ALBERT

Description: Electron measurements on board six spacecraft in geosynchronous orbit are superposed-epoch analyzed for 42 high-speed-stream-driven storms. Using pitch angle–resolved fluxes in the range 30 keV to 1.7 MeV, the evolution of the outer electron radiation belt and the suprathermal tail of the electron plasma sheet are studied. The outer electron radiation belt exhibits perpendicular-dominated anisotropies on the dayside and parallel-dominated anisotropies on the nightside consistent with shell splitting in a distorted magnetosphere. The magnitudes of the radiation-belt anisotropies are weak prior to storm onset and become very large during the storms. The magnitudes of the anisotropies lessen with time as the storm ages and the radiation belt heats, probably owing to a weakening of the magnetic field distortion as the storm ages. When a calm before the storm occurs, the dayside radiation belt approaches isotropy, probably owing to pitch angle scattering in the outer plasmasphere that fills during the calm. If no calm before the storm occurs, the dayside radiation belt is strongly perpendicular dominated. The local-time pattern of anisotropy in storms is very different for the suprathermal tail of the electron plasma sheet, which tends to be perpendicular on the nightside and isotropic elsewhere. The magnitudes of the anisotropies of the suprathermal tail are a factor of ∼10 weaker than the anisotropies of the outer electron radiation belt.

Description: While the average ion mass M (normalized to amu) of bulk plasma at geosynchronous orbit has been calculated at solar maximum (during the era of the Combined Release and Radiation Effects Satellite (CRRES)), the solar cycle dependence of bulk ion composition at geosynchronous orbit is not known. Here, we use measurements of mass density ρm from Alfvén wave frequencies measured by the Geostationary Operational Environmental Satellites and ion density measurements by the Magnetospheric Particle Analyzer (MPA) on Los Alamos National Laboratory (LANL) spacecraft to establish the solar cycle dependence of bulk ion composition. We show that there is a strong correlation between the yearly median value of ρm, ρm,yr−med, and the yearly average of the solar EUV flux F10.7, F10.7,yr−av; log10(ρm,yr−med) $\simeq$ 0.5089 + 0.003607F10.7,yr−av (for ρm values adjusted to a magnetic latitude MLAT of 8°). We calibrate the measurements of the MPA instrument on one spacecraft to those from another by using yearly median density values. Then, using close conjunctions of LANL spacecraft with CRRES (for which we have inferred values of ρm and ne), we calibrate the ideal theoretical value of MPA ion density nMPA−th (the value that MPA would measure if it measured all the ions) to the observed values directly measured by the instrument, nMPA−obs. We find that nMPA−th is approximately 1.47 times the value of nMPA−obs measured by the LANL 1994 spacecraft. Using the yearly median values of ρm as a function of F10.7, the yearly median values of nMPA−th from the MPA instruments, and a model for the concentration of He+, we are able to calculate the solar cycle dependence of the average ion mass M and the O+ concentration ηO+ ≡ nO+/ne. We find that M is typically ∼3.8 at solar maximum and near unity at solar minimum. Typical values of ηO+ vary by 2 orders of magnitude over the solar cycle, from about 0.2 at solar maximum to ∼2 × 10−3 at solar minimum. Furthermore, our results also demonstrate that the typical concentration of He+ must also be very low at solar minimum. Since the median yearly values of density are low, characteristic of the plasma trough, our results are most applicable to that region. Considering, however, that the plasmasphere and plume typically have a low concentration of O+, the concentration of O+ at geosynchronous orbit at solar minimum is likely to be low for all conditions (with the possible exception of very low densities for which the high-energy component might dominate).

Description: Palaeoclimate: East Antarctic retreat Nature Geoscience 4, 135 (2011). doi:10.1038/ngeo1096 Author: George H. Denton The contribution of the East Antarctic ice sheet to the 120 m of sea-level rise since the Last Glacial Maximum is unclear. New terrestrial and marine data suggest the thinning of East Antarctic ice was responsible for only a metre of this rise.

Description: Electron precipitation from the Earth's inner magnetosphere transmits solar variability to the Earth's upper atmosphere and may affect surface level climate. Here we conduct a superposed epoch analysis of energetic electrons observed by the NOAA POES spacecraft during 42 high-speed solar wind stream (HSS) driven geomagnetic storms to determine the temporal evolution and global distribution of the precipitating flux. The flux of trapped and precipitating E 〉 30 keV electrons increases immediately following storm onset and remains elevated during the passage of the HSS. In contrast, the trapped and precipitating relativistic electrons (E 〉 1 MeV) drop out following storm onset and subsequently increase during the recovery phase to levels which eventually exceed the prestorm levels. There is no evidence for enhanced precipitation of relativistic electrons during the MeV flux drop out, suggesting that flux drop outs during the main phase of HSS-driven storms are not due to precipitation to the atmosphere. On average, the flux of precipitating E 〉 30 keV electrons is enhanced by a factor of ∼10 during the passage of the high-speed stream at all geographic longitudes. In contrast, the precipitating relativistic electron count rate is observed to peak in the region poleward of the South Atlantic Anomaly. During the passage of the high-speed stream, the flux of precipitating E 〉 30 keV electrons peaks in the region from 2100 to 1200 magnetic local time at low L (4 〈 L 〈 7) and in the prenoon sector at high L (7 〈 L 〈 9), suggesting that chorus waves are responsible for the precipitation of E 〉 30 keV electrons in both regions.

Description: This chapter reviews the origin and fate of sulfur (S) in silicate melts in the solar system, experiments bearing on the role of S in element partitioning among melts and solids in planets, and finally our current understanding of silicate melts and the role of sulfur in planetary evolution. Sulfur is an important component of undifferentiated meteorites that are precursors to planets. When planetary bodies differentiated into cores and mantles, metal and/or sulfides were removed from silicates. This process can be traced. Then, iron-sulfide cores differentiated into metal and metal-sulfide fractions, some of which are preserved as iron meteorites. The iron meteorites probably fractionated from silicate mantles at much lower pressures than the cores of Earth or Mars. Understanding the role of sulfur in silicate melts is critical to unraveling the history of Earth, the terrestrial planets, and the differentiated asteroids that were once parts of early planetesimals. COSMOCHEMISTRY OF SULFUR Silicate melts and sulfur in primitive source materials Primitive extraterrestrial samples available for laboratory study include 1–20 µm cometary grains collected by the United States’ (NASA) Stardust mission, asteroidal material collected by the Japanese (JAXA) Hyabusa mission, interplanetary dust particles (IDPs) collected from the stratosphere by airplanes, micrometeorites from various collection sites, and meteorites that fall to Earth and are recovered. Sources of primitive meteorites are parent bodies, primarily asteroids, that did not differentiate into silicate mantles and metal-rich cores. The oldest dated solar system rocks are not bulk meteorites, but are the high-temperature, melted components of undifferentiated meteorites, which are a kind of cosmic sedimentary rock. These "chondritic" meteorites are slightly younger than the components that accreted to form them. They have atomic ratios of rock-forming elements (e.g., Fe/Si) that are very similar to those measured in the solar photosphere using spectroscopy. The "primitive" nature of meteorites is established by their radiometric ages, and their lack of aqueous and...

Description: For 15 high-speed-stream-driven geomagnetic activations (weak storms) in 2006–2007, the temporal behaviors of the outer electron radiation belt at geosynchronous orbit and the energetic-electron population of the magnetotail are compared via superposed-epoch averaging of data. The magnetotail measurements are obtained by using GPS-orbit measurements that magnetically map out into the magnetotail. Four temporal phases of high-speed-stream-driven storms are studied: (1) the pre-storm density decay of the electron-radiation belt, (2) the electron-radiation-belt density dropout near the time of storm onset, (3) the rapid density recovery a few hours after dropout, and (4) the heating of the electron radiation belt during the high-speed-stream-driven geomagnetic activity. In all four phases the behaviors of the outer electron radiation belt and of the energetic-electron population in the magnetotail are the same and simultaneous. The physical explanations for the behavior in phase 1 (decay), phase 2 (dropout), and phase 4 (heating) lie in the dipolar regions of the magnetosphere: hence for those three phases it is concluded that the temporal behavior of the energetic-electron population in the magnetotail mimics the behavior of the outer electron radiation belt. Behavior attributable to physical processes in the dipole is seen in the magnetotail energetic-electron population: this implies that the origin of the energetic-electron population of the magnetotail is “leakage” or “outward evaporation” from the outer electron radiation belt in the dipolar magnetosphere.

Description: The magnetosonic (or ion Bernstein) instability is driven by a positive slope in the ion distribution function perpendicular to the magnetic field at energies above about 1 keV. Fifteen years of multisatellite geosynchronous observations are used to determine the statistical occurrence of ion distributions with positive slopes as a function of energy, local time, geomagnetic activity, and phase of the solar cycle. There is no discernable dependence on phase of the solar cycle, but there are clear dependences on the other parameters. Positive slopes are seen primarily in the energy range between ∼3 and ∼24 keV. The peak occurrence of positive slopes is between midmorning and dusk and moves progressively toward earlier local times for higher energies. The occurrence is significantly greater and extends over a broader local time range for low levels of geomagnetic activity than for high activity, for all energies. At high activity levels, the occurrence tends to be more closely confined near noon. Peak occurrence rates are ∼30% at energies just below 10 keV. A superposed epoch analysis of 77 coronal mass ejection (CME)-driven storms and 93 high-speed solar wind (HSS)-driven storms shows a relative suppression of the occurrence frequency of positive slopes during the recovery phase. The suppression is particularly long-lived for HSS-driven streams.