Barry J. Labonte

Moving Dipolar Features in an Emerging Flux Region

On 25 January, 2000, we observed active region NOAAxa08844 with the Flare Genesis Experiment (FGE), a balloon-borne observatory with an 80-cm solar telescope. FGE was equipped with a vector polarimeter and a tunable Fabry–Pérot narrow-band filter. It recorded time series of filtergrams, vector magnetograms and Dopplergrams at the Cau2009i 6122.2xa0Å line, and Hα filtergrams with a cadence between 2.5 and 7.5xa0min. At the time of the observations, NOAAxa08844 was located at approximately 5°xa0N 30°xa0W. The region was growing rapidly; new magnetic flux was constantly emerging in three supergranules near its center. We report on the structure and behavior of peculiar moving dipolar features (MDFs) in the emerging flux, and we describe in detail how the FGE data were analyzed. In longitudinal magnetograms, the MDFs appeared to be small dipoles flowing into sunspots and supergranule boundaries. Previously, dipolar moving magnetic features (MMFs) have only been observed flowing out from sunspots. The FGE vector magnetograms show that the MDFs occurred in a region with nearly horizontal fields, the MDFs being distinguished as undulations in these fields. We identify the MDFs as stitches where the emerging flux ropes were still tied to the photosphere by trapped mass. We present a U-loop model that accounts for their unusual structure and behavior, as well as showing how emerging flux sheds entrained mass.

Reconstruction of an Inductive Velocity Field Vector from Doppler Motions and a Pair of Solar Vector Magnetograms

We outline a general methodology to infer the inductive velocity field vector in solar active regions. For the first time, both the field-aligned and the cross-field velocity components are reconstructed. The cross-field velocity solution accounts for the changes of the vertical magnetic field seen between a pair of successive active region vector magnetograms via the ideal induction equation. The field-aligned velocity is obtained using the Doppler velocity and the calculated cross-field velocity. Solving the ideal induction equation in vector magnetograms measured at a given altitude in the solar atmosphere is an underdetermined problem. In response, our general formalism allows the use of any additional constraint for the inductive cross-field velocity to enforce a unique solution in the induction equation. As a result, our methodology can give rise to new velocity solutions besides the one presented here. To constrain the induction equation, we use a special case of the minimum structure approximation that was introduced in previous studies and is already employed here to resolve the 180° ambiguity in the input vector magnetograms. We reconstruct the inductive velocity for three active regions, including NOAA AR 8210, for which previous results exist. Our solution believably reproduces the horizontal flow patterns in the studied active regions but breaks down in cases of localized rapid magnetic flux emergence or submergence. Alternative approximations and constraints are possible and can be accommodated into our general formalism.

Vertical Lorentz Force and Cross-Field Currents in the Photospheric Magnetic Fields of Solar Active Regions

We demonstrate that the vertical Lorentz force and a corresponding lower limit of the cross-field electric current density can be calculated from vector magnetograms of solar active regions obtained at a single height in the solar atmosphere, provided that the vertical gradient of the magnetic field strength is known at this height. We use a predicted vertical magnetic field gradient derived from a previous analysis. By testing various force-free solutions, we find that the numerical accuracy of our method is satisfactory. Applying the method to active region photospheric vector magnetograms, we find vertical Lorentz forces ranging from several hundredths to a few tenths of the typical photospheric gravitational force, and typical cross-field current densities up to several times 10 mA m-2. The typical vertical current density is found to be 2-3 times smaller, on the order of 10-15 mA m-2. These differences are above the associated uncertainties. The values of the cross-field currents decrease in an averaged vector magnetogram, but the ratio of the cross-field to the vertical current density increases, also above the uncertainties. We conclude that the photospheric active region magnetic fields are not force-free, contrary to the conjectures of some recent studies.

The Imaging Vector Magnetograph at Haleakala –: III. Effects of Instrumental Scattered Light on Stokes Spectra

The scattering of light over the field of view of a solar spectropolarimeter affects all Stokes parameters. The magnetic field vector inferred from the Stokes spectra then has systematic error. The reason is that scattering affects polarized radiation as well as unpolarized. Accurate correction of the Stokes spectra from the Imaging Vector Magnetograph (IVM) of the Mees Solar Observatory illustrates the problem and the solutions.

Sky Brightness Measurements at Haleakala, 1955–2002

Measurements of the brightness of the clear daytime sky at Haleakala, Maui are presented for the interval 1955 through 2002. The observations are made near the direction of the Sun, where forward scattering off aerosols dominates the sky brightness. The Haleakala summit at 3054xa0m is normally above the inversion layer. The Haleakala sky is dark; the observed brightness per airmass has a median of 10 millionths of the solar disk and a mode of 5 millionths, with Rayleigh scattering contributing 1 millionth. There is no demonstrable long-term trend in the data.

Near-infrared chromospheric observatory

NICO, the Near Infrared Chromosphere Observatory, is a platform for determining the magnetic structure and fources of heating for the solar chromosphere. NICO, a balloon-borne observatory, will use the largest solar telescope flying to map the magnetic fields, velocities, and heating events of the chromosphere and photosphere in detail. NICO will introduce new technologies to solar flight missions, such as wavefront sensing for monitoring telescope alignment, real-time correlation tracking and high-speed image motion compensation, and wide aperture Fabry-Perot etalons for extended spectral scanning.