Journal of Geophysical Research: Space Physics

When the Sun spews charged particles toward the Earth, they can enter the magnetosphere and become energized as they move closer to the Earth’s surface. These energetic particles can induce the bright colors of auroras, disrupt navigational satellites, and even distort terrestrial telecommunications. Previous research has found that the energization and transport of these particles—a process known as “particle injection”—may be correlated with the emergence of narrow, fast-flowing channels of Continue reading >

Researchers are learning more about the dynamics of Saturn’s magnetosphere by applying a technique that is commonly used to study Earth’s aurora. Using data from the magnetospheric imaging instrument on the Cassini spacecraft, Carbary and Mitchell tracked blobs of energetic neutral hydrogen atoms within Saturn’s magnetosphere by creating keograms—time versus latitude plots assembled from multiple images, providing an instantaneous global view of azimuthal speeds of the blobs. The energetic neut Continue reading >

The physical interactions that occur in the magnetosphere, from the collisions of high-energy particles in the ring current to the exchange of energy between the solar wind plasma and the electrons of the radiation belts, are explained by complex nonlinear physics. These physical dynamics are anisotropic processes—that is, the interactions are directionally dependent. Computer simulations of the magnetosphere, however, generally represent the physics isotropically—without considering the direct Continue reading >

Saturn has been observed to have periodic radio emissions known as Saturn kilometric radiation (SKR), as well as periodicities in its plasma and magnetic fields. These periodicities have puzzled scientists because they would be expected if the planet’s magnetic field was not aligned with its rotational axis, but Saturn’s magnetic field and rotational axis are, in fact, closely aligned. The puzzle is further complicated by the fact that the Saturn kilometric radiation has slightly different peri Continue reading >

Auroral arcs are a visible manifestation of space weather. A common dynamic observed during geomagnetically disturbed periods is the breakup of auroral arcs into a multitude of small-scale filaments less than 1-kilometer across. These filaments can move rapidly upward along the geomagnetic field lines. Dahlgren et al. observed such “auroral flames” during a breakup event on 1 March 2011, using an advanced high-speed optical system with sensitive low-light detectors. The data provide new insight Continue reading >

For the past few decades the upper reaches of Earth's atmosphere have been cooling much faster than researchers anticipated. While the rising atmospheric concentration of carbon dioxide is heating the air near the ground, that same increase is expected to cool the thermosphere—the atmospheric band that stretches from around 80 kilometers altitude to the exosphere at 500 kilometers—by emitting heat into space. But while carbon dioxide should theoretically cool the thermosphere by around 2 Kelvin Continue reading >

Magnetic field lines in the Earth’s dayside magnetic field can be broken down and swept to the Earth’s nightside by the solar wind. The magnetic field lines reconnect in the magnetotail, in some cases triggering a magnetic substorm. During a substorm, plasma trapped in the magnetotail is sent flowing toward the Earth, and the magnetotail current sheet—the region where magnetic field lines from the Earth’s North and South Poles come together—gets thinner. This thinning of the current sheet can Continue reading >

The ring current that circles the Earth a few Earth radii above the surface consists of energetic ions and electrons and plays an important role in the space environment. During geomagnetic storms, the flow in the ring current rises dramatically. The behavior of the ring current and other features of the inner magnetosphere depend strongly on conditions in other regions of the magnetosphere. The small scale of the particle dynamics that drive the ring current, as compared to the vast spatial sc Continue reading >

Myriametric radio emissions—radio emissions with wavelengths of 10 to 100 kilometers—coming from Earth’s magnetosphere have been observed previously. Now, a new type of myriametric radio emission known as a terrestrial myriametric radio burst (TMRB) has been reported. Fung et al. report simultaneous detection of a TMRB by the widely separated Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) and Geotail satellites on 19 August 2001. The radio burst occurred over a period of about an Continue reading >

Periodic radio emissions, including the strong radio emissions known as the Saturn kilometric radio (SKR) emissions, originate from the northern and southern polar regions and are observed throughout Saturn’s magnetosphere. Scientists have been studying these phenomena but have not been able to pin down the physical mechanism linking periodicities between the inner and outer magnetospheres. One proposed mechanism is a process known as the centrifugal interchange instability, which occurs in ra Continue reading >

The physical process that creates connections between the magnetic fields emanating from the Sun and a planet-a process known as magnetic reconnection-creates a portal through which solar plasma can penetrate the planetary magnetic field. The opening of these portals, known as flux transfer events (FTEs), takes place roughly every 8 minutes at Earth and spawns a rope of streaming plasma that is typically about half of the radius of the Earth in diameter. As early as 1985, scientists analyzing t Continue reading >

Thought to be produced by convection deep within the planet's interior, Saturn's magnetic field stands out among those of the solar system's gas giants in that it has a relatively simple structure and that it is nearly perfectly symmetrical about the planet's rotation axis. However, researchers have noticed some recurring anomalies: periodic changes in plasma density, magnetic field, energetic particle populations, emitted radiation, plasma sheet properties, and others. Analyzing these periodic Continue reading >

As they near the outer reaches of the solar system, for the past several years the two Voyager spacecraft have been sending back observations that challenge scientists' views of the physics at the edge of the heliosphere, the bubble created by charged particles flowing outward from the Sun. A new study looks at magnetic field fluctuations and cosmic ray intensity observed by Voyager 1. In 2004, Voyager I crossed the termination shock, the region where the solar wind begins to slow as it interac Continue reading >

The injection of high-energy particles into the inner magnetotail is often considered a reliable sign of a magnetic substorm. These injections are often thought to be caused by flow bursts, short-lived periods of narrow fast flow streams in the magnetotail. Analyzing records of flow bursts at the entry to the night-side inner magnetosphere, from 8 to 13 Earth radii, as seen by Geotail from 1995 to 2005, and by the Time History of Events and Macroscale Interactions During Substorms (THEMIS) sate Continue reading >

Human society is increasingly reliant on technology that can be disrupted by space weather. For instance, geomagnetic storms can cause high-latitude air flights to be rerouted, costing as much as $100,000 per flight; induce errors of up to 46 m in GPS systems; and affect satellites and the International Space Station. Space weather is determined by how the solar wind, a stream of hot plasma from the Sun, interacts with Earth's magnetic field. In studying space weather, scientists have largely n Continue reading >

At midlatitudes in the ionosphere, just below the auroral region, narrow channels of strong westward flow have been observed. These flows, known as subauroral polarization streams (SAPS), are driven by pressure gradients in near-Earth space and are a manifestation of the coupling between the upper atmosphere and the magnetosphere. To better understand these flows, Clausen et al. (2012) measured the flow velocities inside a SAPS using the new midlatitude chain of Super Dual Auroral Radar Network Continue reading >

Enceladus, which orbits Saturn in the planet's E ring, is one of the few geologically active moons in the outer solar system. It emits a large plume that contains water-ice dust grains. Hill et al. (2012) used instruments on the Cassini spacecraft to observe charged nanometer sized grains of water ice emanating from Enceladus. They measured the charge to mass ratio of each grain and found that the most likely charge per grain is 1 electron charge. In addition, negatively charged grains outnumbe Continue reading >

The onslaught of the solar wind on the Sun-facing side of Earth's magnetic field causes terrestrial magnetic field lines to break through magnetic reconnection. The persistent pressure of the solar wind pulls the field lines and the associated plasma around to the magnetotail on Earth's nightside, where magnetic reconnection occurs once again to form the plasma sheet region. This uneven distribution creates a pressure gradient that drives nightside plasma back toward the planet. The Earthward t Continue reading >

Researchers working with NASA's Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) spacecraft report the frequent detections of Kelvin-Helmholtz (KH) waves at the edge of the innermost planet's magnetosphere. In six different sets of magnetic field measurements made by the orbiter as it passed through Mercury's magnetopause, the boundary that separates the planet's magnetosphere from the solar wind plasma in the magnetosheath, Sundberg et al. (2012) detected the magnetic Continue reading >

Prebreakup arcs (PBAs), thin, faint tendrils of glowing gas stretching thousands of kilometers in either direction, are very different from the multicolored lights typically associated with auroras. PBAs develop a few minutes before the onset of the full display, brightening and expanding ('breaking up') to form the more prominent auroras. Previous research has shown that the breakup of the PBA can be tied to brief pulses of energetic particles (auroral substorms) flowing into the upper atmosph Continue reading >