Flare induced penumbra formation in the sunspot of NOAA 10838

We have observed formation of penumbrae on a pore in the active region NOAA10838 using Dunn Solar Telescope at NSO,Sunpot,USA. Simultaneous observations using different instruments (DLSP,UBF,Gband and CaK) provide us with vector magnetic field at photosphere, intensity images and Doppler velocity at different heights from photosphere to chromosphere. Results from our analysis of this particular data-set suggests that penumbrae are formed as a result of relaxation of magnetic field due to a flare happening at the same time. Images in \Halpha\ show the flare (C 2.9 as per GOES) and vector magnetic fields show a re-orientation and reduction in the global $\alpha$ value (a measure of twist). We feel such relaxation of loop structures due to reconnections or flare could be one of the way by which field lines fall back to the photosphere to form penumbrae.Comment: 4 pages, Presented at IAU symposium 273- Physics of Sun and Starspot

Seeing-Induced Errors in Solar Doppler Velocity Measurements

Imaging systems based on a narrow-band tunable filter are used to obtain Doppler velocity maps of solar features. These velocity maps are created by taking the difference between the blue- and red-wing intensity images of a chosen spectral line. This method has the inherent assumption that these two images are obtained under identical conditions. With the dynamical nature of the solar features as well as the Earth's atmosphere, systematic errors can be introduced in such measurements. In this paper, a quantitative estimate of the errors introduced due to variable seeing conditions for ground-based observations is simulated and compared with real observational data for identifying their reliability. It is shown, under such conditions, that there is a strong cross-talk from the total intensity to the velocity estimates. These spurious velocities are larger in magnitude for the umbral regions compared to the penumbra or quiet-sun regions surrounding the sunspots. The variable seeing can induce spurious velocities up to about 1 km/s It is also shown that adaptive optics, in general, helps in minimising this effect.Comment: 14 page

Global Twist of Sunspot Magnetic Fields Obtained from High Resolution Vector Magnetograms

The presence of fine structures in the sunspot vector magnetic fields has been confirmed from Hinode as well as other earlier observations. We studied 43 sunspots based on the data sets taken from ASP/DLSP, Hinode (SOT/SP) and SVM (USO). In this \emph{Letter}, (i) We introduce the concept of signed shear angle (SSA) for sunspots and establish its importance for non force-free fields. (ii) We find that the sign of global $\alpha$ (force-free parameter) is well correlated with the global SSA and the photospheric chirality of sunspots. (iii) Local $\alpha$ patches of opposite signs are present in the umbra of each sunspot. The amplitude of the spatial variation of local $\alpha$ in the umbra is typically of the order of the global $\alpha$ of the sunspot. (iv) We find that the local $\alpha$ is distributed as alternately positive and negative filaments in the penumbra. The amplitude of azimuthal variation of the local $\alpha$ in the penumbra is approximately an order of magnitude larger than that in the umbra. The contributions of the local positive and negative currents and $\alpha$ in the penumbra cancel each other giving almost no contribution for their global values for whole sunspot. (v) Arc-like structures (partial rings) with a sign opposite to that of the dominant sign of $\alpha$ of the umbral region are seen at the umbral-penumbral boundaries of some sunspots. (vi) Most of the sunspots studied, belong to the minimum epoch of the 23$^{rd}$ solar cycle and do not follow the so-called hemispheric helicity rule.Comment: 15 pages, 3 figures, 1 table; Accepted for publication in the ApJ Letter

On the Weakening of Chromospheric Magnetic Field in Active Regions

Simultaneous measurement of line-of-sight (LOS) magnetic and velocity fields at the photosphere and chromosphere are presented. Fe I line at $\lambda6569$ and $H_{\alpha}$ at $\lambda6563$ are used respectively for deriving the physical parameters at photospheric and chromospheric heights. The LOS magnetic field obtained through the center-of-gravity method show a linear relation between photospheric and chromospheric field for field strengths less than 700 G. But in strong field regions, the LOS magnetic field values derived from $H_{\alpha}$ are much weaker than what one gets from the linear relationship and also from those expected from the extrapolation of the photospheric magnetic field. We discuss in detail the properties of magnetic field observed in $H_{\alpha}$ from the point of view of observed velocity gradients. The bisector analysis of $H_{\alpha}$ Stokes $I$ profiles show larger velocity gradients in those places where strong photospheric magnetic fields are observed. These observations may support the view that the stronger fields diverge faster with height compared to weaker fields.Comment: accepted for publication in Ap

Resources of Ribbon Fish and Cat Fish off the South West Coast of lndia

The acoustic surveys and fishing experiments conducted by the research vessels RASTRELLIGER and SARDINELLA of the Pelagic Fishery Project from Ratnagiri to the Gulf of Mannar for the past four years have considerably enhanced our knowledge of the pelagic fishery resources, their abundance and seasonal distribution and possible methods of exploitation (Anonymous 1974, 1975 & 1976). The average annual landings of ribbon fish and cat fish for the past ten years with 78,000tonnes form only 7.7% of the total marine fish production in India

Resonance Line Polarization in Spherically Symmetric Moving Media: a Parametric Study

In the present paper we consider the problem of resonance line polarization formed in the spherically symmetric expanding atmospheres. For the solution of the concerned polarized transfer equation we use the comoving frame formulation, and apply the Accelerated Lambda Iteration (ALI) method. We restrict ourselves to the non-relativistic regime of velocities wherein mainly Doppler shift effects are significant. For our studies, we consider the scattering on a two-level atom, including the effects of partial frequency redistribution (PFR). We present the dependence of linearly polarized profiles on different atmospheric and atomic parameters.Comment: 10 pages, 6 figures, Proceedings of the 9th Solar Polarization Workshop SPW9, A workshop held in Gottingen, Germany, from August 26 to August 30, 201