Evolution of magnetic fields and energetics of flares in active region 8210

To better understand eruptive events in the solar corona, we combine sequences of multi-wavelength observations and modelling of the coronal magnetic field of NOAA AR 8210, a highly flare-productive active region. From the photosphere to the corona, the observations give us information about the motion of magnetic elements (photospheric magnetograms), the location of flares (e.g., H$\alpha$, EUV or soft X-ray brightenings), and the type of events (H$\alpha$ blueshift events). Assuming that the evolution of the coronal magnetic field above an active region can be described by successive equilibria, we follow in time the magnetic changes of the 3D nonlinear force-free (nlff) fields reconstructed from a time series of photospheric vector magnetograms. We apply this method to AR 8210 observed on May 1, 1998 between 17:00 UT and 21:40 UT. We identify two types of horizontal photospheric motions that can drive an eruption: a clockwise rotation of the sunspot, and a fast motion of an emerging polarity. The reconstructed nlff coronal fields give us a scenario of the confined flares observed in AR 8210: the slow sunspot rotation enables the occurence of flare by a reconnection process close to a separatrix surface whereas the fast motion is associated with small-scale reconnections but no detectable flaring activity. We also study the injection rates of magnetic energy, Poynting flux and relative magnetic helicity through the photosphere and into the corona. The injection of magnetic energy by transverse photospheric motions is found to be correlated with the storage of energy in the corona and then the release by flaring activity. The magnetic helicity derived from the magnetic field and the vector potential of the nlff configuration is computed in the coronal volume. The magnetic helicity evolution shows that AR 8210 is dominated by the mutual helicity between the closed and potential fields and not by the self helicity of the closed field which characterizes the twist of confined flux bundles. We conclude that for AR 8210 the complex topology is a more important factor than the twist in the eruption process

The sensitivity of H alpha profiles to rapid electron beam fluctuations

In order to understand the temporal relationship between H alpha and hard X-ray emission predicted by the nonthermal electron thick target model of impulsive-phase energy transport the time-dependent theoretical H alpha profiles were computed for the dynamic model atmospheres of Fisher, Canfield, and McClymont, which simulate the effects of an impulsively initiated power-law beam of electrons. On the basis of the physical analysis it was expected that a very rapid H alpha response to an instantaneous increase in the flux of a nonthermal deka-keV electron beam, as compared to the timescale associated with the propagation of these electrons over characteristic flare coronal loop spatial scales. It was concluded that observational efforts to test the thick target nonthermal electron model through detection of impulsive H alpha brightenings associated with impulsive hard X-ray or microwave bursts should initially focus attention on the H alpha line center. Additional simultaneous blue-wing measurements will have substantial diagnostic potential

Magnetic Helicity and the Solar Dynamo

The objective of this investigation is to open a new window into the solar dynamo, convection, and magnetic reconnection through measurement of the helicity density of magnetic fields in the photosphere and tracing of large-scale patterns of magnetic helicity in the corona

Joint vector magnetograph observations at BBSO, Huairou Station and Mees Solar Observatory

Joint vector magnetograph observations were carried out at Big Bear Solar Observatory (BBSO), Huairou Solar Observing Station (Huairou), and Mees Solar Observatory (MSO) in late September 1989. Comparisons of vector magnetograms obtained at the three stations show a high degree of consistency in the morphology of both longitudinal and transverse fields. Quantitative comparisons show the presence of noise, cross-talk between longitudinal field and transverse field, Faraday rotation and signal saturation effects in the magnetograms. We have tried to establish how the scatter in measurements from different instruments is apportioned between these sources of error

Performance of Major Flare Watches from the Max Millennium Program (2001-2010)

The physical processes that trigger solar flares are not well understood and significant debate remains around processes governing particle acceleration, energy partition, and particle and energy transport. Observations at high resolution in energy, time, and space are required in multiple energy ranges over the whole course of many flares in order to build an understanding of these processes. Obtaining high-quality, co-temporal data from ground- and space- based instruments is crucial to achieving this goal and was the primary motivation for starting the Max Millennium program and Major Flare Watch (MFW) alerts, aimed at coordinating observations of all flares >X1 GOES X-ray classification (including those partially occulted by the limb). We present a review of the performance of MFWs from 1 February 2001 to 31 May 2010, inclusive, that finds: (1) 220 MFWs were issued in 3,407 days considered (6.5% duty cycle), with these occurring in 32 uninterrupted periods that typically last 2-8 days; (2) 56% of flares >X1 were caught, occurring in 19% of MFW days; (3) MFW periods ended at suitable times, but substantial gain could have been achieved in percentage of flares caught if periods had started 24 h earlier; (4) MFWs successfully forecast X-class flares with a true skill statistic (TSS) verification metric score of 0.500, that is comparable to a categorical flare/no-flare interpretation of the NOAA Space Weather Prediction Centre probabilistic forecasts (TSS = 0.488).Comment: 19 pages, 2 figures, accepted for publication in Solar Physic

An imaging vector magnetograph for the next solar maximum

Measurements of the vector magnetic field in the solar atmosphere with high spatial and temporal resolution over a large field of view are critical to understanding the nature and evolution of currents in active regions. Such measurements, when combined with the thermal and nonthermal X-ray images from the upcoming Solar-A mission, will reveal the large-scale relationship between these currents and sites of heating and particle acceleration in flaring coronal magnetic flux tubes. The conceptual design of an imaging vector magnetograph that combines a modest solar telescope with a rotating quarter-wave plate, an acousto-optical tunable prefilter as a blocker for a servo-controlled Fabry-Perot etalon, CCD cameras, and a rapid digital tape recorder are described. Its high spatial resolution (1/2 arcsec pixel size) over a large field of view (4 x 5 arcmin) will be sufficient to significantly measure, for the first time, the magnetic energy dissipated in major solar flares. Its millisecond tunability and wide spectra range (5000 to 8000 A) enable nearly simultaneous vector magnetic field measurements in the gas-pressure-dominated photosphere and magnetically dominated chromosphere, as well as effective co-alignment with Solar-A's X-ray images

Max '91: Flare research at the next solar maximum

To address the central scientific questions surrounding solar flares, coordinated observations of electromagnetic radiation and energetic particles must be made from spacecraft, balloons, rockets, and ground-based observatories. A program to enhance capabilities in these areas in preparation for the next solar maximum in 1991 is recommended. The major scientific issues are described, and required observations and coordination of observations and analyses are detailed. A program plan and conceptual budgets are provided

Performance of Major Flare Watches from the Max Millennium Program (2001 – 2010)

The physical processes that trigger solar flares are not well understood and significant debate remains around processes governing particle acceleration, energy partition, and particle and energy transport. Observations at high resolution in energy, time, and space are required in multiple energy ranges over the whole course of many flares in order to build an understanding of these processes. Obtaining high-quality, co-temporal data from ground- and space- based instruments is crucial to achieving this goal and was the primary motivation for starting the Max Millennium program and Major Flare Watch (MFW) alerts, aimed at coordinating observations of all flares ≥X1 GOES X-ray classification (including those partially occulted by the limb). We present a review of the performance of MFWs from 1 February 2001 to 31 May 2010, inclusive, that finds: (1) 220 MFWs were issued in 3,407 days considered (6.5% duty cycle), with these occurring in 32 uninterrupted periods that typically last 2-8 days; (2) 56% of flares ≥X1 were caught, occurring in 19% of MFW days; (3) MFW periods ended at suitable times, but substantial gain could have been achieved in percentage of flares caught if periods had started 24 h earlier; (4) MFWs successfully forecast X-class flares with a true skill statistic (TSS) verification metric score of 0.500, that is comparable to a categorical flare/no-flare interpretation of the NOAA Space Weather Prediction Centre probabilistic forecasts (TSS = 0.488)

Joint vector magnetograph observations at BBSO, Huairou Station and Mees Solar Observatory

Joint vector magnetograph observations were carried out at Big Bear Solar Observatory (BBSO), Huairou Solar Observing Station (Huairou), and Mees Solar Observatory (MSO) in late September 1989. Comparisons of vector magnetograms obtained at the three stations show a high degree of consistency in the morphology of both longitudinal and transverse fields. Quantitative comparisons show the presence of noise, cross-talk between longitudinal field and transverse field, Faraday rotation and signal saturation effects in the magnetograms. We have tried to establish how the scatter in measurements from different instruments is apportioned between these sources of error