VLF goniometer has been developed for the study of whistlers and ELF/VLF emissions. It consists of two crossed vertical loops from which a single loop aerial, rotating about a vertical axis at a frequency of 25 sec?1, is synthesized electronically. During periods of high whistler activity, when the same propagation paths may be identified in successive whistler groups, it is possible to determine the bearing of the exit point of such a magnetospheric path with an error, typically, of ± 10–20°. 相似文献
4.
Based on data from the Baksan underground scintillation telescope (BUST) for the period 2001–2004, we searched for cosmic
gamma-ray bursts (GRBs) at primary photon energies of 0.5 TeV or higher. We obtained constraints on the rate of bursts with
durations of 1–10 s for fluences within the range 4.6 × 10−3-1.8 × 10−2 erg cm−2 in the declination band 30° ≤ δ ≤ 80°. We searched for ultrahigh-energy gamma rays from GRBs detected on spacecraft during and within ±2 h of the burst.
No statistically significant excesses above the background of random coincidences were found. The derived constraints on the
ultrahigh-energy gamma-ray fluence during GRBs lie within the range 4.6 × 10−3-3.7 × 10−2 erg cm−2. 相似文献
5.
Masashi Hayakawa 《Planetary and Space Science》1974,22(4):638-642
The non-ducted whistler propagation in the inner magnetosphere is discussed using the broad-band VLF measurement on board the K-9M-26 rocket launched at 1703 hr JST on 24 August 1969 from Kagoshima Space Center (geomagnetic lat 20°N). A large number of whistlers which seemed to be two-hop whistlers originating in the northern hemisphere were observed. The main features of these whistlers are summarized: (1) their dispersion value is widely scattered in the range , (2) their frequency spectra show a broad maximum in the frequency range 2–5 kHz and higher frequency components are likely to disappear. Attempts are made to interpret these properties in terms of ducted or non-ducted propagation. It is then found from the ray tracing studies that the measurements are satisfactorily explained by non-ducted propagation in the inner magnetospheric model with latitudinal density gradient such as the equatorial anomaly. 相似文献
6.
Extremely low frequency (ELF)/Very low frequency (VLF) hiss is whistler mode wave that interacts with energetic electrons
in the magnetosphere. The characteristics features of ELF/VLF hiss observed at low latitude ground station Jammu (Geomag.
lat. 22°16′ N, L=1.17) are reported. It is observed that most of hiss events first propagate in ducted mode along higher L-values (L = 4–5), after reaching lower edge of ionosphere excite the Earth-ionosphere waveguide and propagate towards equator to be
received at low-latitude station Jammu. To understand the generation mechanism of ELF/VLF hiss, incoherent Cerenkov radiated
power from the low-latitude and mid-latitude plasmasphere are evaluated. Considering this estimated power as an input for
wave amplification through wave–particle interaction, the growth rate and amplification factor is evaluated which is too small
to explain the observed wave intensity. It is suggested that some non-linear mechanism is responsible for the generation of
ELF/VLF hiss. 相似文献
7.
The observed periodicity in the whistler occurrence rate recorded at our low latitude ground station at Varanasi (geomagnetic latitude, 14°55'N) is interpreted in terms of duct life time at lowL values. Power spectrum analysis of the whistler data yields a period of about 50 min for the growth and decay of ducts. Further dispersion analysis of the whistlers has qualitatively confirmed the existence of separate ducts during the period of observations. 相似文献
8.
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
9.
The properties of powerful (flux >10−19 W m−2 Hz−1) type III bursts observed in July – August 2002 by the radio telescope UTR-2 at frequencies 10 – 30 MHz are analyzed. Most
bursts have been registered when the active regions associated to these bursts were located near the central meridian or at
40° – 60° to the East or West from it. All powerful type III bursts drift from high to low frequencies with frequency drift
rates 1 – 2.5 MHz s−1. It is important to emphasize that according to our observations the drift rate is linearly increasing with frequency. The
duration of the bursts changes mainly from 6 s at frequency 30 MHz up to 12 s at 10 MHz. The instantaneous frequency bandwidth
does not depend on the day of observations, i.e. on the disk location of the source active region, and is increasing with frequency. 相似文献
10.
Jorda L. Rembor K. Lecacheux J. Colom P. Colas F. Frappa E. Lara L. M. 《Earth, Moon, and Planets》1997,77(3):167-180
We observed comet Hale-Bopp (C/1995 O1) at Pic du Midi Observatory in 1997 from February 2.24 UT to March 31.89 UT with the
1.05-m telescope equipped with a CCD camera and broad- and narrow-band IHW filters. A total of 30000 images were acquired
both during night- and day-time. The images were automatically reduced and all the images obtained within 10 min. were co-added
to give a set of ∼1000 images used during the analysis. We can identify two jets on the images. The position angle of the
brightest jet from February 2.24 UT to March 5.22 UT is measured using an automatic routine which searches for the averaged
position angle of the maximum of brightness at a projected distance of 3200–6100 km from the optocenter. A preliminary model
of nucleus rotation is used to fit the data and retrieve the rotational parameters of the nucleus. The best fit is found for
a source located at a latitude of 64 ± 3°, a sidereal rotation period of 11.35 ± 0.04 h and a right ascension and declination
of the North pole of 275 ± 10° and -57 ± 10°. This preliminary analysis shows no evidence for a precession. Grains with velocities
of 450–600 m s−1 and radii <;∼ 1 μm dominate the optical scattering cross section in the jets.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
We investigate the properties of acoustic events (AEs), defined as spatially concentrated and short duration energy flux,
in the quiet Sun, using observations of a 2D field of view (FOV) with high spatial and temporal resolution provided by the
Solar Optical Telescope (SOT) onboard Hinode. Line profiles of Fe i 557.6 nm were recorded by the Narrow-band Filter Imager (NFI) on a 82″×82″ FOV during 75 min with a time step of 28.75 s
and 0.08″ pixel size. Vertical velocities were computed at three atmospheric levels (80, 130, and 180 km) using the bisector
technique, allowing the determination of energy flux to be made in the range 3 – 10 mHz using two complementary methods (Hilbert
transform and Fourier power spectrum). Horizontal velocities were computed using local correlation tracking (LCT) of continuum
intensities providing divergences. We found that the net energy flux is upward. In the range 3 – 10 mHz, a full FOV space
and time averaged flux of 2700 W m−2 (lower layer 80 – 130 km) and 2000 W m−2 (upper layer 130 – 180 km) is concentrated in less than 1 % of the solar surface in the form of narrow (0.3″) AE. Their total
duration (including rise and decay) is of the order of 103 s. Inside each AE, the mean flux is 1.6×105 W m−2 (lower layer) and 1.2×105 W m−2 (upper). Each event carries an average energy (flux integrated over space and time) of 2.5×1019 J (lower layer) to 1.9×1019 J (upper). More than 106 events could exist permanently on the Sun, with a birth and decay rate of 3500 s−1. Most events occur in intergranular lanes, downward velocity regions, and areas of converging motions. 相似文献
12.
G.H. Jones 《Earth, Moon, and Planets》1997,77(3):281
The Isaac Newton Group’s CoCam instrument obtained wide-field (10°X 20°) CCD images of the H2O+ tail of Hale-Bopp on March 12–15, 19, 20, 25, 28, 29, 31, April1, 7, 9–13, 21, 23–29 and May 4, 1997. A 6185? filter recorded
the distribution of H2O+; 6250?-centered continuum images were also obtained. Initial analysis has revealed the CoCam dataset to be an invaluable
record of the large-scale structure of the comet's ion tail. Several images show evidence of upstream parabolic envelopes
of ions reminiscent of those reported in C/1908 R1 Morehouse (Eddington A. S., Mon. Not. Roy. Astron. Soc. 70, 442–458, 1910).
Studies of these features may help towards a better understanding of the tail ray phenomenon. During most of March and early
April, the tail had a largely consistent quiescent appearance, with numerous rays exhibited, but no major disturbances; most
probably as a result of being in the stream of fast polar solar wind. A significant kink propagated down the tail around April
9/10. Towards the end of April, as the comet entered more variable solar wind at near-equatorial heliographic latitudes, the
tail's morphology became significantly more structured. Striking tail disturbances were recorded in late April and early May,
when the comet was in the vicinity of the heliospheric current sheet. Analysis of the dataset continues.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
E. P. Pavlenko 《Astrophysics》2006,49(1):105-119
Series of photometric CCD observations of the asynchronous polar BY Cam in a low accretion state (R = 14m–16m) were made on the K-380 telescope at the Crimean Astrophysical Observatory (CrAO) over 100 hours in the course of 31 nights
during 2004–2005. A period of P
1 = 0.137120±0.000002 days was found for the variations in the brightness, along with less significant periods of P
2 = 0.139759±0.000003 and P3 = 0.138428±0.000002 days, where P2 and P3 are obviously the orbital and rotation periods, while the dominant period P1 is the sideband period. A modulation in the brightness and an amplitude of 0.137 days in the oscillations at the orbital-rotational
beat period (synodic cycle) of 14.568±0.003 day are found for the first time. The profile of the modulation period is four
humped. This indicates that the magnetic field has a quadrupole component, which shows up well during the low brightness state.
Accretion takes place simultaneously into two or three accretion zones, but at different rates. The times of the times of
maxima for the main accretion zone vary with the phase of the beat period. Three types of variation of this sort are distinguished:
linear, discontinuous, and chaotic, which indicate changes in the accretion regimes. At synodic phases 0.25 and 0.78 the bulk
of the stream switches by 180°, and at phase 0.55, by ∼75°. At phases of 0.25–0.55 and 0.55–0.78, the O-C shift with a period
of 0.1384 days, which can be explained by a retrograde shift of the main accretion zone relative to the magnetic pole and/or
a change in the angle between the field lines and the surface of the white dwarf owing to the asynchronous rotation. For phases
of 0.78–1.25 the motion of the accretion zone is quite chaotic. It is found that synchronization of the components occurs
at a rate of less than dProt/Prot∼10−9 day/day.
__________
Translated from Astrofizika, Vol. 49, No. 1, pp. 121–137 (February 2006). 相似文献
14.
Xingfen Zhu 《Astrophysics and Space Science》1999,268(4):483-495
Using the Hewitt-Burbidge QSO Catalogue (1993) and all-sky catalogue of Abell clusters (ACO, 1989) at the region |b| > 40° we analyze the cross correlation function and find anti-correlation between them at angular separations 3° < θ < 10° , which is mainly caused by optical-selected QSOs, rather than radio-selected QSOs. There is no such anti-correlation between
QSOs and Abell clusters at smaller separations θ < 3°. Considering that this phenomenon may be caused by different characters of the objects, we further estimate the correlation
function with various subsamples. We find that the correlation is independent of the redshift of QSOs, but depends upon the
type of Abell clusters: for the D ≤ 4 clusters there is an obvious tendency of overdensity of quasars at 0° < θ < 5°; around the R ≥ 2 Abell clusters there is about an 18.7% deficit of quasars in the region 3° < θ < 7°. K-S Test shows the overdensity or deficit of quasars around different types of clusters cannot be explained by the projection
effect of background quasars. We get the enhancement factor of quasar overdensity (for D ≤ 4 clusters) q =1.13, and the extinction magnitude factor of QSO deficiency (for R ≥ 2 clusters) Av= 0.14.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
15.
Astrometric CCD observations of 1123 stars with large proper motions (μ > 300 mas yr−1) from the LSPM (I/298) catalog in the declination zone +30°–+70° have been carried out with the Pulkovo normal astrograph
since 2006. The observational program includes mostly stars that previously have not entered into high-accuracy projects to
determine the proper motions. Our studies are aimed at determining new proper motions of fast stars in the HCRF/UCAC3 system
and searching for stars with invisible companions in the immediate Galactic neighborhoods of the Sun. Having analyzed about
10 000 CCD frames, we have obtained the equatorial coordinates of 414 program stars in the HCRF/UCAC3 system at an accuracy
level of 10–50 mas and determined their new proper motions. To derive the proper motions, we have used the data from several
star catalogs and surveys (M2000, CMC14, 2MASS, SDSS) as early epochs. The epoch differences range from 5 to 13 years (on
average, about 10 years); the mean accuracy of the derived proper motions is 4–5 mas yr−1. For 70 stars, we have revealed significant differences between the derived proper motions and those from the LSPM and I/306A
catalogs (these proper motions characterize the mean motion of the photocenter in 50 years or more). Apart from systematic
errors, these differences can result from the existence of invisible components of the program stars. 相似文献
16.
Employing the synoptic maps of the photospheric magnetic fields from the beginning of solar cycle 21 to the end of 23, we
first build up a time – longitude stackplot at each latitude between ±35°. On each stackplot there are many tilted magnetic
structures clearly reflecting the rotation rates, and we adopt a cross-correlation technique to explore the rotation rates
from these tilted structures. Our new method avoids artificially choosing magnetic tracers, and it is convenient for investigating
the rotation rates of the positive and negative fields by omitting one kind of field on the stackplots. We have obtained the
following results. i) The rotation rates of the positive and negative fields (or the leader and follower polarities, depending on the hemispheres
and solar cycles) between latitudes ±35° during solar cycles 21–23 are derived. The reversal times of the leader and follower
polarities are usually not consistent with the years of the solar minimum, nevertheless, at latitudes ±16°, the reversal times
are almost simultaneous with them. ii) The rotation rates of the three solar cycles averaged over each cycle are calculated separately for the positive, negative
and total fields. The latitude profiles of rotation of the positive and negative fields exhibit equatorial symmetries with
each other, and those of the total fields lie between them. iii) The differences in rotation rates between the leader and follower polarities are obtained. They are very small near the
equator, and increase as latitude increases. In the latitude range of 5° – 20°, these differences reach 0.05 deg day−1, and the mean difference for solar cycle 22 is somewhat smaller than cycles 21 and 23 in these latitude regions. Then, the
differences reduce again at latitudes higher than 20°. 相似文献
17.
The effect of ions on whistler dispersion characteristics has been studied. It is shown that the significant changes in the dispersion characteristics of low-latitude whistlers are brought about by the presence of ions. The dispersions for Nainital (geomagnetic lat. 19°1'N) and Gulmarg (geomagnetic lat. 24°10'N) are found to peak around 800 Hz. The short whistler sonograms recorded at Nainital and Gulmarg have been analysed, using the complete dispersion equation and the effect of ions has been shown. At higher frequencies the dispersion is found to decrease steadily and becomes independent of ions. Some examples of short whistlers have been found whose characteristics do not conform to the general trend of low-latitude whistlers, and, on the other hand, these whistlers show a constant dispersion unaffected by ions up to a fairly low frequency and thereafter decrease sharply at lower frequencies. 相似文献
18.
An analysis and interpretation of reflected solar Lyman α intensity data acquired with the Hubble Space Telescope (HST) implies
an equatorially confined atmosphere with SO2 column densities ∼ 1–2 × 1016 cm-2. Poleward of 30° the SO2 density must decrease sharply reaching an asymptotic polar value of < 1015 cm-2 at 45° to achieve the observed 2 kR intensity peaks. The corresponding surface reflectivities must be either a constant 0.047
for higher equatorial SO2 or a variable reflectivity of 0.027 with lower SO2 densities at the equator increasing to a polar value of ∼ 0.05. The average residence time for an atmospheric SO2 molecule is ∼ 2–3 days for the canonical mass loading rate of the Io plasma torus = 1030 amu s-1. With atomic hydrogen in the atmosphere and corona constrained by the HST observations, it is estimated that a pickup proton
density ratio of 0.25–0.4% can be sustained by a supply of Io plasma torus protons neutralized in Io's atmosphere/exosphere,
if protons constitute 7% of the total torus ion density, which is close to the Chust et al. (1999) pickup proton density ratio and under the widely quoted 10% proton content of the torus.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
In the present investigation we measure the differential rotation of strong magnetic flux during solar cycles 21 – 23 with
the method of wavelet transforms. We find that the cycle-averaged synodic rotation rate of strong magnetic flux can be written
as ω=13.47−2.58sin 2
θ or ω=13.45−2.06sin 2
θ−1.37sin 4
θ, where θ is the latitude. They agree well with the results derived from sunspots. A north–south asymmetry of the rotation rate is
found at high latitudes (28°<θ<40°). The strong flux in the southern hemisphere rotates faster than that in the northern hemisphere by 0.2 deg day−1. The asymmetry continued for cycles 21 – 23 and may be a secular property. 相似文献
20.
We analyse data obtained by different ground-based video camera systems during the 1999 Leonid meteor storm. We observe similar
activity profiles at nearby observing sites, but significant differences over distances in the order of 4,000 km. The main
peak occured at 02:03 UT (λ⊙=235.286, J2000, corrected for the time of the topocentric stream encounter). At the Iberian peninsula quasi-periodic activity
fluctuations with a period of about 7 min were recorded. The camera in Jordan detected a broad plateau of activity at 01:39–01:53
UT, but no periodic variations. The Leonid brightness distribution derived from all cameras shows a lack of faint meteors
with a turning point close to +3m, which corresponds to meteoroids of approximately 10-3 g. We find a pin-point radiant at αalpha=153.65 ±0.1, δ=21.80 ±0. (λ⊙=235.290). The radiant positionis identical before and after the storm, and also during the storm no driftis observed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献