Surface functional groups constitute major electroactive components in pyrogenic carbon. However, the electrochemical properties of pyrogenic carbon matrices and the kinetic preference of functional groups or carbon matrices for electron transfer remain unknown. Here we show that environmentally relevant pyrogenic carbon with average H/C and O/C ratios of less than 0.35 and 0.09 can directly transfer electrons more than three times faster than the charging and discharging cycles of surface functional groups and have a 1.5 V potential range for biogeochemical reactions that invoke electron transfer processes. Surface functional groups contribute to the overall electron flux of pyrogenic carbon to a lesser extent with greater pyrolysis temperature due to lower charging and discharging capacities, although the charging and discharging kinetics remain unchanged. This study could spur the development of a new generation of biogeochemical electron flux models that focus on the bacteria–carbon–mineral conductive network.

The impact of geomagnetically induced currents (GICs) on the power networks at middle and low latitudes has attracted attention in recent years with the increase of large-scale power networks. In this study, we report the GIC monitored at two low-latitude 500 kV substations of China during the large storm of 17 March 2015. The GIC due to the storm sudden commencement (SSC) was much higher than that during the storm main phase. This phenomenon is more likely to happen at low-latitude locations, highlighting the importance of SSC in inducing GIC in low-latitude power networks. Furthermore, we ran a global MHD model to simulate the GIC during this SSC event by using the solar wind observation as input. The model results reproduced the main features of the GIC. The study also indicated that the eastward component of the geoelectric field is dominant for low-latitude locations during the SSC events. Further, topology and electrical parameters of the power grids make significant differences in the GIC levels.

Impressive images from the Hubble Space Telescope not only help scientists understand our universe, but also enhance public interest in science, becoming a gateway for the youngest generation to enter Science, Technology, Engineering, and Mathematics (STEM) fields. Heliophysics observatories can also provide dramatic images of our space environment. The Solar and Heliospheric Observatory (SOHO; Domingo et al., 1995) images the dynamic activities of our Sun and its solar corona. Solar Terrestrial Relation Observatory (STEREO; Kaiser et al., 2008) monitors solar wind features propagating through interplanetary space. Imager for Magnetopause-to-Aurora Global Exploration (IMAGE; Burch, 2000) and Two Wide-Angle Imaging Neutral-Atom Spectrometers (TWINS; Goldstein & McComas, 2018) display the activities of the Earth's inner-magnetosphere in response to varying solar wind conditions. Time History of Events and Macroscale Interactions during Substorms (THEMIS) All Sky Imagers (ASI) distributed over the northern portions of North America (Mende et al., 2008) image aurora precipitation resulting from magnetospheric activities. The one missing image is the dayside magnetosphere, the starting point for the solar wind-magnetosphere interaction.

No abstract

Imaging magnetospheric satellite missions provide information, which is complementary to in situ observations. Imaging is often able to provide an instantaneous picture of large-scale structures, whereas in situ measurements, even multipoint in situ measurements, can only provide an average view of large-scale structure. But imaging also presents some challenges. When three-dimensional structures need to be extracted from two-dimensional images, it is necessary to either make suitable assumptions or record a large enough number of images from different viewing geometries to allow a reconstruction (e.g., tomography). Imaging data exist over a wide range of sources including visible light, ultraviolet light, extreme ultraviolet, energetic neutral atoms, and X-rays, each informing different physical mechanisms. In this paper we consider the extraction of the geometry of the magnetopause and the bow shock from single X-ray images expected from the Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) mission. We examine the effect of photon-counting noise in determining the boundary geometries. We also consider the effect of different viewing geometries in the form of orbital vantage point and target look direction. Finally, we consider the effect of background noise. We find that our approach is relatively robust to viewing geometry effects and works at low count rates.

[1] Observations show that the geosynchronous magnetic field in midnight sector sometimes decreases when an interplanetary (IP) fast forward shock (FFS) passes Earth, even though the magnetosphere is always compressed. We perform case studies of the response observed by the GOES spacecraft at geosynchronous orbit near midnight to two IP shocks passing Earth. One shock produces a decrease in B Z (a negative response) and the other an increase in B Z (a positive response). A global 3D MHD code is run to reproduce the responses at geosynchronous orbit, and to further provide information on the initiation and development of B Z variations in the entire magnetosphere. The model reveals that when a FFS sweeps over the magnetosphere, there exist mainly two regions, a positive response region caused by the compressive effect of the shock and a negative response region which is probably associated with the temporary enhancement of earthward convection in the nightside magnetosphere. The spacecraft may observe an increase or decrease of the magnetic field depending on which region it is in. The numerical results reproduce the main characters of the geosynchronous magnetic field response to IP shocks for these two typical cases.Citation: Wang, C., T. R. Sun, X. C. Guo, and J. D. Richardson (2010), Case study of nightside magnetospheric magnetic field response to interplanetary shocks,

The soft X-ray emissions from the Earth's magnetosheath and cusp regions are simulated under different solar wind conditions, based on the PPMLR-MHD code. The X-ray images observed by a hypothetical telescope are presented, and the basic responses of the magnetopause and cusp regions are discernable in these images. From certain viewing geometries, the magnetopause position in the equatorial plane, as well as the latitudinal scales and azimuthal extent of cusp can be directly extracted from the X-ray images. With these reconstructed positions, the issues we are able to analyze include but are not limited to the compression of magnetopause and widening of the cusp after an enhancement of solar wind flux, as well as the erosion of the magnetopause and equatorward motion of cusp after the southward turning of the interplanetary magnetic field. Hence, the X-ray imaging is an appropriate technique to study the large-scale motion of magnetopause and cusps in response to solar wind variations.Recently, a novel approach was proposed to remotely detect the large-scale magnetopause: soft X-ray imaging (Branduardi-Raymont et al., 2012Collier et al., 2012;Sibeck et al., 2018;Walsh et al., 2016). The basic mechanism for soft X-ray emissions in the magnetosheath and cusp regions is the solar wind charge exchange (SWCX) process. On the one hand, heavy ions in high charge states, such as O 7+ , exist in the ambient solar wind. On the other hand, neutral atoms and molecules, such as the hydrogen, are ubiquitous in the geospace environment due to the Earth's exosphere. When they encounter and interact with each other, an electron can be transferred from the neutral to the ion. As a result of capturing the electron, the solar wind ion is in an electronically excited state, and then emits one or more photons in the extreme ultraviolet or soft X-ray bands while decaying to the lower-energy state. In the magnetosheath, the density of the highly charged ions is enhanced as the solar wind slows down after the bow shock. The solar wind cannot directly penetrate the magnetopause, and thus, the plasma with solar wind origin is quite tenuous inside the magnetosphere. This leads to a sharp boundary at the magnetopause in terms of the soft X-ray emissivity. The cusps are special regions on the magnetopause. The solar wind plasma can enter directly, and thus, the X-ray emissivity is expected to be higher inside of the cusps. With different solar wind fluxes and/or interplanetary magnetic fields (IMF), the X-ray emissivity in the magnetosheath and cusps can be

Pyrogenic carbon contains redox-active functional groups and polyaromatic carbon matrices that are both capable of transferring electrons. Several techniques have been explored to characterize the individual electron transfer process of either functional groups or carbon matrices individually. However, simultaneous analysis of both processes remains challenging. Using an approach that employs a four-electrode configuration and dual-interface electron transfer detection, we distinguished the electron transfer by functional groups from the electron transfer by carbon matrices and simultaneously quantified their relative contribution to the total electron transfer to and from pyrogenic carbon. Results show that at low to intermediate pyrolysis temperatures (400-500 °C), redox cycling of functional groups is the major mechanism with a contribution of 100-78% to the total electron transfer; whereas at high temperatures (650-800 °C), direct electron transfer of carbon matrices dominates electron transfer with a contribution of 87-100%. Spectroscopic and diffraction analyses of pyrogenic carbon support the electrochemical measurements by showing a molecular-level structural transition from an enrichment in functional groups to an enrichment in nanosized graphene domains with increasing pyrolysis temperatures. The method described in this study provides a new analytical approach to separately quantify the relative importance of different electron transfer pathways in natural pyrogenic carbon and has potential applications for engineered carbon materials such as graphene oxides.