The Submillimeter Active Region Excess Brightness Temperature during Solar Cycles 23 and 24

AbstractRadio observations play a very important role in understanding the structure of the solar atmosphere. In this paper the quiet sun component of the solar radio emission has been investigated using data obtained from the Solar Indices Bulletin, National Geophysical Data Centre. By statistical method, the quiet sun component is estimated for 84 successive basic periods containing three solar rotations each using data obtained at different frequencies. From the quiet sun component we estimate the brightness temperature in each observing frequency.

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On the regions over sunspots as studied by polarization observations on centimeter wavelengths

Symposium - International Astronomical Union ◽

10.1017/s0074180900050683 ◽

1959 ◽

Vol 9 ◽

pp. 125-128

Author(s):

G. Gelfreich ◽

D. Korol'Kov ◽

N. Rishkov ◽

N. Soboleva

Keyword(s):

Magnetic Field ◽

Active Region ◽

Radio Emission ◽

Brightness Temperature ◽

The Sun ◽

Polarization Rotation

The observations of the sun at centimeter wavelengths made at Pulkovo in 1956–58 have shown: (1) There are regions of appreciable size over the majority of sunspots that have “enhanced” radio emission at centimeter wavelengths [1]. The nature of this emission shows that it belongs to the slowly varying component. In fact, as long as a group of sunspots persists, the flux of such an active region preserves its almost constant value. (2) The emission is partly circular, the polarized flux changing in magnitude but inappreciably. The sign of polarization rotation remains constant [2], which appears to be positive proof that a rather intense and stable magnetic field exists in these regions. (3) The extent of the regions is about that of the spot nuclei [3]. (4) Their brightness temperature amounts to several million degrees. (5) The height at which enhanced radio emission is produced is of the order 1.07 ± 0.02R⊙ [4].

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The influence of eclipses in the stellar radio emission

Proceedings of the International Astronomical Union ◽

10.1017/s1743921317003854 ◽

2016 ◽

Vol 12 (S328) ◽

pp. 305-307

Author(s):

Caius Lucius Selhorst ◽

Adriana Valio

Keyword(s):

Active Region ◽

Radio Emission ◽

Light Curve ◽

Brightness Temperature ◽

Quadratic Function ◽

Stellar Radius ◽

Optical Light Curve ◽

Hot Jupiter

AbstractHere we simulate the shape of a planetary transit observed at radio wavelengths. The simulations use a light curve of the K4 star HAT-P-11 and its hot Jupiter companion as proxy. From the HAT-P-11 optical light curve, a prominent spot was identified (1.10 RP and 0.6 IC). On the radio regime, the limb brighting of 30% was simulated by a quadratic function, and the active region was assumed to have the same size of the optical spot. Considering that the planet size is 6.35% of the the stellar radius, for the quiet star regions the transit depth is smaller than 0.5%, however, this value can increase to ~2% when covering an active region with 5.0 times the quiet star brightness temperature.

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In-depth survey of sunspot and active region catalogs

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311015286 ◽

2010 ◽

Vol 6 (S273) ◽

pp. 221-225 ◽

Cited By ~ 1

Author(s):

Laure Lefèvre ◽

Frédéric Clette ◽

Tunde Baranyi

Keyword(s):

Active Region ◽

Sunspot Group ◽

Solar Cycles ◽

Time Intervals ◽

Long Time ◽

Comprehensive Survey ◽

Central Database ◽

Index Time Series ◽

Activity Indices ◽

Sunspot Groups

AbstractWhen consulting detailed photospheric catalogs for solar activity studies spanning long time intervals, solar physicists face multiple limitations in the existing catalogs: finite or fragmented time coverage, limited time overlap between catalogs and even more importantly, a mismatch in contents and conventions. In view of a study of new sunspot-based activity indices, we have conducted a comprehensive survey of existing catalogs.In a first approach, we illustrate how the information from parallel catalogs can be merged to form a much more comprehensive record of sunspot groups. For this, we use the unique Debrecen Photoheliographic Data (DPD), which is already a composite of several ground observatories and SOHO data, and the USAF/Mount Wilson catalog from the Solar Optical Observing Network (SOON). We also describe our semi-interactive cross-identification method, which was needed to match the non-overlapping solar active region nomenclature, the most critical and subtle step when working with multiple catalogs. This effort, focused here first on the last two solar cycles, should lead to a better central database collecting all available sunspot group parameters to address future solar cycle studies beyond the traditional sunspot index time series Ri.

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Spectral signature of solar active region in millimetre and submillimetre wavelengths

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3354 ◽

2020 ◽

Vol 500 (2) ◽

pp. 1964-1969

Author(s):

J F Valle Silva ◽

C G Giménez de Castro ◽

C L Selhorst ◽

J-P Raulin ◽

A Valio

Keyword(s):

Active Region ◽

Brightness Temperature ◽

Flux Density ◽

Spatial Resolution ◽

Spectral Band ◽

Active Regions ◽

Spectral Signature ◽

Emission Mechanism ◽

Operational Characteristics ◽

The Mean

ABSTRACT Active regions were observed with different instruments covering the spectral band from 17 to 405 GHz. The observations were made with the Nobeyama Radioheliograph (17 GHz), the Atacama Large Millimetre Array (107 and 238 GHz), and the Solar Submillimeter Telescope (212 and 405 GHz). A procedure was developed that allows the comparison between observations taken with telescopes of different operational characteristics and mainly of different spatial resolution. The brightness temperature and density flux spectra of several active regions corresponding to a different phase of its lifetime were obtained. The flux density invariably increases in all cases from 107 to 405 GHz and the mean spectral index is ∼2 showing that the dominant emission mechanism at submillimeter frequencies is still thermal. We show that Solar Submillimeter Telescope (SST) and Atacama Large Millimeter/submillimeter Array (ALMA) observations are compatible within the uncertainties, a result of great interest for future joint observations.

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A statistical study on photospheric active-region magnetic nonpotentiality and associated flares during solar cycles 22 – 23

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313003335 ◽

2012 ◽

Vol 8 (S294) ◽

pp. 587-588

Author(s):

Xiao Yang ◽

HongQi Zhang ◽

GangHua Lin ◽

Yu Gao ◽

Juan Guo

Keyword(s):

Machine Learning ◽

Active Region ◽

Statistical Study ◽

Prediction Performance ◽

Solar Cycles ◽

Effective Distance ◽

Machine Learning Technique ◽

Strength Evolution ◽

Learning Technique

AbstractUsing photospheric data obtained by vector magnetograph in Huairou Solar Observing Station of China, we have statistically studied the strength evolution of several magnetic nonpotentiality measures, along with a quantified parameter characterizing the active-region magnetic complexity – effective distance, and their relationship with associated flares during the latest 22nd and 23rd solar cycles. And the flare-prediction performance of these magnetic nonpotentiality and complexity parameters is verified by a machine learning technique.

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SMARPs and SHARPs: Two Solar Cycles of Active Region Data

The Astrophysical Journal Supplement Series ◽

10.3847/1538-4365/ac1f1d ◽

2021 ◽

Vol 256 (2) ◽

pp. 26

Author(s):

Monica G. Bobra ◽

Paul J. Wright ◽

Xudong Sun ◽

Michael J. Turmon

Keyword(s):

Active Region ◽

Solar Cycles ◽

Region Data

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Dual Frequency Variability Study of an Active Region

Symposium - International Astronomical Union ◽

10.1017/s0074180900088495 ◽

1990 ◽

Vol 142 ◽

pp. 489-493

Author(s):

R. K. Shevgaonkar ◽

M. R. Kundu

Keyword(s):

Active Region ◽

Brightness Temperature ◽

Temperature Variation ◽

Transition Region ◽

Time Variability ◽

Dual Frequency ◽

Brightness Temperatures ◽

Region Model ◽

Short Time ◽

Variability Study

A short-time variability study of a solar active region simultaneously at 6 and 2 cm wavelengths was carried out using the VLA. The observations show interesting uncorrelated brightness temperature variation at the two wavelengths. The observed low brightness temperatures indicate that the emission is mainly originating from the chromosphere - corona transition region.A transition region model with constant pressure and power-law temperature variation as a function of height has been assumed to analyse the data. The uncorrelated variation of the observed brightness temperature at the two wavelengths suggest different dominant emission mechanisms (bremsstahlung at 2cm and gyro-resonance at 6cm) operative at the two wavelengths. It is shown that an independent variation of a few percent in the magnetic field (900 ±45 G) and a factor of two variation in the density (2 to 4 × 1010 cm−3) over a time scale of few hours is required to explain the uncorrelated brightness temperature variations at the two wavelengths.

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Spatial–temporal evolution of photospheric weak-field shifts in solar cycles 21–24

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936917 ◽

2021 ◽

Vol 645 ◽

pp. A47

Author(s):

K. Mursula ◽

T. Getachew ◽

I. I. Virtanen

Keyword(s):

Magnetic Field ◽

Active Region ◽

Magnetic Fields ◽

Large Scale ◽

Temporal Evolution ◽

Solar Surface ◽

Weak Field ◽

Solar Cycles ◽

Field Shift

Context. Weak magnetic field elements make a dominant contribution to the total magnetic field on the solar surface. Even so, little is known of their long-term occurrence. Aims. We study the long-term spatial–temporal evolution of the weak-field shift and skewness of the distribution of photospheric magnetic field values during solar cycles 21−24 in order to clarify the role and relation of the weak field values to the overall magnetic field evolution. Methods. We used Wilcox Solar Observatory (WSO) and the Synoptic Optical Long-term Investigations of the Sun Vector SpectroMagnetograph synoptic maps to calculate weak-field shifts for each latitude bin of each synoptic map, and thereby constructed a time–latitude butterfly diagram for shifts. We also calculated butterfly diagrams for skewness for all field values and for weak field values only. Results. The weak-field shifts and (full-field) skewness depict a similar spatial–temporal solar cycle evolution to that of the large-scale surface magnetic field. The field distribution has a systematic non-zero weak-field shift and a large skewness already at (and after) the emergence of the active region, even at the highest resolution. We find evidence for coalescence of opposite-polarity fields during the surge evolution. This is clearly more effective at the supergranulation scale. However, a similar dependence of magnetic field coalescence on spatial resolution was not found in the unipolar regions around the poles. Conclusions. Our results give evidence for the preference of even the weakest field elements toward the prevailing magnetic polarity since the emergence of an active region, and for a systematic coalescence of stronger magnetic fields of opposite polarities to produce weak fields during surge evolution and at the poles. We also find that the supergranulation process is reduced or turned off in the unipolar regions around the poles. These observations improve the understanding not only of the development of the weakest magnetic field elements, but also of the dynamics of magnetic fields at large, and even of processes below the solar surface.

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Predicting Solar Flares using CNN and LSTM on Two Solar Cycles of Active Region Data

10.1002/essoar.10508256.2 ◽

2021 ◽

Author(s):

Zeyu Sun ◽

Monica Bobra ◽

Xiantong Wang ◽

Yu Wang ◽

Hu Sun ◽

...

Keyword(s):

Active Region ◽

Solar Flares ◽

Solar Cycles ◽

Region Data

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