On the evaluation of magnetic shear from H-alpha pictures

The recently reported pre-flare activity in H-alpha filaments (Sivaraman, K. R., Rausaria, R. R., and Aleem, S. M.: 1992,Solar Phys. 138,353) is shown to be unrelated to changes in magnetic shear. An alternative interpretation for these observations is suggested.     

Development of solar scintillometer

The index of scintillation measurement is a good parameter to compare different sites for image quality or ‘seeing’. We have developed a scintillometer, which is deployed on the high resolution SPAR telescope in the island site of Udaipur Solar Observatory, for the site characterization to specify the proposed MAST (Multi Application Solar Telescope). The scintillometer consists of a miniature telescope, termed as micro telescope (4 mm aperture, 15 mm focal length) mounted on a drive which tracks the Sun continuously, associated amplifiers and a data acquisition system. A photodiode is used as the detector. The telescope along with detector was obtained from National Solar Observatory (NSO), and is similar to the one used for Advanced Technology Solar Telescope (ATST) site survey. At USO we developed the amplifier and data acquisition system for the scintillometer. A 24-bit analog to digital converter based system was designed, assembled, tested and used as the data acquisition system (DAS). In this paper, we discuss the instrumentation and present the initial results.     

Evaluation of drainage networks developed in hard rock terrain

An attempt was made to study the influence of various factors such as geology, landforms, slope, soil, landuse/cover on the development of the drainage network. To compare and evaluate drainage networks developed in various geologic terrains, differing in rock type and structure, three sub-basins of the Bhadra river basin, located in Chikmagalur district, Karnataka, India were selected for the study. Quantitative morphometric analysis was carried out for both linear aspects and areal aspects for all three sub-basins. The applicability of Horton's laws was also studied. Each of the quantitative parameters was interrelated with thematic details derived from remote sensing data. The results of the study indicate that the drainage characteristics are entirely different for all three sub-basins. The study has also established the applicability of Horton's laws pertaining to quantitative morphometry of the sub-basins.     

Effect of the annular solar eclipse of 15 January 2010 on the lower atmospheric boundary layer over a tropical rural station

This paper documents the effect of the annular solar eclipse of 15 January 2010 on the lower atmospheric boundary layer dynamics over a complex terrain environment at Gadanki (13.5°N, 79.2°E,) using a suite of instruments namely automatic weather station, mini boundary layer mast (15 m), Doppler SODAR, GPS radiosonde and ozonesonde observations. The net heating rates are estimated using radiative transfer algorithm before, during and after the eclipse. Effect on soil temperature is seen clearly up to 20 cm depth and at all the levels up to 15 m. Decrease in the thermal plume level, a dip in the surface layer and a strong vertical downdrafts (subsidence) are noticed during the peak eclipse. Upper layer winds did not show any variation during the eclipse. It is also found to have pronounced effect on all the surface meteorological parameters for a two-day period.     

Simulations of Severe Tropical Cyclone Nargis over the Bay of Bengal Using RIMES Operational System

The Regional Integrated Multi-Hazard Early Warning System (RIMES), an international, intergovernmental organization based in Thailand is engaged in disaster risk reduction over the Asia–Pacific region through early warning information. In this paper, RIMES’ customized Weather Research Forecast (WRF) model has been used to evaluate the simulations of cyclone Nargis which hit Myanmar on 2 May 2008, the most deadly severe weather event in the history of Myanmar. The model covers a domain of 35oE to 145oE in the east—west direction and 12oS to 40oN in the north—south direction in order to cover Asia and east Africa with a resolution of 9?km in the horizontal and 28 vertical levels. The initial and boundary conditions for the simulations were provided by the National Center for Environmental Prediction-Global Forecast System (NCEP-GFS) available at 1o lon/lat resolution. An attempt is being made to critically evaluate the simulation of cyclone Nargis by seven set of simulations in terms of track, intensity and landfall time of the cyclone. The seven sets of model simulations were initialized every 12?h starting from 0000 UTC 28 April to 01 May 2008. Tropical Rainfall Measurement Mission (TRMM) precipitation (mm) is used to evaluate the performance of the simulations of heavy rainfall associated with the tropical cyclone. The track and intensity of the simulated cyclone are compared by making use of Joint Typhoon Warning Center (JTWC) data sets. The results indicate that the landfall time, the distribution and intensity of the rainfall, pressure and wind field are well simulated as compared with the JTWC estimates. The average landfall track error for all seven simulations was 64?km with an average time error of about 5?h. The average intensity error of central pressure in all the simulations were found out to be approximately 6?hPa more than the JTWC estimates and in the case of wind, the simulations under predicted it by an average of 12?m?s^?1.     

Development of a low-order Adaptive Optics system at Udaipur Solar Observatory

A low-order Adaptive Optics (AO) system is being developed at the Udaipur Solar Observatory and we present in this paper the status of the project, which includes the image stabilization system and calibration of wavefront sensor and deformable mirror. The image stabilization system comprises of a piezo driven tip-tilt mirror, a high speed camera (955 fps), a frame grabber system for sensing the overall tilt and a Linux based Intel Pentium 4 control computer with Red Hat Linux OS. The system operates under PID control. In the closed loop, an rms image motion of 0.1–0.2 arcsec was observed with the improvement factor varying from 10–20 depending on the external conditions. Error rejection bandwidth of the system at 0 dB is 80–100 Hz. In addition to that, we report the on-going efforts in the calibration of lenslet array and deformable mirror for sensing and correcting the local tilt of the wavefront.     

Onset of hydrodynamic non-equilibrium in helmet streamers

The steady-state solar wind solution is examined for different geometries of the flow tube that mimics a helmet streamer. Onset of non-equilibrium is seen whenever the spatial variation of the flow geometry crosses critical values. It is suggested that the dynamical response of the flow to the onset of non-equilibrium can manifest as a coronal mass ejection.     

Ellipsometry of coelostat coatings using a Babinet compensator: Simulation of the experimental accuracy

The precise measurement of solar magnetic fields requires an accurate measurement of the Muller matrix of the optical components in the path of the light beam, which again requires a careful measurement of the optical constants of the reflecting surfaces in the case of a 3-mirror coelostat system. Here we present a method to measure the optical constants (the real and imaginary part of the refractive index) to an accuracy of the order of 1% for bulk aluminium. This work is directed towards the measurement of instrumental polarisation at the Kodaikanal solar tower telescope, although it can be used for any metallic coated optics.