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Analysis of sudden variations in photospheric magnetic fields during a large flare and their influences in the solar atmosphere

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Research in Astronomy and Astrophysics 2016年第8期16卷 95-112页

作者： Brajesh Kumar Ankala Raja Bayanna Parameswaran Venkatakrishnan Shibu Kuchandy Mathew udaipur solar observatory Physical Research Laboratory Dewali Badi Road Udaipur 313004 Rajasthan India Indian Institute of Astrophysics Ⅱ Block Koramangala Bangalore 560034 India

The solar active region NOAA 11719 produced a large two-ribbon flare on 2013 April 11. We have investigated sudden variations in the photospheric magnetic fields in this active region during the flare by employing magnetograms obtained in the spectral line Fe I 6173 A acquired by the Helioseismic and Magnetic Imager （HMI） onboard the solar Dynamics observatory （SDO） spacecraft. The analysis of the line-of-sight magnetograms from HMI show sudden and persistent magnetic field changes at different locations of the active region before the onset of the flare and during the flare. The vector magnetic field observations available from HMI also show coincident variations in the total magnetic field strength and its inclination angle at these locations. Using the simultaneous Dopplergrams obtained from HMI, we observe perturbations in the photospheric Doppler signals following the sudden changes in the magnetic fields in the aforementioned locations. The power spectrum analysis of these velocity signals shows enhanced acoustic power in these affected locations during the flare as compared to the pre-flare condition. Accompanying these observations, we have also used nearly simultaneous chromospheric observations obtained in the spectral line Ha 6562.8 A by the Global Oscillation Network Group （GONG） to study the evolution of flare- ribbons and intensity oscillations in this active region. The Ha intensity oscillations also show enhanced oscillatory power during the flare in the aforementioned locations. These results indicate that the transient Lorentz force associated with sudden changes in the magnetic fields could drive localized photospheric and chromospheric oscillations, like the flare-induced oscillations in the solar atmosphere.

关键词： Sun sunspots -- Sun flares -- Sun magnetic fields -- Sun oscillations -- Sun photosphere-- Sun chromosphere

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Flux emergence in the solar active region NOAA 11158: the evolution of net current

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Research in Astronomy and Astrophysics 2015年第9期15卷 1547-1558页

作者： Panditi Vemareddy Parameswaran Venkatakrishnan Solipuram Karthikreddy Indian Institute of Astrophysics udaipur solar observatory Physical Research Laboratory Department of Earth and Space Sciences Indian Institute of Space Science and Technology

We present a detailed investigation of the evolution of observed net vertical current using a time series of vector magnetograms of the active region （AR） NOAA 11158 obtained from the Helioseismic and Magnetic Imager. We also discuss the relation of net current to the observed eruptive events. The AR evolved from the βγ to βγδ3 configuration over a period of six days. The AR had two sub-regions of activity with opposite chirality： one dominated by sunspot rotation producing a strong CME, and the other showing large shear motions producing a strong flare. The net current in each polarity over the CME producing sub-region increased to a maximum and then decreased when the sunspots were separated. The time profile of net current in this sub-region followed the time profile of the rotation rate of the south-polarity sunspot in the same sub-region. The net current in the flaring sub-region showed a sudden increase at the time of the strong flare and remained unchanged until the end of the observation, while the sunspots maintained their close proximity. The systematic evo- lution of the observed net current is seen to follow the time evolution of total length of strongly sheared polarity inversion lines in both of the sub-regions. The observed photospheric net current could be explained as an inevitable product of the emergence of a twisted flux rope, from a higher pressure confinement below the photosphere into the lower pressure environment of the photosphere.

关键词： Sun:active regions -- magnetic fields -- activity -- coronal mass ejec-tions -- non-potentiality -- electric current

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A study of the relation between intensity oscillations and magnetic field parameters in a sunspot: Hinode observations

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Research in Astronomy and Astrophysics 2014年第11期14卷 1458-1468页

作者： A.Raja Bayanna Shibu K.Mathew Brajesh Kumar Rohan E.Louis P.Venkatakrishnan udaipur solar observatory Physical Research Laboratory Leibniz-Institut für Astrophysik Potsdam (AIP) An der Sternwarte 16 14482 PotsdamGermany

We present properties of intensity oscillations of a sunspot in the photo- sphere and chromosphere using G band and Ca u H filtergrams from Hinode. Intensity power maps as function of magnetic field strength and frequency reveal reduction of power in the G band with an increase in photospheric magnetic field strength at all frequencies. In Ca II H, however, stronger fields exhibit more power at high frequen- cies, particularly in the 4.5-8.0 mHz band. Power distributions in different locations of the active region show that the oscillations in Ca II H exhibit more power compared to that of the G band. We also relate the power in intensity oscillations with differ- ent components of the photospheric vector magnetic field using near simultaneous spectro-polarimetric observations of the sunspot from the Hinode spectropolarime- ter. The photospheric umbral power is strongly anti-correlated with the magnetic field strength and its line-of-sight component but there is a good correlation with the trans- verse component. A reversal of this trend is observed in the chromosphere except at low frequencies （V≤ 1.5 mHz）. The power in sunspot penumbrae is anti-correlated with the magnetic field parameters at all frequencies （1.0 ≤ v ≤ 8.0 mHz） in both the photosphere and chromosphere, except that the chromospheric power shows a strong correlation in the frequency range 3-3.5 mHz.

关键词： Sun photosphere -- Sun chromosphere -- Sun oscillations -- Sun magnetic fields -- Sun Hinode

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Investigation of two coronal mass ejections from circular ribbon source region:Origin,Sun-Earth propagation and Geoeffectiveness

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Research in Astronomy and Astrophysics 2021年第12期21卷 531-549页

作者： M.Syed Ibrahim Wahab Uddin Bhuwan Joshi Ramesh Chandra Arun Kumar Awasthi aryabhatta research institute of observational sciences nainital 263002 india kodaikanal solar observatory indian institute of astrophysicskodaikanal-624103tamil naduindia udaipur solar observatory physical research laboratoryudaipur 313004india department of physics dsb campuskumaun universitynainital 263002india cas key laboratory of geospace environment department of geophysics and planetary sciencesuniversity of science and technology of chinahefei 230026china

In this article,we compare the properties of two coronal mass ejections(CMEs)that show similar source region characteristics but different evolutionary behaviors in the later *** discuss the two events in terms of their near-Sun characteristics,interplanetary evolution and *** carefully analyzed the initiation and propagation parameters of these events to establish the precise CMEinterplanetary CME(ICME)connection and their near-Earth *** first event is associated with poor geomagnetic storm disturbance index(Dst≈-20 n T)while the second event is associated with an intense geomagnetic storm of DST≈-119 n *** configuration of the sunspots in the active regions and their evolution are observed by Helioseismic and Magnetic Imager(HMI).For source region imaging,we rely on data obtained from Atmospheric Imaging Assembly(AIA)on board solar Dynamics observatory(SDO)and Hαfiltergrams from the solar Tower Telescope at Aryabhatta Research Institute of Observational Sciences(ARIES).For both the CMEs,flux rope eruptions from the source region triggered flares of similar intensities(≈M1).At the solar source region of the eruptions,we observed a circular ribbon flare(CRF)for both cases,suggesting fan-spine magnetic configuration in the active region *** multi-channel SDO observations confirm that the eruptive flares and subsequent CMEs were intimately related to the filament *** the Large Angle and Spectrometric Coronograph(LASCO)field of view(FOV)the two CMEs propagated with linear speeds of 671 and 631 km s-1,*** CMEs were tracked up to the Earth by solar Terrestrial Relations observatory(STEREO)*** find that the source region evolution of CMEs,guided by the large-scale coronal magnetic field configuration,along with near-Sun propagation characteristics,such as CME-CME interactions,played important roles in deciding the evolution of CMEs in the interplanetary medium and subsequently their geoeffec

关键词： Sun:coronal mass ejections(CMEs) Sun:flares

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On the line profile changes observed during the X2.2 class flare in the active region NOAA 11158

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Research in Astronomy and Astrophysics 2014年第2期14卷 207-220页

作者： Ankala Raja Bayanna Brajesh Kumar Parameswaran Venkatakrishnan Shibu Kunchandy Mathew Belur Ravindra Savita Mathur Rafael A Garcia udaipur solar observatory Physical Research LaboratoryDewaliBadi RoadUdaipur 313 004India Indian Institute of Astrophysics II BlockKoramanglaBangalore 560034India Space Science Institute 4750 Walnut Street Suite#205BoulderCO 80301USA Laboratoire AIM CEA/DSM-CNRSUniversit'e Paris 7 DiderotIRFU/SApCentre de Saclay91191Gif-sur-YvetteFrance

The solar active region NOAA 11158 produced a series of flares during its passage through the solar disk. The first major flare （of class X2.2） of the current solar cycle occurred in this active region on 2011 February 15 around 01：50 UT. We have analyzed the Dopplergrams and magnetograms obtained by the Helioseismic and Magnetic Imager （HMI） instrument onboard solar Dynamics observatory to examine the photospheric velocity and magnetic field changes associated with this flare. The HMI instrument provides high-quality Doppler and magnetic maps of the solar disk with 0.5＂ spatial scale at a cadence of 45 s along with imaging spectroscopy. We have identified five locations of velocity transients in the active region during the flare. These transient velocity signals are located in and around the flare ribbons as observed by Hinode in the Ca II H wavelength and the footpoints of hard X-ray enhancement are in the energy range 12-25 keV from RHESSI. The changes in shape and width of two circular polarization states have been observed at the time of transients in three out of five locations. Forward modeling of the line profiles shows that the change in atmospheric parameters such as magnetic field strength, Doppler velocity and source function could explain the observed changes in the line profiles with respect to the pre-flare condition.

关键词： Sun: activity -- Sun: sunspot -- Sun: flares -- Sun: spectroscopy --Sun: velocity and magnetic fields

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Long-Term Changes in Night Time Airglow Emission at 557.7 nm over Mid Latitude Japanese Station i.e., Kiso (35.79oN, 137.63oE)

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American Journal of Climate Change 2012年第4期1卷 210-216页

作者： Brij Mohan Vyas Vimal Saraswat Department of Physics M. L. Sukhadia University Udaipur India

The present study describes the long-term changes in Pre-midnight and Midnight airglow intensities of 557.7 nm during the period 1979-1994 over mid latitude Japanese station i.e., Kiso, Tokyo Astronomical observatory, University of Tokyo (35.79oN, 137.63oE;1130 m), Japan. It has observed that there is a positive increasing decadal change in Midnight and Pre-midnight mesospheric airglow intensity of the range 25 - 88 R. This range is the order of 10 to 30% of the observed MARV and average night airglow intensity of 250 R. Besides this long-term trend, inter-annual monthly variation is also seen from fluctuation of yearly variation of deviation values from MARV to particular average monthly values. The present observations about the positive decadal change in night time mesospheric airglow intensity has been further linked to the reduction of mesospheric electron densities and temperature or shrinking and cooling of the lower ionosphere as established from the long-term behavior of mesospheric parameters such as a negative decadal change in thermal structure, electron density, neutral density parameters as per studies reported by other researchers.

关键词： Airglow Long-Term Changes Ionosphere

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