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Register a new userCold prominence materials detected within magnetic clouds during 1998-2007
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Coronal mass ejections (CMEs) are intense solar explosive eruptions, and they are frequently correlated with prominence eruptions. Previous observations show that about $70%$ of CMEs are associated with prominence eruptions. However, there are only a handful of reported observations of prominence plasma materials within interplanetary CMEs (ICMEs), which are the interplanetary manifestations of CMEs. Moreover, approximately $4%$ of ICMEs exhibit the presence of prominence materials, and approximately $12%$ of magnetic clouds (MCs) contain prominence materials. We aim to comprehensively search for cold prominence materials in MCs observed by the Advanced Composition Explorer (ACE) spacecraft during 1998-2007. Using the criteria of unusual $O^{5+}$ and (or) $Fe^{6+}$ abundances, we examined 76 MCs observed by ACE during 1998-2007 to search for cold prominence materials. Our results revealed that out of the 76 MCs, 27 ($36%$) events contained prominence material regions with low-charge-state signatures. Although the fraction is still lower than the approximately $70%$ of CMEs associated with prominence eruptions, it is much higher than $12%$. The unusual $O^{5+}$ and (or) $Fe^{6+}$ abundances may be simple and reliable criteria to investigate prominence materials in the interplanetary medium.
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Previous studies indicate that interplanetary small magnetic flux ropes (SMFRs) are manifestations of microflare-associated small coronal mass ejections (CMEs), and the hot material with high charge states heated by related microflares are found in SMFRs. Ordinary CMEs are frequently associated with prominence eruptions,and cool prominencematerialsare found within some magnetic clouds (MCs). Therefore, the predicted small CMEs may also be frequently associated with small prominence eruptions. In this work, we aim to search for cool prominence materials within SMFRs.We examined all the O5+ and Fe6+ fraction data obtained by the Advanced Composition Explorer spacecraft during 1998 to 2008 and found that 13 SMFRs might exhibit low-charge-state signatures of unusual O5+and/or Fe6+abundances.One of the 13 SMFRs also exhibited signatures of high ionic charge states. We also reported a SMFR with highFe6+ fraction, but the values of Fe6+is a little lower than the threshold defining unusualFe6+.However, the SDO/AIA observations confirmed that the progenitor CME of this SMFR is associated with a small eruptive prominence, and the observations also supported the prominence materials were embedded in the CME.These observations are at the edge of the capabilities of ACE/SWICS and it cannot be ruled out that they are solely caused by instrumental effects. If these observations are real, they provide new evidence for the conjecture that SMFRs are small-scale MCs but also imply that the connected small CMEs could be associated with flares and prominence eruptions.
Low-energy ions of ionospheric origin constitute a significant contributor to the magnetospheric plasma population. Measuring cold ions is difficult though. Observations have to be done at sufficiently high altitudes and typically in regions of space where spacecraft attain a positive charge due to solar illumination. Cold ions are therefore shielded from the satellite particle detectors. Furthermore, spacecraft can only cover key regions of ion outflow during segments of their orbit, so additional complications arise if continuous longtime observations, such as during a geomagnetic storm, are needed. In this paper we suggest a new approach, based on a combination of synoptic observations and a novel technique to estimate the flux and total outflow during the various phases of geomagnetic storms. Our results indicate large variations in both outflow rates and transport throughout the storm. Prior to the storm main phase, outflow rates are moderate, and the cold ions are mainly emanating from moderately sized polar cap regions. Throughout the main phase of the storm, outflow rates increase and the polar cap source regions expand. Furthermore, faster transport, resulting from enhanced convection, leads to a much larger supply of cold ions to the near-Earth region during geomagnetic storms.
A large amount of magnetized plasma is frequently ejected from the Sun as coronal mass ejections (CMEs). Some of these ejections are detected in the solar wind as magnetic clouds (MCs) that have flux rope signatures. Magnetic clouds are structures that typically expand in the inner heliosphere. We derive the expansion properties of MCs in the outer heliosphere from one to five astronomical units to compare them with those in the inner heliosphere. We analyze MCs observed by the Ulysses spacecraft using insitu magnetic field and plasma measurements. The MC boundaries are defined in the MC frame after defining the MC axis with a minimum variance method applied only to the flux rope structure. As in the inner heliosphere, a large fraction of the velocity profile within MCs is close to a linear function of time. This is indicative of} a self-similar expansion and a MC size that locally follows a power-law of the solar distance with an exponent called zeta. We derive the value of zeta from the insitu velocity data. We analyze separately the non-perturbed MCs (cases showing a linear velocity profile almost for the full event), and perturbed MCs (cases showing a strongly distorted velocity profile). We find that non-perturbed MCs expand with a similar non-dimensional expansion rate (zeta=1.05+-0.34), i.e. slightly faster than at the solar distance and in the inner heliosphere (zeta=0.91+-0.23). The subset of perturbed MCs expands, as in the inner heliosphere, at a significantly lower rate and with a larger dispersion (zeta=0.28+-0.52) as expected from the temporal evolution found in numerical simulations. This local measure of the expansion also agrees with the distribution with distance of MC size,mean magnetic field, and plasma parameters. The MCs interacting with a strong field region, e.g. another MC, have the most variable expansion rate (ranging from compression to over-expansion).
The twisted local magnetic field at the front or rear regions of the magnetic clouds (MCs) associated with interplanetary coronal mass ejections (ICMEs) is often nearly opposite to the direction of the ambient interplanetary magnetic field (IMF). There is also observational evidence for magnetic reconnection (MR) outflows occurring within the boundary layers of MCs. In this paper a MR event located at the western flank of the MC occurring on 2000-10-03 is studied in detail. Both the large-scale geometry of the helical MC and the MR outflow structure are scrutinized in a detailed multi-point study. The ICME sheath is of hybrid propagation-expansion type. Here the freshly reconnected open field lines are expected to slip slowly over the MC resulting in plasma mixing at the same time. As for MR, the current sheet geometry and the vertical motion of the outflow channel between ACE-Geotail-WIND spacecraft was carefully studied and tested. The main findings on MR include: (1) First-time observation of non-Petschek-type slow-shock-like discontinuities in the inflow regions; (2) Observation of turbulent Hall magnetic field associated with a Lorentz force deflected electron jet; (3) Acceleration of protons by reconnection electric field and their back-scatter from the slow shock-like discontinuity; (4) Observation of relativistic electron near the MC inflow boundary/separatrix; these electron populations can presumably appear as a result of non-adiabatic acceleration, gradient B drift and via acceleration in the electrostatic potential well associated with the Hall current system; (5) Observation of Doppler shifted ion-acoustic and Langmuir waves in the MC inflow region.
The relationship between magnetic reconnection and plasma turbulence is investigated using multipoint in-situ measurements from the Cluster spacecraft within a high-speed reconnection jet in the terrestrial magnetotail. We show explicitly that work done by electromagnetic fields on the particles, $mathbf{J}cdotmathbf{E}$, has a non-Gaussian distribution and is concentrated in regions of high electric current density. Hence, magnetic energy is converted to kinetic energy in an intermittent manner. Furthermore, we find the higher-order statistics of magnetic field fluctuations generated by reconnection are characterized by multifractal scaling on magnetofluid scales and non-Gaussian global scale invariance on kinetic scales. These observations suggest $mathbf{J}cdotmathbf{E}$ within the reconnection jet has an analogue in fluid-like turbulence theory in that it proceeds via coherent structures generated by an intermittent cascade. This supports the hypothesis that turbulent dissipation is highly nonuniform, and thus these results could have far reaching implications for space and astrophysical plasmas.
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