Organized Subsurface Flows near Active Regions

Local helioseismic techniques, such as ring analysis and time-distance helioseismology, have already shown that large-scale flows near the surface converge towards major active regions. Ring analysis has further demonstrated that at greater depths some active regions exhibit strong outflows. A critique leveled at the ring-analysis results is that the Regularized Least Squares (RLS) inversion kernels on which they are based have negative sidelobes near the surface. Such sidelobes could result in a surface inflow being misidentified as a diverging outflow at depth. In this paper we show that the Optimally Located Averages (OLA) inversion technique, which produces kernels without significant sidelobes, generates flows markedly similar to the RLS results. Active regions are universally zones of convergence near the surface, while large complexes evince strong outflows deeper down.     

The Jovian ammonia abundance from interferometric observations of limb darkening at 3.4 mm

The interferometer visibility of Jupiter, observed at a wavelength of 3.4 mm, is used to determine the global limb darkening of the planet's brightness. From a single-parameter fit to the visibility curve, we find an ammonia-to-molecular hydrogen mixing ratio of 6.4[+5.1, ?1.9] × 10^?5, which corresponds to 35[+28, ?10]% of the solar nitrogen abundance if all of the nitrogen is in the form of ammonia. The fitting procedure uses a simple model atmosphere for the Jovian atmosphere which is based on other observations of the planet. The dependence of the result on the various model parameters is studied.     

The Global Context of Solar Activity During the Whole Heliosphere Interval Campaign

The Whole Heliosphere Interval (WHI) was an international observing and modeling effort to characterize the 3-D interconnected ??heliophysical?? system during this solar minimum, centered on Carrington Rotation 2068, March 20??C?April 16, 2008. During the latter half of the WHI period, the Sun presented a sunspot-free, deep solar minimum type face. But during the first half of CR 2068 three solar active regions flanked by two opposite-polarity, low-latitude coronal holes were present. These departures from the quiet Sun led to both eruptive activity and solar wind structure. Most of the eruptive activity, i.e., flares, filament eruptions and coronal mass ejections (CMEs), occurred during this first, active half of the interval. We determined the source locations of the CMEs and the type of associated region, such as active region, or quiet sun or active region prominence. To analyze the evolution of the events in the context of the global solar magnetic field and its evolution during the three rotations centered on CR 2068, we plotted the CME source locations onto synoptic maps of the photospheric magnetic field, of the magnetic and chromospheric structure, of the white light corona, and of helioseismological subsurface flows. Most of the CME sources were associated with the three dominant active regions on CR 2068, particularly AR 10989. Most of the other sources on all three CRs appear to have been associated with either isolated filaments or filaments in the north polar crown filament channel. Although calculations of the flux balance and helicity of the surface magnetic features did not clearly identify a dominance of one region over the others, helioseismological subsurface flows beneath these active regions did reveal a pronounced difference among them. These preliminary results suggest that the ??twistedness?? (i.e., vorticity and helicity) of subsurface flows and its temporal variation might be related to the CME productivity of active regions, similar to the relationship between flares and subsurface flows.     

A Snapshot of the Sun Near Solar Minimum: The Whole Heliosphere Interval

We present an overview of the data and models collected for the Whole Heliosphere Interval, an international campaign to study the three-dimensional solar?Cheliospheric?Cplanetary connected system near solar minimum. The data and models correspond to solar Carrington Rotation 2068 (20 March??C?16 April 2008) extending from below the solar photosphere, through interplanetary space, and down to Earth??s mesosphere. Nearly 200 people participated in aspects of WHI studies, analyzing and interpreting data from nearly 100 instruments and models in order to elucidate the physics of fundamental heliophysical processes. The solar and inner heliospheric data showed structure consistent with the declining phase of the solar cycle. A closely spaced cluster of low-latitude active regions was responsible for an increased level of magnetic activity, while a highly warped current sheet dominated heliospheric structure. The geospace data revealed an unusually high level of activity, driven primarily by the periodic impingement of high-speed streams. The WHI studies traced the solar activity and structure into the heliosphere and geospace, and provided new insight into the nature of the interconnected heliophysical system near solar minimum.     

A mixed finite element method for the solution of the magnetostatic problem with highly discontinuous coefficients in 3D

This paper present a new a mixed finite element method for the simulation of magnetostatic problems with highly discontinuous permeability. The method is derived from the well studied mixed formulation for the div-grad system that is known to be accurate for very large discontinuities. The method robustness is demonstrated on a test model problem.     

Inversion of time domain three-dimensional electromagnetic data

We present a general formulation for inverting time domain electromagnetic data to recover a 3-D distribution of electrical conductivity. The forward problem is solved using finite volume methods in the spatial domain and an implicit method (Backward Euler) in the time domain. A modified Gauss–Newton strategy is employed to solve the inverse problem. The modifications include the use of a quasi-Newton method to generate a pre-conditioner for the perturbed system, and implementing an iterative Tikhonov approach in the solution to the inverse problem. In addition, we show how the size of the inverse problem can be reduced through a corrective source procedure. The same procedure can correct for discretization errors that inevidably arise. We also show how the inverse problem can be efficiently carried out even when the decay time for the conductor is significantly larger than the repetition time of the transmitter wave form. This requires a second processor to carry an additional forward modelling. Our inversion algorithm is general and is applicable for any electromagnetic field  ( E , H , d B / dt )  measured in the air, on the ground, or in boreholes, and from an arbitrary grounded or ungrounded source. Three synthetic examples illustrate the basic functionality of the algorithm, and a result from a field example shows applicability in a larger-scale field example.     

Solar shear flows deduced from helioseismic dense-pack samplings of ring diagrams

We report on large-scale horizontal flows in the solar convection zone and their variability in time and space using a local-helioseismology technique known as ring-diagram analysis. By performing this analysis on a dense mosaic of individual regions on the solar disk, i.e., a `Dense-Pack' sampling, and repeating the analysis periodically on several time scales, we are able to assess the variation of horizontal flows from day-to-day, week-to-week, and year-to-year. We find that although there are changes in the flows on all these time scales, there are also basic patterns that persist. On a daily time scale we observe that the flow is reduced in those areas which are occupied by large active regions. On somewhat longer time-scales we see bands of persistent fast and slow zonal flow that are identifiable as torsional oscillations. As we examine these bands during a series of years, we find that these bands migrate toward the equator as solar activity increases. Similarly, the latitudes at which the meridional flow reaches maximum follow these regions of fast zonal flow as they migrate equatorwards. These Dense-Pack samplings also reveal substantial differences in the zonal and meridional flow patterns in the northern and southern hemispheres.     

Latest Results Found with Ring-Diagram Analysis

Ring-diagram analysis is a helioseismic tool useful for studying the near-surface layers of the Sun. It has been employed to study near-surface shear, meridional circulation, flows around sunspots, and thermal structure beneath active regions. We review recent results obtained using ring-diagram analysis, state some of the more important outstanding difficulties in the technique, and point out several extensions to the technique that are just now beginning to bear fruit.     

Modeling the Subsurface Structure of Sunspots

While sunspots are easily observed at the solar surface, determining their subsurface structure is not trivial. There are two main hypotheses for the subsurface structure of sunspots: the monolithic model and the cluster model. Local helioseismology is the only means by which we can investigate subphotospheric structure. However, as current linear inversion techniques do not yet allow helioseismology to probe the internal structure with sufficient confidence to distinguish between the monolith and cluster models, the development of physically realistic sunspot models are a priority for helioseismologists. This is because they are not only important indicators of the variety of physical effects that may influence helioseismic inferences in active regions, but they also enable detailed assessments of the validity of helioseismic interpretations through numerical forward modeling. In this article, we provide a critical review of the existing sunspot models and an overview of numerical methods employed to model wave propagation through model sunspots. We then carry out a helioseismic analysis of the sunspot in Active Region 9787 and address the serious inconsistencies uncovered by Gizon et al. (2009a, 2009b). We find that this sunspot is most probably associated with a shallow, positive wave-speed perturbation (unlike the traditional two-layer model) and that travel-time measurements are consistent with a horizontal outflow in the surrounding moat.     

Large-Scale Zonal Flows Near the Solar Surface

Migrating bands of weak, zonal flow, associated with the activity bands in the solar cycle, have been observed at the solar surface for some time. More recently, these flows have been probed deep within the convection zone using global helioseismology and examined in more detail close to the surface with the techniques of local helioseismology. We compare the near-surface results from global and local helioseismology using data from the Michelson Doppler Imager and the Global Oscillation Network Group with surface Doppler velocity measurements from the Mount Wilson 150-foot tower and find that the results are in reasonable agreement, with some explicable differences in detail. All of the data sets show zones of faster rotation approaching the equator from mid-latitudes during the solar cycle, with a variation at any given location that can be approximately, but not completely, described by a single sinusoid and an amplitude that does not drop off steeply below the surface.