EVIDENCE FOR A CURRENT SHEET ABOVE A SUNSPOT UMBRA

We present observational evidence for the existence of a current sheet in the chromosphere above a sunspot umbra based on high angular resolution two-dimensional spectroscopic observations in the Ca II 854.21 nm line. In the core of this line we observe a very stable bright ribbon-like structure separating magnetic field configurations that connect to different parts of the active region. We make plausible that the structure is a string of sheets carrying vertical currents that result from dissipation when the different parts of the active region are moved around in the photosphere. To our knowledge this is the first direct observation of the heating caused by the dissipation in such a current sheet in the chromosphere

Spectral Signatures of Penumbral Transients

In this work we investigate the properties of penumbral transients observed in the upper photospheric and chromospheric region above a sunspot penumbra using two-dimensional spectroscopic observations of the Ca II 854.21 nm line with a 5 s cadence. In our 30 minutes of observations, we identify several penumbral-micro jets (PMJs) with cotemporal observations from Dunn Solar Telescope/IBIS and Hinode/SOT. We find that the line profiles of these PMJ events show emission in the two wings of the line (±0.05 nm), but little modification of the line core. These are reminiscent of the line profiles of Ellerman bombs observed in plage and network regions. Furthermore, we find evidence that some PMJ events have a precursor phase starting 1 minute prior to the main brightening that might indicate initial heating of the plasma prior to an acoustic or bow shock event. With the IBIS data, we also find several other types of transient brightenings with timescales of less than 1 minute that are not clearly seen in the Hinode/SOT data. The spectral profiles and other characteristics of these events are significantly different from those of PMJs. The different appearances of all these transients are an indicator of the general complexity of themore » chromospheric magnetic field and underscore the highly dynamic behavior above sunspots. It also highlights the care that is needed in interpreting broadband filter images of chromospheric lines, which may conceal very different spectral profiles, and the underlying physical mechanisms at work.« les

Tracing the Chromospheric and Coronal Magnetic Field with AIA, IRIS, IBIS, and ROSA Data

The aim of this study is to explore the suitability of chromospheric images for magnetic modeling of active regions. We use high-resolutionimages (≈0.2"-0.3"), from the Interferometric Bidimensional Spectrometer in the Ca II 8542 Å line, the Rapid Oscillations in the Solar Atmosphere instrument in the Hα 6563Å line, the Interface Region Imaging Spectrograph in the 2796Å line, and compare non-potential magnetic field models obtainedfrom those chromospheric images with those obtained from images of the Atmospheric Imaging Assembly in coronal (171 Å, etc.) and inchromospheric (304 Å) wavelengths. Curvi-linear structures are automatically traced in those images with the OCCULT-2 code, to which we forward-fitted magnetic field lines computed with the Vertical-current Approximation Nonlinear Force Free Field code. We find that the chromospheric images: (1) reveal crisp curvi-linear structures (fibrils, loop segments, spicules) that are extremely well-suited for constraining magnetic modeling; (2) that these curvi-linear structures arefield-aligned with the best-fit solution by a median misalignment angle of μ2 ≈ 4°–7° (3) the free energy computed from coronal data may underestimate that obtained from chromospheric data by a factor of ≈2–4, (4) the height range of chromospheric features is confined to h≲4000 km, while coronal features are detected up to h = 35,000 km; and (5) the plasma-β parameter is β ≈ 10^-5 - 10^-1 for all traced features. We conclude that chromospheric images reveal important magnetic structures that are complementary to coronal images and need to be included in comprehensive magnetic field models, something that is currently not accomodated in standard NLFFF codes

The Transformation of Rice Value Chains in Bangladesh and India: Implications for Food Security

This paper reports the survey findings that rice value chains are transforming in Bangladesh and India. The main elements of the transformation are as follows: First, rice value chains in both countries have begun to "geographically lengthen" and "intermediationally shorten." Second, farmers capture about 60% of the final urban retail price of rice; this can be compared to about 23% in 1998 and 37% in 1980 in the United States. Third, the corollary is that about 40% of the value chain is formed by the postharvest segments of the rice value chain - in milling, trading, and retailing. Fourth, while much policy debate centers on direct government operations in food value chains, such operations were, in general, quite small in the rice value chain, except for the Government of India's purchases from mills. Fifth, the indirect roles of governments have been important in enabling change and at times in providing incentives for transformation. Sixth, government subsidies had important effects, but the evidence of accessibility to subsidies and the impact of the services were mixed. Seventh, the study points to the importance of farm input supply chains upstream from farmers and of midstream and downstream postharvest activities such as logistics and wholesale, milling, and retailing. Policy implications are drawn in the final section of the paper