678 research outputs found
A First Comparison of Millimeter Continuum and Mg II Ultraviolet Line Emission from the Solar Chromosphere
We present joint observations of the Sun by the Atacama Large
Millimeter/submillimeter Array (ALMA) and the Interface Region Imaging
Spectrograph (IRIS). The observations were made of a solar active region on
2015 December 18 as part of the ALMA science verification effort. A map of the
Sun's continuum emission of size was obtained by ALMA at a
wavelength of 1.25 mm (239 GHz) using mosaicing techniques. A contemporaneous
map of size was obtained in the Mg II h doublet line at
2803.5\AA\ by IRIS. Both mm/submm continuum emission and ultraviolet
(UV) line emission are believed to originate from the solar chromosphere and
both have the potential to serve as powerful and complementary diagnostics of
physical conditions in this poorly understood layer of the solar atmosphere.
While a clear correlation between mm- brightness temperature and
the Mg II h line radiation temperature is observed the slope is ,
perhaps as a result of the fact that these diagnostics are sensitive to
different parts of the chromosphere and/or the Mg II h line source function
includes a scattering component. There is a significant offset between the mean
(1.25 mm) and mean (Mg II), the former being
greater than the latter. Partitioning the maps into "sunspot", "quiet regions",
and "plage regions" we find that the slope of the scatter plots between the
IRIS Mg II h line and the ALMA brightness temperature is 0.4
(sunspot), 0.56 (quiet regions), and 0.66 (plage regions). We suggest that this
change may be caused by the regional dependence of the formation heights of the
IRIS and ALMA diagnostics, and/or the increased degree of coupling between the
UV source function and the local gas temperature in the hotter, denser gas in
plage regions.Comment: 8 pages, 2 figure
Ultraviolet spectroscopy of narrow coronal mass ejections
We present Ultraviolet Coronagraph Spectrometer (UVCS) observations of 5
narrow coronal mass ejections (CMEs) that were among 15 narrow CMEs originally
selected by Gilbert et al. (2001). Two events (1999 March 27, April 15) were
"structured", i.e. in white light data they exhibited well defined interior
features, and three (1999 May 9, May 21, June 3) were "unstructured", i.e.
appeared featureless. In UVCS data the events were seen as 4-13 deg wide
enhancements of the strongest coronal lines HI Ly-alpha and OVI (1032,1037 A).
We derived electron densities for several of the events from the Large Angle
Spectrometric Coronagraph (LASCO) C2 white light observations. They are
comparable to or smaller than densities inferred for other CMEs. We modeled the
observable properties of examples of the structured (1999 April 15) and
unstructured (1999 May 9) narrow CMEs at different heights in the corona
between 1.5 and 2 R(Sun). The derived electron temperatures, densities and
outflow speeds are similar for those two types of ejections. They were compared
with properties of polar coronal jets and other CMEs. We discuss different
scenarios of narrow CME formation either as a jet formed by reconnection onto
open field lines or CME ejected by expansion of closed field structures.
Overall, we conclude that the existing observations do not definitively place
the narrow CMEs into the jet or the CME picture, but the acceleration of the
1999 April 15 event resembles acceleration seen in many CMEs, rather than
constant speeds or deceleration observed in jets.Comment: AASTeX, 22 pages, incl. 3 figures (2 color) and 3 tables. Accepted
for publication in Ap.
EUV jets, type III radio bursts and sunspot waves investigated using SDO/AIA observations
Images from the Solar Dynamics Observatory (SDO) at 211A are used to identify
the solar source of the type III radio bursts seen in WIND/WAVES dynamic
spectra. We analyse a 2.5 hour period during which six strong bursts are seen.
The radio bursts correlate very well with the EUV jets coming from the western
side of a sunspot in AR11092. The EUV jet emission also correlates well with
brightening at what looks like their footpoint at the edge of the umbra. For
10-15 min after strong EUV jets are ejected, the footpoint brightens at roughly
3 min intervals. In both the EUV images and the extracted light curves, it
looks as though the brightening is related to the 3-min sunspot oscillations,
although the correlation coefficient is rather low. The only open field near
the jets is rooted in the sunspot. We conclude that active region EUV/X-ray
jets and interplanetary electron streams originate on the edge of the sunspot
umbra. They form along a current sheet between the sunspot open field and
closed field connecting to underlying satellite flux. Sunspot running penumbral
waves cause roughly 3-min jet footpoint brightening. The relationship between
the waves and jets is less clear.Comment: 4 pages, 7 figures, Accepted by A&A Letters. For associated gif
movie, see http://www.mps.mpg.de/data/outgoing/innes/jets/losb_304_211_rd.gi
Thermo-mechanic-electrical coupling in phospholipid monolayers near the critical point
Lipid monolayers have been shown to represent a powerful tool in studying
mechanical and thermodynamic properties of lipid membranes as well as their
interaction with proteins. Using Einstein's theory of fluctuations we here
demonstrate, that an experimentally derived linear relationship both between
transition entropy S and area A as well as between transition entropy and
charge q implies a linear relationships between compressibility \kappa_T, heat
capacity c_\pi, thermal expansion coefficient \alpha_T and electric capacity
CT. We demonstrate that these couplings have strong predictive power as they
allow calculating electrical and thermal properties from mechanical
measurements. The precision of the prediction increases as the critical point
TC is approached
Polar Field Reversal Observations with Hinode
We have been monitoring yearly variation in the Sun's polar magnetic fields
with the Solar Optical Telescope aboard {\it Hinode} to record their evolution
and expected reversal near the solar maximum. All magnetic patches in the
magnetic flux maps are automatically identified to obtain the number density
and magnetic flux density as a function of th total magnetic flux per patch.
The detected magnetic flux per patch ranges over four orders of magnitude
( -- Mx). The higher end of the magnetic flux in the polar
regions is about one order of magnitude larger than that of the quiet Sun, and
nearly that of pores. Almost all large patches ( Mx) have the
same polarity, while smaller patches have a fair balance of both polarities.
The polarity of the polar region as a whole is consequently determined only by
the large magnetic concentrations. A clear decrease in the net flux of the
polar region is detected in the slow rising phase of the current solar cycle.
The decrease is more rapid in the north polar region than in the south. The
decrease in the net flux is caused by a decrease in the number and size of the
large flux concentrations as well as the appearance of patches with opposite
polarity at lower latitudes. In contrast, we do not see temporal change in the
magnetic flux associated with the smaller patches ( Mx) and that of
the horizontal magnetic fields during the years 2008--2012.Comment: 21 pages, 7 figures. Accepted for publication in Ap
First analysis of solar structures in 1.21 mm full-disc ALMA image of the Sun
Various solar features can be seen on maps of the Sun in the mm and sub-mm
wavelength range. The recently installed Atacama Large Millimeter/submillimeter
Array (ALMA) is capable of observing the Sun in that wavelength range with an
unprecedented spatial, temporal and spectral resolution. To interpret solar
observations with ALMA the first important step is to compare ALMA maps with
simultaneous images of the Sun recorded in other spectral ranges. First we
identify different structures in the solar atmosphere seen in the optical, IR
and EUV parts of the spectrum (quiet Sun (QS), active regions (AR), prominences
on the disc, magnetic inversion lines (IL), coronal holes (CH) and coronal
bright points (CBPs)) in a full disc solar ALMA image. The second aim is to
measure the intensities (brightness temperatures) of those structures and
compare them with the corresponding QS level. A full disc solar image at 1.21
mm obtained on December 18, 2015 during a CSV-EOC campaign with ALMA is
calibrated and compared with full disc solar images from the same day in
H\alpha, in He I 1083 nm core, and with SDO images (AIA at 170 nm, 30.4 nm,
21.1 nm, 19.3 nm, and 17.1 nm and HMI magnetogram). The brightness temperatures
of various structures are determined by averaging over corresponding regions of
interest in the ALMA image. Positions of the QS, ARs, prominences on the disc,
ILs, CHs and CBPs are identified in the ALMA image. At 1.21 mm ARs appear as
bright areas (but sunspots are dark), while prominences on the disc and CHs are
not discernible from the QS background, although having slightly less intensity
than surrounding QS regions. ILs appear as large, elongated dark structures and
CBPs correspond to ALMA bright points. These results are in general agreement
with sparse earlier measurements at similar wavelengths. The identification of
CBPs represents the most important new result.Comment: 9 pages, 3 figure
Ionic Conductivities of Molten CuI and AgI-CuI Mixtures
Ionic conductivities σ for molten CuI and AgI-CuI mixtures were measured in the temperature ranges of approximately 580-800 and 500-850 °C, respectively. The value of σ for molten CuI in the range is smaller than that for molten CuBr and CuCl. σ for molten AgI-CuI mixtures decreases with increasing CuI-concentration. The activation energies Ea for molten AgI-CuI system were determined from the analysis of temperature dependence of σ by using the by Arrhenius type equation. Ea for molten AgI-CuI gradually increase with increasing CuIconcentration
Micro-Sigmoids as Progenitors of Coronal Jets - Is Eruptive Activity Self-Similarly Multi-Scaled?
Observations from the X-ray telescope (XRT) on Hinode are used to study the
nature of X-ray bright points, sources of coronal jets. Several jet events in
the coronal holes are found to erupt from small-scale, S-shaped bright regions.
This finding suggests that coronal micro-sigmoids may well be progenitors of
coronal jets. Moreover, the presence of these structures may explain numerous
observed characteristics of jets such as helical structures, apparent
transverse motions, and shapes. In analogy to large-scale sigmoids giving rise
to coronal mass ejections (CMEs), a promising future task would perhaps be to
investigate whether solar eruptive activity, from coronal jets to CMEs, is
self-similar in terms of properties and instability mechanisms.Comment: 8 pages, 5 figures, 1 tabl
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