Magnetic flux changes associated with the solar flares of August 1972

The active region associated with Mt. Wilson sunspot group 18 935 (McMath, 11 976) which had a central meridian passage on August 4 and 5, 1972 produced a number of flares during transit. These included two importance 3B flares on August 4 and 7 as well as several of importance 1 and 2. Calculations of the total magnetic flux in this region were made during the period July 31 through August 9 using data from six observatories. For the 3B flare on August 4, the total flux changed from about 7.2 × 10²² Mx just before onset to about 5.6 × 10²² Mx two hours after onset. For the 3B flare on August 7, the flux was about 6.4 × 10²² Mx three hours before onset and about 5.2 × 10²² Mx three hours after onset. An importance 2B flare on August 2 had no measurable effect on the flux nor did any of several 1N or 1B flares which also occurred in this region during the period. The flux changes measured for the 3B flares occurred in the umbral and penumbral fields and no significant changes were observed in facular fields.The Aerospace Corporation, P.O. Box 92957, Los Angeles, Calif. 90009, U.S.A.     

Flux Cancellation Rates and Converging Speeds of Canceling Magnetic Features

Canceling magnetic features are commonly believed to result from magnetic reconnection in the low atmosphere. According to the Sweet–Parker type reconnection model, the rate of flux cancellation in a canceling magnetic feature is related to the converging speed of each pole. To test this prediction observationally, we have analyzed the time variation of two canceling magnetic features in detail using the high-resolution magnetograms taken by the Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory (SOHO). As a result, we have obtained the rate and converging speed of flux cancellation in each feature: 1.3×10¹⁸ Mx hr^–1 (or 1.1×10⁶ G cm s^–1 per unit contact length) and 0.35 km s^–1 in the smaller one, and 3.5×10¹⁸ Mx hr^–1 (1.2×10⁶ G cm s^–1) and 0.27 km s^–1 in the bigger one. The observed speeds are found to be significantly bigger than the theoretically expected ones, but this discrepancy can be resolved if uncertainty factors such as low area filling factor of magnetic flux and low electric conductivity are taken into account.     

A model of the Solar Magnetic Carpet

There are four key processes that dictate the behaviorof the magnetic flux concentrations that form the so-called `magnetic carpet' of the quiet photosphere. These processes are emergence, cancellation, coalescence, and fragmentation. Rates of emergence have been estimated from observations, but the rates of cancellation, coalescence, and fragmentation are much more difficult to determine observationally. A model is set up to simulate an area of magnetic carpet in the quiet Sun. In the model there are three imposed parameters: the rate of emergence of new flux, the distribution of emerged flux and the rate of fragmentation of flux concentrations. The rate of cancellation and the rate of coalescence are deduced from the model. From the simulations it is estimated that the average emergence rate of new flux in the quiet Sun must be between 6×10^–6 and 10^{– 5} Mx cm^–2 s^–1 to maintain an absolute flux density of between 2.5 and 3 G. For this rate of emergence a fragmentation rate of more than 12×10^–5 s^–1 is required to produce the observed exponential index for the number density of flux concentrations. This is equivalent to each fragment canceling more than once every 200 minutes. The rate of cancellation is calculated from the model and is found naturally to be equivalent to the rate of emergence. However, it is found that the frequency of cancellation is much greater than the frequency of emergence. In fact, it is likely that there are several orders of magnitude more cancellation events than emergence events. This implies that flux is injected in relatively large concentrations whereas cancellation occurs though the disappearance of many small concentrations.     

Solar Magnetic Carpet I: Simulation of Synthetic Magnetograms

This paper describes a new 2D model for the photospheric evolution of the magnetic carpet. It is the first in a series of papers working towards constructing a realistic 3D non-potential model for the interaction of small-scale solar magnetic fields. In the model, the basic evolution of the magnetic elements is governed by a supergranular flow profile. In addition, magnetic elements may evolve through the processes of emergence, cancellation, coalescence and fragmentation. Model parameters for the emergence of bipoles are based upon the results of observational studies. Using this model, several simulations are considered, where the range of flux with which bipoles may emerge is varied. In all cases the model quickly reaches a steady state where the rates of emergence and cancellation balance. Analysis of the resulting magnetic field shows that we reproduce observed quantities such as the flux distribution, mean field, cancellation rates, photospheric recycle time and a magnetic network. As expected, the simulation matches observations more closely when a larger, and consequently more realistic, range of emerging flux values is allowed (4×10¹⁶ – 10¹⁹ Mx). The model best reproduces the current observed properties of the magnetic carpet when we take the minimum absolute flux for emerging bipoles to be 4×10¹⁶ Mx. In future, this 2D model will be used as an evolving photospheric boundary condition for 3D non-potential modeling.     

On the magnetic field in pores

The magnetic field in an axisymmetric pore is current free and can be represented by a flux tube with a magnetic potential of the formAJ ₀(kr)e ^-kz. For a given magnetic flux the field in this pore model is uniquely defined if the magnetic pressure balances the gas pressure at two levels. For models with fluxes of 0.5–3.0 × 10²⁰ mx the surface radius varies from 1100–2700 km (diameters of 3–8 arc-sec) and the Wilson depression is estimated at 200 km. As the flux increases, the field becomes nearly horizontal at the edge of the pore and eventually a penumbra is formed. The distinction between pores and sunspots is investigated; the critical flux is about 10²⁰ Mx, corresponding to a radius of 1500 km.Visitor, as a member of the High Altitude Observatory Solar Project, at Sacramento Peak Observatory, Sunspot, N.M., U.S.A.     

Small-Scale Flux Emergence Observed Using <Emphasis Type="Italic">Hinode</Emphasis>/SOT

The aim of this paper is to determine the flux emergence rate due to small-scale magnetic features in the quiet Sun using high-resolution Hinode SOT NFI data. Small-scale magnetic features are identified in the data using two different feature identification methods (clumping and downhill); then three methods are applied to detect flux emergence events. The distribution of the intranetwork peak emerged fluxes is determined. When combined with previous emergence results, from ephemeral regions to sunspots, the distribution of all fluxes are found to follow a power-law distribution which spans nearly seven orders of magnitude in flux (10¹⁶ – 10²³ Mx) and 18 orders of magnitude in frequency. The power-law fit to all these data is of the form

The hemispheric sign rule of current helicity during the rising phase of cycle 23

We compute the signs of two different current helicity parameters (i.e., &amp;#x03B1;_best andH _c) for 87 active regions during the rise of cycle 23 The results indicate that 59% of the active regions in the northern hemisphere have negative &amp;#x03B1;_best and 65% in the southern hemisphere have positive. This is consistent with that of the cycle 22. However, the helicity parameterH _cshows a weaker opposite hemispheric preference in the new solar cycle. Possible reasons are discussed.     

22-Year periodicity in the solar differential rotation

Using the data on sunspot groups compiled during 1879&amp;#x2013;1975, we determined variations in the differential rotation coefficientsA andB during the solar cycle. The variation in the equatorial rotation rateA is found to be significant only in the odd numbered cycles, with an amplitude &amp;#x223C; 0.01 &amp;#x03BC; rads^-1. There exists a good anticorrelation between the variations of the differential rotation rateB derived from the odd and even numbered cycles, suggesting existence of a &amp;#x2018;22-year&amp;#x2019; periodicity inB. The amplitude of the variation ofB is &amp;#x223C; 0.05 &amp;#x03BC; rad s^-1.     

An estimate of the energy spectrum of gamma rays from the central region of the Galaxy and some implications

High resolution surveys of the galactic centre suggest the existence of an extended nonthermal source (Bulge) with an intensity much larger than the total background radiation in that direction. In this paper, we have first evaluated the physical conditions existing in this restricted region of space from an analysis of the radio spectrum and shown that if the distribution of matter, magnetic fieldB(r) and cosmic ray densityk(r) in the plane of the Galaxy is of gaussian type then at the centreB (0)=25–30 G andk(0)=25–35 times that in the near interstellar space. It is also found that most of the absorption in the Sagittarius A spectrum at low frequencies takes place in the Bulge and one requires a small additional absorption to take place in the line of sight corresponding to n _e ²10 cm^–6 pc at a temperature typically of clouds 100 K. The gamma ray spectra from the Bulge arising from interactions of cosmic rays with matter and radiation are then calculated in detail. A comparison made with the estimated background gamma ray spectra from the disk reveals that a detector with angular resolution 6° having a threshold of a few times 10^–6 photons cm^–2 s^–1 can detect this source; this bulge is not found to be a good X-ray source for detection. From a comparison of these calculations with the observed flux above 100 MeV, the following inferences have been deduced: (i) the lower limit to the magnetic field strength at the centre is 12 G, (ii) the observed gamma ray flux towards the Anti-centre can be well explained as due to interactions of cosmic rays with matter alone and a similar explanation towards the center reveals that cloud complexes could be more in the inner parts of the Galaxy than in the outer parts, and (iii) the observed flux values are found to be inconsistent with the existence of submillimeter radiation in the galactic scale.     

The flux-rope-fibre theory of solar magnetic fields

The flux-rope theory of solar magnetic fields is reviewed briefly and, together with the dynamo theory, compared with various observational results. Dynamo and related theories are based on fields controlled by the plasma, and it is shown that such fields cannot account for the strong surface fields or even emerge without becoming tangled. Observations which appear uniquely explicable in terms of powerful (4000 G), helically twisted flux ropes and their many twisted flux fibres (3×10¹⁸ Mx) are listed as follows. (i) Emerging magnetic flux is seen first as pairs of small, closely spaced flux concentrations whose motions suggest magnetic control to provide bipolar regions of extent10⁵ km. The associated system of arch filaments rotates on the disk as would a series of emerging flux fibres twisted into a rope. (ii) Sunspots form by the accretion of pores and magnetic knots of like polarity, sometimes moving along curved paths between stationary elements of opposite polarity. (iii) Fluxes of10²² Mx in large sunspots must have been concentrated to strengths of4000 G before emerging, and also strongly helically twisted to avoid the flute instability. (iv) The trumpet-shaped flux-rope-fibre sunspot model (Figure 6) accounts readily for the phenomena of the moat convection, the sunspot energy deficit, the complex Evershed flow, penumbral filaments (flux 3×10¹⁸ Mx) and temporary light bridges. (v) Asymmetries in sunspot groups (in spot size, lifetime and proper motion) show that the spot fields are extensions of two submerged magnetic structures comprising strong fields. (vi) Sunspots decay by the loss of magnetic knots with strong fields and flux 5×10¹⁸ Mx. These must be isolated flux tubes, twisted to account for their stability. (vii) Flux fibres leaving a spot are prone to the kink instability, thus accounting for their sudden appearance in pairs, the transport of total flux several times that of the spot and net flux equal to that of the spot. (viii) Ephemeral active regions and X-ray bright points are explained similarly without invoking improbably huge quantities of new flux. (ix) Atmospheric structures show a high prevalence of helical twists (force-free fields) and rotary motions on all scales from spicules to large prominences. It is difficult to account for these twists unless they are present in emerging flux. (x) In and above the photosphere the flux fibres (3×10¹⁸ Mx) fray into loose associations of flux threads (3×10¹⁷ Mx) to provide a simple, selfconsistent model of the solar filigree and the chromospheric rosette (bush) with its group of mottles (spicules). (xi) Global patterns of surface and coronal magnetic fields reveal puzzling features such as the migration of large unipolar regions and the freedom from differential rotation of some structures. Submerged flux ropes peeling out of the Sun provide a starting point for explaining these effects. These results provide a strong case for the flux-rope theory against the entrenched dynamo theory, and suggest that more observations should be made of the above ten phenomena. Where possible, simultaneous observations should be made of Zeeman effects and of plasma distributions and velocity field seen in white light and spectral lines.     

The smallest observable elements of magnetic flux

We have followed disappearing elements of magnetic flux to determine the smallest elements detectable with the Big Bear videomagnetograph. All the elements followed were disappearing through interaction with elements of opposite polarity. The last remaining visible segment of magnectic field of such features can be used to infer the total magnetic flux of these and other small flux elements visible on the magnetograms.We used both photographic and digital videomagnetograms combining 4096 Zeeman frames made at Big Bear. Fifteen elements were measured near the vanishing point, in a 2–8 hr period. The minimum observable fluxes fall in the range of 1.0 × 10¹⁶ to 1.4 × 10¹⁷ Mx, and the apparent size of these elements is in the range of 1 to 9 square arc sec. The process of disappearance appears to be a smooth one. The smallest detectable elements of network field and ephemeral regions (ER) appear to be the same as the small intra-network (IN) field elements. The present limit is still instrumental; elements smaller than 1 × 10¹⁶ would not have been detected.Visiting Associates from Beijing Observatory, Academia Sinica, Beijing, China.     

An Evolving Synoptic Magnetic Flux map and Implications for the Distribution of Photospheric Magnetic Flux

We describe a procedure intended to produce accurate daily estimates of the magnetic flux distribution on the entire solar surface. Models of differential rotation, meridional flow, supergranulation, and the random emergence of background flux elements are used to regularly update unobserved or poorly observed portions of an initial traditional magnetic synoptic map that acts as a seed. Fresh observations replace model estimates when available. Application of these surface magnetic transport models gives us new insight into the distribution and evolution of magnetic flux on the Sun, especially at the poles where canopy effects, limited spatial resolution, and foreshortening result in poor measurements. We find that meridional circulation has a considerable effect on the distribution of polar magnetic fields. We present a modeled polar field distribution as well as time series of the difference between the northern and southern polar magnetic flux; this flux imbalance is related to the heliospheric current sheet tilt. We also estimate that the amount of new background magnetic flux needed to sustain the `quiet-Sun' magnetic field is about 1.1×10²³ Mx d^–1 (equivalent to several large active regions) at the spatial resolution and epoch of our maps. We comment on the diffusive properties of supergranules, ephemeral regions, and intranetwork flux. The maps are available on the NSO World Wide Web page.     

Quiescent Reconnection Rate Between Emerging Active Regions and Preexisting Field,with Associated Heating: NOAA AR 11112

When magnetic flux emerges from beneath the photosphere, it displaces the preexisting field in the corona, and a current sheet generally forms at the boundary between the old and new magnetic domains. Reconnection in the current sheet relaxes this highly stressed configuration to a lower energy state. This scenario is most familiar and most often studied in flares, where the flux transfer is rapid. We present here a study of steady, quiescent flux transfer occurring at a rate three orders of magnitude lower than that in a large flare. In particular, we quantify the reconnection rate and the related energy release that occurred as the new polarity emerged to form NOAA Active Region 11112 (SOL16 October 2010T00:00:00L205C117) within a region of preexisting flux. A bright, low-lying kernel of coronal loops above the emerging polarity, observed with the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory and the X-ray Telescope onboard Hinode, originally showed magnetic connectivity only between regions of newly emerged flux when overlaid on magnetograms from the Helioseismic and Magnetic Imager. Over the course of several days, this bright kernel advanced into the preexisting flux. The advancement of an easily visible boundary into the old flux regions allows measuring the rate of reconnection between old and new magnetic domains. We compare the reconnection rate with the inferred heating of the coronal plasma. To our knowledge, this is the first measurement of steady, quiescent heating related to reconnection. We determined that the newly emerged flux reconnects at a fairly steady rate of 0.38×10¹⁶ Mx?s^?1 over two days, while the radiated power varies between (2?–?8)×10²⁵ erg?s^?1 over the same time. We found that as much as 40 % of the total emerged flux at any given time may have reconnected. The total amounts of transferred flux (～?1×10²¹ Mx) and radiated energy (～?7.2×10³⁰ ergs) are comparable to that of a large M- or small X-class flare, but are stretched out over 45 hours.     

On the relationship between polar faculae and large-scale magnetic field

We investigate a latitude–time distribution of polar faculae observed at Ussuriysk Observatory in years 1966–1986. The distribution is compared with the longitude-averaged (zonal) magnetic field of the Sun calculated from the data obtained at Mount Wilson Observatory in the years 1966–1976, and at Kitt Peak National Observatory during the period from 1976 to 1985. We found that slow, poleward-directed migration of the polar faculae zones occurring during the course of the solar cycle is not a continuous process, but it contains several episodes of appearance and fast poleward drift of new zones of polar faculae. At the rising phase of the solar cycle, new zones of polar faculae appear at latitudes as low as 40°, but the ones observed during the declining phase of the solar cycle originate at higher latitudes of 50–55°. Such episodes of appearance and fast migration of the polar faculae zones are associated with the poleward-directed streams of magnetic field originated at low latitudes. Moreover, we found some evidence for existence of an additional component of the polar faculae activity that reveals an equatorward migration during the course of the solar cycle. We also investigated a relationship between the number of polar faculae, n, and absolute magnetic flux _z of the zonal mode of the solar magnetic field. We found that within the polar zones of the Sun, substantial correlation between temporal variations of n and _z takes place both on the time scale of the solar cycle and on a shorter time scale of 2–4 years. The relationship between the number of polar faculae and magnetic flux may be approximated by a linear dependence n=0.12_z (where _z is expressed in 10²¹ Mx), except for time interval 1977 through 1980 for which the factor of proportionality is found to have a systematically larger value of 0.20.     

Cosmic neutrinos of ultra-high energies and detection possibility

The fluxes and spectra of galactic and extragalactic neutrinos at energy 10¹¹–10¹⁹ eV are calculated. In particular, the neutrino flux from the normal galaxies is calculated taking into account the spectral index distribution. The only assumption that seriously affects the calculated neutrino flux atE _v 10¹⁷ eV is the power-like generation spectrum of protons in the entire considered energy region.The normal galaxies with the accepted parameters generate the metagalactic equivalent electron component (electrons+their radiation) with energy density _e8.5×10^–7 eV cm^–3, while the density of the observed diffuse X-ray radiation alone is 100 times higher. This requires the existence of other neutrino sources and we found the minimized neutrino flux under two limitations: (1) the power-law generation spectrum of protons and (2) production of the observed energy density of the diffuse X-an -radiation. These requirements are met in the evolutionary model of origin of the metagalactic cosmic rays with modern energy density _M83.6×10^–7 eV cm^–3.The possibility of experiments with cosmic neutrinos of energyE _v 3×10¹⁷ eV is discussed. The upper bound on neutrino-nucleon cross-section <2.2×10^–29 cm² is obtained in evolutionary model from the observed zenith angular distribution of extensive air showers.In Appendix 2 the diffuse X-and -ray flux arising together with neutrino flux is calculated. It agrees with observed flux in the entire energy range from 1 keV up to 100 MeV.     

Detection of H2 emission towards the wolf-rayet nebula NGC 2359

We report the first detection of molecular hydrogen emission in the vicinity of a Wolf-Rayet star and nebula. The spatial distribution of the excited molecular gas is filamentary and is not correlated with the distribution of the ionised gas as traced by optical emission lines. The typical H₂ surface brightness in the filaments is 5× 10^–5 ergs s^–1 cm^–2 str^–1. We demonstrate that the excitation mechanism can be shocks or fluorescence from the strong ultraviolet flux of the WR star.     

Effects of Complexity on the Flux-Tube Tectonics Model

The quiet-Sun magnetic field emerges through the solar photosphere in a multitude of mixed-polarity magnetic concentrations and is subsequently tangled up into intricate regions of interconnecting flux. Moreover, since these discrete concentrations are likely to be extremely small in size, with fluxes of around only 10¹⁷ Mx, the number of such flux sources in, say, a supergranule, will be extremely large. The flux-tube tectonics model of Priest, Heyvaerts, and Title (2002) demonstrated how the formation and dissipation of current sheets along the separatrices that separate the regions of different connectivity are likely to make an important contribution to coronal heating. Since the full complexity of the magnetic field is below present observable scales, this study examines the effect of having the magnetic flux emerge through configurations structured on smaller and smaller scales. It is found that, by fixing the amount of flux emerging into a given 2D region, the main factors influencing the current build-up along the separatrices are the number of sources through which the flux emerges and the spatial distribution of the sources on the photosphere. The free energy (i.e., that above potential) is stored lower and lower in the atmosphere as the complexity of the system increases. A simple comparison is then made between coronal heating by separator currents and by separatrix currents. It is found that both result in comparable amounts of energy release, with separatrix heating being the more dominant.     

Comparing Simulations of Rising Flux Tubes Through the Solar Convection Zone with Observations of Solar Active Regions: Constraining the Dynamo Field Strength

We study how active-region-scale flux tubes rise buoyantly from the base of the convection zone to near the solar surface by embedding a thin flux tube model in a rotating spherical shell of solar-like turbulent convection. These toroidal flux tubes that we simulate range in magnetic field strength from 15 kG to 100 kG at initial latitudes of 1^° to 40^° in both hemispheres. This article expands upon Weber, Fan, and Miesch (Astrophys. J. 741, 11, 2011) (Article 1) with the inclusion of tubes with magnetic flux of 10²⁰ Mx and 10²¹ Mx, and more simulations of the previously investigated case of 10²² Mx, sampling more convective flows than the previous article, greatly improving statistics. Observed properties of active regions are compared to properties of the simulated emerging flux tubes, including: the tilt of active regions in accordance with Joy’s Law as in Article 1, and in addition the scatter of tilt angles about the Joy’s Law trend, the most commonly occurring tilt angle, the rotation rate of the emerging loops with respect to the surrounding plasma, and the nature of the magnetic field at the flux tube apex. We discuss how these diagnostic properties constrain the initial field strength of the active-region flux tubes at the bottom of the solar convection zone, and suggest that flux tubes of initial magnetic field strengths of ≥?40 kG are good candidates for the progenitors of large (10²¹ Mx to 10²² Mx) solar active regions, which agrees with the results from Article 1 for flux tubes of 10²² Mx. With the addition of more magnetic flux values and more simulations, we find that for all magnetic field strengths, the emerging tubes show a positive Joy’s Law trend, and that this trend does not show a statistically significant dependence on the magnetic flux.     

High-energy proton,helium, and gamma-ray observations on OSO-III

A report on preliminary results obtained from the analysis of the first 700 orbits of data obtained in the University of Rochester particle telescope, carried in the wheel section of OSO-III, is presented. The telescope is sensitive to high-energy -rays (threshold 50 MeV) and the nuclear component of the cosmic radiation. An upper limit of 3.2 × 10^–4 /cm²secster. is set on the intensity of the diffuse primary -radiation, on the assumption it arises from the decay of ° mesons produced in nuclear interactions. An upper limit to the flux from the sun, on the same assumptions, is set at 5.5 × 10^–5 /cm² sec. The analysis of the charged particle data yields the integral rigidity spectra of proton and helium nuclei from 3 to 15 GV; the results indicate that the He spectrum is slightly steeper than the proton spectrum and that the ratio P/He increases slowly from a value of approximately 6 at 3 GV to 8 at 15 GV.NASA Predoctoral Trainee.     

Solar Intranetwork Magnetic Elements: Flux Distributions

The current study aims at quantifying the flux distributions of solar intranetwork (IN) magnetic field based on the data taken in four quiet and two enhanced network areas with the Narrow-band Filter Imager of the Solar Optical Telescope on board the Hinode satellite. More than 14000 IN elements and 3000 NT elements were visually identified. They exhibit a flux distribution function with a peak at 1?–?3×10¹⁶ Mx (maxwell) and 2?–?3×10¹⁷ Mx, respectively. We found that the IN elements contribute approximately to 52 % of the total flux and an average flux density of 12.4 gauss of the quiet region at any given time. By taking the lifetime of IN elements of about 3 min (Zhou et al., Solar Phys. 267, 63, 2010) into account, the IN fields are estimated to have total contributions to the solar magnetic flux up to 3.8×10²⁶ Mx per day. No fundamental distinction can be identified in IN fields between the quiet and enhanced network areas.