scholarly journals The Sun at millimeter wavelengths

2020 ◽  
Vol 635 ◽  
pp. A71 ◽  
Author(s):  
Sven Wedemeyer ◽  
Mikolaj Szydlarski ◽  
Shahin Jafarzadeh ◽  
Henrik Eklund ◽  
Juan Camilo Guevara Gomez ◽  
...  
Keyword(s):  
Brightness Temperature ◽  
Large Scale ◽  
Angular Resolution ◽  
Band 3 ◽  
Total Power ◽  
Small Scale ◽  
Solar Chromosphere ◽  
The Sun ◽  
Brightness Temperatures ◽  
Diagnostic Potential

Context. The Atacama Large Millimeter/submillimeter Array (ALMA) started regular observations of the Sun in 2016, first offering receiver Band 3 at wavelengths near 3 mm (100 GHz) and Band 6 at wavelengths around 1.25 mm (239 GHz). Aims. Here we present an initial study of one of the first ALMA Band 3 observations of the Sun. Our aim is to characterise the diagnostic potential of brightness temperatures measured with ALMA on the Sun. Methods. The observation covers a duration of 48 min at a cadence of 2 s targeting a quiet Sun region at disc-centre. Corresponding time series of brightness temperature maps are constructed with the first version of the Solar ALMA Pipeline and compared to simultaneous observations with the Solar Dynamics Observatory (SDO). Results. The angular resolution of the observations is set by the synthesised beam, an elliptical Gaussian that is approximately 1.4″ × 2.1″ in size. The ALMA maps exhibit network patches, internetwork regions, and 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 Å, 131 Å, and 304 Å 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 8000−9000 K and in extreme moments up to 10 000 K. Conclusions. 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, however, that the radiation mapped in ALMA Band 3 might have contributions from a wider 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 a large potential for quantitative studies of the small-scale structure and dynamics of the solar chromosphere.

scholarly journals Characterization of shock wave signatures at millimetre wavelengths from Bifrost simulations

2020 ◽  
Vol 379 (2190) ◽  
pp. 20200185 ◽  
Author(s):  
Henrik Eklund ◽  
Sven Wedemeyer ◽  
Ben Snow ◽  
David B. Jess ◽  
Shahin Jafarzadeh ◽  
...  
Keyword(s):  
Shock Wave ◽  
Wave Propagation ◽  
Brightness Temperature ◽  
Spectral Band ◽  
Three Dimensional ◽  
Strong Shock ◽  
Shock Wave Propagation ◽  
Small Scale ◽  
Solar Chromosphere ◽  
Brightness Temperatures

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 three-dimensional radiative magnetohydrodynamic 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 b ) maps are calculated with the Advanced Radiative Transfer code at the wavelengths 1.309 mm and 1.204 mm, which represents opposite sides of spectral band 6 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 approximately 0.7 and 1.4 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 6 can potentially be used as a diagnostics tool in understanding the small-scale dynamics at the sampled layers. This article is part of the Theo Murphy meeting issue ‘High-resolution wave dynamics in the lower solar atmosphere’.

scholarly journals High-frequency oscillations in small chromospheric bright features observed with Atacama Large Millimetre/Submillimetre Array

2020 ◽  
Vol 379 (2190) ◽  
pp. 20200184 ◽  
Author(s):  
J. C. Guevara Gómez ◽  
S. Jafarzadeh ◽  
S. Wedemeyer ◽  
M. Szydlarski ◽  
M. Stangalini ◽  
...  
Keyword(s):  
Brightness Temperature ◽  
High Frequency ◽  
Small Scale ◽  
High Temporal Resolution ◽  
Solar Chromosphere ◽  
Wave Dynamics ◽  
High Frequency Oscillations ◽  
Diagnostic Potential ◽  
Kink Waves ◽  
Outer Atmosphere

We report detection of oscillations in brightness temperature, size and horizontal velocity of three small bright features in the chromosphere of a plage/enhanced-network region. The observations, which were taken with high temporal resolution (i.e. 2 s cadence) with the Atacama large millimetre/ submillimetre array (ALMA) in Band 3 (centred at 3 mm; 100 GHz), exhibit three small-scale features with oscillatory behaviour with different, but overlapping, distributions of period on the order of, on average, 90 ± 22 s, 110 ± 12 s and 66 ± 23 s, respectively. We find anti-correlations between perturbations in brightness, temperature and size of the three features, which suggest the presence of fast sausage-mode waves in these small structures. In addition, the detection of transverse oscillations (although with a larger uncertainty) may also suggest the presence of Alfvénic oscillations which are likely representative of kink waves. This work demonstrates the diagnostic potential of high-cadence observations with ALMA for detecting high-frequency magnetohydrodynamic waves in the solar chromosphere. Such waves can potentially channel a vast amount of energy into the outer atmosphere of the Sun. This article is part of the Theo Murphy meeting issue ‘High-resolution wave dynamics in the lower solar atmosphere’.

scholarly journals How to make the Sun look less like the Sun and more like a star?

2016 ◽  
Vol 12 (S328) ◽  
pp. 237-239
Author(s):  
A. A. Vidotto
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Vector Fields ◽  
Radial Component ◽  
Field Vector ◽  
Small Scale ◽  
General Context ◽  
The Sun ◽  
Flux Transport ◽  
Large Scale Magnetic Field

AbstractSynoptic maps of the vector magnetic field have routinely been made available from stellar observations and recently have started to be obtained for the solar photospheric field. Although solar magnetic maps show a multitude of details, stellar maps are limited to imaging large-scale fields only. In spite of their lower resolution, magnetic field imaging of solar-type stars allow us to put the Sun in a much more general context. However, direct comparison between stellar and solar magnetic maps are hampered by their dramatic differences in resolution. Here, I present the results of a method to filter out the small-scale component of vector fields, in such a way that comparison between solar and stellar (large-scale) magnetic field vector maps can be directly made. This approach extends the technique widely used to decompose the radial component of the solar magnetic field to the azimuthal and meridional components as well, and is entirely consistent with the description adopted in several stellar studies. This method can also be used to confront synoptic maps synthesised in numerical simulations of dynamo and magnetic flux transport studies to those derived from stellar observations.

scholarly journals Transient brightenings in the quiet Sun detected by ALMA at 3 mm

2020 ◽  
Vol 638 ◽  
pp. A62 ◽  
Author(s):  
A. Nindos ◽  
C. E. Alissandrakis ◽  
S. Patsourakos ◽  
T. S. Bastian
Keyword(s):  
Solar Atmosphere ◽  
Power Law ◽  
Small Scale ◽  
Solar Chromosphere ◽  
Average Intensity ◽  
Quiet Sun ◽  
Brightness Temperatures ◽  
Weak Preference ◽  
Thermal Origin ◽  
First Time

Aims. We investigate transient brightenings, that is, weak, small-scale episodes of energy release, in the quiet solar chromosphere; these episodes can provide insights into the heating mechanism of the outer layers of the solar atmosphere. Methods. Using Atacama Large Millimeter/submillimeter Array (ALMA) observations, we performed the first systematic survey for quiet Sun transient brightenings at 3 mm. Our dataset included images of six 87″ × 87″ fields of view of the quiet Sun obtained with angular resolution of a few arcsec at a cadence of 2 s. The transient brightenings were detected as weak enhancements above the average intensity after we removed the effect of the p-mode oscillations. A similar analysis, over the same fields of view, was performed for simultaneous 304 and 1600 Å data obtained with the Atmospheric Imaging Assembly. Results. We detected 184 3 mm transient brightening events with brightness temperatures from 70 K to more than 500 K above backgrounds of ∼7200 − 7450 K. All events showed light curves with a gradual rise and fall, strongly suggesting a thermal origin. Their mean duration and maximum area were 51.1 s and 12.3 Mm2, respectively, with a weak preference of appearing at network boundaries rather than in cell interiors. Both parameters exhibited power-law behavior with indices of 2.35 and 2.71, respectively. Only a small fraction of ALMA events had either 304 or 1600 Å counterparts but the properties of these events were not significantly different from those of the general population except that they lacked their low-end energy values. The total thermal energies of the ALMA transient brightenings were between 1.5 × 1024 and 9.9 × 1025 erg and their frequency distribution versus energy was a power law with an index of 1.67 ± 0.05. We found that the power per unit area provided by the ALMA events could account for only 1% of the chromospheric radiative losses (10% of the coronal ones). Conclusions. We were able to detect, for the first time, a significant number of weak 3 mm quiet Sun transient brightenings. However, their energy budget falls short of meeting the requirements for the heating of the upper layers of the solar atmosphere and this conclusion does not change even if we use the least restrictive criteria possible for the detection of transient brightenings.

scholarly journals Observations of Solar Continuum Emission at Decameter Wavelengths

1990 ◽  
Vol 142 ◽  
pp. 513-514
Author(s):  
Ch. V. Sastry
Keyword(s):  
Electron Temperature ◽  
Brightness Temperature ◽  
Large Scale ◽  
Continuum Emission ◽  
The Sun ◽  
Temperature Variations ◽  
One Dimensional ◽  
Wave Radio ◽  
Grating Interferometer ◽  
The Continuum

We observed the continuum emission from the radio sun when there is no burst activity at λ = 8.7 m with the large decameter wave radio telescope at Gauribidanur (Latitude 13° 36‘ 12“ N and 77° 27‘ 07“ E) with a resolution of 26'/40'. A compound grating interferometer with one dimensional resolution of 3' is also used. These observations are made during August 1983 and June 1986. The brightness temperature at the center of the sun varied from 0.2 106 K to 0.8 106 K during these periods on time scales of several hours to a day. Since the sun is absolutely quiet during these periods we believe that the radiation is purely thermal in nature. In this case the observed brightness temperature variations imply large scale density variations by more than a factor of three if the corona is optically thin at these wavelengths. Alternatively if the corona is optically thick the observations imply real electron temperature variations with or without accompanying density variations.

Solar Dynamo

2020 ◽  
Author(s):  
Robert Cameron
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Differential Rotation ◽  
Large Scale ◽  
Toroidal Field ◽  
Solar Dynamo ◽  
Small Scale ◽  
The Sun ◽  
The Magnetic Field

The solar dynamo is the action of flows inside the Sun to maintain its magnetic field against Ohmic decay. On small scales the magnetic field is seen at the solar surface as a ubiquitous “salt-and-pepper” disorganized field that may be generated directly by the turbulent convection. On large scales, the magnetic field is remarkably organized, with an 11-year activity cycle. During each cycle the field emerging in each hemisphere has a specific East–West alignment (known as Hale’s law) that alternates from cycle to cycle, and a statistical tendency for a North-South alignment (Joy’s law). The polar fields reverse sign during the period of maximum activity of each cycle. The relevant flows for the large-scale dynamo are those of convection, the bulk rotation of the Sun, and motions driven by magnetic fields, as well as flows produced by the interaction of these. Particularly important are the Sun’s large-scale differential rotation (for example, the equator rotates faster than the poles), and small-scale helical motions resulting from the Coriolis force acting on convective motions or on the motions associated with buoyantly rising magnetic flux. These two types of motions result in a magnetic cycle. In one phase of the cycle, differential rotation winds up a poloidal magnetic field to produce a toroidal field. Subsequently, helical motions are thought to bend the toroidal field to create new poloidal magnetic flux that reverses and replaces the poloidal field that was present at the start of the cycle. It is now clear that both small- and large-scale dynamo action are in principle possible, and the challenge is to understand which combination of flows and driving mechanisms are responsible for the time-dependent magnetic fields seen on the Sun.

scholarly journals Evolution of Large and Small Scale Magnetic Fields in the Sun

1991 ◽  
Vol 130 ◽  
pp. 218-222
Author(s):  
Peter A. Fox ◽  
Michael L. Theobald ◽  
Sabatino Sofia
Keyword(s):  
Numerical Simulation ◽  
Magnetic Fields ◽  
Time Dependence ◽  
Large Scale ◽  
Sunspot Cycle ◽  
Small Scale ◽  
The Sun ◽  
Solar Magnetic Fields ◽  
Magnetic Resistivity ◽  
Statistical Evolution

AbstractThis paper will discuss issues relating to the detailed numerical simulation of solar magnetic fields, those on the small scale which are directly observable on the surface, and those on larger scales whose properties must be deduced indirectly from phenomena such as the sunspot cycle. Results of simulations using the ADISM technique will be presented to demonstrate the importance of the treatment of Alfvén waves, the boundary conditions, and the statistical evolution of small scale convection with magnetic fields. To study the large scale fields and their time dependence, the magnetic resistivity plays an important role; its use will be discussed in the paper.

Validation of a Large-Scale Simulated Brightness Temperature Dataset Using SEVIRI Satellite Observations

2009 ◽  
Vol 48 (8) ◽  
pp. 1613-1626 ◽  
Author(s):  
Jason A. Otkin ◽  
Thomas J. Greenwald ◽  
Justin Sieglaff ◽  
Hung-Lung Huang
Keyword(s):  
Brightness Temperature ◽  
Large Scale ◽  
Model Simulation ◽  
Probability Distributions ◽  
Relative Proportion ◽  
Tropical Convection ◽  
Radiative Properties ◽  
Model Errors ◽  
Ice Clouds ◽  
Brightness Temperatures

Abstract In this study, the accuracy of a simulated infrared brightness temperature dataset derived from a unique large-scale, high-resolution Weather Research and Forecasting (WRF) Model simulation is evaluated through a comparison with Spinning Enhanced Visible and Infrared Imager (SEVIRI) observations. Overall, the analysis revealed that the simulated brightness temperatures realistically depict many of the observed features, although several large discrepancies were also identified. The similar shapes of the simulated and observed probability distributions calculated for each infrared band indicate that the model simulation realistically depicted the cloud morphology and relative proportion of clear and cloudy pixels. A traditional error analysis showed that the largest model errors occurred over central Africa because of a general mismatch in the locations of deep tropical convection and intervening regions of clear skies and low-level cloud cover. A detailed inspection of instantaneous brightness temperature difference (BTD) imagery showed that the modeling system realistically depicted the radiative properties associated with various cloud types. For instance, thin cirrus clouds along the edges of deep tropical convection and within midlatitude cloud shields were characterized by much larger 10.8 − 12.0-μm BTD than optically thicker clouds. Simulated ice clouds were effectively discriminated from liquid clouds and clear pixels by the close relationship between positive 8.7 − 10.8-μm BTD and the coldest 10.8-μm brightness temperatures. Comparison of the simulated and observed BTD probability distributions revealed that the liquid and mixed-phase cloud-top properties were consistent with the observations, whereas the narrower BTD distributions for the colder 10.8-μm brightness temperatures indicated that the microphysics scheme was unable to simulate the full dynamic range of ice clouds.

scholarly journals Quasi-periodic oscillations of small-scale magnetic structures and a specific method for measuring the differential rotation of the Sun

2019 ◽  
Vol 5 (1) ◽  
pp. 4-12
Author(s):  
Иван Живанович ◽  
Ivan Zhivanovich ◽  
Александр Риехокайнен ◽  
Aleksandr Riehokainen ◽  
Александр Соловьев ◽  
...  
Keyword(s):  
Fourier Analysis ◽  
Differential Rotation ◽  
Rotation Curve ◽  
Angular Resolution ◽  
Small Scale ◽  
Specific Method ◽  
The Sun ◽  
Periodic Oscillations ◽  
Magnetic Structures ◽  
Good Agreement

The SDO/HMI data with an angular resolution of 1 arcsec have been used to explore the differential rotation on the Sun, using an original “p2p” effect on the basis of the movement of small-scale magnetic structures in the photosphere of the Sun. It is shown that a stable p2p artifact inherent in the SDO/HMI data can be an effective tool for measuring the speed of various tracers on the Sun. In particular, in combination with the Fourier analysis, it allows us to investigate the differential rotation of the Sun at various latitudes. The differential rotation curve obtained from the SDO/HMI magnetograms by this method is in good agreement with the curves obtained earlier from ground-based observations.

scholarly journals Quasi-periodic oscillations of small-scale magnetic structures and a specific method for measuring the differential rotation of the Sun

2019 ◽  
pp. 3-10
Author(s):  
Иван Живанович ◽  
Ivan Zhivanovich ◽  
Александр Риехокайнен ◽  
Alexandr Riehokainen ◽  
Александр Соловьев ◽  
...  
Keyword(s):  
Fourier Analysis ◽  
Differential Rotation ◽  
Rotation Curve ◽  
Angular Resolution ◽  
Small Scale ◽  
Specific Method ◽  
The Sun ◽  
Periodic Oscillations ◽  
Magnetic Structures ◽  
Good Agreement

The SDO/HMI data with an angular resolution of 1 arcsec have been used to explore the differential rotation on the Sun, using an original “p2p” effect on the basis of the movement of small-scale magnetic structures in the photosphere of the Sun. It is shown that a stable p2p artifact inherent in the SDO/HMI data can be an effective tool for measuring the speed of various tracers on the Sun. In particular, in combination with the Fourier analysis, it allows us to investigate the differential rotation of the Sun at various latitudes. The differential rotation curve obtained from the SDO/HMI magnetograms by this method is in good agreement with the curves obtained earlier from ground-based observations.

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