We investigate the evolution of the properties of planetary period magnetic field oscillations observed by the Cassini spacecraft in Saturn's magnetosphere over the interval from late 2004 to early ...2011, spanning equinox in mid‐2009. Oscillations within the inner quasi‐dipolar region (L ≤ 12) consist of two components of close but distinct periods, corresponding essentially to the periods of the northern and southern Saturn kilometric radiation (SKR) modulations. These give rise to modulations of the combined amplitude and phase at the beat period of the two oscillations, from which the individual oscillation amplitudes and phases (and hence periods) can be determined. Phases are also determined from northern and southern polar oscillation data when available. Results indicate that the southern‐period amplitude declines modestly over this interval, while the northern‐period amplitude approximately doubles to become comparable with the southern‐period oscillations during the equinox interval, producing clear effects in pass‐to‐pass oscillation properties. It is also shown that the periods of the two oscillations strongly converge over the equinox interval, such that the beat period increases significantly from ∼20 to more than 100 days, but that they do not coalesce or cross during the interval investigated, contrary to recent reports of the behavior of the SKR periods. Examination of polar oscillation data for similar beat phase effects yields a null result within a ∼10% upper limit on the relative amplitude of northern‐period oscillations in the south and vice versa. This result strongly suggests a polar origin for the two oscillation periods.
Key Points
Near rotation period phenomena at Saturn are studied using magnetic field data
We study seasonal changes in both period and amplitude of the oscillations
The result strongly suggests a polar origin for the two oscillation periods
Outer planet auroras have been imaged for more than a decade, yet understanding their physical origin requires simultaneous remote and in situ observations. The first such measurements at Saturn were ...obtained in January 2007, when the Hubble Space Telescope imaged the ultraviolet aurora, while the Cassini spacecraft crossed field lines connected to the auroral oval in the high‐latitude magnetosphere near noon. The Cassini data indicate that the noon aurora lies in the boundary between open‐ and closed‐field lines, where a layer of upward‐directed field‐aligned current flows whose density requires downward acceleration of magnetospheric electrons sufficient to produce the aurora. These observations indicate that the quasi‐continuous main oval is produced by the magnetosphere‐solar wind interaction through the shear in rotational flow across the open‐closed‐field line boundary.
The CORNISH project is the highest resolution radio continuum survey of the Galactic plane to date. It is the 5 GHz radio continuum part of a series of multi-wavelength surveys that focus on the ...northern GLIMPSE region (10degrees < l < 65degrees), observed by the Spitzer satellite in the mid-infrared. Observations with the Very Large Array in B and BnA configurations have yielded a 1".5 resolution Stokes I map with a root mean square noise level better than 0.4 mJy beam super(-1). Here we describe the data-processing methods and data characteristics, and present a new, uniform catalog of compact radio emission. This includes an implementation of automatic deconvolution that provides much more reliable imaging than standard CLEANing. A rigorous investigation of the noise characteristics and reliability of source detection has been carried out. We show that the survey is optimized to detect emission on size scales up to 14" and for unresolved sources the catalog is more than 90% complete at a flux density of 3.9 mJy. We have detected 3062 sources above a 7sigma detection limit and present their ensemble properties. The catalog is highly reliable away from regions containing poorly sampled extended emission, which comprise less than 2% of the survey area. Imaging problems have been mitigated by down-weighting the shortest spacings and potential artifacts flagged via a rigorous manual inspection with reference to the Spitzer infrared data. We present images of the most common source types found: H II regions, planetary nebulae, and radio galaxies. The CORNISH data and catalog are available online at http://cornish.leeds.ac.uk.
We show that the plasma and magnetic fields in the inner region of Saturn's plasma disk rotate in synchronism with the time-variable modulation period of Saturn's kilometric radio emission. This ...relation suggests that the radio modulation has its origins in the inner region of the plasma disk, most likely from a centrifugally driven convective instability and an associated plasma outflow that slowly slips in phase relative to Saturn's internal rotation. The slippage rate is determined by the electrodynamic coupling of the plasma disk to Saturn and by the drag force exerted by its interaction with the Enceladus neutral gas torus.
Abstract Background context The objective of the North American Spine Society's (NASS) Evidence-Based Clinical Guideline for the Diagnosis and Treatment of Lumbar Disc Herniation with Radiculopathy ...is to provide evidence-based recommendations to address key clinical questions surrounding the diagnosis and treatment of lumbar disc herniation with radiculopathy. The guideline is intended to reflect contemporary treatment concepts for symptomatic lumbar disc herniation with radiculopathy as reflected in the highest quality clinical literature available on this subject as of July 2011. The goals of the guideline recommendations are to assist in delivering optimum efficacious treatment and functional recovery from this spinal disorder. Purpose To provide an evidence-based educational tool to assist spine specialists in the diagnosis and treatment of lumbar disc herniation with radiculopathy. Study design Systematic review and evidence-based clinical guideline. Methods This guideline is a product of the Lumbar Disc Herniation with Radiculopathy Work Group of NASS' Evidence-Based Guideline Development Committee. The work group consisted of multidisciplinary spine care specialists trained in the principles of evidence-based analysis. A literature search addressing each question and using a specific search protocol was performed on English-language references found in Medline, Embase (Drugs and Pharmacology), and four additional evidence-based databases to identify articles. The relevant literature was then independently rated using the NASS-adopted standardized levels of evidence. An evidentiary table was created for each of the questions. Final recommendations to answer each clinical question were developed via work group discussion, and grades were assigned to the recommendations using standardized grades of recommendation. In the absence of Level I to IV evidence, work group consensus statements have been developed using a modified nominal group technique, and these statements are clearly identified as such in the guideline. Results Twenty-nine clinical questions were formulated and addressed, and the answers are summarized in this article. The respective recommendations were graded by strength of the supporting literature, which was stratified by levels of evidence. Conclusions The clinical guideline has been created using the techniques of evidence-based medicine and best available evidence to aid practitioners in the care of patients with symptomatic lumbar disc herniation with radiculopathy. The entire guideline document, including the evidentiary tables, suggestions for future research, and all the references, is available electronically on the NASS Web site at http://www.spine.org/Pages/PracticePolicy/ClinicalCare/ClinicalGuidlines/Default.aspx and will remain updated on a timely schedule.
ABSTRACT We describe the motivation, design, and implementation of the CORNISH survey, an arcsecond-resolution radio continuum survey of the inner galactic plane at 5 GHz using the Very Large Array ...(VLA). It is a blind survey coordinated with the northern Spitzer GLIMPSE I region covering 10° < l < 65° and |b| < 1° at similar resolution. We discuss in detail the strategy that we employed to control the shape of the synthesised beam across this survey, which covers a wide range of fairly low declinations. Two snapshots separated by 4h kept the beam elongation to less that 1.5 over 75% of the survey area and less than 2 over 98% of the survey. The prime scientific motivation is to provide an unbiased survey for ultra-compact H II regions to study this key phase in massive star formation. A sensitivity around 2 mJy will allow the automatic distinction between radio-loud and radio-quiet mid-IR sources found in the Spitzer surveys. This survey has many legacy applications beyond star formation, including evolved stars, active stars and binaries, and extragalactic sources. The CORNISH survey for compact ionized sources complements other Galactic plane surveys that target diffuse and nonthermal sources, as well as atomic and molecular phases to build up a complete picture of the interstellar medium in the Galaxy.
ABSTRACT
Observations of the nearby universe reveal an increasing fraction of active galactic nuclei (AGNs) with decreasing projected separation for close galaxy pairs, relative to control galaxies. ...This implies galaxy interactions play a role in enhancing AGN activity. However, the picture at higher redshift is less established, partly due to limited spectroscopic redshifts. We combine spectroscopic surveys with photometric redshift probability distribution functions for galaxies in the CANDELS and COSMOS surveys, to produce the largest ever sample of galaxy pairs used in an AGN fraction calculation for cosmic noon (0.5 < z < 3). We present a new technique for assessing galaxy pair probability (based on line-of-sight velocities ±1000 km s−1) from photometric redshift posterior convolutions and use these to produce weighted AGN fractions. Over projected separations 5–100 kpc, we find no evidence for enhancement, relative to isolated control galaxies, of X-ray (LX > 1042 erg s−1) or infrared-selected AGN in major (mass ratios up to 4:1) or minor (4:1 to 10:1) galaxy pairs. However, defining the most obscured AGN as those detected in the infrared but not in X-rays, we observe a trend of increasing obscured AGN enhancement at decreasing separations. The peak enhancement, relative to isolated controls, is a factor of 2.08 ± 0.61 for separations <25 kpc. Our simulations with mock data, indicates this could be a lower limit of the true enhancement. If confirmed with improved infrared imaging (e.g. with JWST) and redshifts (e.g. with forthcoming multi-object spectrograph surveys), this would suggest that galaxy interactions play a role in enhancing the most obscured black hole growth at cosmic noon.
We discuss observations of the journey throughout the Solar System of a large interplanetary coronal mass ejection (ICME) that was ejected at the Sun on 14 October 2014. The ICME hit Mars on 17 ...October, as observed by the Mars Express, Mars Atmosphere and Volatile EvolutioN Mission (MAVEN), Mars Odyssey, and Mars Science Laboratory (MSL) missions, 44 h before the encounter of the planet with the Siding-Spring comet, for which the space weather context is provided. It reached comet 67P/Churyumov-Gerasimenko, which was perfectly aligned with the Sun and Mars at 3.1 AU, as observed by Rosetta on 22 October. The ICME was also detected by STEREO-A on 16 October at 1 AU, and by Cassini in the solar wind around Saturn on the 12 November at 9.9 AU. Fortuitously, the New Horizons spacecraft was also aligned with the direction of the ICME at 31.6 AU. We investigate whether this ICME has a nonambiguous signature at New Horizons. A potential detection of this ICME by Voyager 2 at 110-111 AU is also discussed. The multispacecraft observations allow the derivation of certain properties of the ICME, such as its large angular extension of at least 116deg, its speed as a function of distance, and its magnetic field structure at four locations from 1 to 10 AU. Observations of the speed data allow two different solar wind propagation models to be validated. Finally, we compare the Forbush decreases (transient decreases followed by gradual recoveries in the galactic cosmic ray intensity) due to the passage of this ICME at Mars, comet 67P, and Saturn.
We examine the planetary‐period oscillations in Saturn's magnetic field observed by the Cassini spacecraft on 23 near‐equatorial periapsis passes in the inner magnetosphere spanning October 2004 to ...July 2006. Overall, we find that the phase of the magnetic oscillations is well organized by the long‐timescale modulation phase of Saturn kilometric radiation (SKR) determined over the same interval by Kurth et al. (2007), suggesting that the slow period variation of the latter relates to inner magnetosphere processes. The relative phases of the oscillations in the spherical polar r and ϕ magnetic field components imply the presence of a quasi‐uniform equatorial field rotating near the SKR period, while the sense of the θ component indicates that the perturbation field lines form loops with apices in the Northern Hemisphere. No consistent evidence is found for a sign reversal in any field component across the equatorial plane, within ±20° in latitude. The relative SKR phasing is such that the peak radio power occurs when the r and θ component maxima lie at ∼0200 LT ± 2 hours. However, a slow drift of the magnetic phase relative to the SKR phase is also discerned, amounting to ∼75° over the study interval. This drift lies within the envelope of scatter in the SKR phase determinations, suggesting that it represents the refinement of a common periodicity. A revised magnetic phase or longitude model is derived that should form an improved organizational system for oscillatory phenomena observed during this interval of the Cassini mission. The magnetic oscillations are also found to exhibit pass‐to‐pass phase “jitter” about the long‐term variation, of RMS amplitude ∼20°, with r and ϕ strongly correlated, but not θ. The relation with the solar wind‐modulated short‐timescale phase variations reported in SKR data by Zarka et al. (2007) remains to be investigated, though the latter are 5 times larger in magnitude.
Earth-based detection of Uranus' aurorae Lamy, L.; Prangé, R.; Hansen, K. C. ...
Geophysical research letters,
April 2012, Letnik:
39, Številka:
7
Journal Article
Recenzirano
Odprti dostop
This study is based on multi‐planet multi‐wavelength observations of planetary aurorae throughout the heliosphere, acquired along the propagation path of a series of consecutive interplanetary ...shocks. The underlying motivation to track the shocks was to increase the probability of detection of auroral emissions at Uranus. Despite several Earth‐based attempts in the past few years, at Far‐UV (FUV) and Near‐IR (NIR) wavelengths, such emissions have never been unambiguously re‐observed since their discovery by Voyager 2 in 1986. Here, we present a campaign of FUV observations of Uranus obtained in November 2011 with the Hubble Space Telescope (HST) during active solar wind conditions. We positively identify auroral signatures in several of these HST measurements, together with some obtained in 1998, representing the first images of Uranus' aurorae. We analyze their characteristics and discuss the implications for the asymmetric Uranian magnetosphere and its highly variable interaction with the solar wind flow from near‐solstice (1986) to near‐equinox (2011) configurations.
Key Points
We report the first Earth‐based detections of Uranus aurorae
This enabled us to investigate the atypical Uranian magnetosphere
This opens a wide field of investigations of this poorly understood magnetosphere
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