95 research outputs found
Unified Relationship between Cold Plasma Ejections and Flare Energies Ranging from Solar Microflares to Giant Stellar Flares
We often find spectral signatures of chromospheric cold plasma ejections
accompanied by flares in a wide range of spatial scales in the solar and
stellar atmospheres. However, the relationship between physical quantities
(such as mass, kinetic energy, and velocity) of cold ejecta and flare energy
has not been investigated in a unified manner for the entire range of flare
energies to date. This study analyzed the spectra of cold plasma ejections
associated with small-scale flares and solar flares (energy
) to supply smaller energy samples. We performed
H imaging spectroscopy observation by the Solar Dynamics Doppler Imager
on the Solar Magnetic Activity Research Telescope (SMART/SDDI). We determined
the physical quantities of the ejecta by cloud model fitting to the H
spectrum. We determined flare energy by differential emission measure analysis
using Atmospheric Imaging Assembly onboard Solar Dynamics Observatory (SDO/AIA)
for small-scale flares and by estimating the bolometric energy for large-scale
flares. As a result, we found that the ejection mass and the total flare
energy follow a relation of . We show that the scaling law derived from a simple
physical model explains the solar and stellar observations with a coronal
magnetic field strength as a free parameter. We also found that the kinetic
energy and velocity of the ejecta correlate with the flare energy. These
results suggest a common mechanism driven by magnetic fields to cause cold
plasma ejections with flares on the Sun and stars.Comment: 23 pages, 10 figures; accepted for publication in Ap
Thermodynamic properties of small flares in the quiet Sun observed by H and EUV: plasma motion of the chromosphere and time evolution of temperature/emission measure
Small flares frequently occur in the quiet Sun. Previous studies have noted
that they share many common characteristics with typical solar flares in active
regions. However, their similarities and differences are not fully understood,
especially their thermal properties. In this study, we performed imaging
spectroscopic observations in the H line taken with the Solar Dynamics
Doppler Imager on the Solar Magnetic Activity Research Telescope (SMART/SDDI)
at the Hida Observatory and imaging observations with the Atmospheric Imaging
Assembly onboard Solar Dynamics Observatory (SDO/AIA). We analysed 25 cases of
small flares in the quiet Sun over the thermal energy range of
, paying particular attention to their thermal
properties. Our main results are as follows: (1) We observe a redshift together
with line centre brightening in the H line associated with more than
half of the small flares. (2) We employ differential emission measure analysis
using AIA multi-temperature (channel) observations to obtain the emission
measure and temperature of the small flares. The results are consistent with
the Shibata & Yokoyama (1999, 2002) scaling law. From the scaling law, we
estimated the coronal magnetic field strength of small flares to be 5 --15 G.
(3) The temporal evolution of the temperature and the density shows that the
temperature peaks precede the density peaks in more than half of the events.
These results suggest that chromospheric evaporations/condensations play an
essential role in the thermal properties of some of the small flares in the
quiet Sun, as does for large flares.Comment: 14 pages, 12 figures, accepted for publication in MNRA
Introduction pathways and evolutionary mechanisms of alien species of Lolium spreading across sandy coasts in Japan
1. Estimating the role of specific processes in the spread of alien species necessitates the determination of introduction pathways and source populations of invaded areas. Alien grasses in the genus Lolium that have extensively invaded Japan provide a unique opportunity to estimate the expansion process through direct comparison between source and naturalised populations because the introduction pathways, contaminants in grain commodities and commercial cultivars for fodder crops or revegetation materials are well-known. Therefore, by directly comparing source and naturalised populations, we estimated the introduction pathways and whether adaptative evolution occurred in Lolium species on sandy coasts in Japan. 2. Lolium individuals sampled from naturalised populations in croplands, seaports, and sandy coasts were compared with those from two introduction sources for morphological and genetic variations based on a genome-wide single nucleotide polymorphism analysis and a common garden experiment. Furthermore, we conducted a reciprocal transplant experiment between cropland and sandy coast. 3. Populations naturalised in croplands were closely related to the cultivars, whereas those naturalised in seaports and sandy coasts were associated with contaminants. These results indicate that the cropland and sandy coast populations are derived from cultivars and contaminants, respectively. In addition, asymmetric gene flow from cropland populations to sandy coast populations was observed. The reciprocal transplant experiment clearly demonstrated the home site advantage; populations derived from croplands yielded higher floret numbers than those derived from other habitats at the cropland site; sandy coast populations had higher survival rates than those from croplands at the coastal site. Port populations exhibited a similar tendency as sandy coast populations, indicating that contaminants may be originally adapted to salty and dry environments, such as that in sandy coasts. The flowering phenology in the sandy coast populations evolved in the late flowering; therefore, late flowering alleles may have been transferred from cropland populations to sandy coast populations. 4. Synthesis. We demonstrated that two congeneric species with different ecological characteristics were introduced through multiple introduction pathways and spread across different habitats. A direct comparison between source and naturalised populations can considerably elucidate the patterns and processes of biological invasions
Relationship between three-dimensional velocity of filament eruptions and CME association
AbstractIt is widely recognised that filament disappearances or eruptions are frequently associated with Coronal Mass Ejections (CMEs). Since CMEs are a major source of disturbances of the space environment surrounding the Earth, it is important to investigate these associations in detail for the better prediction of CME occurrence. However, the proportion of filament disappearances associated with CMEs is under debate. The estimates range from
∼
10 to
∼
90% and could be affected by the manners to select the events. In this study, we aim to reveal what parameters control the association between filament eruptions and CMEs. We analysed the relationships between CME associations and the physical parameters of filaments including their length, maximum ascending velocity, and direction of eruptions using 28 events of filament eruptions observed in H
α
. We found that the product of the maximum radial velocity and the filament length is well correlated with the CME occurrence. If the product is larger than
8.0
×
10
6
km
2
s
-
1
, the filament will become a CME with a probability of 93%, and if the product is smaller than this value, it will not become a CME with a probability of 100%. We suggest a kinetic-energy threshold above which filament eruptions are associated with CMEs. Our findings also suggest the importance of measuring the velocity vector of filament eruption in three-dimensional space for the better prediction of CME occurrence.</jats:p
Spicule Dynamics over Plage Region
We studied spicular jets over a plage area and derived their dynamic
characteristics using Hinode Solar Optical Telescope (SOT) high-resolution
images. The target plage region was near the west limb of the solar disk. This
location permitted us to study the dynamics of spicular jets without the
overlapping effect of spicular structures along the line of sight.
In this work, to increase the ease with which we can identify spicules on the
disk, we applied the image processing method `MadMax' developed by Koutchmy et
al. (1989). It enhances fine, slender structures (like jets), over a diffuse
background. We identified 169 spicules over the target plage. This sample
permits us to derive statistically reliable results regarding spicular
dynamics.
The properties of plage spicules can be summarized as follows: (1) In a plage
area, we clearly identified spicular jet features. (2) They were shorter in
length than the quiet region limb spicules, and followed ballistic motion under
constant deceleration. (3) The majority (80%) of the plage spicules showed the
cycle of rise and retreat, while 10% of them faded out without a complete
retreat phase. (4) The deceleration of the spicule was proportional to the
velocity of ejection (i.e. the initial velocity).Comment: 12 pages, 9 figures, accepted for publication in PAS
Early Spectroscopy of the 2010 Outburst of U Scorpii
We present early spectroscopy of the recurrent nova U~Sco during the outburst
in 2010. We successfully obtained time-series spectra at 0.37--0.44~d, where denotes the time from the discovery of the
present outburst. This is the first time-resolved spectroscopy on the first
night of U Sco outbursts. At ~d the H line consists
of a blue-shifted ( km s) narrow absorption component and a wide
emission component having triple peaks, a blue ( km s), a
central ( km s) and a red ( km s) ones. The
blue and red peaks developed more rapidly than the central one during the first
night. This rapid variation would be caused by the growth of aspherical wind
produced during the earliest stage of the outburst. At ~d the
H line has a nearly flat-topped profile with weak blue and red peaks at
km s. This profile can be attributed to a nearly
spherical shell, while the asphericity growing on the first night still
remains. The wind asphericity is less significant after d.Comment: 5 pages, 3 figures, Accepted for publication of PASJ Letter
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