3,742 research outputs found
Rigidity spectrum of Forbush decrease
Using data from neutron monitors and muon telescopes at surface and underground stations, the average rigidity spectrum of Forbush decreases (Fds) during the period of 1978-1982 were obtained. Thirty eight Ed-events are classified into two groups Hard Fd and Soft Fd according to size of Fd at Sakashita station. It is found that a spectral form of fractional-power type (P to the-gamma sub 1 (P+P sub c) to the -gamma sub2) is more suitable for the present purpose than that of power-exponential type or of power type with an upper limiting rigidity. The best fitted spectrum of fractional-power type is expressed by gamma sub1 = 0.37, gamma sub2 = 0.89 and P subc = 10 GV for Hard Fd and gamma sub1 = 0.77, gamma sub2 = 1.02 and P sub c - 14GV for Soft Fd
IMF-sense-dependent cosmic ray anisotropy produced from diffusion-convection in heliosphere
It was demonstrated that an interplanetary magnetic field (IMF) sense dependent 2nd order anisotropy is produced by the diffusion convection of cosmic rays in the heliomagnetosphere. The result implies that the anisotropy cannot be expressed only by the pitch angle with respect to the IMF axis
Formulation of cosmic-ray solar daily variation and its seasonal variation, produced from generalized stationary anisotropy of solar origin
In previous papers, a formulation was presented of cosmic ray daily variations produced from solar anisotropies stationary through a year, and also of their annual (or seasonal) modulation caused by the annual variation of the rotation axis of the Earth relative to that of the Sun. These anisotropies are symmetric for an arbitrary rotation around an axis. From observations of the tri-diurnal variation, it has been suggested that solar anisotropies also contain some axis-asymmetric term of the third order with respect to the IMF-axis. This suggestion has recently found support in a theoretical study by Munakata and Nagashima. According to their results, the terms of axis-asymmetry with respect to IMF-axis appear also in the 2nd order anisotropy, together with some different kinds of axis-symmetric terms. The contribution of these anisotropies to the daily variation is different from that of those discussed previously. The above mentioned formulation is extended to a case of a generalized anisotropy
Corrected sidereal anisotropy for underground moons
Data from underground muon telescopes in New Mexico and Bolivia are analyzed in sidereal time and anti-sidereal time in the rigidity range 20 GV to a few 100's of GV. Using both vertical and north- and south- pointing telescopes in both hemispheres, a latitude range of 70 N to 50 S is covered. It is shown that there is an anti-sidereal variation of the P 1 over 2 type, having opposite phase in the Northern and Southern Hemispheres, and maximum amplitude at mid latitudes. The anti-sidereal data are used to correct the sidereal data, using the Nagashima method (Nagashima, 1984); the resulting corrected sidereal vectors for northern hemisphere telescopes have their sidereal maxima close to 3h sidereal time, in reasonable agreement with sidereal data at higher energies from small air showers. The Nagashima correction also eliminates effects due to the reversal of the Sun's polar magnetic field which show up in the uncorrected sidereal data
Analytic Approach to the Cloud-in-cloud Problem for Non-Gaussian Density Fluctuations
We revisit the cloud-in-cloud problem for non-Gaussian density fluctuations.
We show that the extended Press-Schechter (EPS) formalism for non-Gaussian
fluctuations has a flaw in describing mass functions regardless of type of
filtering. As an example, we consider non-Gaussian models in which density
fluctuations at a point obeys a \chi^2 distribution with \nu degrees of
freedom. We find that mass functions predicted by using an integral formula
proposed by Jedamzik, and Yano, Nagashima and Gouda, properly taking into
account correlation between objects at different scales, deviate from those
predicted by using the EPS formalism, especially for strongly non-Gaussian
fluctuations. Our results for the mass function at large mass scales are
consistent with those by Avelino and Viana obtained from numerical simulations.Comment: 10 pages, 7 EPS files, submitted to Ap
Formation of the Galactic globular clusters with He-rich stars in low-mass halos virialized at high redshift
Recent observations have reported that the Galactic globular clusters (GCs)
with unusually extended horizontal-branch (EHB) morphologies show a
significantly lower velocity dispersion compared with that of the entire
Galactic GC system. We consider that the observed distinctive kinematics of GCs
with EHB has valuable information on the formation epochs of GCs and
accordingly discuss this observational result based on cosmological N-body
simulations with a model of GC formation. We assume that GCs in galaxies were
initially formed in low-mass halos at high redshifts and we investigate final
kinematics of GCs in their host halos at . We find that GCs formed in
halos virialized at z>10 show lower velocity dispersions on average than those
formed at z>6 for halos with GCs at z=0. We thus suggest that the origin of the
observed lower velocity dispersion for the Galactic GCs with EHBs is closely
associated with earlier formation epochs (z>10) of halos initially hosting the
GCs in the course of the Galaxy formation. Considering that the origin of EHBs
can be due to the presence of helium-enhanced second-generation stars in GCs,
we discuss the longstanding second parameter problem of GCs in the context of
different degrees of chemical pollution in GC-forming gas clouds within
low-mass halos virialized at different redshifts.Comment: 5 pages, 3 figures, accepted by MNRAS Letter
Seismic Halos Around Active Regions: An MHD Theory
Comprehending the manner in which magnetic fields affect propagating waves is
a first step toward constructing accurate helioseismic models of active region
sub-surface structure and dynamics. Here, we present a numerical method to
compute the linear interaction of waves with magnetic fields embedded in a
solar-like stratified background. The ideal Magneto-Hydrodynamic (MHD)
equations are solved in a 3-dimensional box that straddles the solar
photosphere, extending from 35 Mm within to 1.2 Mm into the atmosphere. One of
the challenges in performing these simulations involves generating a
Magneto-Hydro-Static (MHS) state wherein the stratification assumes horizontal
inhomogeneity in addition to the strong vertical stratification associated with
the near-surface layers. Keeping in mind that the aim of this effort is to
understand and characterize linear MHD interactions, we discuss a means of
computing statically consistent background states. Power maps computed from
simulations of waves interacting with thick flux tubes of peak photospheric
field strengths 600 G and 3000 G are presented. Strong modal power reduction in
the `umbral' regions of the flux tube enveloped by a halo of increased wave
power are seen in the simulations with the thick flux tubes. These enhancements
are also seen in Doppler velocity power maps of active regions observed in the
Sun, leading us to propose that the halo has MHD underpinnings.Comment: submitted to Ap
Cosmic ray sidereal diurnal variation of galactic origin observed by neutron monitors
Cosmic ray sidereal diurnal variations observed by neutron monitors are analyzed for the period 1961 to 1978, by adding 134 station years data to the previous paper (Nagashima, et al., 1983). Also the dependence of the sidereal variations on Sun's polar magnetic field polarity is examined for two periods; the period of negative polarity in the northern region, 1961 to 1969 and the period of positive polarity, 1970 to 1978. It is obtained that for the former period, the amplitude A=0.0203 + or 0.0020% and the phase phi=6.1 + or - 0.4 h LST and for the latter period, 0.0020% and phi=8.6 + or - 4 h LST, respectively
Statistical Study of the Reconnection Rate in Solar Flares Observed with YOHKOH/SXT
We report a statistical study of flares observed with the Soft X-ray
Telescope (SXT) onboard Yohkoh in the year of 2000. We measure physical
parameters of 77 flares, such as the temporal scale, the size, and the magnetic
flux density and find that the sizes of flares tend to be distributed more
broadly as the GOES class becomes weaker and that there is a lower limit of
magnetic flux density that depends on the GOES class. We also examine the
relationship between these parameters and find weak correlation between
temporal and spatial scales of flares. We estimate reconnection inflow
velocity, coronal Alfven velocity, and reconnection rate using above observed
values. The inflow velocities are distributed from a few km/s to several tens
km/s and the Alfven velocities in the corona are in the range from 10^3 to 10^4
km/s. Hence the reconnection rate is 10^-3 - 10^-2. We find that the
reconnection rate in a flare tends to decrease as the GOES class of the flare
increases. This value is within one order of magnitude from the theoretical
maximum value predicted by the Petschek model, although the dependence of the
reconnection rate on the magnetic Reynolds number tends to be stronger than
that in the Petschek model.Comment: 21 pages, 8 figures, accepted for publication in Ap
Anomalous increase of solar anisotropy above 150GV in 1981-1983
An analysis was carried out of the observed data with Nagoya (surface). Misato (34mwe) and Sakashita (80mwe) multidirectional muon telescope, for the solar activity maximum period of 1978-1983. These data respond to primaries extending over the median rigidity range 60GV to 600GV. The observed amplitude at Sakashita station in 1981-1983 increased, especially in 1982; the amplitude is twice as large as that in 1978-1980, when those at Nagoya and Misato stations are nearly the same as those in 1978-1980. Uni-directional anisotropy is derived by the best fit method by assuming the flat rigidity spectrum with the upper cutoff rigidity Pu. The value of Pu obtained is 270GV in 1981-1983 and 150GV in 1978-1980
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