47 research outputs found
The solar chromosphere at millimetre and ultraviolet wavelengths. I. Radiation temperatures and a detailed comparison
Solar observations with the Atacama Large Millimeter/submillimeter Array
(ALMA) provide us with direct measurements of the brightness temperature in the
solar chromosphere. We study the temperature distributions obtained with ALMA
Band 6 (in four sub-bands at 1.21, 1.22, 1.29, and 1.3 mm) for various areas
at, and in the vicinity of, a sunspot, comprising quasi-quiet and active
regions with different amounts of underlying magnetic fields. We compare these
temperatures with those obtained at near- and far-ultraviolet (UV) wavelengths
(and with the line-core intensities of the optically-thin far-UV spectra),
co-observed with the Interface Region Imaging Spectrograph (IRIS) explorer.
These include the emission peaks and cores of the Mg II k 279.6 nm and Mg II h
280.4 nm lines as well as the line cores of C II 133.4 nm, O I 135.6 nm, and Si
IV 139.4 nm, sampling the mid-to-high chromosphere and the low transition
region. Splitting the ALMA sub-bands resulted in an slight increase of spatial
resolution in individual temperature maps, thus, resolving smaller-scale
structures compared to those produced with the standard averaging routines. We
find that the radiation temperatures have different, though somewhat
overlapping, distributions in different wavelengths and in the various magnetic
regions. Comparison of the ALMA temperatures with those of the UV diagnostics
should, however, be interpreted with great caution, the former is formed under
the local thermodynamic equilibrium (LTE) conditions, the latter under non-LTE.
The mean radiation temperature of the ALMA Band 6 is similar to that extracted
from the IRIS C II line in all areas with exception of the sunspot and pores
where the C II poses higher radiation temperatures. In all magnetic regions,
the Mg II lines associate with the lowest mean radiation temperatures in our
sample. These will provide constraints for future numerical models.Comment: Accepted for publication in the Astronomy & Astrophysics journa
High-frequency Oscillations in Small Magnetic Elements Observed with Sunrise/SuFI
We characterize waves in small magnetic elements and investigate their
propagation in the lower solar atmosphere from observations at high spatial and
temporal resolution. We use the wavelet transform to analyze oscillations of
both horizontal displacement and intensity in magnetic bright points found in
the 300 nm and the Ca II H 396.8 nm passbands of the filter imager on board the
Sunrise balloon-borne solar observatory. Phase differences between the
oscillations at the two atmospheric layers corresponding to the two passbands
reveal upward propagating waves at high frequencies (up to 30 mHz). Weak
signatures of standing as well as downward propagating waves are also obtained.
Both compressible and incompressible (kink) waves are found in the small-scale
magnetic features. The two types of waves have different, though overlapping,
period distributions. Two independent estimates give a height difference of
approximately 450+-100 km between the two atmospheric layers sampled by the
employed spectral bands. This value, together with the determined short travel
times of the transverse and longitudinal waves provide us with phase speeds of
29+-2 km/s and 31+-2 km/s, respectively. We speculate that these phase speeds
may not reflect the true propagation speeds of the waves. Thus, effects such as
the refraction of fast longitudinal waves may contribute to an overestimate of
the phase speed.Comment: 14 pages, 7 figure
High-resolution wave dynamics in the lower solar atmosphere
The magnetic and convective nature of the Sun's photosphere provides a unique
platform from which generated waves can be modelled, observed, and interpreted
across a wide breadth of spatial and temporal scales. As oscillations are
generated in-situ or emerge through the photospheric layers, the interplay
between the rapidly evolving densities, temperatures, and magnetic field
strengths provides dynamic evolution of the embedded wave modes as they
propagate into the tenuous solar chromosphere. A focused science team was
assembled to discuss the current challenges faced in wave studies in the lower
solar atmosphere, including those related to spectropolarimetry and radiative
transfer in the optically thick regions. Following the Theo Murphy
international scientific meeting held at Chicheley Hall during February 2020,
the scientific team worked collaboratively to produce 15 independent
publications for the current Special Issue, which are introduced here.
Implications from the current research efforts are discussed in terms of
upcoming next-generation observing and high performance computing facilities.Comment: 16 pages, 4 figures, Introduction to the "High-resolution wave
dynamics in the lower solar atmosphere" special issue of the Philosophical
Transactions A: https://walsa.team/u/rst
The Sun at millimeter wavelengths -- II. Small-scale dynamic events in ALMA Band 3
Solar observations with the Atacama Large Millimeter/sub-millimeter Array
(ALMA) facilitate studying the atmosphere of the Sun at chromospheric heights
at high spatial and temporal resolution at millimeter wavelengths. ALMA
intensity data at mm-wavelengths are used for a first detailed systematic
assessment of the occurrence and properties of small-scale dynamical features
in the quiet Sun. ALMA Band 3 data (~ mm / GHz) with spatial
resolution ~ - arcsec and a duration of ~ min are analysed
together with SDO/HMI magnetograms. The temporal evolution of the mm-maps is
studied to detect pronounced dynamical features which are connected to
dynamical events via a k-means clustering algorithm. The physical properties of
the resulting events are studied and it is explored if they show properties
consistent with propagating shock waves. For this purpose, observable shock
wave signatures at mm wavelengths are calculated from one- and
three-dimensional model atmospheres. There are 552 dynamical events detected
with an excess in brightness temperature () of at least
K. The events show a large variety in size up to ~ arcsec,
amplitude up to ~ K with typical values between ~
- K and lifetime at FWHM of between ~ -
s, with typical values between ~ - s. Furthermore, many of the
events show signature properties that suggest that they are likely produced by
propagating shock waves. There are a lot of small-scale dynamic structures
detected in the Band 3 data, even though the spatial resolution sets
limitations of the size of events that can be detected. The amount of dynamic
signatures in the ALMA mm data is very low in areas with photospheric
footpoints with stronger magnetic fields, which is consistent with the
expectation for propagating shock waves.Comment: Accepted for publication in Astronomy & Astrophysics, 17 pages, 15
figure
Estimativa da composição elementar de solos do Azerbaijão oeste, Irã, utilizando-se modelos espectrais de infravermelho
[Abstract] Characterizing the elemental composition provides useful information about the weathering degree of soils. In Miandoab County, Northern Iran, this characterization was missing, and thus the objectives of this work were to evaluate the weathering degrees for the most typical soils in the area from their elemental compositions, and to estimate this elemental composition using Fourier transform infrared spectroscopy and Random Forest models. Five soil profiles, including Aridisols and Inceptisols, were selected as the most representative of the area. Major elemental oxides were determined in each genetic horizon by X-ray fluorescence, showing that these soils were at early developmental stages. Only Al2O3 and CaO were accurately estimated, with R2 values of 0.8, and out-of-bag mean square errors of 0.2 and 1.1, respectively. The other oxides were not predicted satisfactorily, probably due to small differences in their elemental compositions. Random Forest provided the important spectral bands related to the content of each element. For Al2O3, these bands were between 500 and 650 cm-1, which represent out-of-plane OH bending vibrations and Al-O gibbsite and alumino-silicate vibrations. For CaO, the most important bands are related to carbonate content. A combination of Fourier transform infrared spectra and Random Forest models can be used as a rapid and low-cost technique to estimate the elemental composition of arid and semi-arid soils of Northern Iran.[Resumo] A caracterização da composição elementar fornece informações úteis para caracterizar o grau de alteração dos solos. Em Miandoab, norte do Irã, esta caracterização não existe. Os objetivos deste trabalho foram avaliar o grau de intemperismo dos solos tÃpicos da região usando a sua composição elementar e estimar esta composição usando espectroscopia infravermelha com transformada de Fourier (FTIR) e modelos Random Forest (RF). Foram selecionados cinco perfis de solo, incluindo Aridisolos e Inceptisolos, como os mais representativos da área. Os principais óxidos elementares foram determinados por fluorescência de raios-X em cada horizonte genético, mostrando que estes solos estavam em um estágio de baixo grau de desenvolvimento. Apenas o Al2O3 e o CaO foram estimados com precisão, com valores de R2 de 0,8 e erro quadrático médio nos dados utilizados para validação de 0,2 e 1,1, respectivamente, enquanto os outros óxidos não foram preditos satisfatoriamente, provavelmente devido à s pequenas diferenças na sua composição. O modelo Random Forest forneceu importantes bandas espectrais relacionadas com o conteúdo de cada elemento. Para o Al2O3, estes atingiram a região 500 a 650 cm-1, o que foi atribuÃdo a vibrações de flexão de OH e vibrações de Al-O de gibbsita e alumino-silicatos. Para o CaO, as bandas mais importantes estavam relacionadas ao teor de carbonatos. Os resultados indicam que uma combinação de espectros infravermelha de transformada de Fourier e modelos Random Forest pode ser usada como uma técnica rápida e de baixo custo para estimar a composição elementar de solos do norte do Irã
Characterisation of shock wave signatures at millimetre wavelengths from Bifrost simulations
Observations at millimetre wavelengths provide a valuable tool to study the
small scale dynamics in the solar chromosphere. We evaluate the physical
conditions of the atmosphere in the presence of a propagating shock wave and
link that to the observable signatures in mm-wavelength radiation, providing
valuable insights into the underlying physics of mm-wavelength observations. A
realistic numerical simulation from the 3D radiative Magnetohydrodynamic (MHD)
code Bifrost is used to interpret changes in the atmosphere caused by shock
wave propagation. High-cadence (1 s) time series of brightness temperature
(T) maps are calculated with the Advanced Radiative Transfer (ART)
code at the wavelengths mm and mm, which represents opposite
sides of spectral band~ of the Atacama Large Millimeter/submillimeter Array
(ALMA). An example of shock wave propagation is presented. The brightness
temperatures show a strong shock wave signature with large variation in
formation height between to Mm. The results demonstrate that
millimetre brightness temperatures efficiently track upwardly propagating shock
waves in the middle chromosphere. In addition, we show that the gradient of the
brightness temperature between wavelengths within ALMA band can potentially
be utilised as a diagnostics tool in understanding the small-scale dynamics at
the sampled layers.Comment: 16 pages, 6 figures. Accepted for publication in Philosophical
Transactions A of the Royal Societ
Morphological properties of slender Ca II H fibrils observed by SUNRISE II
We use seeing-free high spatial resolution Ca II H data obtained by the
SUNRISE observatory to determine properties of slender fibrils in the lower
solar chromosphere. In this work we use intensity images taken with the SUFI
instrument in the Ca II H line during the second scientific flight of the
SUNRISE observatory to identify and track elongated bright structures. After
the identification, we analyze theses structures in order to extract their
morphological properties. We identify 598 slender Ca II H fibrils (SCFs) with
an average width of around 180 km, a length between 500 km and 4000 km, an
average lifetime of ~400 s, and an average curvature of 0.002 arcsec^-1. The
maximum lifetime of the SCFs within our time series of 57 minutes is ~2000 s.
We discuss similarities and differences of the SCFs with other small-scale,
chromospheric structures such as spicules of type I and II, or Ca II K fibrils.Comment: Accepted for publication in The Astrophysical Journal Supplement
Serie
Kinematics of Magnetic Bright Features in the Solar Photosphere
Convective flows are known as the prime means of transporting magnetic fields
on the solar surface. Thus, small magnetic structures are good tracers of the
turbulent flows. We study the migration and dispersal of magnetic bright
features (MBFs) in intergranular areas observed at high spatial resolution with
Sunrise/IMaX. We describe the flux dispersal of individual MBFs as a diffusion
process whose parameters are computed for various areas in the quiet Sun and
the vicinity of active regions from seeing-free data. We find that magnetic
concentrations are best described as random walkers close to network areas
(diffusion index, gamma=1.0), travelers with constant speeds over a
supergranule (gamma=1.9-2.0), and decelerating movers in the vicinity of flux
emergence and/or within active regions (gamma=1.4-1.5). The three types of
regions host MBFs with mean diffusion coefficients of 130 km^2/s, 80-90 km^2/s,
and 25-70 km^2/s, respectively. The MBFs in these three types of regions are
found to display a distinct kinematic behavior at a confidence level in excess
of 95%.Comment: 8 pages, 4 figure
The Sun at millimeter wavelengths I. Introduction to ALMA Band 3 observations
We present an initial study of one of the first ALMA Band 3 observations of
the Sun with the aim to characterise the diagnostic potential of brightness
temperatures measured with ALMA on the Sun. The observation covers 48min at a
cadence of 2s targeting a Quiet Sun region at disk-centre. Corresponding time
series of brightness temperature maps are constructed with the first version of
the Solar ALMA Pipeline (SoAP) and compared to simultaneous SDO observations.
The angular resolution of the observations is set by the synthesized beam
(1.4x2.1as). The ALMA maps exhibit network patches, internetwork regions and
also elongated thin features that are connected to large-scale magnetic loops
as confirmed by a comparison with SDO maps. The ALMA Band 3 maps correlate best
with the SDO/AIA 171, 131 and 304 channels in that they exhibit network
features and, although very weak in the ALMA maps, imprints of large-scale
loops. A group of compact magnetic loops is very clearly visible in ALMA Band
3. The brightness temperatures in the loop tops reach values of about
8000-9000K and in extreme moments up to 10 000K. ALMA Band 3 interferometric
observations from early observing cycles already reveal temperature differences
in the solar chromosphere. The weak imprint of magnetic loops and the
correlation with the 171, 131, and 304 SDO channels suggests though that the
radiation mapped in ALMA Band 3 might have contributions from a larger range of
atmospheric heights than previously assumed but the exact formation height of
Band 3 needs to be investigated in more detail. The absolute brightness
temperature scale as set by Total Power measurements remains less certain and
must be improved in the future. Despite these complications and the limited
angular resolution, ALMA Band 3 observations have large potential for
quantitative studies of the small-scale structure and dynamics of the solar
chromosphere.Comment: 14 pages, 9 figures; accepted for publication in A&