The interaction of the solar wind with Earth's magnetosphere gives rise to the bright polar aurorae and to geomagnetic storms, but the relation between the solar wind and the dynamics of the outer ...planets' magnetospheres is poorly understood. Jupiter's magnetospheric dynamics and aurorae are dominated by processes internal to the jovian system, whereas Saturn's magnetosphere has generally been considered to have both internal and solar-wind-driven processes. This hypothesis, however, is tentative because of limited simultaneous solar wind and magnetospheric measurements. Here we report solar wind measurements, immediately upstream of Saturn, over a one-month period. When combined with simultaneous ultraviolet imaging we find that, unlike Jupiter, Saturn's aurorae respond strongly to solar wind conditions. But in contrast to Earth, the main controlling factor appears to be solar wind dynamic pressure and electric field, with the orientation of the interplanetary magnetic field playing a much more limited role. Saturn's magnetosphere is, therefore, strongly driven by the solar wind, but the solar wind conditions that drive it differ from those that drive the Earth's magnetosphere.
Extremely high speed solar wind: 29–30 October 2003 Skoug, R. M.; Gosling, J. T.; Steinberg, J. T. ...
Journal of Geophysical Research - Space Physics,
September 2004, Volume:
109, Issue:
A9
Journal Article
Peer reviewed
Open access
On 29–30 October 2003 the Solar Wind Electron Proton Alpha Monitor (SWEPAM) instrument on the Advanced Composition Explorer (ACE) spacecraft measured solar wind speeds in excess of 1850 km/s, some of ...the highest speeds ever directly measured in the solar wind. These speeds were observed following two large coronal mass ejection (CME) driven shocks. Surprisingly, despite the unusually high speeds, many of the other solar wind parameters were not particularly unusual in comparison with other large transient events. The magnetic field reached −68 nT, a large but not unprecedented value. The proton temperatures were significantly higher than typical for a CME in the solar wind at 1 AU (>107 K), but the proton densities were moderate, leading to low to moderate proton beta. The solar wind dynamic pressure was not unusual for large events but, when coupled with the large negative Bz, was sufficient to cause intense geomagnetic disturbances.
We present techniques for comparing measurements of velocity, temperature, and density with constraints imposed by the plasma physics of magnetized bi‐Maxwellian ions. Deviations from these ...physics‐based constraints are interpreted as arising from measurement errors. Two million ion spectra from the Solar Wind Experiment Faraday Cup instruments on the Wind spacecraft are used as a case study. The accuracy of velocity measurements is determined by the fact that differential flow between hydrogen and helium should be aligned with the ambient magnetic field. Modeling the breakdown of field alignment suggests velocity uncertainties are less than 0.16% in magnitude and 3° in direction. Temperature uncertainty is found by examining the distribution of observed temperature anisotropies in high‐beta solar wind intervals where the firehose, mirror, and cyclotron microinstabilities should drive the distribution to isotropy. The presence of a finite anisotropy at high beta suggests overall temperature uncertainties of 8%. Hydrogen and helium number densities are compared with the electron density inferred from observations of the local electron plasma frequency as a function of solar wind speed and year. We find that after accounting for the contribution of minor ions, the results are consistent with a systematic offset between the two instruments of 3–4%. The temperature and density methods are sensitive to non‐Maxwellian features such as heat flux and proton beams and as a result are more suited to slow solar wind where these features are rare. These procedures are of general use in identifying the accuracy of observations from any solar wind ion instrument.
At suprathermal energies, interplanetary electrons commonly exhibit a magnetic field‐aligned beam referred to as the strahl. The finite strahl width is a consequence of competition between magnetic ...focusing as the interplanetary field weakens with distance from the Sun, and particle scattering acting to broaden the strahl along its propagation path. We present a statistical survey of the strahl using ACE Solar Wind Electron, Proton, and Alpha Monitor (SWEPAM) measurements from 1998 to 2002. A systematic fitting algorithm was applied to pitch angle distributions to identify unidirectional or counterstreaming strahl features and to quantify beam widths and intensities. The analysis indicated that a strahl is present ≥75% of the time, while counterstreaming strahls were observed about 10% of the time. The strahl width ranges from 5° to 90°; importantly, the strahl cannot be characterized by any typical width. Within counterstreaming intervals the strahl peak intensity anticorrelates with beam width while the integrated fluxes of the two simultaneously observed strahls are similar, within a factor of 2 for 75% of counterstreaming periods. Observations are consistent with a model in which integrated strahl flux leaving the corona varies over a limited range, but the degree of beam scattering along the propagation path to 1 AU varies widely. The difference between two concurrent counterstreaming strahls is likely due to different scattering profiles along the different legs of a closed field line loop, both rooted in similar coronal regions. Narrow strahls (<20°) are strongly associated with counterstreaming intervals, as well as high‐speed streams. Strahl width can either increase or decrease with energy.
Key Points
Strahl varies widely and cannot be characterized by any typical width
Strahl peak intensity anticorrelates with the beam width
Very narrow strahls are associated with counterstreaming intervals
While many studies of coral bleaching report on broad, regional scale responses, fewer examine variation in susceptibility among coral taxa and changes in community structure, before, during and ...after bleaching on individual reefs. Here we report in detail on the response to bleaching by a coral community on a highly disturbed reef site south of mainland Singapore before, during and after a major thermal anomaly in 2010. To estimate the capacity for resistance to thermal stress, we report on: a) overall bleaching severity during and after the event, b) differences in bleaching susceptibility among taxa during the event, and c) changes in coral community structure one year before and after bleaching. Approximately two thirds of colonies bleached, however, post-bleaching recovery was quite rapid and, importantly, coral taxa that are usually highly susceptible were relatively unaffected. Although total coral cover declined, there was no significant change in coral taxonomic community structure before and after bleaching. Several factors may have contributed to the overall high resistance of corals at this site including Symbiodinium affiliation, turbidity and heterotrophy. Our results suggest that, despite experiencing chronic anthropogenic disturbances, turbid shallow reef communities may be remarkably resilient to acute thermal stress.
ABSTRACT
In this paper, we present evidence for magnetic transients with small radial extents ranging from 0.025 to 0.118 AU measured in situ by the
Solar-Terrestrial Relations Observatory
(
STEREO
) ...and the near-Earth
Advanced Composition Explorer
(
ACE
) and
Wind
spacecraft. The transients considered in this study are much smaller (<0.12 AU) than the typical sizes of magnetic clouds measured near 1 AU (∼0.23 AU). They are marked by low plasma beta values, generally lower magnetic field variance, short timescale magnetic field rotations, and are all entrained by high-speed streams by the time they reach 1 AU. We use this entrainment to trace the origin of these small interplanetary transients in coronagraph images. We demonstrate that these magnetic field structures originate as either small or large mass ejecta. The small mass ejecta often appear from the tip of helmet streamers as arch-like structures and other poorly defined white-light features (the so-called blobs). However, we have found a case of a small magnetic transient tracing back to a small and narrow mass ejection erupting from below helmet streamers. Surprisingly, one of the small magnetic structures traces back to a large mass ejection; in this case, we show that the central axis of the coronal mass ejection is along a different latitude and longitude to that of the in situ spacecraft. The small size of the transient is related to the in situ measurements being taken on the edges or periphery of a larger magnetic structure. In the last part of the paper, an ejection with an arch-like aspect is tracked continuously to 1 AU in the
STEREO
images. The associated in situ signature is not that of a magnetic field rotation but rather of a temporary reversal of the magnetic field direction. Due to its “open-field topology,” we speculate that this structure is partly formed near helmet streamers due to reconnection between closed and open magnetic field lines. The implications of these observations for our understanding of the variability of the slow solar wind are discussed.
To examine the association of neuropsychiatric symptom (NPS) severity with risk of transition to all-cause dementia, Alzheimer disease (AD), and vascular dementia (VaD).
Survival analysis of time to ...dementia, AD, or VaD onset.
Population-based study.
230 participants diagnosed with cognitive impairment, no dementia (CIND) from the Cache County Study of Memory Health and Aging were followed for a mean of 3.3 years.
The Neuropsychiatric Inventory (NPI) was used to quantify the presence, frequency, and severity of NPS. Chi-squared statistics, t-tests, and Cox proportional hazard ratios were used to assess associations.
The conversion rate from CIND to all-cause dementia was 12% per year, with risk factors including an APOE ε4 allele, lower Mini-Mental State Examination, lower 3MS, and higher CDR sum-of-boxes. The presence of at least one NPS was a risk factor for all-cause dementia, as was the presence of NPS with mild severity. Nighttime behaviors were a risk factor for all-cause dementia and of AD, whereas hallucinations were a risk factor for VaD.
These data confirm that NPS are risk factors for conversion from CIND to dementia. Of special interest is that even NPS of mild severity are a risk for all-cause dementia or AD.
Evidence for water ice near the lunar poles Feldman, W. C.; Maurice, S.; Lawrence, D. J. ...
Journal of Geophysical Research,
25 October 2001, Volume:
106, Issue:
E10
Journal Article, Conference Proceeding
Peer reviewed
Open access
Improved versions of Lunar Prospector thermal and epithermal neutron data were studied to help discriminate between potential delivery and retention mechanisms for hydrogen on the Moon. Improved ...spatial resolution at both poles shows that the largest concentrations of hydrogen overlay regions in permanent shade. In the north these regions consist of a heavily cratered terrain containing many small (less than ∼10‐km diameter), isolated craters. These border circular areas of hydrogen abundance (H) that is only modestly enhanced above the average equatorial value but that falls within large, flat‐bottomed, and sunlit polar craters. Near the south pole, H is enhanced within several 30‐km‐scale craters that are in permanent shade but is only modestly enhanced within their sunlit neighbors. We show that delivery by the solar wind cannot account for these observations because the diffusivity of hydrogen at the temperatures within both sunlit and permanently shaded craters near both poles is sufficiently low that a solar wind origin cannot explain their differences. We conclude that a significant portion of the enhanced hydrogen near both poles is most likely in the form of water molecules.
ABSTRACT
Classical novae are shock-powered multiwavelength transients triggered by a thermonuclear runaway on an accreting white dwarf. V1674 Her is the fastest nova ever recorded (time to declined ...by two magnitudes is t2 = 1.1 d) that challenges our understanding of shock formation in novae. We investigate the physical mechanisms behind nova emission from GeV γ-rays to cm-band radio using coordinated Fermi-LAT, NuSTAR, Swift, and VLA observations supported by optical photometry. Fermi-LAT detected short-lived (18 h) 0.1–100 GeV emission from V1674 Her that appeared 6 h after the eruption began; this was at a level of (1.6 ± 0.4) × 10−6 photons cm−2 s−1. Eleven days later, simultaneous NuSTAR and Swift X-ray observations revealed optically thin thermal plasma shock-heated to kTshock = 4 keV. The lack of a detectable 6.7 keV Fe Kα emission suggests super-solar CNO abundances. The radio emission from V1674 Her was consistent with thermal emission at early times and synchrotron at late times. The radio spectrum steeply rising with frequency may be a result of either free-free absorption of synchrotron and thermal emission by unshocked outer regions of the nova shell or the Razin–Tsytovich effect attenuating synchrotron emission in dense plasma. The development of the shock inside the ejecta is unaffected by the extraordinarily rapid evolution and the intermediate polar host of this nova.
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