The variation of relative magnetic helicity around major flares

We have investigated the variation of magnetic helicity over a span of several days around the times of 11 X-class flares which occurred in seven active regions (NOAA 9672, 10030, 10314, 10486, 10564, 10696, and 10720) using the magnetograms taken by the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO). As a major result we found that each of these major flares was preceded by a significant helicity accumulation over a long period (0.5 to a few days). Another finding is that the helicity accumulates at a nearly constant rate and then becomes nearly constant before the flares. This led us to distinguish the helicity variation into two phases: a phase of monotonically increasing helicity and the following phase of relatively constant helicity. As expected, the amount of helicity accumulated shows a modest correlation with time-integrated soft X-ray flux during flares. However, the average helicity change rate in the first phase shows even stronger correlation with the time-integrated soft X-ray flux. We discuss the physical implications of this result and the possibility that this characteristic helicity variation pattern can be used as an early warning sign for solar eruptions

Investigating the origins of two extreme solar particle events: proton source profile and associated electromagnetic emissions

We analyze the high-energy particle emission from the Sun in two extreme solar particle events, in which protons are accelerated to relativistic energies and can cause a significant signal even in the ground-based particle detectors. Analysis of a relativistic proton event is based on modeling of the particle transport and interaction, from a near-Sun source through the solar wind and the Earth’s magnetosphere and atmosphere to a detector on the ground. This allows us to deduce the time profile of the proton source at the Sun and compare it with observed electromagnetic emissions. The 2 May 1998 event is associated with flare and coronal mass ejection (CME) well observed by the Nan¸cay Radioheliograph, so that the images of radio sources are available. For the 2 November 2003 event, there are available the low-corona images of the CME liftoff obtained at the Mauna Loa Solar Observatory. Those complementary data sets are analyzed jointly with the broadband dynamic radio spectra, EUV images and other data available for both events. We find a common scenario for both eruptions, including the flare’s dual impulsive phase, the CME-launch-associated decimetric-continuum burst, and the late, low-frequency type III radio bursts at the time of the relativistic proton injection into the interplanetary medium. The analysis supports the idea that the two considered events start with emission of relativistic protons previously accelerated during the flare and CME launch, then trapped in large-scale magnetic loops and later released by the expanding CME

Investigating the Origins of Two Extreme Solar Particle Events: Proton Source Profile and Associated Electromagnetic Emissions

We analyze the high-energy particle emission from the Sun in two extreme solar particle events. in which protons are accelerated to relativistic energies and can cause a significant signal even in the ground-based particle detectors. Analysis of a relativistic proton event is based on modeling of the particle transport and interaction, from a near-Sun source through the solar wind and the Earth's magnetosphere and atmosphere to a detector on the ground. This allows us to deduce the time profile of the proton source at the Sun and compare it with observed electromagnetic emissions. The 1998 May 2 event is associated with a. flare and a coronal mass ejection (CME), which were well observed by the Nancay Radioheliograph, thus. the images of the. radio sources are available. For the 2003 November 2 event, the low corona images of the CME liftoff obtained at the Mauna Loa Solar Observatory. are available. Those complementary data sets are analyzed jointly with the broadband dynamic radio spectra, EUV images, and other data available for both events. We find a common scenario for both eruptions, including the flare's dual impulsive phase, the CME-launch-associated decimetric-continuum burst, and the late, low-frequency type III radio bursts at the time of the relativistic proton injection into the interplanetary medium. The analysis supports the idea that the two considered events start with emission of relativistic protons previously accelerated during the flare and CME launch, then trapped in large-scale magnetic loops and later released by the expanding CME

The effect of seeing on solar magnetic flux mesurments

We investigate the influence of seeing upon measurement of magnetic flux of photospheric fields. For this purpose we quantify seeing variation in one day's observation at Big Bear Solar Observatory in terms of the Fried function, a Modulation Transfer Function for the atmospheric seeing. The temporal variation of seeing quality is compared with that of magnetic flux measured in a quiet region with size 5′ x 4′ near the solar disk center. A good correlation is found between the seeing change and apparent evolution of magnetic flux values, implying, as a possibility, that magnetic flux measurement might have been modulated by seeing. Based on a simple model of ensembles of Gaussian magnetic elements we argue that even the net flux as well as the total flux can change due to seeing variation if the magnetograph has a finite detection threshold and if the intrinsic fluxes in one and the other polarities are unbalanced

Power spectra of solar network and non-network fields

We report new properties of solar magnetic fields in a quiet region as found from their magnetic power spectra. The power spectra of network and intranetwork fields (non-network fields) are separately calculated from a Big Bear magnetogram obtained with moderately high spatial resolution of 1.5 arc sec and a high sensitivity reaching 2 Mx cm⁻². The effect of seeing on the power spectrum has been corrected using Fried's (1966) Modulation Transfer Function with the seeing parameter determined in our previous analysis of the magnetogram. As a result, it is found that the two-dimensional power spectra of network and non-network fields appear in a form: Γ(k₀ ≲ k ≲ k₁) ∼ k⁻¹ and Γ(k ≳ k₁) ∼ k^(3.5). Here k₀ ≈ 0.47 Mm⁻¹ for network fields and k₀ ≈ 0.69 Mm⁻¹ for non-network fields, the latter of which corresponds to the size of mesogranulation; k₁ ≈ 3.0 Mm⁻¹ for both, which is about the size of a large granule. The network field spectrum below k₀ appears nearly flat, whereas that of non-network fields instead decreases towards lower wave numbers as Γ(k) ∼ k^(1.3). The turnover behavior of magnetic field spectra around k₁ coincides with that found for the velocity power spectrum, which may justify the kinetic approach taken in previous theoretical studies of the solar magnetic power spectra

The imaging capabilities of the Frequency Agile Solar

The Frequency Agile Solar Radiotelescope (FASR) will observe the Sun over a wide range of radio frequencies and make high spatial resolution images at many frequencies nearly simultaneously. FASR will need to be able to observe both the very bright, usually compact emission from solar flares as well as much fainter fluctuations in the solar chromosphere across a broad range of spatial scales (from 1 arcsec to 1 degree) at high time resolution, and these constraints impose severe requirements on telescope design. We discuss the problem of imaging the Sun at radio wavelengths and present simulations of imaging the thermal free-free emission from the Sun's atmosphere using models based on EUV data

The imaging capabilities of the Frequency Agile Solar

The Frequency Agile Solar Radiotelescope (FASR) will observe the Sun over a wide range of radio frequencies and make high spatial resolution images at many frequencies nearly simultaneously. FASR will need to be able to observe both the very bright, usually compact emission from solar flares as well as much fainter fluctuations in the solar chromosphere across a broad range of spatial scales (from 1 arcsec to 1 degree) at high time resolution, and these constraints impose severe requirements on telescope design. We discuss the problem of imaging the Sun at radio wavelengths and present simulations of imaging the thermal free-free emission from the Sun’s atmosphere using models based on EUV data