370 research outputs found
Dynamics of solar wind protons reflected by the Moon
Solar system bodies that lack a significant atmosphere and significant
internal magnetic fields, such as the Moon and asteroids, have been considered
as passive absorbers of the solar wind. However, ion observations near the Moon
by the SELENE spacecraft show that a fraction of the impacting solar wind
protons are reflected by the surface of the Moon. Using new observations of the
velocity spectrum of these reflected protons by the SARA experiment on-board
the Chandrayaan-1 spacecraft at the Moon, we show by modeling that the
reflection of solar wind protons will affect the global plasma environment.
These global perturbations of the ion fluxes and the magnetic fields will
depend on microscopic properties of the object's reflecting surface. This solar
wind reflection process could explain past ion observations at the Moon, and
the process should occur universally at all atmosphereless non-magnetized
objects.Comment: 12 pages, 8 figure
Geoeffectiveness and efficiency of CIR, Sheath and ICME in generation of magnetic storms
We investigate relative role of various types of solar wind streams in
generation of magnetic storms. On the basis of the OMNI data of interplanetary
measurements for the period of 1976-2000 we analyze 798 geomagnetic storms with
Dst < -50 nT and their interplanetary sources: corotating interaction regions
(CIR), interplanetary CME (ICME) including magnetic clouds (MC) and Ejecta and
compression regions Sheath before both types of ICME. For various types of
solar wind we study following relative characteristics: occurrence rate; mass,
momentum, energy and magnetic fluxes; probability of generation of magnetic
storm (geoeffectiveness) and efficiency of process of this generation. Obtained
results show that despite magnetic clouds have lower occurrence rate and lower
efficiency than CIR and Sheath they play an essential role in generation of
magnetic storms due to higher geoeffectiveness of storm generation (i.e higher
probability to contain large and long-term southward IMF Bz component).Comment: 23 pages, 4 figures, 3 tables, submitted to JGR special issue
"Response of Geospace to High-Speed Streams
Recovery phase of magnetic storms induced by different interplanetary drivers
Statistical analysis of Dst behaviour during recovery phase of magnetic
storms induced by different types of interplanetary drivers is made on the
basis of OMNI data in period 1976-2000. We study storms induced by ICMEs
(including magnetic clouds (MC) and Ejecta) and both types of compressed
regions: corotating interaction regions (CIR) and Sheaths. The shortest,
moderate and longest durations of recovery phase are observed in ICME-, CIR-,
and Sheath-induced storms, respectively. Recovery phases of strong ( nT) magnetic storms are well approximated by hyperbolic functions
with constant times for all types of drivers
while for moderate ( nT) storms profile can not
be approximated by hyperbolic function with constant because
hyperbolic time increases with increasing time of recovery phase.
Relation between duration and value for storms induced by ICME and
Sheath has 2 parts: and duration correlate at small durations while
they anticorrelate at large durations.Comment: 18 pages, 4 figures, 2 tables, submitted to JGR special issue
"Response of Geospace to High-Speed Streams
Temperature Anisotropy in a Shocked Plasma: Mirror-Mode Instabilities in the Heliosheath
We show that temperature anisotropies induced at a shock can account for
interplanetary and planetary bow shock observations. Shocked plasma with
enhanced plasma beta is preferentially unstable to the mirror mode instability
downstream of a quasi-perpendicular shock and to the firehose instability
downstream of a quasi-parallel shock, consistent with magnetic fluctuations
observed downstream of a large variety of shocks. Our theoretical analysis of
the solar wind termination shock suggests that the magnetic holes observed by
Voyager 1 in the heliosheath are produced by the mirror mode instability. The
results are also of astrophysical interest, providing an energy source for
plasma heating.Comment: 11 pages, 2 figures, accepted for publication in ApJ Letter
Multiwavelength Study on Solar and Interplanetary Origins of the Strongest Geomagnetic Storm of Solar Cycle 23
We study the solar sources of an intense geomagnetic storm of solar cycle 23
that occurred on 20 November 2003, based on ground- and space-based
multiwavelength observations. The coronal mass ejections (CMEs) responsible for
the above geomagnetic storm originated from the super-active region NOAA 10501.
We investigate the H-alpha observations of the flare events made with a 15 cm
solar tower telescope at ARIES, Nainital, India. The propagation
characteristics of the CMEs have been derived from the three-dimensional images
of the solar wind (i.e., density and speed) obtained from the interplanetary
scintillation data, supplemented with other ground- and space-based
measurements. The TRACE, SXI and H-alpha observations revealed two successive
ejections (of speeds ~350 and ~100 km/s), originating from the same filament
channel, which were associated with two high speed CMEs (~1223 and ~1660 km/s,
respectively). These two ejections generated propagating fast shock waves
(i.e., fast drifting type II radio bursts) in the corona. The interaction of
these CMEs along the Sun-Earth line has led to the severity of the storm.
According to our investigation, the interplanetary medium consisted of two
merging magnetic clouds (MCs) that preserved their identity during their
propagation. These magnetic clouds made the interplanetary magnetic field (IMF)
southward for a long time, which reconnected with the geomagnetic field,
resulting the super-storm (Dst_peak=-472 nT) on the Earth.Comment: 24 pages, 16 figures, Accepted for publication in Solar Physic
Plasma Depletion and Mirror Waves Ahead of Interplanetary Coronal Mass Ejections
We find that the sheath regions between fast interplanetary coronal mass
ejections (ICMEs) and their preceding shocks are often characterized by plasma
depletion and mirror wave structures, analogous to planetary magnetosheaths. A
case study of these signatures in the sheath of a magnetic cloud (MC) shows
that a plasma depletion layer (PDL) coincides with magnetic field draping
around the MC. In the same event, we observe an enhanced thermal anisotropy and
plasma beta as well as anti-correlated density and magnetic fluctuations which
are signatures of mirror mode waves. We perform a superposed epoch analysis of
ACE and Wind plasma and magnetic field data from different classes of ICMEs to
illuminate the general properties of these regions. For MCs preceded by shocks,
the sheaths have a PDL with an average duration of 6 hours (corresponding to a
spatial span of about 0.07 AU) and a proton temperature anisotropy -1.3, and are marginally unstable to the
mirror instability. For ICMEs with preceding shocks which are not MCs, plasma
depletion and mirror waves are also present but at a reduced level. ICMEs
without shocks are not associated with these features. The differences between
the three ICME categories imply that these features depend on the ICME geometry
and the extent of upstream solar wind compression by the ICMEs. We discuss the
implications of these features for a variety of crucial physical processes
including magnetic reconnection, formation of magnetic holes and energetic
particle modulation in the solar wind.Comment: fully refereed, accepted for publication in J. Geophys. Re
Space Weather Application Using Projected Velocity Asymmetry of Halo CMEs
Halo coronal mass ejections (HCMEs) originating from regions close to the
center of the Sun are likely to be responsible for severe geomagnetic storms.
It is important to predict geo-effectiveness of HCMEs using observations when
they are still near the Sun. Unfortunately, coronagraphic observations do not
provide true speeds of CMEs due to the projection effects. In the present
paper, we present a new technique allowing estimate the space speed and
approximate source location using projected speeds measured at different
position angles for a given HCME (velocity asymmetry). We apply this technique
to HCMEs observed during 2001-2002 and find that the improved speeds are better
correlated with the travel times of HCMEs to Earth and with the magnitudes
ensuing geomagnetic storms.Comment: accepted for [publication in Solar Physic
Intense space storms: Critical issues and open disputes
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94671/1/jgra16863.pd
Selfâconsistent modeling of the largeâscale distortions in the geomagnetic field during the 24â27 September 1998 major magnetic storm
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94715/1/jgra17531.pd
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