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 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 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 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.

Evolutionary and flare-associated magnetic shear variations observed in a complex, flare-productive active region

Solar Physics ◽  
1993 ◽  
Vol 148 (2) ◽  
pp. 277-299 ◽  
Author(s):  
Ashok Ambastha ◽  
Mona J. Hagyard ◽  
E. A. West
Keyword(s):  
Active Region ◽  
Magnetic Shear
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