16 research outputs found
Oxygen and hydrogen ion abundance in the near-Earth magnetosphere: Statistical results on the response to the geomagnetic and solar wind activity conditions
The composition of ions plays a crucial role for the fundamental plasma
properties in the terrestrial magnetosphere. We investigate the
oxygen-to-hydrogen ratio in the near-Earth magnetosphere from -10 RE<XGSE}< 10
RE. The results are based on seven years of ion flux measurements in the energy
range ~10 keV to ~955 keV from the RAPID and CIS instruments on board the
Cluster satellites. We find that (1) hydrogen ions at ~10 keV show only a
slight correlation with the geomagnetic conditions and interplanetary magnetic
field changes. They are best correlated with the solar wind dynamic pressure
and density, which is an expected effect of the magnetospheric compression; (2)
~10 keV O+ ion intensities are more strongly affected during disturbed phase of
a geomagnetic storm or substorm than >274 keV O+ ion intensities, relative to
the corresponding hydrogen intensities; (3) In contrast to ~10 keV ions, the
>274 keV O+ ions show the strongest acceleration during growth phase and not
during the expansion phase itself. This suggests a connection between the
energy input to the magnetosphere and the effective energization of energetic
ions during growth phase; (4) The ratio between quiet and disturbed times for
the intensities of ion ionospheric outflow is similar to those observed in the
near-Earth magnetosphere at >274 keV. Therefore, the increase of the energetic
ion intensity during disturbed time is more likely due to the intensification
than to the more effective acceleration of the ionospheric source. In
conclusion, the energization process in the near-Earth magnetosphere is mass
dependent and it is more effective for the heavier ions
The Polar Wind Modulated by the Spatial Inhomogeneity of the Strength of the Earth's Magnetic Field
When the geomagnetic field is weak, the small mirror force allows precipitating charged particles to deposit energy in the ionosphere. This leads to an increase in ionospheric outflow from the Earth's polar cap region, but such an effect has not been previously observed because the energies of the ions of the polar ionospheric outflow are too low, making it difficult to detect the lowâenergy ions with a positively charged spacecraft. In this study, we found an anticorrelation between ionospheric outflow and the strength of the Earth's magnetic field. Our results suggest that the electron precipitation through the polar rain can be a main energy source of the polar wind during periods of high levels of solar activity. The decreased magnetic field due to spatial inhomogeneity of the Earth's magnetic field and its effect on outflow can be used to study the outflow in history when the magnetic field was at similar levels.publishedVersio
Massâloading the Earth's dayside magnetopause boundary layer and its effect on magnetic reconnection
When the interplanetary magnetic field is northward for a period of time, O+ from the highâlatitude ionosphere escapes along reconnected magnetic field lines into the dayside magnetopause boundary layer. Dualâlobe reconnection closes these field lines, which traps O+ and mass loads the boundary layer. This O+ is an additional source of magnetospheric plasma that interacts with magnetosheath plasma through magnetic reconnection. This mass loading and interaction is illustrated through analysis of a magnetopause crossing by the Magnetospheric Multiscale spacecraft. While in the O+ârich boundary layer, the interplanetary magnetic field turns southward. As the Magnetospheric Multiscale spacecraft cross the highâshear magnetopause, reconnection signatures are observed. While the reconnection rate is likely reduced by the mass loading, reconnection is not suppressed at the magnetopause. The highâlatitude dayside ionosphere is therefore a source of magnetospheric ions that contributes often to transient reduction in the reconnection rate at the dayside magnetopause.publishedVersio
Human subcortical brain asymmetries in 15,847 people worldwide reveal effects of age and sex
The two hemispheres of the human brain differ functionally and structurally. Despite over a century of research, the extent to which brain asymmetry is influenced by sex, handedness, age, and genetic factors is still controversial. Here we present the largest ever analysis of subcortical brain asymmetries, in a harmonized multi-site study using meta-analysis methods. Volumetric asymmetry of seven subcortical structures was assessed in 15,847 MRI scans from 52 datasets worldwide. There were sex differences in the asymmetry of the globus pallidus and putamen. Heritability estimates, derived from 1170 subjects belonging to 71 extended pedigrees, revealed that additive genetic factors influenced the asymmetry of these two structures and that of the hippocampus and thalamus. Handedness had no detectable effect on subcortical asymmetries, even in this unprecedented sample size, but the asymmetry of the putamen varied with age. Genetic drivers of asymmetry in the hippocampus, thalamus and basal ganglia may affect variability in human cognition, including susceptibility to psychiatric disorders
Comparison of Quality Measures for Walén Relation
The standard method for identifying magnetohydrodynamic rotational discontinuities in spacecraft data has been to examine how well the WalĂ©n relation is satisfied. In this paper, we apply two different versions of the WalĂ©n test to a database of nearly 1,000 dayside magnetopause crossings by the Magnetospheric Multi-Scale spacecraft, with the objective of comparing their performance. The first approach is to evaluate the WalĂ©n relation as a jump condition, by determining the level of agreement between the change in plasma velocity across a discontinuity with the corresponding change in the AlfvĂ©n velocity. For this purpose, we use a recently developed quality index, Q, for which Q=±1 indicates perfect agreement. As was the case for a previously used quality index, ÎVâ, this new index employs data from two carefully chosen measurement times, located on opposite sides of the discontinuity. The second approach is to check the level of AlfvĂ©nicity of the flow for all measurements between those two points. Here, the quality index used is Wsl, the slope of the regression line in a scatter plot of plasma velocity components (after transformation into the deHoffmann-Teller frame) versus the corresponding AlfvĂ©n velocity components, with Wsl=±1 indicating perfect agreement. For the two indices to give comparable numbers of rotational discontinuity candidates, a substantially higher threshold value is needed for |Q| than for |Wsl|. Even so, the events selected by the two methods are not identical. We also identify statistical relationships between Wsl and its associated correlation coefficient, Wcc, as well as between Wsl and Q and between Wsl and ÎVâ
The Polar Wind Modulated by the Spatial Inhomogeneity of the Strength of the Earth's Magnetic Field
When the geomagnetic field is weak, the small mirror force allows precipitating charged particles to deposit energy in the ionosphere. This leads to an increase in ionospheric outflow from the Earth's polar cap region, but such an effect has not been previously observed because the energies of the ions of the polar ionospheric outflow are too low, making it difficult to detect the lowâenergy ions with a positively charged spacecraft. In this study, we found an anticorrelation between ionospheric outflow and the strength of the Earth's magnetic field. Our results suggest that the electron precipitation through the polar rain can be a main energy source of the polar wind during periods of high levels of solar activity. The decreased magnetic field due to spatial inhomogeneity of the Earth's magnetic field and its effect on outflow can be used to study the outflow in history when the magnetic field was at similar levels