63 research outputs found
Combined radio and space-based solar observations: from techniques to new results – preface
The phenomena observed at the Sun have a variety of unique radio signatures that can be used to diagnose the processes in the solar atmosphere. The insights provided by radio observations are further enhanced when they are combined with observations from space-based telescopes. This Topical collection demonstrates the power of combination methodology at work and provides new results on i) type I solar radio bursts and thermal emission to study active regions; ii) type II and IV bursts to better understand the structure of coronal mass ejections; and iii) non-thermal gyro-synchrotron and/or type III bursts to improve the characterisation of particle acceleration in solar flares. The ongoing improvements in time, frequency, and spatial resolutions of ground-based telescopes reveal new levels in the complexity of solar phenomena and pose new questions
Constraints on the variable nature of the slow solar wind with the Wide-Field Imager on board the Parker Solar Probe
In a previous work we analysed the white-light coronal brightness as a
function of elongation and time from Wide-Field Imager (WISPR) observations on
board the Parker Solar Probe (PSP) mission when PSP reached a minimum
heliocentric distance of ~ 28 Rs. We found 4-5 transient outflows per day over
a narrow wedge in the PSP orbital plane, which is close to the solar equatorial
plane. However, the elongation versus time map (J-map) analysis supplied only
lower limits on the number of released density structures due to the small
spatial-scales of the transient outflows and line-of-sight integration effects.
In this work we place constraints on the properties of slow solar wind
transient mass release from the entire solar equatorial plane. We simulated the
release and propagation of transient density structures in the solar equatorial
plane for four scenarios: (1) periodic release in time and longitude with
random speeds; (2) corotating release in longitude, periodic release in time
with random speeds; (3) random release in longitude, periodic release in time
and speed; and (4) random release in longitude, time, and speed. The
simulations were used in the construction of synthetic J-maps, which are
similar to the observed J-map. The four considered scenarios have similar
ranges (35-45 for the minimum values and 96-127 for the maximum values) of
released density structures per day from the solar equatorial plane and
consequently from the streamer belt, given its proximity to the solar
equatorial plane during the WISPR observation. Our results also predict that
density structures with sizes in the range 2-8 Rs, covering 1-20 % of the
perihelion could have been detectable by PSP in situ observations during that
interval.Comment: A&A, 2023, in pres
Implications for electron acceleration and transport from non-thermal electron rates at looptop and footpoint sources in solar flares
The interrelation of hard X-ray (HXR) emitting sources and the underlying physics of electron acceleration and transport presents one of the major questions in the high energy solar flare physics. Spatially resolved observations of solar flares often demonstrate the presence of well separated sources of bremsstrahlung emission, so-called coronal and foot-point sources. Using spatially resolved X-ray observations by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and recently improved imaging techniques, we investigate in detail the spatially resolved electron distributions in a few well observed solar flares. The selected flares can be interpreted as having a standard geometry with chromospheric HXR foot-point sources related to thick-target X-ray emission and the coronal sources characterised by a combination of thermal and thin-target bremsstrahlung. Using imaging spectroscopy technique, we deduce the characteristic electron rates and spectral indices required to explain the coronal and foot-points X-ray sources. We found that, during the impulsive phase, the electron rate at the loop-top is several times (a factor of 1.7-8) higher than at the foot-points. The results suggest sufficient number of electrons accelerated in the loop-top to explain the precipitation into the foot-points and implies electrons accumulation in the loop-top. We discuss these results in terms of magnetic trapping, pitch-angle scattering and injection properties. Our conclusion is that the accelerated electrons must be subject to magnetic trapping and/or pitch-angle scattering, keeping a fraction of the population trapped inside the coronal loops. These findings put strong constraints on the particle transport in the coronal source, and provide a quantitative limits on deka-keV electron trapping/scattering in the coronal source
Solar Science with the Atacama Large Millimeter/Submillimeter Array — A New View of Our Sun
The Atacama Large Millimeter/submillimeter Array (ALMA) is a new powerful tool for observing the Sun at high spatial, temporal, and spectral resolution. These capabilities can address a broad range of fundamental scientific questions in solar physics. The radiation observed by ALMA originates mostly from the chromosphere—a complex and dynamic region between the photosphere and corona, which plays a crucial role in the transport of energy and matter and, ultimately, the heating of the outer layers of the solar atmosphere. Based on first solar test observations, strategies for regular solar campaigns are currently being developed. State-of-the-art numerical simulations of the solar atmosphere and modeling of instrumental effects can help constrain and optimize future observing modes for ALMA. Here we present a short technical description of ALMA and an overview of past efforts and future possibilities for solar observations at submillimeter and millimeter wavelengths. In addition, selected numerical simulations and observations at other wavelengths demonstrate ALMA’s scientific potential for studying the Sun for a large range of science cases
Microflares and the Statistics of X-ray Flares
This review surveys the statistics of solar X-ray flares, emphasising the new
views that RHESSI has given us of the weaker events (the microflares). The new
data reveal that these microflares strongly resemble more energetic events in
most respects; they occur solely within active regions and exhibit
high-temperature/nonthermal emissions in approximately the same proportion as
major events. We discuss the distributions of flare parameters (e.g., peak
flux) and how these parameters correlate, for instance via the Neupert effect.
We also highlight the systematic biases involved in intercomparing data
representing many decades of event magnitude. The intermittency of the
flare/microflare occurrence, both in space and in time, argues that these
discrete events do not explain general coronal heating, either in active
regions or in the quiet Sun.Comment: To be published in Space Science Reviews (2011
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