scholarly journals Toward magnetic field dissipation during the 23 July 2002 solar flare measured with Solar and Heliospheric Observatory/Michelson Doppler Imager (SOHO/MDI) and Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)

2005 ◽  
Vol 110 (A8) ◽  
Author(s):  
Valentina V. Zharkova ◽  
Sergey I. Zharkov ◽  
Stanley S. Ipson ◽  
Ali K. Benkhalil
Keyword(s):  
Magnetic Field ◽  
Solar Flare ◽  
High Energy ◽  
Michelson Doppler Imager ◽  
Heliospheric Observatory ◽  
Doppler Imager

scholarly journals Photospheric high-frequency acoustic power excess in sunspot umbra: signature of magneto-acoustic modes

2013 ◽  
Vol 31 (8) ◽  
pp. 1357-1364 ◽  
Author(s):  
S. Zharkov ◽  
S. Shelyag ◽  
V. Fedun ◽  
R. Erdélyi ◽  
M. J. Thompson
Keyword(s):  
Magnetic Field ◽  
Acoustic Waves ◽  
High Frequency ◽  
Acoustic Power ◽  
Solar Photosphere ◽  
Heliospheric Observatory ◽  
Magnetohydrodynamic Waves ◽  
Sunspot Umbra ◽  
Doppler Imager ◽  
Power Enhancement

Abstract. We present observational evidence for the presence of MHD (magnetohydrodynamic) waves in the solar photosphere deduced from SOHO/MDI (Solar and Heliospheric Observatory/Michelson Doppler Imager) Dopplergram velocity observations. The magneto-acoustic perturbations are observed as acoustic power enhancement in the sunspot umbra at high-frequency bands in the velocity component perpendicular to the magnetic field. We use numerical modelling of wave propagation through localised non-uniform magnetic field concentration along with the same filtering procedure as applied to the observations to identify the observed waves. Guided by the results of the numerical simulations we classify the observed oscillations as magneto-acoustic waves excited by the trapped sub-photospheric acoustic waves. We consider the potential application of the presented method as a diagnostic tool for magnetohelioseismology.

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 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 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 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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