ALBERT

Description: Ideally, the sources of type III solar radio bursts, which are produced mainly by flare-accelerated electron beams, trace the magnetic field lines along which the beams propagate from the Sun to interplanetary space. A recently developed 2-D approach for large-scale mapping of magnetic field lines between the Sun and Earth in the solar equatorial plane is applied to the sources of the 7 April 1995 type III radio burst imaged by Ulysses and Wind. The approach uses near-Earth solar wind data and a solar wind model with intrinsic non-radial magnetic field at the source surface of the solar wind. Quantitative agreement is found between the mapped field lines, the observed path of the radio source centroids, and the field configurations inferred from solar wind suprathermal electrons observed by Wind. Moreover, the mapped field lines are consistent with Wind not observing the in situ type III electron beam, Langmuir waves, and local radio emission for this type III event.

Description: The statistical altitude distribution of auroral density cavities located between 3.0 to 6.5 R E is investigated using in-situ observations from flux tubes exhibiting auroral acceleration. The locations of the observations are described using a pseudo altitude derived from the distribution of the parallel potential drop above and below the satellite. The upper edge of the auroral acceleration region is observed between 4.375 and 5.625 R E . Above 6.125 R E , noneof the events exhibits precipitating inverted-V electrons, though the upward ion beam can be observed. This indicates that the satellites are located inside the same flux tube as, but above, the auroral acceleration region. The electron density decreases as we move higher into the acceleration region. The spacecraft potential continues to decrease once above the acceleration region, indicating that the density cavity extends above the acceleration region. From 3.0 to 4.375 R E the pseudo altitude increases by 0.20 per R E , consistent with a distributed parallel electric field. Between 4.375 and 5.625 R E the pseudo altitude increases weakly, by 0.01 per R E , due to an increasing number of events per altitude bin, which are occurring above the acceleration region. Above 5.625 R E the pseudo altitude increases by 0.28 per R E , due to a rapid increase in the number of events per altitude bin occurring above the acceleration region, indicating that the remaining parallel potential drop is concentrated in a narrow region at the upper edge of the acceleration region, rather than in a distributed parallel electric field.

Description: As the most populated region of the world, Asia is a major source of aerosols with potential large impact over vast downstream areas. Papers published in this special section describe the variety of aerosols observed in China and their effects and interactions with the regional climate as part of the East Asian Study of Tropospheric Aerosols and their Impact on Regional Climate (EAST-AIRC). The majority of the papers are based on analyses of observations made under three field projects, namely, the Atmospheric Radiation Measurements (ARM) Mobile Facility mission in China (AMF-China), the East Asian Study of Tropospheric Aerosols: An International Regional Experiment (EAST-AIRE), and the Atmospheric Aerosols of China and their Climate Effects (AACCE). The former two are U.S.-China collaborative projects, and the latter is a part of the China's National Basic Research program (or often referred to as “973 project”). Routine meteorological data of China are also employed in some studies. The wealth of general and specialized measurements lead to extensive and close-up investigations of the optical, physical, and chemical properties of anthropogenic, natural, and mixed aerosols; their sources, formation, and transport mechanisms; horizontal, vertical, and temporal variations; direct and indirect effects; and interactions with the East Asian monsoon system. Particular efforts are made to advance our understanding of the mixing and interaction between dust and anthropogenic pollutants during transport. Several modeling studies were carried out to simulate aerosol impact on radiation budget, temperature, precipitation, wind and atmospheric circulation, fog, etc. In addition, impacts of the Asian monsoon system on aerosol loading are also simulated.

Description: Results are presented from a statistical study of high-altitude electric fields and plasma densities using Cluster satellite data collected during 9.5 years between 2 and 4 R E . The average electric fields are most intense on the night-side and associated with an extensive plasma density cavity, with densities of 1 cm -3 or less. The intense electric fields are concentrated in two regions, separated by an altitude gap at about 2.8 R E . Below this, the average electric field magnitudes reach about 50 mV/m (mapped to the ionosphere) between 22 and 01 Magnetic Local Time (MLT). Above 3 R E , the fields are about twice as high, and spread over a broader MLT range. These fields occur in a region where the (ΔE/ΔB)/V A ratio is close to unity, which suggests an Alfvénic origin. The intense low-altitude electric fields are interpreted to be quasi-static, associated with the auroral acceleration region. This is supported by their location in MLT and altitude, and by a (ΔE/ΔB)/V A ratio much below unity. The local electric field minimum between the two regions indicates a partial closure of the electrostatic potentials in the lower region. These results show similarities with model results of reflected Alfvén waves by Lysak and Dum [1983], and with the O-shaped potential model, with associated wave-particle interaction at its top, proposed by Janhunen et al., [2000].

Description: In this paper, a c m -model is proposed to quantify structural states of soft mudrocks, which are dependent on clay fractions and porosities. Physical properties of natural and reconstituted soft mudrock samples are used to derive two parameters in the c m -model. With the c m -model, a simplified homogenization approach is proposed to estimate geomechanical properties and fabric orientation distributions of soft mudrocks based on the mixture theory. Soft mudrocks are treated as a mixture of non-clay minerals and clay-water composites. Non-clay minerals have a high stiffness and serve as a structural framework of mudrocks when they have a high volume fraction. Clay-water composites occupy the void space among non-clay minerals and serve as an in-fill matrix. With the increase of volume fraction of clay-water composites, there is a transition in the structural state from the state of framework-supported to the state of matrix-supported. The decreases in shear strength and pore size as well as increases in compressibility and anisotropy in fabric are quantitatively related to such transition. The new homogenization approach based on the proposed c m -model yields better performance evaluation than common effective medium modeling approaches because the interactions among non-clay minerals and clay-water composites are considered. With wireline logging data, the c m -model is applied to quantify the structural states of Colorado shale formations at different depths in the Cold Lake area, Alberta, Canada. Key geomechancial parameters are estimated based on the proposed homogenization approach and the critical intervals with low strength shale formations are identified.

Description: In the solar wind, magnetic field power spectra usually show several power-laws. In this paper, magnetic field data from the Cluster mission during an undisturbed interval of slow solar wind is analyzed at 0.28 Hz, near the spectral break point between the ion inertial and dissipation/dispersion ranges. Assuming Taylor's frozen-in condition, it corresponds to a proton kinetic scale of k v A / Ω p ∼0.38, where v A and Ω p are the Alfvén speed and proton angular gyrofrequency, respectively. Data show that the Cluster spacecraft passed through a series of wavepackets. A strong isolated wavepacket is found to be in accordance with the four Cluster satellites crossing an Alfvén vortex, a nonlinear solution to the incompressible MHD equations. A strong agreement is seen between the data from four satellites and a model vortex with a radius of the order of 40 times the local proton gyro-radii. The polarization at different spacecraft is compared and is found to agree with the vortex model, whereas it cannot be explained solely by the linear plane wave approach.

Description: The nature of turbulence, dissipation, and heating in plasma media has been an attractive and challenge problem in space physics as well as in basic plasma physics. A wide continuous spectrum of Alfvénic turbulence from large MHD-scale Alfvén waves (AWs) in the inertial turbulence regime to small kinetic-scale kinetic AWs (KAWs) in the dissipation turbulence regime is a typical paradigm of plasma turbulence. The incorporation of current remote observations of AWs in the solar atmosphere, in situ satellite measurements of Alfvénic turbulence in the solar wind, and experimental investigations of KAWs on large plasma devices in laboratory provides a chance synthetically to study the physics nature of plasma turbulence, dissipation, and heating. A session entitled “ Nature of Turbulence, Dissipation, and Heating in Space Plasmas: From Alfvén Waves to Kinetic Alfvén Waves ” was held as a part of the 12th AOGS (Asia Oceania Geosciences Society) Annual Meeting, which took place in Singapore between 2 and 7 August 2015. This special section is organized based on the session.

Description: Large-scale magnetic field configurations are important for the transport of solar wind strahl electrons, which are suprathermal and directed along the field outwards from the Sun. Strahl electrons are routinely used to infer not only the field configurations between the Sun and Earth but also local field structures, i.e., field inversions, where the magnetic field is locally folded back or inverted. Using solar wind data from ACE observations and a 2-D data-driven solar wind model with nonzero azimuthal magnetic field at the solar wind source surface, magnetic field lines are mapped between the Sun and Earth and beyond, in the solar equatorial plane. Standard verification metrics are used to assess, for 5 solar rotations at different phases of solar cycle 23, the performance of the mapping predictions for observed inversions, which are inferred from solar wind suprathermal electrons and magnetic fields measured by ACE. The probability of detection is consistently ≈0.70 across the different phases. The success ratio, the Hanssen-Kuipers skill score, and the Heidke skill score are ≈0.55 − 0.70 for the 4 rotations in the rising, solar maximum, and declining phases; but ≈0.35 − 0.60 for the rotation near solar minimum, during which almost half of the samples have undetermined field configurations. Our analyses confirm the persistence of inversions throughout solar cycle 23, suggest for most observed inversions a solar/coronal origin at the wind's source surface or below, and predict inversions should be less common for larger heliocentric distance r ≳ 3 AU than for smaller r .

Description: Magnetic field topologies between the Sun and Earth are important for the connectivity to Earth of solar suprathermal particles, e.g., solar energetic particles and beam electrons in type III solar radio bursts. An approach is developed for mapping large-scale magnetic field lines near the solar equatorial plane, using near-Earth observations and a solar wind model with nonzero azimuthal magnetic field at the source surface. Unlike Parker's spiral model, which restricts the in-ecliptic angle Φ B in the Geocentric Solar Ecliptic coordinates to (90° − 180°, 270° − 360°), and so is unable to predict field configurations for the other Φ B values frequently observed in the solar wind, our approach can account for all the observed Φ B values. A set of predicted maps show that near both minimal and maximal solar activity the field lines are typically open and that loops with both ends either connected to or disconnected from the Sun are relatively rare. The open field lines, nonetheless, often do not closely follow the Parker spiral, being less or more tightly wound, or strongly azimuthally or radially oriented, or inverted. The time-varying classes, e.g., bidirectional electrons, of suprathermal electron pitch angle distributions (PADs) at 1 AU are predicted from the mapped field line configurations and compared with Wind observations for two solar rotations, one each near solar minimum and solar maximum. PAD predictions by our approach agree quantitatively (≈ 90%) with the PAD observations and outperform (by ≈ 20%) PAD predictions using Parker's model.