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* News 04/04/20 * The archive is using a new backend database. This has thrown up a few SQL errors in the last few days. If you have any issues please email adavey@nso.edu with either the number of eprint you are trying to edit or a link to your preprint.

Response of SDO/HMI observables to heating of the solar atmosphere by precipitating high-energy electrons  

Viacheslav Sadykov   Submitted: 2020-03-06 13:15

We perform an analysis of the line-of-sight (LOS) observables of the SDO/HMI for models of the solar atmosphere heated by precipitating high-energy electrons during solar flares. The radiative hydrodynamic (RADYN) flare models are obtained from the F-CHROMA database. The Stokes profiles for the Fe 6173 Å line observed by SDO/HMI are calculated using the radiative transfer code RH1.5D assuming statistical equilibrium for atomic level populations and imposing uniform background vertical magnetic field of various strength. The SDO/HMI observing sequence and LOS data processing pipeline algorithm are applied to derive the observables (continuum intensity, line depth, Doppler velocity, LOS magnetic field). Our results reveal that the strongest deviations of the observables from the actual spectroscopic line parameters are found for the model with a total energy deposited of Etotal=1.0x1012 erg cm-2, injected with power-law spectral index of δ=3 above a low-energy cutoff of Ec=25 keV. The magnitudes of the velocity and magnetic field deviations depend on the imposed magnetic field, and can reach 0.35 km s-1 for LOS velocities, 90 G for LOS magnetic field, and 3% for continuum enhancement for the 1000 G imposed LOS magnetic field setup. For Etotal≥3.0x1011 erg cm-2 models, the velocity and magnetic field deviations are most strongly correlated with the energy flux carried by ~50 keV electrons, and the continuum enhancement is correlated with the synthesized ~55-60 keV hard X-ray photon flux. The relatively low magnitudes of perturbations of the observables and absence of magnetic field sign reversals suggest that the considered radiative hydrodynamic beam heating models augmented with the uniform vertical magnetic field setups cannot explain strong transient changes found in the SDO/HMI observations.

Authors: Viacheslav M Sadykov, Alexander G Kosovichev, Irina N Kitiashvili, Graham S Kerr
Projects: SDO-HMI

Publication Status: Accepted to ApJ
Last Modified: 2020-03-07 09:29
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Relationships Between Characteristics of the Line-of-Sight Magnetic Field and Solar Flare Forecasts  

Viacheslav Sadykov   Submitted: 2017-04-12 08:57

Studying connection between solar flares and properties of magnetic field in active regions is very important for understanding the flare physics and developing space weather forecasts. In this work, we analyze relationship between the flare X-ray peak flux from the GOES satellite, and characteristics of the line-of-sight (LOS) magnetograms obtained by the SDO/HMI instrument during the period of April, 2010 - June, 2016. We try to answer two questions: 1) What characteristics of the LOS magnetic field are most important for the flare initiation and magnitude? 2) Is it possible to construct a reliable forecast of >=M1.0 and >=X1.0 class flares based only on the LOS magnetic field characteristics? To answer these questions, we apply a Polarity Inversion Line (PIL) detection algorithm, and derive various properties of the PIL and the corresponding Active Regions (AR). The importance of these properties for flare forecasting is determined by their ability to separate flaring cases from non-flaring, and their Fisher ranking score. It is found that the PIL characteristics are of special importance for the forecasts of both >=M1.0 and >=X1.0 flares, while the global AR characteristics become comparably discriminative only for >=X1.0 flares. We use the Support Vector Machine (SVM) classifier and train it on the six characteristics of the most importance for each case. The obtained True Skill Statistics (TSS) values of 0.70 for >=M1.0 flares and 0.64 for >=X1.0 flares are better than the currently-known expert-based predictions. Therefore, the results confirm the importance of the LOS magnetic field data and, in particular, the PIL region characteristics for flare forecasts.

Authors: Viacheslav M Sadykov, Alexander G Kosovichev
Projects: GOES X-rays,SDO-HMI

Publication Status: Submitted to the ApJ
Last Modified: 2017-04-12 17:38
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Interactive Multi-Instrument Database of Solar Flares  

Viacheslav Sadykov   Submitted: 2017-02-15 15:42

Solar flares represent a complicated physical phenomenon observed in a broad range of the electromagnetic spectrum, from radiowaves to gamma-rays. For a complete understanding of the flares it is necessary to perform a combined multi-wavelength analysis using observations from many satellites and ground-based observatories. For efficient data search, integration of different flare lists and representation of observational data, we have developed the Interactive Multi-Instrument Database of Solar Flares (https://solarflare.njit.edu/). The web database if fully functional and allows the user to search for uniquely-identified flare events based on their physical descriptors and availability of observations of a particular set of instruments. Currently the data from three primary flare lists (GOES, RHESSI and HEK) and a variety of other event catalogs (Hinode, Fermi GBM, Konus-Wind, OVSA flare catalogs, CACTus CME catalog, Filament eruption catalog) and observing logs (IRIS and Nobeyama coverage), are integrated, and an additional set of physical descriptors (temperature and emission measure) is provided along with observing summary, data links and multi-wavelength light curves for each flare event since January, 2002. We think that the created instrument will allow researchers significantly speed up the search of events of interest for statistical and case studies.

Authors: Viacheslav M Sadykov, Rishabh Gupta, Alexander G Kosovichev, Vincent Oria, Gelu M Nita
Projects: Other

Publication Status: Submitted to Solar Physics journal
Last Modified: 2017-02-16 08:47
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Response of SDO/HMI observables to heating of the solar atmosphere by precipitating high-energy electrons
Relationships Between Characteristics of the Line-of-Sight Magnetic Field and Solar Flare Forecasts
Interactive Multi-Instrument Database of Solar Flares

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