Interpretation of the Filament Depression at Millimetric and Centimetric Wavelengths

1979 ◽  
Vol 44 ◽  
pp. 131-134
Author(s):  
A. Raoult ◽  
P. Lantos ◽  
E. Fürst
Keyword(s):  
Radio Telescope ◽  
Active Regions ◽  
Simple Shape ◽  
Quiet Sun ◽  
Unstable Process

The depressions at centimetric and millimetric wavelengths associated with the filaments are studied using already published maps as well as unpublished observations from the Effelsberg 100 m radio telescope of the M.P.I., Bonn. The study has been restricted to large Ha quiescent prominences of relatively simple shape, situated far from the limb and from active regions. The data has been reduced employing one method whose main characteristics are choice of a local quiet sun definition and avoidance of the unstable process of deconvolution.

scholarly journals Observations of the Quiet Sun with 6″ Resolution

1980 ◽  
Vol 86 ◽  
pp. 53-55
Author(s):  
M. R. Kundu ◽  
A. P. Rao ◽  
F. T. Erskine ◽  
J. D. Bregman
Keyword(s):  
High Resolution ◽  
Radio Emission ◽  
Transition Region ◽  
Spatial Resolution ◽  
Radio Telescope ◽  
Solar Radio ◽  
High Spatial Resolution ◽  
Solar Radio Emission ◽  
Quiet Sun ◽  
Millimeter Wavelengths

Solar radio emission at centimeter and millimeter wavelengths originates in the chromosphere and transition region and is a useful probe for the temperature and density in these regions. High spatial resolution observations of the quiet sun provide valuable information on the structure of the solar atmosphere. We have performed high resolution (~ 6″ (E-W) x 15″ (N-S)) observations at 6 cm with the Westerbork Synthesis Radio Telescope (WSRT) in June 1976 in order to search for the radio analog of the supergranulation network and to study the extent and symmetry of limb brightening. The use of the WSRT for high spatial resolution solar mapping has been described by Bregman and Felli (1976), Kundu et al. (1977), and others.

scholarly journals Magnetic power spectrum in the undisturbed solar photosphere

2020 ◽  
Vol 1 (1) ◽  
pp. 1-5
Author(s):  
Valentina Abramenko ◽  
Olga Kutsenko
Keyword(s):  
Power Spectrum ◽  
Power Spectra ◽  
Active Regions ◽  
Reliable Estimate ◽  
Small Scale ◽  
Solar Photosphere ◽  
Dynamo Action ◽  
Quiet Sun ◽  
Turbulent Dynamo ◽  
Wide Range

Using the magnetic field data obtained with the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO), an investigation of magnetic power spectra in the undisturbed solar photosphere was performed. The results are as follows. 1) To get a reliable estimate of a magnetic power spectrum from the uniformly distributed quiet-sun magnetic flux, a sample pattern of no less than 300 pixels length should be adopted. With smaller patterns, energy on all observable scales might be overestimated. 2) For patterns of different magnetic intensity (e.g., a coronal hole, a quiet-sun area, an area of supergranulation), the magnetic power spectra in a range of (2.5-10) Mm exhibit very close spectral indices of about -1. The observed spectrum is more shallow than the Kolmogorov-type spectrum (with a slope of -5/3) and it differs from steep spectra of active regions. Such a shallow spectrum cannot be explained by the only direct Kolmogorov’s cascade, but it can imply a small-scale turbulent dynamo action in a wide range of scales: from tens of megameters down to at least 2.5 Mm. On smaller scales, the HMI/SDO data do not allow us to reliably derive the shape of the spectrum. 3) Data make it possible to conclude that a uniform mechanism of the small-scale turbulent dynamo is at work all over the solar surface outside active regions.

TRACE Emission Heights Estimated from TRACE Limb Observations

2001 ◽  
Vol 203 ◽  
pp. 431-433
Author(s):  
M. Zhang
Keyword(s):  
Transition Region ◽  
Coronal Holes ◽  
Active Regions ◽  
Height Variation ◽  
Quiet Sun ◽  
Trace Data ◽  
Coronal Structures

While TRACE data have provided us much information of transition region and coronal structures, many TRACE data users would like to have a knowledge of emission heights of TRACE bands. By analyzing TRACE limb observations, we give an average estimation of emission heights of TRACE 171, 195 and 1216 bands for different features like quiet Sun regions, active regions and coronal holes. Average emission heights over the limb are also discussed. Previous equator-to-pole height variation is further confirmed by TRACE data when averaging on quiet Sun regions. If averaging for all fluxes, a reverse equator-to-pole height variation is shown.

scholarly journals Is magnetic topology important for heating the solar atmosphere?

2015 ◽  
Vol 373 (2042) ◽  
pp. 20140264 ◽  
Author(s):  
Clare E. Parnell ◽  
Julie E. H. Stevenson ◽  
James Threlfall ◽  
Sarah J. Edwards
Keyword(s):  
Magnetic Fields ◽  
Open Field ◽  
Solar Atmosphere ◽  
Active Regions ◽  
Energy Losses ◽  
Wave Dissipation ◽  
Quiet Sun ◽  
Topological Features ◽  
Complex Topology ◽  
Global And Local

Magnetic fields permeate the entire solar atmosphere weaving an extremely complex pattern on both local and global scales. In order to understand the nature of this tangled web of magnetic fields, its magnetic skeleton, which forms the boundaries between topologically distinct flux domains, may be determined. The magnetic skeleton consists of null points, separatrix surfaces, spines and separators. The skeleton is often used to clearly visualize key elements of the magnetic configuration, but parts of the skeleton are also locations where currents and waves may collect and dissipate. In this review, the nature of the magnetic skeleton on both global and local scales, over solar cycle time scales, is explained. The behaviour of wave pulses in the vicinity of both nulls and separators is discussed and so too is the formation of current layers and reconnection at the same features. Each of these processes leads to heating of the solar atmosphere, but collectively do they provide enough heat, spread over a wide enough area, to explain the energy losses throughout the solar atmosphere? Here, we consider this question for the three different solar regions: active regions, open-field regions and the quiet Sun. We find that the heating of active regions and open-field regions is highly unlikely to be due to reconnection or wave dissipation at topological features, but it is possible that these may play a role in the heating of the quiet Sun. In active regions, the absence of a complex topology may play an important role in allowing large energies to build up and then, subsequently, be explosively released in the form of a solar flare. Additionally, knowledge of the intricate boundaries of open-field regions (which the magnetic skeleton provides) could be very important in determining the main acceleration mechanism(s) of the solar wind.

scholarly journals Irradiance Models Based on Solar Magnetic Fields

1994 ◽  
Vol 143 ◽  
pp. 217-225 ◽  
Author(s):  
Karen L. Harvey
Keyword(s):  
Active Region ◽  
Magnetic Fields ◽  
Magnetic Flux ◽  
Coronal Holes ◽  
Active Regions ◽  
Spectral Irradiance ◽  
Solar Magnetic Fields ◽  
Quiet Sun ◽  
Possible Cause

A method to separate the active region and quiet network components of the magnetic fields in the photosphere is described and compared with the corresponding measurements of the He I λ 10830 absorption. The relation between the total He I absorption and total magnetic flux in active regions is roughly linear and differs between cycles 21 and 22. There appears to no relation between these two quantities in areas outside of active regions. The total He I absorption in the quiet Sun (comprised of network, filaments, and coronal holes) exceeds that in active regions at all times during the cycle. As a whole, active regions of cycle 22 appear to be less complex than the active regions of cycle 21, hinting at one possible cause for a differing relation between spectral-irradiance variations and the underlying magnetic flux for these two cycles.

scholarly journals The Radio Brightness of the Quiet Sun at 21 cm Wavelength Near Sunspot Maximum

1960 ◽  
Vol 13 (4) ◽  
pp. 700 ◽  
Author(s):  
NR Labrum
Keyword(s):  
Active Regions ◽  
Residual Effects ◽  
High Angular Resolution ◽  
Radio Brightness ◽  
Sunspot Maximum ◽  
One Dimensional ◽  
Quiet Sun ◽  
Limits Of Error ◽  
Very High ◽  
Intense Radiation

An investigation has been made of the radio emission from the quiet Sun at 21� 2 em wavelength in 1958 (near sunspot maximum). Two different methods have been used, both involving observations with very high angular resolution, to distinguish between the quiet-Sun component and the radiation from localized active regions. In one method, the Sun was scanned with a narrow pencil-beam; in the other, a fan-shaped aerial beam was used to give one-dimensional strip scans. In both cases it was necessary, when analysing the data, to take into account the residual effects of the very intense radiation from the localized sources. The two independent measurements gave results which agree within the limits of error. The apparent disk temperature was found to be approximately 140 000 oK, or twice the value for the same wavelength at sunspot minimum.

scholarly journals Inferring depth-dependent plasma motions from surface observations using the DeepVel neural network

2020 ◽  
Author(s):  
Benoit Tremblay ◽  
Jean-François Cossette ◽  
Maria D. Kazachenko ◽  
Paul Charbonneau ◽  
Alain Patrick Vincent
Keyword(s):  
Neural Network ◽  
Data Assimilation ◽  
Numerical Simulations ◽  
Active Regions ◽  
Transverse Component ◽  
Small Scale ◽  
Solar Photosphere ◽  
Quiet Sun ◽  
The Neural Network ◽  
Spatial Coverage

Coverage of plasma motions is limited to the line-of-sight component at the Sun's surface. Multiple tracking and inversion methods were developed to infer the transverse motions from observational data. Recently, the DeepVel neural network was trained with computations performed by numerical simulations of the solar photosphere to recover the missing transverse component at surface and at two additional optical depths simultaneously from the surface white light intensity in the Quiet Sun. We argue that deep learning could provide additional spatial coverage to existing observations in the form of depth-dependent synthetic observations, i.e. estimates generated through the emulation of numerical simulations. We trained different versions of DeepVel using slices from numerical simulations of both the Quiet Sun and Active Region at various optical and geometrical depths in the solar atmosphere, photosphere and upper convection zone to establish the upper and lower limits at which the neural network can generate reliable synthetic observations of plasma motions from surface intensitygrams. Flow fields inferred in the photosphere and low chromosphere $\tau \in [0.1, 1)$ are comparable to inversions performed at the surface ($\tau \approx 1$) and are deemed to be suitable for use as synthetic observations in data assimilation processes and data-driven simulations. This upper limit extends closer to the transition region ($\tau \approx 0.01$) in the Quiet Sun, but not for Active Regions. Subsurface flows inferred from surface intensitygrams fail to capture the small-scale features of turbulent convective motions as depth crosses a few hundred kilometers. We suggest that these reconstructions could be used as first estimates of a model's velocity vector in data assimilation processes to nowcast and forecast short term solar activity and space weather.

scholarly journals Observations of the Quiet Sun during the Deepest Solar Minimum of the Past Century with Chandrayaan-2 XSM: Sub-A-class Microflares outside Active Regions

2021 ◽  
Vol 912 (1) ◽  
pp. L13
Author(s):  
Santosh V. Vadawale ◽  
N. P. S. Mithun ◽  
Biswajit Mondal ◽  
Aveek Sarkar ◽  
P. Janardhan ◽  
...  
Keyword(s):  
Solar Minimum ◽  
Active Regions ◽  
Past Century ◽  
Quiet Sun ◽  
The Past
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