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21.
We present a comprehensive survey of 230 interplanetary CMEs (ICMEs) during 1995 – 2004 using Wind and ACE in situ observations near one AU, and examine the solar-cycle variation of the occurrence rate, shock association rate, scale size,
velocity change, and other properties of ICMEs. The ICME occurrence rate increases (from 5 in 1996 to 40 in 2001) with solar
activity; and 66% of all ICMEs occurred with shock(s). A compound parameter, the total pressure perpendicular to the magnetic
field (Pt), i.e., the sum of magnetic and perpendicular plasma thermal pressures, assists us in effectively distinguishing ICMEs from other
solar-wind structures such as stream interactions, and in quantifying the interaction strength. We interpret the characteristic
signatures of the Pt temporal variation in terms of the inferred distance perpendicular to the flow to the center of the obstacle. Group 1 includes
events that appear to be traversed near the ICME center, showing an apparent enhanced central Pt; Group 3 represents ICMEs passed far away from the center, displaying a rapid rise and then gradual decay in Pt; and Group 2 includes events with intermediate signatures. About 36% of 198 classifiable ICMEs are Group 1 events, consistent
with the conventional wisdom that at one AU a magnetic cloud is found during crossings of only ~1/3 of ICMEs. Our set of Group
1 ICMEs and the set of magnetic clouds from other researchers have significant overlap and a similar solar-cycle dependence.
The rough decline of the Group 1 fraction as solar activity increases, is consistent with rough increases of scale size, shock
percentage, and peak Pt. These results call into question the need to have different mechanisms to create differently appearing ICMEs. Rather it
is possible that all ICMEs have a central flux rope that is traversed about 33% of the time, but in the majority of cases
is missed by the spacecraft.
Electronic Supplementary Material Supplementary material is available for this article at 相似文献
22.
K. Brinkfeldt H. Gunell P. C:son Brandt R.A. Frahm E. Kallio Y. Futaana R. Lundin M. Yamauchi J.R. Sharber A.J. Coates D.O. Kataria T. Säles W. Schmidt J. Luhmann D. Williams C.C. Curtis B.R. Sandel M. Carter A. Fedorov S. McKenna-Lawler R. Cerulli-Irelli P. Wurz N. Krupp M. Fränz C. Dierker 《Icarus》2006,182(2):439-447
We present measurements with an Energetic Neutral Atom (ENA) imager on board Mars Express when the spacecraft moves into Mars eclipse. Solar wind ions charge exchange with the extended Mars exosphere to produce ENAs that can spread into the eclipse of Mars due to the ions' thermal spread. Our measurements show a lingering signal from the Sun direction for several minutes as the spacecraft moves into the eclipse. However, our ENA imager is also sensitive to UV photons and we compare the measurements to ENA simulations and a simplified model of UV scattering in the exosphere. Simulations and further comparisons with an electron spectrometer sensitive to photoelectrons generated when UV photons interact with the spacecraft suggest that what we are seeing in Mars' eclipse are ENAs from upstream of the bow shock produced in charge exchange with solar wind ions with a non-zero temperature. The measurements are a precursor to a new technique called ENA sounding to measure solar wind and planetary exosphere properties in the future. 相似文献
23.
E. Kallio A. Fedorov T. Säles W. Schmidt P. Riihelä R. Lundin H. Gunell Y. Futaana M. Yamauchi J.-A. Sauvaud J.D. Winningham J.R. Sharber A.J. Coates D.O. Kataria J.G. Luhmann D. Williams C.C. Curtis B.R. Sandel M. Carter S. Orsini M. Maggi P. Bochsler J. Woch K. Asamura 《Icarus》2006,182(2):350-359
We have analysed ion escape at Mars by comparing ASPERA-3/Mars Express ion measurements and a 3-D quasi-neutral hybrid model. As Mars Express does not have a magnetometer onboard, the analysed IMA data are from an orbit when the IMF clock angle was possible to determine from the magnetic field measurements of Mars Global Surveyor. We found that fast escaping planetary ions were observed at the place which, according to the 3-D model, is anticipated to contain accelerated heavy ions originating from the martian ionosphere. The direction of the interplanetary magnetic field was found to affect noticeably which regions can be magnetically connected to Mars Express and to the overall 3-D Mars-solar wind interaction. 相似文献
24.
D. Ulusen J.G. Luhmann Y.J. Ma K.E. Mandt J.H. Waite M.K. Dougherty J.E. Wahlund C.T. Russell T.E. Cravens N.J.T. Edberg K. Agren 《Icarus》2012,217(1):43-54
Recent papers suggest the significant variability of conditions in Saturn’s magnetosphere at the orbit of Titan. Because of this variability, it was expected that models would generally have a difficult time regularly comparing to data from the Titan flybys. However, we find that in contrast to this expectation, it appears that there is underlying organization of the interaction features roughly above ～1800 km (1.7 Rt) altitude by the average external field due to Saturn’s dipole moment. In this study, we analyze Cassini’s plasma and magnetic field data collected at 9 Titan encounters during which the external field is close to the ideal southward direction and compare these observations to the results from a 2-fluid (1 ion, 1 electron) 7-species MHD model simulations obtained under noon SLT conditions. Our comparative analysis shows that under noon SLT conditions the Titan plasma interaction can be viewed in two layers: an outer layer between 6400 and 1800 km where interaction features observed in the magnetic field are in basic agreement with a purely southward external field interaction and an inner layer below 1800 km where the magnetic field measurements show strong variations and deviate from the model predictions. Thus the basic features inferred from the Voyager 1 flyby seem to be generally present above ～1800 km in spite of the ongoing external variations from SLT excursions, time variability and magnetospheric current systems as long as a significant southward external field component is present. At around ～1800 km kinetic effects (such as mass loading and heavy ion pickup) and below 1800 km ionospheric effects (such as drag of ionospheric plasma due to coupling with neutral winds and/or magnetic memory of Titan’s ionosphere) complicate what is observed. 相似文献
25.
Solar Physics - The generally low interplanetary magnetic field magnitude around the minimum between Solar Cycles 23 and 24 (SC 23/24 minimum) allows us to identify weak and small solar wind... 相似文献
26.
Unipolar streamers (also known as pseudo-streamers) are coronal structures that, at least in coronagraph images, and when
viewed at the correct orientation, are often indistinguishable from dipolar (or “standard”) streamers. When interpreted with
the aid of a coronal magnetic field model, however, they are shown to consist of a pair of loop arcades. Whereas dipolar streamers
separate coronal holes of the opposite polarity and whose cusp is the origin of the heliospheric current sheet, unipolar streamers
separate coronal holes of the same polarity and are therefore not associated with a current sheet. In this study, we investigate
the interplanetary signatures of unipolar streamers. Using a global MHD model of the solar corona driven by the observed photospheric
magnetic field for Carrington rotation 2060, we map the ACE trajectory back to the Sun. The results suggest that ACE fortuitously
traversed through a large and well-defined unipolar streamer. We also compare heliospheric model results at 1 AU with ACE
in-situ measurements for Carrington rotation 2060. The results strongly suggest that the solar wind associated with unipolar streamers
is slow. We also compare predictions using the original Wang–Sheeley (WS) empirically determined inverse relationship between
solar wind speed and expansion factor. Because of the very low expansion factors associated with unipolar streamers, the WS
model predicts high speeds, in disagreement with the observations. We discuss the implications of these results in terms of
theories for the origin of the slow solar wind. Specifically, premises relying on the expansion factor of coronal flux tubes
to modulate the properties of the plasma (and speed, in particular) must address the issue that while the coronal expansion
factors are significantly different at dipolar and unipolar streamers, the properties of the measured solar wind are, at least
qualitatively, very similar. 相似文献
27.
Most work on coronal mass ejection (CME) interpretation focuses on the involved active region rather than on the large-scale coronal context. In this paper a global potential-field source-surface model of the coronal magnetic field is used to evaluate the sensitivity of the coronal field configuration to the location, orientation, and strength of a bipolar active region relative to a background polar field distribution. The results suggest that the introduction of antiparallel components between the field of the active region and the background field can cause significant topological changes in the large-scale coronal magnetic field resembling observations during some simple CMEs. Antiparallel components can be introduced in the real corona by the diffusion and convection of photospheric fields, flux emergence, or erupted or shear-induced twist of active-region fields. Global MHD models with time-dependent boundary conditions could easily test the stability of such configurations and the nature of any related transients. 相似文献
28.
29.
A. Fedorov C. Ferrier S. Barabash C. Mazelle H. Gunell K. Brinkfeldt A. Grigoriev M. Yamauchi W. Baumjohann A.J. Coates D.R. Linder K.C. Hsieh J.-J. Thocaven H. Koskinen T. Sales P. Riihela N. Krupp J. Luhmann S. Orsini A. Mura M. Maggi P. Brandt K. Szego R.A. Frahm J.R. Sharber P. Bochsler 《Planetary and Space Science》2008,56(6):812-817
We have an unique opportunity to compare the magnetospheres of two non-magnetic planets as Mars and Venus with identical instrument sets Aspera-3 and Aspera-4 on board of the Mars Express and Venus Express missions. We have performed both statistical and case studies of properties of the magnetosheath ion flows and the flows of planetary ions behind both planets. We have shown that the general morphology of both magnetotails is generally identical. In both cases the energy of the light (H+) and the heavy (O+, etc.) ions decreases from the tail periphery (several keV) down to few eV in the tail center. At the same time the wake center of both planets is occupied by plasma sheet coincident with the current sheet of the tail. Both plasma sheets are filled by accelerated (500-1000 eV) heavy planetary ions. We report also the discovery of a new feature never observed before in the tails of non-magnetic planets: the plasma sheet is enveloped by consecutive layers of He+ and H+ with decreasing energies. 相似文献
30.
Y. Futaana S. Barabash S. McKenna-Lawlor J.G. Luhmann E. Carlsson J.D. Winningham P. Wurz H. Gunell W. Baumjohann J.R. Sharber H. Andersson K. Brinkfeldt K. Asamura A.J. Coates D.O. Kataria B.R. Sandel C. Mazelle M. Grande T. Sales P. Riihela N. Krupp M. Fränz S. Orsini A. Mura M. Maggi P. Brandt J. Scherrer 《Planetary and Space Science》2008,56(6):873-880
In December 2006, a single active region produced a series of proton solar flares, with X-ray class up to the X9.0 level, starting on 5 December 2006 at 10:35 UT. A feature of this X9.0 flare is that associated MeV particles were observed at Venus and Mars by Venus Express (VEX) and Mars Express (MEX), which were ∼80° and ∼125° east of the flare site, respectively, in addition to the Earth, which was ∼79° west of the flare site. On December 5, 2006, the plasma instruments ASPERA-3 and ASPERA-4 on board MEX and VEX detected a large enhancement in their respective background count levels. This is a typical signature of solar energetic particle (SEP) events, i.e., intensive MeV particle fluxes. The timings of these enhancements were consistent with the estimated field-aligned travel time of particles associated with the X9.0 flare that followed the Parker spiral to reach Venus and Mars. Coronal mass ejection (CME) signatures that might be related to the proton flare were twice identified at Venus within <43 and <67 h after the flare. Although these CMEs did not necessarily originate from the X9.0 flare on December 5, 2006, they most likely originated from the same active region because these characteristics are very similar to flare-associated CMEs observed on the Earth. These observations indicate that CME and flare activities on the invisible side of the Sun may affect terrestrial space weather as a result of traveling more than 90° in both azimuthal directions in the heliosphere. We would also like to emphasize that during the SEP activity, MEX data indicate an approximately one-order of magnitude enhancement in the heavy ion outflow flux from the Martian atmosphere. This is the first observation of the increase of escaping ion flux from Martian atmosphere during an intensive SEP event. This suggests that the solar EUV flux levels significantly affect the atmospheric loss from unmagnetized planets. 相似文献