290 research outputs found
In-Network Distributed Solar Current Prediction
Long-term sensor network deployments demand careful power management. While
managing power requires understanding the amount of energy harvestable from the
local environment, current solar prediction methods rely only on recent local
history, which makes them susceptible to high variability. In this paper, we
present a model and algorithms for distributed solar current prediction, based
on multiple linear regression to predict future solar current based on local,
in-situ climatic and solar measurements. These algorithms leverage spatial
information from neighbors and adapt to the changing local conditions not
captured by global climatic information. We implement these algorithms on our
Fleck platform and run a 7-week-long experiment validating our work. In
analyzing our results from this experiment, we determined that computing our
model requires an increased energy expenditure of 4.5mJ over simpler models (on
the order of 10^{-7}% of the harvested energy) to gain a prediction improvement
of 39.7%.Comment: 28 pages, accepted at TOSN and awaiting publicatio
Are Solar Panels a Viable Power Source for a Green Energy Vehicle?
A solar cell powered go-kart has been built and tested. The result shows using solar energy alone cannot meet the requirement of running a regular passenger car. This is due to the limited surface area of the passenger car. This thesis also discusses the operating principles of solar panels, the physics of P type and N type semiconductors, and the formation of the PN junction, as well as the solar current. Modifications of an existing go-kart are described in detail in this thesis. Suggestions for making green vehicles are discussed as well
3D coupled tearing-thermal evolution in solar current sheets
Combined tearing-thermal evolution plays an important role in the disruption
of current sheets, and formation of cool condensations within the solar
atmosphere. However, this has received limited attention to date. We
numerically explore a combined tearing and thermal instability that causes the
break up of an idealized current sheet in the solar atmosphere. The thermal
component leads to the formation of localized, cool condensations within an
otherwise 3D reconnecting magnetic topology. We construct a 3D resistive
magnetohydrodynamic simulation of a force-free current sheet under solar
atmospheric conditions that incorporate the non-adiabatic influence of
background heating, optically thin radiative energy loss, and magnetic field
aligned thermal conduction with the open source code MPI-AMRVAC. Multiple
levels of adaptive mesh refinement reveal the self-consistent development of
finer-scale condensation structures within the evolving system. The instability
in the current sheet is triggered by magnetic field perturbations concentrated
around the current sheet plane, and subsequent tearing modes develop. This in
turn drives thermal runaway associated with the thermal instability of the
system. We find subsequent, localized cool plasma condensations that form under
the prevailing low plasma- conditions, and demonstrate that the density
and temperature of these condensed structures are similar to more quiescent
coronal condensations. Synthetic counterparts at Extreme-UltraViolet (EUV) and
optical wavelengths show the formation of plasmoids (in EUV), and coronal
condensations similar to prominences and coronal rain blobs in the vicinity of
the reconnecting sheet. Our simulations imply that 3D reconnection in solar
current sheets may well present an almost unavoidable multi-thermal aspect,
that forms during their coupled tearing-thermal evolution.Comment: Accepted for publication in Astronomy and Astrophysics journa
Particle interactions with single or multiple 3D solar reconnecting current sheets
The acceleration of charged particles (electrons and protons) in flaring
solar active regions is analyzed by numerical experiments. The acceleration is
modelled as a stochastic process taking place by the interaction of the
particles with local magnetic reconnection sites via multiple steps. Two types
of local reconnecting topologies are studied: the Harris-type and the X-point.
A formula for the maximum kinetic energy gain in a Harris-type current sheet,
found in a previous work of ours, fits well the numerical data for a single
step of the process. A generalization is then given approximating the kinetic
energy gain through an X-point. In the case of the multiple step process, in
both topologies the particles' kinetic energy distribution is found to acquire
a practically invariant form after a small number of steps. This tendency is
interpreted theoretically. Other characteristics of the acceleration process
are given, such as the mean acceleration time and the pitch angle distributions
of the particles.Comment: 18 pages, 9 figures, Solar Physics, in pres
The Radial Distribution of Magnetic Helicity in the Solar Convective Zone: Observations and Dynamo Theory
We continue our attempt to connect observational data on current helicity in
solar active regions with solar dynamo models. In addition to our previous
results about temporal and latitudinal distributions of current helicity
(Kleeorin et al. 2003), we argue that some information concerning the radial
profile of the current helicity averaged over time and latitude can be
extracted from the available observations. The main feature of this
distribution can be presented as follows. Both shallow and deep active regions
demonstrate a clear dominance of one sign of current helicity in a given
hemisphere during the whole cycle. Broadly speaking, current helicity has
opposite polarities in the Northern and Southern hemispheres, although there
are some active regions that violate this polarity rule. The relative number of
active regions violating the polarity rule is significantly higher for deeper
active regions. A separation of active regions into `shallow', `middle' and
`deep' is made by comparing their rotation rate and the helioseismic rotation
law. We use a version of Parker's dynamo model in two spatial dimensions, that
employs a nonlinearity based on magnetic helicity conservation arguments. The
predictions of this model about the radial distribution of solar current
helicity appear to be in remarkable agreement with the available observational
data; in particular the relative volume occupied by the current helicity of
"wrong" sign grows significantly with the depth.Comment: 12 pages, 8 Postscript figures, uses mn2e.cl
Thermally enhanced tearing in solar current sheets: explosive reconnection with plasmoid-trapped condensations
In flare-relevant current sheets, tearing instability may trigger explosive
reconnection and plasmoid formation. We explore how the thermal and tearing
modes reinforce each other in the fragmentation of a current sheet in the solar
corona through an explosive reconnection process, characterized by the
formation of plasmoids which interact and trap condensing plasma. We use a
resistive magnetohydrodynamic (MHD) simulation of a 2D current layer,
incorporating the non-adiabatic effects of optically thin radiative energy loss
and background heating using \texttt{MPI-AMRVAC}. Our parametric survey
explores different resistivities and plasma- to quantify the instability
growth rate in the linear and nonlinear regimes. We notice that for
dimensionless resistivity values within , we get
explosive behavior where thermal instability and tearing behavior reinforce
each other. This is clearly below the usual critical Lundquist number range of
pure resistive explosive plasmoid formation. The non-linear growth rates follow
weak power-law dependency with resistivity. The fragmentation of the current
sheet and the formation of the plasmoids in the nonlinear phase of the
evolution due to the thermal and tearing instabilities are obtained. The
formation of plasmoids is noticed for the Lundquist number () range . We quantify the temporal variation of the
plasmoid numbers and the density filling factor of the plasmoids for different
physical conditions. We also find that the maximum plasmoid numbers scale as
. Within the nonlinearly coalescing plasmoid chains, localized
cool condensations gather, realizing density and temperature contrasts similar
to coronal rain or prominences.Comment: Accepted for publication in the Astronomy and Astrophysics journa
Operational reliability assessment of the GEOS A spacecraft
Decision theory application to GEOS A spacecraft operational reliability assessmen
Analysis of Solar Flux and Sunspot Correlation Case Study: A Statistical Perspective
This analysis examines the relationship between the number of solar flares and the number of sunspots in 2005 using 11 observations in months 2 to 12. The number of solar currents measures the intensity of the radiation emitted by the Sun, while the number of sunspots measures the number of sunspots on the surface of the Sun. Multivariate linear regression analysis was used to analyze the relationship between Solar Current Rate and Number of Sunspots. The results of the analysis show that the coefficient of the Amount of Solar Current is 1.1239 with a significant t value of 2.510 (probability that there is no effect on the Number of Sunspots is 3.33%). The linear regression model has good results with an F-statistic value of 6.301 and a p-value of 0.0333, with an R-squared value of 0.4118 which indicates that 41.18% of the variation in the number of sunspots is influenced by variations in the amount of solar currents. The corrected R-squared value is 0.3464 indicating that there are still variations in the number of sunspots that cannot be explained by variations in the number of solar currents. ARIMA analysis results show an MA coefficient of 0.7351 with an average value of 45.9542 and a s.e value of 0.2590 and 6.1550 respectively. The AIC, AICc, and BIC values are 92.97, 96.4, and 94.16. The error results in the training set show that the ME value is 0.2615561, the RMSE value is 12.16969, the MAE value is 9.03306, the MPE value is -15.14689, the MAPE value is 30.42013, and the MASE value is 0.674109. The ACF1 value in the exercise set is 0.0808969
Magnetic clouds in the solar wind
Two interplanetary magnetic clouds, characterized by anomalous magnetic field directions and unusually high magnetic field strengths with a scale of the order of 0.25 AU, are identified and described. As the clouds moved past a spacecraft located in the solar wind near Earth, the magnetic field direction changed by rotating approximately 180 deg nearly parallel to a plane which was essentially perpendicular to the ecliptic. The configuration of the magnetic field in the clouds might be that of a tightly wound cylindrical helix or a series of closed circular loops. One of the magnetic clouds was in a cold stream preceded by a shock, and it caused both a geomagnetic storm and a depression in the galactic cosmic ray intensity. No stream, geomagnetic storm, or large cosmic ray decrease was associated with the other magnetic cloud
Nonlinear force-free models for the solar corona I. Two active regions with very different structure
With the development of new instrumentation providing measurements of solar
photospheric vector magnetic fields, we need to develop our understanding of
the effects of current density on coronal magnetic field configurations. The
object is to understand the diverse and complex nature of coronal magnetic
fields in active regions using a nonlinear force-free model. From the observed
photospheric magnetic field we derive the photospheric current density for two
active regions: one is a decaying active region with strong currents (AR8151),
and the other is a newly emerged active region with weak currents (AR8210). We
compare the three-dimensional structure of the magnetic fields for both active
region when they are assumed to be either potential or nonlinear force-free.
The latter is computed using a Grad-Rubin vector-potential-like numerical
scheme. A quantitative comparison is performed in terms of the geometry, the
connectivity of field lines, the magnetic energy and the magnetic helicity
content. For the old decaying active region the connectivity and geometry of
the nonlinear force-free model include strong twist and strong shear and are
very different from the potential model. The twisted flux bundles store
magnetic energy and magnetic helicity high in the corona (about 50 Mm). The
newly emerged active region has a complex topology and the departure from a
potential field is small, but the excess magnetic energy is stored in the low
corona and is enough to trigger powerful flares.Comment: 11 pages, 11 figure
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