Can overturning motions in penumbral filaments be detected?

Numerical simulations indicate that the filamentation of sunspot penumbrae and the associated systematic outflow (the Evershed effect) are due to convectively driven fluid motions constrained by the inclined magnetic field. We investigate whether these motions, in particular the upflows in the bright filaments and the downflows at their edges can be reliably observed with existing instrumentation. We use a snapshot from a sunspot simulation to calculate 2D maps of synthetic line profiles for the spectral lines Fe\sci 7090.4 \AA ~ and C\sci 5380.34 \AA. The maps are spatially and spectrally degraded according to typical instrument properties. Line-of-sight velocities are determined from line bisector shifts. We find that the detectability of the convective flows is strongly affected by spatial smearing, particularly so for the downflows. Furthermore, the line-of-sight velocities are dominated by the Evershed flow unless the observation is made very near to disk center. These problems may have compromised recent attempts to detect overturning penumbral convection. Lines with a low formation height are best suited to detect the convective flows.Comment: 8 pages, 12 figures, accepted for publication in ApJ on 28th Ju

Enhanced Joule Heating in Umbral Dots

We present a study of magnetic profiles of umbral dots (UDs) and its consequences on the Joule heating mechanisms. Hamedivafa (2003) studied Joule heating using vertical component of magnetic field. In this paper UDs magnetic profile has been investigated including the new azimuthal component of magnetic field which might explain the relatively larger enhancement of Joule heating causing more brightness near circumference of UD.Comment: 8 pages, 1 figure, accepted in Solar Physic

Spectropolarimetery of umbral fine structures from Hinode: Evidence for magnetoconvection

We present spectropolarimetric analysis of umbral dots and a light bridge fragment that show dark lanes in G-band images. Umbral dots show upflow as well as associated positive Stokes V area asymmetry in their central parts. Larger umbral dots show down flow patches in their surrounding parts that are associated with negative Stokes V area asymmetry. Umbral dots show weaker magnetic field in central part and higher magnetic field in peripheral area. Umbral fine structures are much better visible in total circularly polarized light than in continuum intensity. Umbral dots show a temperature deficit above dark lanes. The magnetic field inclination show a cusp structure above umbral dots and a light bridge fragment. We compare our observational findings with 3D magnetohydrodynamic simulations.Comment: Accepted for publication in MNRAS, 6 pages, 6 figure

Probing the Role of Magnetic-Field Variations in NOAA AR 8038 in Producing Solar Flare and CME on 12 May 1997

We carried out a multi-wavelength study of a CME and a medium-size 1B/C1.3 flare occurring on 12 May 1997. We present the investigation of magnetic-field variations in the NOAA Active Region 8038 which was observed on the Sun during 7--16 May 1997. Analyses of H{\alpha} filtergrams and MDI/SOHO magnetograms revealed continual but discrete surge activity, and emergence and cancellation of flux in this active region. The movie of these magnetograms revealed two important results that the major opposite polarities of pre-existing region as well as in the emerging flux region (EFR) were approaching towards each other and moving magnetic features (MMF) were ejecting out from the major north polarity at a quasi-periodicity of about ten hrs during 10--13 May 1997. These activities were probably caused by the magnetic reconnection in the lower atmosphere driven by photospheric convergence motions, which were evident in magnetograms. The magnetic field variations such as flux, gradient, and sunspot rotation revealed that free energy was slowly being stored in the corona. The slow low-layer magnetic reconnection may be responsible for this storage and the formation of a sigmoidal core field or a flux rope leading to the eventual eruption. The occurrence of EUV brightenings in the sigmoidal core field prior to the rise of a flux rope suggests that the eruption was triggered by the inner tether-cutting reconnection, but not the external breakout reconnection. An impulsive acceleration revealed from fast separation of the H{\alpha} ribbons of the first 150 seconds suggests the CME accelerated in the inner corona, which is consistent with the temporal profile of the reconnection electric field. In conclusion, we propose a qualitative model in view of framework of a solar eruption involving, mass ejections, filament eruption, CME, and subsequent flare.Comment: 8 figures, accepted for publication in Solar Physic

Seroprevalence of transfusion transmitted infections among blood donors at a Tertiary Care Hospital Blood Bank in North India

Background: Blood transfusion service is a sensitive issue as it is covered by “Drug and Cosmetics Act” and has legal implications. Strict criteria are followed while selecting a donor so that proper blood free of all pathogens is available for recipient. Aim: To study seroprevalence of transfusion-transmitted major infections (HIV, hepatitis B virus [HBV], hepatitis C virus [HCV], syphilis, and malaria) among blood donors at a Tertiary Care Government Hospital Blood Bank in North India and to compare positivity of markers of these infections in voluntary and replacement donors. Subjects and Methods: This study was conducted over a period of 5 years (July 2010–June 2015). A total number of donors screened during this period was 130,920. Samples were tested for HIV, HBV, HCV, syphilis, and malaria and retested if found positive by third generation ELISA tests (HIV, hepatitis B surface antigen [HBsAg], HCV). Comparative analysis was done using Chi-square for linear trend. Comparison between prevalence rates among voluntary and replacement donors was done using Chi-square tests using Microsoft Excel 2007 software. Results: Of total 130,920 donors, 114,214 (87%) were voluntary and 16,706 (13%) were replacement donors. Male donors predominated, 128,781 (98.37%) male and female 2139 (1.63%). Average seropositivity of HIV, HBsAg, anti-HCV, syphilis, and malaria was 0.10%, 1.60%, 0.18%, 0.89%, and 0.04% among all donors. Significant difference (P < 0.001) in the seropositivity of HIV, HBsAg, HCV, and syphilis was seen between voluntary and replacement donors. Seroprevalence of HIV, HBsAg, HCV, syphilis, and malaria was 0.08%, 1.56%, 0.13%, 0.71%, 0.03%, and 0.25%, 1.90% 0.51%, 2.12%, and 0.04% in voluntary blood donor and replacement blood donor, respectively. Conclusion: Comparing a retrospective data over a long period showed decreasing trend in seroprevalence of HIV, HBsAg, anti-HCV, syphilis, and malaria. Results of the study reflect the prevalence of these infections in the healthy population and warrant measures that should be taken to detect these infections and prevent transmission