1,721,025 research outputs found
Relationship between the midnight equatorward auroral oval boundary and the geomagnetic activity level for different solar wind regimes,
No full textFor a better understanding of auroral phenomena it is necessary to evaluate in detail the magnetospheric/ionospheric response to different solar wind triggers. The equatorward magnetic latitude of the auroral oval midnight sector (MLat), detected by the Defense Meteorological Satellite Program (Cedarweb), was investigated for different solar wind conditions during the ascending phase of the on-going solar activity cycle (n. 23). The correlation between MLat and each one of the geomagnetic indices was performed separating corotating from transient plasma streams. Moreover the correlation was repeated considering also the interplanetary parameters variability (e.g. solar wind speed, pressure and density, magnetic field intensity, dawn-dusk electric field, etc.). It was found that MLat depends on the solar wind regimes in different ways. An attempt to derive useful algorithms for auroral forecast works was initiated and some results are shown
The diurnal modulation of the geomagnetic activity induced by the southward component of the interplanetary magnetic field
No full textThe role of drift and convection–diffusion mechanisms in small energy global cosmic ray modulation: Application to the hysteresis phenomenon of proton and alpha particle satellite data
No full textThe hysteresis effect for small energies of galactic cosmic rays is due to two effects. The first is the same as for neutron monitor
energies – the delay of the interplanetary processes responsible for cosmic ray modulation with respect to the initiating solar processes,
according to the effective velocity of solar wind and shock waves propagation. Then, the observed cosmic ray intensity is
connected to the solar activity variations during many months before the time of cosmic ray measurement. The second is caused
by the time delay of small energy cosmic ray diffusion from the boundary of modulation region to the Earth's orbit. The model
describing the connection between solar activity variation and cosmic ray convection–diffusion global modulation for neutron monitor
energies is here developed by taking into account also the time-lag of the small energy particle diffusion in the Heliosphere. We
use theoretical results on drifts and analytically approximate the dependences of drifts from tilt angle, and take into account the
dependence from the sign of primary particles, and from the sign of polar magnetic field (A > 0 or A < 0). The obtained results
are applied on proton and alpha-particle satellite data. We analyze satellite 5-min data of proton fluxes with energies >1 MeV,
>2 MeV, >5 MeV, >10 MeV, >30 MeV, >50 MeV, >60 MeV, >100 MeV, and in intervals 10–30 MeV, 30–60 MeV, and 60–
100 MeV during January 1986–December 1999. We exclude periods with great cosmic ray increases caused by particle acceleration
in solar flare events. Then, we determine monthly averaged fluxes, as well as 5-month and 11-month smoothed data. We analyze also
satellite 5-min data on alpha-particle fluxes in the energy intervals 60-160 MeV, 160–260 MeV and 330–500 MeV during January
1986–May 2000. We correct observation data for drifts and then compare with what is expected according to the convection–diffusion
mechanism. We assume different dimensions of the modulation region (by the time propagation X0 of solar wind from the
Sun to the boundary of modulation region), for X0 values from 1 to 60 average months, by one-month steps. For each value of X0 we
determine the correlation coefficient between variations of expected and observed cosmic ray intensities (the estimation of cosmic ray
intensities values is given in Section 3 by Eq. (9), and the determination of correlation and regression coefficients in Section 3 by Eq.
(8)). The dimension of modulation region is determined by the value of X0 max, for which the correlation coefficient reaches the maximum
value. Then the effective radial diffusion coefficient and residual modulation in small energy region can be estimated.
© 2005 COSPAR. Published by Elsevier Ltd. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
CR-SA hysteresis phenomenon on the basis of alpha-particle satellite data
No full textWe analyzed satellite 5-min data on alpha-particle fluxes in energy intervals 60-160 MeV, 160-260 MeV and 330-500 MeV during January 1986 – May 2000. In the first we excluded periods with great CR increases caused by particle acceleration in solar flare events. Then we determined monthly averaged fluxes as well as 5 months and 11 months smooth averaged data. We corrected these data on drift effects according to the procedure described in Dorman (2004) in dependence of alpha-particle energies. Corrected on drifts alpha-particles fluxes we compare with expected according to convection-diffusion modulation for different values of supposed dimension of the modulation region (measured by time of solar wind propagation from the Sun to the boundary of this region Xo from 1 to 60 av. months; described in Dorman, 2004). By this way we can determine Xomax, at what the correlation coefficient reaches the maximum value. Then it can be determined the dimension of modulation region (with taking into account the influence of nonlinear processes on the solar wind speed in the outer Heliosphere according to Le Roux and Fichtner, 1997), the radial diffusion coefficient and transport path as well as expected alpha-particle intensity out of the modulation region and absolute alpha-particle modulation (relative to the alpha-particle intensity level in the interstellar space)
Sito Web del progetto Astro-Scienze: Didattica e divulgazione dell'Astronomia, della Fisica e delle Scienze Naturali.
No full textSi veda: (S)progetti pilota: Scienze fisiche - Progetto Astro-Scienze (Miur,"Iniziative per la diffusione della cultura scientifica" L. 6/2000
Cosmic ray survey to Antarctica and coupling functions for neutron component near solar minimum (1996-1997), 2. Determination of meteorologic effects
No full text3He-counter tests for a 3He-neutron monitor section: Results from a preliminary evaluation
No full textDuring the year's couple 2002-2003 several tests were performed at the SVIRCO OBSERVATORY (CNR-IFSI -UNIRomaTre collaboration) to evaluate the possible use of 3He proportional counters in standard neutr:on monitors. Preliminary results suggest the compatibility of the 3He counters with the 10BF3 ones
AE index variability during corotating fast solar wind streams
No full text[ 1] We examine the AE index variability while 12 corotating fast solar wind streams pass the Earth during the ascending phase of the ongoing solar activity cycle. We apply the Discrete Fourier Transform analysis to the associated interplanetary magnetic field ( B) data and AE time series with similar to 1 min resolution. Results show noticeable periodicities in the 1-10 hour range. Moreover, the B and AE periodicities in each event are well correlated. For this reason a direct relationship between interplanetary Alfvenic waves and AE oscillations is proposed while those streams pass the Earth
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