scholarly journals The behavior of the spotless active regions during the solar minimum 23-24

2016 ◽  
Vol 12 (S328) ◽  
pp. 137-139
Author(s):  
Alexandre José de Oliveira e Silva ◽  
Caius Lucius Selhorst
Keyword(s):  
Solar Minimum ◽  
Solar Surface ◽  
Active Regions ◽  
Physical Parameters ◽  
Michelson Doppler Imager ◽  
Heliospheric Observatory ◽  
Doppler Imager

AbstractIn this work, we analysed the physical parameters of the spotless actives regions observed during solar minimum 23 – 24 (2007 – 2010). The study was based on radio maps at 17 GHz obtained by the Nobeyama Radioheliograph (NoRH) and magnetograms provided by the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO). The results shows that the spotless active regions presents the same radio characteristics of a ordinary one, they can live in the solar surface for long periods (>10 days), and also can present small flares.

scholarly journals Observation of Seismic Effects of Solar Flares from the SOHO Michelson Doppler Imager

1998 ◽  
Vol 185 ◽  
pp. 191-194
Author(s):  
A.G. Kosovichev ◽  
V.V. Zharkova
Keyword(s):  
Solar Flares ◽  
Seismic Waves ◽  
Solar Surface ◽  
Active Regions ◽  
Impulsive Phase ◽  
High Energy ◽  
Solar Interior ◽  
Michelson Doppler Imager ◽  
Seismic Effects ◽  
Doppler Imager

Solar flares are the strongest localized seismic disturbances on the solar surface. During the impulsive phase a high-energy electron beam heats the chromosphere, resulting in explosive evaporation of chromospheric plasma at supersonic velocities. This upward motion is balanced by a downward recoil in the lower part of the chromosphere that excites propagating waves in the solar interior. On the solar surface the outgoing circular flare waves resemble ripples from a pebble thrown into a pond. We report on first observations of the seismic effects of a solar flare from the SOHO Michelson Doppler Imager (MDI) and compare the results with a theoretical model. Observation of flare seismic waves provide important information about the flare mechanism and about the subphotospheric structure of active regions.

scholarly journals Source Regions of Coronal Mass Ejections

2001 ◽  
Vol 203 ◽  
pp. 362-373
Author(s):  
K. P. Dere ◽  
P. Subramanian
Keyword(s):  
Active Region ◽  
Coronal Mass Ejections ◽  
Solar Minimum ◽  
Active Regions ◽  
The Other ◽  
Small Scale ◽  
Minimum Phase ◽  
Michelson Doppler Imager ◽  
Doppler Imager ◽  
Source Regions

Observations of the solar corona with the LASCO and EIT instruments on SOHO provide an unprecedented opportunity to study coronal mass ejections (CMEs) from their initiation through their evolution out to 30 R⊙. The objective of this study is to gain an understanding of the source regions from which the CMEs emanate. To this end, we have developed a list of 32 CMEs whose source regions are located on the solar disk and are well observed in EIT 195 Å data during the solar minimum phase of January 1996-May 1998. We compare the EIT source regions with photospheric magnetograms from the Michelson Doppler Imager (MDI) instrument on SOHO and the NSO/Kitt Peak Observatory and also with Hα data from various sources. The overall results of our study show that 59% of the CME related transients observed in EIT 195 Å images are associated with active regions without prominences, 22% are associated with eruptions of prominences embedded in active regions and 19% are associated with eruptions of quiescent prominences. We describe 3 especially well observed events, one from each of these 3 categories. These case studies suggest that active region CMEs are associated with active regions with lifetimes between 11-80 days. They are also often associated with small scale emerging or cancelling flux over timescales of 6-7 hours. CMEs associated with active region prominence eruptions, on the other hand, are typically associated with old active regions with lifetimes ~ 6-7 months.

scholarly journals One solar cycle of solar astrometry with MDI/SOHO

2009 ◽  
Vol 5 (S264) ◽  
pp. 21-32 ◽  
Author(s):  
Marcelo Emilio ◽  
Jeff R. Kuhn ◽  
Rock I. Bush
Keyword(s):  
Solar Cycle ◽  
Solar Radius ◽  
Michelson Doppler Imager ◽  
Heliospheric Observatory ◽  
Radius Variation ◽  
Doppler Imager ◽  
Upper Limit ◽  
The Absolute ◽  
The Difference

AbstractIn this work we describe the method and results of precise solar astrometry made with the Michelson Doppler Imager (MDI), on board the Solar and Heliospheric Observatory (SOHO), during one complete solar cycle. We measured an upper limit to the solar radius variation, the absolute solar radius value and the solar shape. Our results are 22 mas peak-to-peak upper limit for the solar radius variation over the solar cycle, the absolute radius was measured as 959.28 ± 0.15 arcsec at 1 AU and the difference between polar and equatorial solar radii in 1997 was 5 km and about three times larger in 2001.

scholarly journals Two classes of eruptive events during Solar Minimum

2021 ◽  
Author(s):  
Prantika Bhowmik ◽  
Anthony Yeates
Keyword(s):  
Magnetic Field ◽  
Free Energy ◽  
Magnetic Flux ◽  
Solar Minimum ◽  
Large Scale ◽  
Solar Surface ◽  
Coronal Holes ◽  
Active Regions ◽  
Coronal Magnetic Field ◽  
The Magnetic Field

<p>During Solar Minimum, the Sun is perceived to be quite inactive with barely any spots emerging on the solar surface. Consequently, we observe a drop in the number of highly energetic events such as solar flares and coronal mass ejections (CMEs), which are often associated with active regions on the photosphere. However, our magnetofrictional simulations during the minimum period suggest that the solar corona could still be significantly dynamic while evolving in response to the large-scale shearing velocities on the solar surface. The non-potential evolution of the corona leads to the accumulation of magnetic free energy and helicity, which is periodically lost through eruptive events. Our study shows that these events can be categorised into two distinct classes. One set of events are caused due to full-scale eruption of low-lying coronal flux ropes and could be associated with occasional filament erupting CMEs observed during Solar Minimum. The other set of events are not driven by destabilisation of low-lying structures but rather by eruption from overlying sheared arcades. These could be linked with streamer blowouts or stealth CMEs. The two classes differ considerably in the amount of magnetic flux and helicity shed through the outer coronal boundary. We additionally investigate how other measurables such as current, open magnetic flux, free energy, coronal holes area, and the horizontal component of the magnetic field on the outer model boundary vary during the two classes of event. This study demonstrates and emphasises the importance and necessity of understanding the dynamics of the coronal magnetic field during Solar Minimum.</p>

scholarly journals Evolution and decay of an active region: Magnetic shear, flare and CME activity

2000 ◽  
Vol 39 (1) ◽  
pp. 73-80
Author(s):  
L. van Driel-Gresztelyi ◽  
B. Thompson ◽  
S. Punkett ◽  
P. Démoulin ◽  
G. Aulanier
Keyword(s):  
Active Region ◽  
Michelson Doppler Imager ◽  
Magnetic Shear ◽  
Heliospheric Observatory ◽  
Doppler Imager

Desde abril de 1996 y hasta febrero de 1997, se observó en el disco solar un complejo de actividad. Este complejo exhibió su nivel más alto de actividad durante el nacimiento de la región activa (AR) 7978. Nuestro análisis se extiende a lo largo de seis rotaciones solares, desde la aparición de AR 7978 (julio de 1996) hasta el decaimiento y dispersión de su flujo (noviembre de 1996). Los datos en varias longitudes de onda provistas por los instrumentos a bordo del Solar and Heliospheric Observatory (SOHO) y del satélite japonés Yohkoh, nos permiten seguir la evolución de la región desde la fotosfera hasta la corona. Usando los magnetogramas del disco completo obtenidos por el Michelson Doppler Imager (SOHO/MDI) como condiciones de contorno, calculamos el campo magnético coronal y determinamos su apartamiento de la potencialidad ajustando las líneas de campo calculadas a los arcos observados en rayos X blandos. Discutimos la evolución de la torsión del campo magnético coronal y su probable relación con la actividad observada en forma de eyecciones de masa coronal (CMEs) y fulguraciones.

scholarly journals Using CME Progenitors to Assess CME Geoeffectiveness

2021 ◽  
Vol 257 (2) ◽  
pp. 33
Author(s):  
Kashvi Mundra ◽  
V. Aparna ◽  
Petrus Martens
Keyword(s):  
Magnetic Field ◽  
Extreme Ultraviolet ◽  
Geomagnetic Storms ◽  
Solar Surface ◽  
Axial Direction ◽  
Solar Observatory ◽  
Field Orientation ◽  
Heliospheric Observatory ◽  
Doppler Imager ◽  
Time Period

Abstract There have been a few previous studies claiming that the effects of geomagnetic storms strongly depend on the orientation of the magnetic cloud portion of coronal mass ejections (CMEs). Aparna & Martens, using halo-CME data from 2007 to 2017, showed that the magnetic field orientation of filaments at the location where CMEs originate on the Sun can be used to credibly predict the geoeffectiveness of the CMEs being studied. The purpose of this study is to extend their survey by analyzing the halo-CME data for 1996–2006. The correlation of filament axial direction on the solar surface and the corresponding Bz signatures at L1 are used to form a more extensive analysis for the results previously presented by Aparna & Martens. This study utilizes Solar and Heliospheric Observatory Extreme-ultraviolet Imaging Telescope 195 Å, Michelson Doppler Imager magnetogram images, and Kanzelhöhe Solar Observatory and Big Bear Solar Observatory Hα images for each particular time period, along with ACE data for interplanetary magnetic field signatures. Utilizing all these, we have found that the trend in Aparna & Martens’ study of a high likelihood of correlation between the axial field direction on the solar surface and Bz orientation persists for the data between 1996 and 2006, for which we find a match percentage of 65%.

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