84 research outputs found
The large longitudinal spread of solar energetic particles during the January 17, 2010 solar event
We investigate multi-spacecraft observations of the January 17, 2010 solar
energetic particle event. Energetic electrons and protons have been observed
over a remarkable large longitudinal range at the two STEREO spacecraft and
SOHO suggesting a longitudinal spread of nearly 360 degrees at 1AU. The flaring
active region, which was on the backside of the Sun as seen from Earth, was
separated by more than 100 degrees in longitude from the magnetic footpoints of
each of the three spacecraft. The event is characterized by strongly delayed
energetic particle onsets with respect to the flare and only small or no
anisotropies in the intensity measurements at all three locations. The presence
of a coronal shock is evidenced by the observation of a type II radio burst
from the Earth and STEREO B. In order to describe the observations in terms of
particle transport in the interplanetary medium, including perpendicular
diffusion, a 1D model describing the propagation along a magnetic field line
(model 1) (Dr\"oge, 2003) and the 3D propagation model (model 2) by (Dr\"oge et
al., 2010) including perpendicular diffusion in the interplanetary medium have
been applied, respectively. While both models are capable of reproducing the
observations, model 1 requires injection functions at the Sun of several hours.
Model 2, which includes lateral transport in the solar wind, reveals high
values for the ratio of perpendicular to parallel diffusion. Because we do not
find evidence for unusual long injection functions at the Sun we favor a
scenario with strong perpendicular transport in the interplanetary medium as
explanation for the observations.Comment: The final publication is available at http://www.springerlink.co
Solar Wind Turbulence and the Role of Ion Instabilities
International audienc
Impact of CIR Storms on Thermosphere Density Variability during the Solar Minimum of 2008
The solar minimum of 2008 was exceptionally quiet, with sunspot numbers at
their lowest in 75 years. During this unique solar minimum epoch, however,
solar wind high - speed streams emanating from near-equatorial coronal holes
occurred frequently and were the primary contributor to the recurrent
geomagnetic activity at Earth. These conditions enabled the isolation of
forcing by geomagnetic activity on the preconditioned solar minimum state of
the upper atmosphere caused by Corotating Interaction Regions (CIRs).
Thermosphere density observations around 400 km from the CHAMP satellite are
used to study the thermosphere density response to solar wind high - speed
streams/CIRs. Superposed epoch results show that thermosphere density responds
to high - speed streams globally, and the density at 400 km changes by 75% on
average. The relative changes of neutral density are comparable at different
latitudes, although its variability is largest at high latitudes. In addition,
the response of thermosphere density to high - speed streams is larger at night
than in daytime, indicating the preconditioning effect of the thermosphere
response to storms. Finally, the thermosphere density variations at the periods
of 9 and 13.5 days associated with CIRs are linked to the spatial distribution
of low - middle latitude coronal holes on the basis of the EUVI observations
from the STEREO.Comment: Solar Physics, accepted, April 2010, and the final version of this
paper will appear in the website of Solar Physics soon
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure
AI-ready data in space science and solar physics: problems, mitigation and action plan
In the domain of space science, numerous ground-based and space-borne data of various phenomena have been accumulating rapidly, making analysis and scientific interpretation challenging. However, recent trends in the application of artificial intelligence (AI) have been shown to be promising in the extraction of information or knowledge discovery from these extensive data sets. Coincidentally, preparing these data for use as inputs to the AI algorithms, referred to as AI-readiness, is one of the outstanding challenges in leveraging AI in space science. Preparation of AI-ready data includes, among other aspects: 1) collection (accessing and downloading) of appropriate data representing the various physical parameters associated with the phenomena under study from different repositories; 2) addressing data formats such as conversion from one format to another, data gaps, quality flags and labeling; 3) standardizing metadata and keywords in accordance with NASA archive requirements or other defined standards; 4) processing of raw data such as data normalization, detrending, and data modeling; and 5) documentation of technical aspects such as processing steps, operational assumptions, uncertainties, and instrument profiles. Making all existing data AI-ready within a decade is impractical and data from future missions and investigations exacerbates this. This reveals the urgency to set the standards and start implementing them now. This article presents our perspective on the AI-readiness of space science data and mitigation strategies including definition of AI-readiness for AI applications; prioritization of data sets, storage, and accessibility; and identifying the responsible entity (agencies, private sector, or funded individuals) to undertake the task
Sharp changes of solar wind ion flux and density within and outside current sheets
Analysis of the Interball-1 spacecraft data (1995-2000) has shown that the
solar wind ion flux sometimes increases or decreases abruptly by more than 20%
over a time period of several seconds or minutes. Typically, the amplitude of
such sharp changes in the solar wind ion flux (SCIFs) is larger than 0.5x10^8
cm^-2 s^-1. These sudden changes of the ion flux were also observed by the
Solar Wind Experiment (SWE), on board the WIND spacecraft, as the solar wind
density increases and decreases with negligible changes in the solar wind
velocity. SCIFs occur irregularly at 1 AU, when plasma flows with specific
properties come to the Earth's orbit. SCIFs are usually observed in slow,
turbulent solar wind with increased density and interplanetary magnetic field
strength. The number of times SCIFs occur during a day is simulated using the
solar wind density, magnetic field, and their standard deviations as input
parameters for a period of 5 years. A correlation coefficient of ~0.7 is
obtained between the modelled and the experimental data. It is found that SCIFs
are not associated with coronal mass ejections (CMEs), corotating interaction
regions (CIRs), or interplanetary shocks; however, 85% of the sector boundaries
are surrounded by SCIFs. The properties of the solar wind plasma for days with
5 or more SCIF observations are the same as those of the solar wind plasma at
the sector boundaries. One possible explanation for the occurrence of SCIFs
(near sector boundaries) is magnetic reconnection at the heliospheric current
sheet or local current sheets. Other probable causes of SCIFs (inside sectors)
are turbulent processes in the slow solar wind and at the crossings of flux
tubes.Comment: 33 pages, 8 figures, 6 tables, Solar Physics 2011, in pres
The variation of geomagnetic storm duration with intensity
Variability in the near-Earth solar wind conditions can adversely affect a number of ground- and space-based technologies. Such space-weather impacts on ground infrastructure are expected to increase primarily with geomagnetic storm intensity, but also storm duration, through time-integrated effects. Forecasting storm duration is also necessary for scheduling the resumption of safe operating of affected infrastructure. It is therefore important to understand the degree to which storm intensity and duration are correlated. The long-running, global geomagnetic disturbance index, aa , has recently been recalibrated to account for the geographic distribution of the component stations. We use this aaH index to analyse the relationship between geomagnetic storm intensity and storm duration over the past 150 years, further adding to our understanding of the climatology of geomagnetic activity. Defining storms using a peak-above-threshold approach, we find that more intense storms have longer durations, as expected, though the relationship is nonlinear. The distribution of durations for a given intensity is found to be approximately log-normal. On this basis, we provide a method to probabilistically predict storm duration given peak intensity, and test this against the aaH dataset. By considering the average profile of storms with a superposed-epoch analysis, we show that activity becomes less recurrent on the 27-day timescale with increasing intensity. This change in the dominant physical driver, and hence average profile, of geomagnetic activity with increasing threshold is likely the reason for the nonlinear behaviour of storm duration
The Earth: Plasma Sources, Losses, and Transport Processes
This paper reviews the state of knowledge concerning the source of magnetospheric plasma at Earth. Source of plasma, its acceleration and transport throughout the system, its consequences on system dynamics, and its loss are all discussed. Both observational and modeling advances since the last time this subject was covered in detail (Hultqvist et al., Magnetospheric Plasma Sources and Losses, 1999) are addressed
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