286 research outputs found
Heliospheric Evolution of Magnetic Clouds
Interplanetary evolution of eleven magnetic clouds (MCs) recorded by at least
two radially aligned spacecraft is studied. The in situ magnetic field
measurements are fitted to a cylindrically symmetric Gold-Hoyle force-free
uniform-twist flux-rope configuration. The analysis reveals that in a
statistical sense the expansion of studied MCs is compatible with self-similar
behavior. However, individual events expose a large scatter of expansion rates,
ranging from very weak to very strong expansion. Individually, only four events
show an expansion rate compatible with the isotropic self-similar expansion.
The results indicate that the expansion has to be much stronger when MCs are
still close to the Sun than in the studied 0.47 - 4.8 AU distance range. The
evolution of the magnetic field strength shows a large deviation from the
behavior expected for the case of an isotropic self-similar expansion. In the
statistical sense, as well as in most of the individual events, the inferred
magnetic field decreases much slower than expected. Only three events show a
behavior compatible with a self-similar expansion. There is also a discrepancy
between the magnetic field decrease and the increase of the MC size, indicating
that magnetic reconnection and geometrical deformations play a significant role
in the MC evolution. About half of the events show a decay of the electric
current as expected for the self-similar expansion. Statistically, the inferred
axial magnetic flux is broadly consistent with it remaining constant. However,
events characterized by large magnetic flux show a clear tendency of decreasing
flux.Comment: 64 pages, 10 figure
Multifield Ultralight Dark Matter
Ultralight dark matter (ULDM) is usually taken to be a single scalar field.
Here we explore the possibility that ULDM consists of light scalar fields
with only gravitational interactions. This configuration is more consistent
with the underlying particle physics motivations for these scenarios than a
single ultralight field. ULDM halos have a characteristic granular structure
that increases stellar velocity dispersion and can be used as observational
constraints on ULDM models. In multifield simulations, we find that inside a
halo the amplitude of the total density fluctuations decreases as
and that the fields do not become significantly correlated over cosmological
timescales. Smoother halos heat stellar orbits less efficiently, reducing the
velocity dispersion relative to the single field case and thus weakening the
observational constraints on the field mass. Analytically, we show that for
equal-mass fields with mass the ULDM contribution to the stellar velocity
dispersion scales as . Lighter fields heat the most efficiently and
if the smallest mass is significantly below the other field masses the
dispersion scales as .Comment: 11 pages, 7 figures, to be submitted to PR
Attic dust: an archive of historical air contamination of the urban environment and potential hazard to health?
A comprehensive study of attic dust in an urban area is presented. Its entire life cycle, from determining historical emission sources to recognising the processes that take place in attic dust and its potential to impact human health is discussed. Its chemical composition and morphological characteristics of individual solid particles reflect past anthropogenic activities. High levels of Be-Cd-Cu-Sb-Sn-Pb-Te-Zn and occurrence of Cu-Zn shavings are typical for an industrial zone characterised by a foundry and a battery factory. High levels of Co-Fe-Mo-Ni-W-Ba-Cr-Mg-Mn-Nb-Ti and occurrence of various solid Fe-oxides, particularly spherical particles, were identified in another industrial zone, which was dominated by the automotive and metal-processing industries. Emissions from coal combustion affected the distribution of S-Se-Hg-Tl-As-Ag-U. The predominant mineral in attic dust is gypsum, which was presumably formed in situ by the reaction of carbonate dust particles and atmospheric SO2 gas. The high oral bioaccessibility of As-Cd-Cu-Pb-Zn in the gastric phase and high bioaccessibility of As-Cu-Cd-Ni in the gastrointestinal phase were identified. Determined characteristics of attic dust and identified possibilities of prolonged human exposure to it indicate that attic dust should be treated as an excellent proxy for historical air contamination as well as a potentially hazardous material for human health
A statistical study of long-term evolution of coronal hole properties as observed by SDO
The study of the evolution of coronal holes (CHs) is especially important in
the context of high-speed solar wind streams (HSS) emanating from them. Stream
interaction regions may deliver large amount of energy into the Earths system,
cause geomagnetic storms, and shape interplanetary space. By statistically
analysing 16 long-living CHs observed by the SDO, we focus on coronal,
morphological and underlying photospheric magnetic field characteristics as
well as investigate the evolution of the associated HSSs. We use CATCH to
extract and analyse CHs using observations taken by AIA and HMI. We derive
changes in the CH properties and correlate them to the CH evolution. Further we
analyse the properties of the HSS signatures near 1au from OMNI data by
manually extracting the peak bulk velocity of the solar wind plasma. We find
that the area evolution of CHs mostly shows a rough trend of growing to a
maximum followed by a decay. No correlation of the area evolution to the
evolution of the signed magnetic flux and signed magnetic flux density enclosed
in the projected CH area was found. From this we conclude that the magnetic
flux within the extracted CH boundaries is not the main cause for its area
evolution. We derive CH area change rates (growth and decay) of 14.2 +/- 15.0 *
10^8 km^2/day showing a reasonable anti-correlation (cc =-0.48) to the solar
activity, approximated by the sunspot number. The change rates of the signed
mean magnetic flux density (27.3 +/- 32.2 mG/day) and the signed magnetic flux
(30.3 +/- 31.5 * 10^18 Mx/day) were also found to be dependent on solar
activity (cc =0.50 and cc =0.69 respectively) rather than on the individual CH
evolutions. Further we find that the CH area-to-HSS peak velocity relation is
valid for each CH over its evolution but revealing significant variations in
the slopes of the regression lines.Comment: Accepted at A&
CME-HSS Interaction and Characteristics Tracked from Sun to Earth
In a thorough study, we investigate the origin of a remarkable plasma and magnetic field configuration observed in situ on June 22, 2011, near L1, which appears to be a magnetic ejecta (ME) and a shock signature engulfed by a solar wind high-speed stream (HSS). We identify the signatures as an Earth-directed coronal mass ejection (CME), associated with a C7.7 flare on June 21, 2011, and its interaction with a HSS, which emanates from a coronal hole (CH) close to the launch site of the CME. The results indicate that the major interaction between the CME and the HSS starts at a height of 1.3 R⊙ up to 3 R⊙. Over that distance range, the CME undergoes a strong north-eastward deflection of at least 30∘ due to the open magnetic field configuration of the CH. We perform a comprehensive analysis for the CME–HSS event using multi-viewpoint data (from the Solar TErrestrial RElations Observatories, the Solar and Heliospheric Observatory and the Solar Dynamics Observatory), and combined modeling efforts (nonlinear force-free field modeling, Graduated Cylindrical Shell CME modeling, and the Forecasting a CME’s Altered Trajectory – ForeCAT model). We aim at better understanding its early evolution and interaction process as well as its interplanetary propagation and related in situ signatures, and finally the resulting impact on the Earth’s magnetosphere
Lessons learned from synthetic research projects based on the ostrom workshop frameworks
A generalized knowledge of social-ecological relationships is needed to address current environmental challenges. Broadly comparative and synthetic research is a key method for establishing this type of knowledge. To date, however, most work on social-ecological systems has applied idiosyncratic methods to specific systems. Several projects, each based on the frameworks developed by Elinor Ostrom and colleagues, stand out for their application of consistent methods across a broad range of cases. In this paper we compare seven of these projects and draw conclusions regarding their potential benefits and the challenges that scholars can expect in conducting this type of research. The two main challenges that we identified are (1) the collective-action dilemmas that collaborators face in producing and maintaining the social and technical infrastructure that is needed for such projects; and (2) balancing complexity and comparability in the structure of the databases used and the associated methods for characterizing complex social-ecological cases. We discuss approaches for meeting these challenges, and present a guiding checklist of questions for project design and implementation to provide guidance for future broadly comparative research
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