000048   Pagano P;Mackay D H;Poedts S (School of Mathematics and Statistics, Univ of St Andrews, St Andrews, UK, Email: pp25@st-andrews.ac.uk) : Numerical simulations of a flux rope ejection. J Astrophys Astr 2015, 36(1), 123-55.

Coronal mass ejections (CMEs) are the most violent phenomena observed on the Sun. One of the most successful models to explain CMEs is the flux rope ejection model, where a magnetic flux rope is expelled from the solar corona after a long phase along which the flux rope stays in equilibrium while magnetic energy is being accumulated. However, still many questions are outstanding on the detailed mechanism of the ejection and observations continuously provide new data to interpret and put in the context. Currently, extreme ultraviolet (EUV) images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO) are providing new insights into the early phase of CME evolution. In particular, observations show the ejection of magnetic flux ropes from the solar corona and how they evolve into CMEs. However, these observations are difficult to interpret in terms of basic physical mechanisms and quantities, thus, we need to compare equivalent quantities to test and improve our models. In our work, we intend to bridge the gap between models and observations with our model of flux rope ejection where we consistently describe the full life span of a flux rope from its formation to ejection. This is done by coupling the global non-linear force-free model (GNLFFF) built to describe the slow low-β formation phase, with a full MHD simulation run with the software MPI-AMRVAC, suitable to describe the fast MHD evolution of the flux rope ejection that happens in a heterogeneous β regime. We also explore the parameter space to identify the conditions upon which the ejection is favoured (gravity stratification and magnetic field intensity) and we produce synthesised AIA observations (171 Å and 211 Å). To carry this out, we run 3D MHD simulation in spherical coordinates where we include the role of thermal conduction and radiative losses, both of which are important for determining the temperature distribution of the solar corona during a CME. Our model of flux rope ejection is successful in realistically describing the entire life span of a flux rope and we also set some conditions for the backgroud solar corona to favour the escape of the flux rope, so that it turns into a CME. Furthermore, our MHD simulation reproduces many of the features found in the AIA observations.

16 illus, 58 ref

000047   Korsos M B;Gyenge N;Baranyi T;Ludmany A (Heliophysical Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Debrecen, P.O. Box 30, H-4010, Hungary, Email: korsos.marianna@csfk.mta.hu) : Dynamic precursors of flares in active region NOAA 10486. J Astrophys Astr 2015, 36(1), 111-21.

Four different methods are applied here to study the precursors of flare activity in the Active Region NOAA 10486. Two approaches track the temporal behaviour of suitably chosen features (one, the weighted horizontal gradient WG_M, is the generalized form of the horizontal gradient of the magnetic field, GM; the other is the sum of the horizontal gradient of the magnetic field, GS, for all sunspot pairs). WG_M is a photospheric indicator, that is a proxy measure of magnetic non-potentiality of a specific area of the active region, i.e., it captures the temporal variation of the weighted horizontal gradient of magnetic flux summed up for the region where opposite magnetic polarities are highly mixed. The third one, referred to as the separateness parameter, 5_1-f, considers the overall morphology. Further, GS and 5_l-f are photospheric, newly defined quick-look indicators of the polarity mix of the entire active region. The fourth method is tracking the temporal variation of small X-ray flares, their times of succession and their energies observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager instrument. All approaches yield specific pre-cursory signatures for the imminence of flares.

5 illus, 2 table, 25 ref

000046   Joshi S;Joshi Y C (NO, Aryabhatta Research Institute of Observational Science (ARIES), Manora Peak, Nainital-263 002, Email: santosh@aries.res.in) : Asteroseismology of pulsating stars. J Astrophys Astr 2015, 36(1), 33-80.

The success of helioseismology is due to its capability of measuring p-mode oscillations in the Sun. This allows us to extract information on the internal structure and rotation of the Sun from the surface to the core. Similarly, asteroseismology is the study of the internal structure of the stars as derived from stellar oscillations. In this review we highlight the progress in the observational asteroseismology, including some basic theoretical aspects. In particular, we discuss our contributions to asteroseismology through the study of chemically peculiar stars under the 'Nainital-Cape Survey' project being conducted at ARIES, Nainital, since 1999. This survey aims to detect new rapidly-pulsating Ap (roAp) stars in the northern hemisphere. We also discuss the contribution of ARIES towards the asteroseismic study of the compact pulsating variables. We comment on the future prospects of our project in the light of the new optical 3.6-m telescope to be installed at Devasthal (ARIES). Finally, we present a preliminary optical design of the high-speed imaging photometers for this telescope.

29 illus, 2 tables, 212 ref

000045   Gyenge N;Bennett S;Erdelyi R (Debrecen Heliophysical Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Debrecen, P.O. Box 30, H-4010, Hungary, Email: gyenge.norbert@csfk.mta.hu) : Non-homogeneous behaviour of the spatial distribution of macrospicules. J Astrophys Astr 2015, 36(1), 103-9.

In this paper the longitudinal and latitudinal spatial distribution of macrospicules is examined. We found a statistical relationship between the active longitude (determined by sunspot groups) and the longitudinal distribution of macrospicules. This distribution of macrospicules shows an inhomogeneity and non-axisymmetrical behaviour in the time interval between June 2010 and December 2012, covered by observations of the Solar Dynamic Observatory (SDO) satellite. The enhanced positions of the activity and its time variation have been calculated. The migration of the longitudinal distribution of macrospicules shows a similar behaviour to that of the sunspot groups.

3 illus, 24 ref

000044   Griffiths M K;Fedun V;Erdelyi R (Corporate Information and Computing Services, The Univ of Sheffield, 10-12 Brunswick Street, Sheffield S10 2FN, UK, Email: m.griffiths@sheffield.ac.uk ) : A fast MHD code for gravitationally stratified media using graphical processing units: SMAUG. J Astrophys Astr 2015, 36(1), 197-223.

Parallelization techniques have been exploited most successfully by the gaming/graphics industry with the adoption of graphical processing units (GPUs), possessing hundreds of processor cores. The opportunity has been recognized by the computational sciences and engineering communities, who have recently harnessed successfully the numerical performance of GPUs. For example, parallel magnetohydrody-namic (MHD) algorithms are important for numerical modelling of highly inhomogeneous solar, astrophysical and geophysical plasmas. Here, we describe the implementation of SMAUG, the Sheffield Magnetohydrody-namics Algorithm Using GPUs. SMAUG is a 1-3D MHD code capable of modelling magnetized and gravitationally stratified plasma. The objective of this paper is to present the numerical methods ami techniques used for porting the code to this novel and highly parallel compute architecture. The methods employed are justified by the performance benchmarks and validation results demonstrating that the code successfully simulates the physics for a range of test scenarios including a full 3D realistic model of wave propagation in the solar atmosphere.

16 illus, 45 ref

000043   Filippov B;Martsenyuk O;Srivastava A K;Uddin W (NO, Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Russian Academy of Sciences (IZMIRAN), Troitsk, Moscow 142190, Russia, Email: bfilip@izmiran.ru) : Solar magnetic flux ropes. J Astrophys Astr 2015, 36(1), 157-84.

In the early 1990s, it was found that the strongest disturbances of the space-weather were associated with huge ejections of plasma from the solar corona, which took the form of magnetic clouds when moved from the Sun. It is the collisions of the magnetic clouds with the Earth's magnetosphere that lead to strong, sometimes catastrophic changes in space-weather. The onset of a coronal mass ejection (CME) is sudden and no reliable forerunners of CMEs have been found till date. The CME prediction methodologies are less developed compared to the methods developed for the prediction of solar flares. The most probable initial magnetic configuration of a CME is a flux rope consisting of twisted field lines which fill the whole volume of a dark coronal cavity. The flux ropes can be in stable equilibrium in the coronal magnetic field for weeks and even * months, but suddenly they lose their stability and erupt with high speed. Their transition to the unstable phase depends on the parameters of the flux rope (i.e., total electric current, twist, mass loading, etc.), as well as on the properties of the ambient coronal magnetic field. One of the major governing factors is the vertical gradient of the coronal magnetic field, which is estimated as decay index (n). Cold dense prominence material can be collected in the lower parts of the helical flux tubes. Filaments are, therefore, good tracers of the flux ropes in the corona, which become visible long before the beginning of the eruption. The perspectives of the filament eruptions and following CMEs can be estimated by a comparison of observed filament heights with calculated decay index distributions. The present paper reviews the formation of magnetic flux ropes, their stable and unstable phases, eruption conditions, and also discusses their physical implications in the solar corona.

15 illus, 153 ref

000042   Dwivedi B N;Wilhelm K (Physics Dep, Indian Institute of Technology (Banaras Hindu Univ), Varanasi-221 005, Email: bholadwivedi@gmail.com) : Solar coronal plumes and the fast solar wind. J Astrophys Astr 2015, 36(1), 185-95.

The spectral profiles of the coronal Ne VIII line at 77 nm have different shapes in quiet-Sun regions and Coronal Holes (CHs). A single Gaussian fit of the line profile provides an adequate approximation in quiet-Sun areas, whereas, a strong shoulder on the long-wavelength side is a systematic feature in CHs. Although this has been noticed since 1999, no physical reason for the peculiar shape could be given. In an attempt to identify the cause of this peculiarity, we address three problems that could not be conclusively resolved, in a review article by a study team of the International Space Science Institute (ISSI) (Wilhelm et al. 2011): (1) The physical processes operating at the base and inside of plumes, as well as their interaction with the Solar Wind (SW). (2) The possible contribution of plume plasma to the fast SW streams. (3) The signature of the First-Ionization Potential (FIP) effect between plumes and inter-plume regions (IPRs). Before the spectroscopic peculiarities in IPRs and plumes in Polar Coronal Holes (PCHs) can be further investigated with the instrument Solar Ultraviolet Measurements of Emitted Radiation (SUMER) aboard the Solar and Heliospheric Observatory (SOHO), it is mandatory to summarize the results of the review to place the spectroscopic observations into context. Finally, a plume model is proposed that satisfactorily explains the plasma flows up and down the plume field lines and leads to the shape of the neon line in PCHs.

3 illus, 54 ref

000041   Choudhuri A R (Physics Dep, Indian Institute of Scinece, Bangalore-560 012, Email: arnab@physics.iisc.ernet.in) : Critical assessment of the flux transport dynamo. J Astrophys Astr 2015, 36(1), 5-14.

Authors first discuss how the flux transport dynamo with reasonably high diffusion can explain both the regular and the irregular features of the solar cycle quite well. Then, we critically examine the inadequacies of the model and the challenge posed by some recent observational data about meridional circulation, arriving at a conclusion that this model can still work within the bounds of observational data.

2 illus, 74 ref

020536   Ram Sagar;Naja M;Maheswar G;Srivastava A K (NASI-Senior Scientist Platinum Jubilee Fellow, Indian Institute of Astrophysics, Bangalore-560 034, Email: ram_sagar0@yahoo.co.in) : Science at high-altitude sites of ARIES - astrophysics and atmospheric sciences. Proc Indian Natn Sci Acad 2014, 80(4-5spl), 759-90.

In this article authors discuss various frontline research activities those are being carried out in the fields of Astronomy and Astrophysics and Atmospheric Sciences at Aryabhatta Research Institute of Observational Sciences (ARIES) using the existing and upcoming observational facilities at two high latitude sites - Manora Peak and Devasthal. Both sites are located at Devabhumi of Nainital District, Uttarakhand in the central Himalayas. The important results obtained from these research activities are highlighted and upcoming international observational facilities in the institute are discussed.

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020535   Prabhu T P (NO, Indian Institute of Astrophysics, Bangalore-560 034, Email: _tpp@iiap.res.in) : Indian astronomical observatory, Leh-Hanle. Proc Indian Natn Sci Acad 2014, 80(4-5spl), 887-912.

Indian Astronomical Observatory (IAO), Hanle, was set up by the Indian Institute of Astrophysics (IIA), in the year 1997 in Changthang region of Leh district of Jammu & Kashmir at an altitude of 4500 m above mean sea level. Though the primary interest was to undertake astronomical studies from the high altitude cold desert site that provides the largest number of clear and highly transparent skies in India, the presence of IIA in the pristine, geographically unique site has spurred development of many experiments in several branches of science. Since the activities of the observatory now span the entire area of Leh district, the office and laboratories of the observatory are being set up in Leh, the district headquarters. Site characterization of Hanle began in 1994 and the infrastructure development in 1996. The first phase of development ended in 2000 with the commissioning of 2-m Himalayan Chandra Telescope. The telescope was remotely controlled and equipped with instruments for regular use since 2003. Utilizing this infrastructure, very high energy gamma ray astronomy was initiated with the commissioning of HAGAR in 2007 and MACE to be installed beginning 2015 summer. Different institutions have utilized the infrastructure for various experiments in earth sciences.

^iia11 illus, 4 tables, 107 ref

020534   Hasan S S;Bagare S P;Rangarajan K E (NO, Indian Institute of Astrophysics, Bangalore-560 034, Email: hasan@iiap.res.in) : Solar astronomy a high altitude. Proc Indian Natn Sci Acad 2014, 80(4-5spl), 815-25.

A major project called the National Large Solar Telescope (NLST) has been proposed for pursuing Solar Astronomy at High Altitude. The project envisages the development of a state-of-the-art 2-m class telescope to carry out high-resolution studies of the solar atmosphere. This project is led by the Indian Institute of Astrophysics and has national and international partners. Its geographical location will fill the longitudinal gap between Japan and Europe and is expected to be the largest solar telescope with an aperture larger than 1.5m till ATST and EST come into operation. NLST is an on-axis alt-azimuth Gregorian multi-purpose open telescope with the provision of carrying out nighttime stellar observations using a spectrograph at the Nasmyth focus. The telescope utilizes an innovative design with low number of reflections to achieve a high throughput and low polarization. High order adaptive optics is integrated into the design that works with a modest Frieds parameter of 7-cm to give diffraction limited performance. The telescope will be equipped with a suite of post-focus instruments including broad and narrow band imagers, a high-resolution spectrograph and a polarimeter. A comprehensive site characterization programme has demonstrated the presence of at least two excellent sites for setting up observational facilities for solar astronomy at high altitude in India.

^iia6 illus, 4 tables, 25 ref

020533   Gupta S K (NO, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai-400 005, Email: gupta@grapes.tifr.res.in) : High energy astroparticle physics at Ooty and the GRAPES-3 experiment. Proc Indian Natn Sci Acad 2014, 80(4-5spl), 827-76.

The astroparticle studies at Ooty have their roots going way back into the fifties, when studies using cosmic rays were initiated with cloud chambers of progressively larger sizes as the primary detector and measuring device to obtain properties of hadrons at high energies. This study was subsequently strengthened with the installation of a total absorption calorimeter and a modest extensive air shower array to probe the composition of the primary cosmic rays to very high energies. The discovery of pulsars provided a thrust for the exploration of these compact objects as the sources of γ-rays at TeV energies with the aid of atmospheric Cerenkov detectors in the seventies. With the rapid technological advances occurring during the subsequent years in detectors, electronics and computers, physicists world-wide were able to set up very large and remarkably sensitive experiments that were hard to imagine a decade earlier. With the increasing sophistication and complexity the modern experiments require participation of very large teams of scientists. This development has made the formation of collaboration of large number of physicists both experimental and theoretical, engineers, technicians etc., from a number of institutions and universities, a prerequisite for setting up any major experimental facility. The GRAPES-3 experiment is a collaboration of 34 scientists from 13 institutions, including 8 from India and 5 from Japan. The ORAPES-3 experiment contains a dense extensive air shower array operating with <126> 400 scintillator detectors and a 560 m^{2 tracking muon detector (Em <62> 1 GeV), at Ooty in India. 25% of scintillator detectors are instrumented with two fast photomultiplier tubes (PMTs) for extending the dynamic range to <126> 5x103 particles m-2. The scintillators, signal processing electronics and data recording systems were fabricated in-house to cut costs and optimize performance. The muon multiplicity distribution of the EAS is used to probe the composition of primary cosmic rays below the 'knee', with an overlap with direct measurements. Search for multi-TeV γ-rays from point sources is done with the aid of the muon detector. A good angular resolution of 0.7° at 30 TeV, is measured from shadow of the Moon on the isotropic flux of cosmic rays. Sensitive limit on the diffuse flux of 100 TeV γ-rays is placed by using muon detector to filter out the charged cosmic ray background. The tracking muon detector allows sensitive measurements on the coronal mass ejections and solar flares through Forbush decrease events. We have major expansion plans to enhance the sensitivity of the GRAPES-3 experiment in the areas listed above.}

33 illus, 4 tables, 118 ref

020532   Ghosh S K;Raha S (Physics Dep, Bose Institute, 93/1, A.P.C. Road, Kolkata-700 009, Email: sanjay@jcbose.ac.in ) : Darjeeling facility: cosmic rasy and atmospheric sciences. Proc Indian Natn Sci Acad 2014, 80(4-5spl), 791-814.

Centre for Astroparticle Physics and Space Science - a national high altitude facility has been established at the Darjeeling campus of Bose Institute. Here we discuss the various programmes in the areas of cosmic ray and atmospheric science research at this facility.

4 illus, 41 ref

020531   Chitnis V R;Acharya B S (NO, Tata Institute of Fundamental Research, Homi Bhabha Road, Calaba, Mumbai-400 005, Email: vchitnis@tifr.res.in) : Gamma ray astronomy from high altitudes: HAGAR. Proc Indian Natn Sci Acad 2014, 80(4-5spl), 877-86.

High Altitute Gamma Ray (HAGAR) experiment, an array of seven atmospheric Cherenkov telescopes, is installed at Hanle in Ladakh, at an altitude of 4300 m, in 2008. This experiment is designed to study very high energy gamma rays from astronomical sources. Taking advantage of high altitude location HAGAR has achieved energy threshold of about 200 GeV. Design details and performance parameters of HAGRA are discussed here. Also preliminary results for Crab nebula, which is a standard candle, are discussed.

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020530   Acharya B S;Koul R (NO, Tata Institute of Fundamental Research, Mumbai-400 005, Email: acharya.tifr@gmail.com) : Ground-based Tev γ-ray astronomy in India - historical perspective and recent developments. Proc Indian Natn Sci Acad 2014, 80(4-5spl), 749-57.

Short historical account of TeV γ-ray astronomy in India is presented. Special attention is given to the development of experimental techniques vis-a-vis world-wide development of the field.

^iia13 illus, 38 ref

018428   Singh B;Pundhir D (Electronics and Communication Engineering Dep, RBS Engineering Technical Campus, Bichpuri, Agra-283 105, Email: bbsagra@gmail.com) : Some results of Schumann resonance studies at a low latitude station Agra, India during post period of solar cycle minimum 2008-2009. Indian J Radio Space Phys 2014, 43(6), 325-32.

The characteristics of Schumann resonance (SR) have been studied at a low latitude station Agra (geographic latitude 27.2°N, longitude 78°E), India and the results obtained during two periods (01 April 2007 - 31 March 2008 and 01 March 2011 - 29 February 2012) corresponding to pre and post period of solar cycle minimum (SCM) of 2008-2009 are compared. The results show that (i) there is a shift in the peak thunderstorm activity from the month of July in the pre-SCM to August in post-SCM; (ii) the first mode frequency increases with the increasing SCM; and (iii) there are distinct drops in the frequency range dF1 in the months of August and December 2012 corresponding to effective lightning areas during the post-SCM. The seasonal variation of first mode SR frequency shows that it is theoretically dependent on source-observer distance.

5 illus, 1 table, 23 ref

018427   Madhavi Latha T;Peddi Naidu P;Madhusudhana Rao D N;Indira Devi M (Physics Dep, Anil Neerukonda Institute of Technology and Sciences, Visakhapatnam-531 162, Email: madhavilatha809@gmail.com) : Anomalous behaviour of very low frequency signals during the earthquake events. Indian J Radio Space Phys 2014, 43(6), 333-9.

The seismo-ionospheric coupling has been extensively studied in the recent years adopting various ionospheric parameters, like the critical frequency of F₂ and E_s layers and total electron content (TEC). There have been reports of seismic signatures in the amplitude and phase of the very low frequency (VLF) waves when an intense earthquake occurs near the propagation path. In the present paper, the amplitude of VLF waves transmitted from GQD (UK), GBZ (UK) and TBB (Turkey) received in South France during the period 2010-2013 has been studied for the precursory effect of earthquakes on the morning and evening terminator timings (TT). Six earthquake events of magnitude greater than 5 have been considered. The results of the present study show that the evening terminator undergoes many fluctuations during the pre-earthquake period of 5-15 days. But the pre-earthquake fluctuations in the morning terminator are predominant for three events, namely 8 March 2010, 11 April 2010 and 22 May 2012. The VLF day (time between morning terminator and evening terminator) is observed to be longer in the pre-earthquake period for three events.

5 illus, 1 table, 16 ref

018426   Falade J A;Adesanya S O;Akinyemi G A (Physical Sciences Dep, Redeemer's Univ, Mowe, Nigeria, Email: falade_a@yahoo.com) : Variability of meteorological factors on surface refractive index over Mowe, a coastal area in Nigeria. Indian J Radio Space Phys 2014, 43(6), 355-61.

Radio climatology is an important factor in understanding radio wave propagation particularly in the troposphere where time varying properties due to weather conditions are prevalent. Therefore, the diurnal and seasonal variations of surface radio refractivity for Mowe (06°E, 52°N) via Lagos in South-West Nigeria are studied. Particular emphasis is laid on diurnal variations of the surface refractivity, which is high through the night and drops sharply just before sunrise and starts to pick up slightly around 14:00 to 15:00 hrs LT. It drops to minimum around 16:00 hrs LT before it increases again. The sinusoidal patterns of plots are obtained for temperature, relative humidity and refractivity. The patterns of the profile obtained are attributed to the oscillatory movement of inter-tropical discontinuity (ITD), which largely dictate the condition of weather and account for high rainfall in the coastal region where the study is undertaken. The results show that surface radio refractivity, generally, has higher value during the rainy season than dry season, which partly coincide with the harmattan period.

5 illus, 17 ref

015452   Katore S D;Sancheti M M;Hatkar S P (Mathematics Dep, S.G.B. Amravati Univ, Amravati-444 602, Email: schnhatkar@gmail.com) : Quark matter coupled to domain walls in bianchi types II, VIII and IX universes. Pramana J Phys 2014, 83(4), 619-30.

In this study of Bianchi types II, VIII and IX Universes, quark matter coupled to domain walls in the context of general relativity are explored. To obtain deterministic solution of the Einstein's field equations, various techniques are adopted. The features of the obtained solution are discussed.

3 illus, 49 ref

014540   Xian Fenz Z;Huan Yu J (NO, College of Mechanical and Electronic Engineering, Chuzhou Univ, Chuzhou-239 000, Email: zhaopioneer.student@sina.com) : Surface gravitational redshift of the neutron star PSR B2303+46. Bull Astr Soc India 2013, 41(4), 291-8.

Surface gravitational redshift of the neutron star PSR B2303+46 is investigated within the framework of relativistic mean field theory for the baryon octet system through adjusting the hyperon coupling constants. Obtained any models for the neutron star B2303+46 by choosing suitable hyperon coupling constants x_σh and x_ωh with x_ρh being determined by SU(6) symmetry and the nucleon coupling constant being chosen as CZ11. The calculations show that the radius and the surface gravitational redshift of the neutron star PSR B2303+46 are determined as R=12.477<126>12.493 km and z=0.2184<126>0.2187, respectively. Our results are not consistent with the recent discovery of the massive neutron star PSR J1614-2230 and PSR J0348+0432.

5 illus, 3 tables, 30 ref

014539   Tan L M;Thu N N;Ha T Q;Marbouti M (Faculty of Natural Science and Technology, Tay Nguyen Univ, 567-Le Duan, Buon Ma Thuot City, Dak Lak Province 632025, Vietnam, Email: tantaynguyen82@yahoo.com) : Study of solar flare induced D-region ionosphere changes using VLF amplitude observations at a low latitude site. Indian J Radio Space Phys 2014, 43(3), 197-204.

About 26 solar flare events from C2.56 to X3.2 classes were obtained and analyzed at Tay Nguyen University, Vietnam (12.56°N, 108.02°E) during May - December 2013 using very low frequency remote sensing to understand the responses of low latitude D-region ionosphere during solar flares. The observed VLF amplitude perturbations are used as the input parameters for the simulated Long Wavelength Propagation Capability (LWPC) program, using Wait's model of lower ionosphere, to calculate two Wait's parameters, viz. the reflection height (H') and the sharpness factor (β). The results reveal that when X-ray irradiance is increased, β increased from 0.3 to 0.506 km-1, while H' decreased from 74 to 60 km. The electron density increased at the height of 74 km with 1-3 orders of magnitude during solar flares. These phenomena can be explained as: the ionization due to X-ray irradiance becomes greater than that due to cosmic rays and Lyman-a radiation, which increases the electron density profile. The present results are in agreement with the earlier results. The 3D representation of the electron density changes with altitude and time supports to fully understand the shape of the electron density changes due to X-ray flares. The shape variation of electron density is roughly followed to the variation of the amplitude perturbation and keeps this rule for different altitudes. It is also found that the electron density versus the height in lower latitude D-region ionosphere increases more rapidly during solar flares.

10 illus, 1 table, 24 ref

014538   Subramaniam A;Adara B (NO, Indian Institute of Astrophysics, Koramangala, Bangalore-560 034, Email: purni@iiap.res.in ) : Classification and disk parameters of Herbig Ae/Be stars using WISE and AKARI data. Bull Astr Soc India 2013, 41(4), 247-79.

Present the classification and disk parameters of 50 Herbig Ae/Be stars using WISE and AKARI data. These stars have been classified into 4 groups based on the scheme proposed by Koenig et al. (2012) using WISE pass bands and by constructing their SEDs using data up to 12 pass bands. We could successfully classify 18 sources as Class I, 22 as Class II, 6 as Class III and 4 as sources with transitional disk. One-third of the sample (classification of 14 of 50 and disk parameters of 19 of 50) were studied for the first time. SEDs created with and without AKARI data were found to be similar for a good fraction of sources, though some sources showed large deviation. The SEDs are also used to derive the stellar as well as the circumstellar disk parameters. Our analysis suggests that sources more massive than <126>6 MaS" may have a very short Class II phase. We have studied the correlation between various stellar and disk parameters. Among the present sample, this study tentatively suggests that one set of stars are found to lose their disk rapidly, within 3-4 Myr, whereas another set of sources are found to retain their disk as well as accretion till 6-8 Myr.

17 illus, 13 tables, 31 ref

014537   Ojo J S;Falodun S E;Odiba O (Physics Dep, the Federal Univ of Technology, Akure, P M B 704, Akure, Nigeria, Email: josnno@yahoo.com) : 0° isotherm height distribution for earth-space communication satellite links in Nigeria. Indian J Radio Space Phys 2014, 43(3), 225-34.

For an optimum performance of Earth-space satellite communication links, a number of meteorological parameters are needed to be considered along the Earth-space path for specific locations and the height of the 0°C isotherm (freezing level height) is among such parameters. Information regarding this parameter is always based on the recommendation of ITU-RP-839 in the form of contour maps. Since the meteorological parameters are location dependent, there is a need for the establishment of these parameters for specific locations. In addition, ITU-R model uses an yearly averaged constant rain height for the attenuation estimation, which may not be appropriate for tropical regions. In the present paper, the 0°C isotherm (ZDI) height has been established using two years of data collected on-board the precipitation radar of the Tropical Rain Measuring Mission (TRMM) satellite. The result shows the seasonal dependence of the 0°C isotherm height. It is observed, among other things, that the height is higher during the wet season as compared to the dry season. Rain induced attenuation at frequencies above 10 GHz is also estimated using the 0°C isotherm height derived for each of the locations over the elevation angle of the NIGCOMSAT-1R in Nigeria.

7 illus, 5 tables, 21 ref

014536   Ogolo E O (Physics Dep, The Federal Univ of Technology, Akure, Nigeria, Email: eoogolo@futa.edu.ng) : Estimation of global solar radiation in Nigeria using a modified angstrom model and the trend analysis of the allied meteorological components. Indian J Radio Space Phys 2014, 43(3), 213-24.

The trend of some common and related atmospheric variables were investigated in the light of climate change on annual time scale and a suitable scheme was further developed for the simulation of annual global solar radiation in Nigeria. In this connection, annual trends of global solar radiation, air temperature, precipitation, relative humidity and sunshine hours was carried out, covering about 13 tropical stations during 1975-2006 in Nigeria using F-test as the significance test technique. It was found that nine stations exhibited an upward trend in global solar radiation series, of which 6 passed F-test at 1% significant level. At 11 stations, precipitation had shown an increasing trends but none passed F-test at 2.5% and hence, not significant. About 98.8% of the stations displayed an upward trend in sunshine hours of which 16% passed F-test at 1% significant level. On trend analysis for relative humidity series, eight stations exhibited a positive trend and only one station passed F-test at 1% significant level. The trend of temperature series in Nigeria under the period under investigation was found to be increasing at 12 stations and eight stations passed the F-test at 1% significant level. The other objective of this study was to determine a more suitable empirical equation by modifying Angstrom model for the estimation of global solar radiation using all data for all 14 stations pooled together to predict global solar radiation using linear and multiple linear regression. This was done to improve the low performance of the Angstrom model used for the annual estimation of global solar radiation. The model parameters 'a' and 'b' of Angstrom model were parameterized in terms of the geographical locations (latitude, longitude and elevation) and the meteorological variables (sunshine hour, precipitation, relative humidity and temperature), respectively. This scheme gave better simulation of the global solar radiation compared with other schemes and the original Angstrom models. In addition, the preferential consideration of relative humidity to precipitation as potent contributing factor in the estimation of global solar radiation was also established.

3 illus, 7 tables, 38 ref

014535   Kiran Kumar A S;Chauhan P (NO, Space Applications Centre (ISRO), Ahmedabad-380 015, Email: kiran@sac.isro.gov.in) : Scientific exploration of Mars by first Indian interplanetary space probe: Mars orbiter mission. Curr Sci 2014, 107(7), 1096-7.

2 illus, 1 ref

014534   Kazeem A K;Adeniyi J O;Adediji A T (Physics Dep, Ilorin Univ, P M B 1515, Ilorin, Nigeria, Email: kunleadediji2002@yahoo.co.uk) : Modelling of the equatorial ionospheric E-layer based on cosχ index. Indian J Radio Space Phys 2014, 43(3), 205-12.

Daytime hourly values of the critical frequency of the ionospheric E-layer, foE, obtained at Ouagadougou Ionospheric Observatory (12.4°N, 1.5°W) in Burkina Faso, West Africa, an equatorial station, during the solar cycle 22 (1985 - 1995) have been used to develop a model based on solar zenith angle through cosχ index factor using the relation foE = a (cosχ)^{n, The average value of the diurnal cosχ index, n, at Ouagadougou was found to be 0.30 for both low and high solar activity. The model was tested with foE data from Korhogo (9.3°N, 5.4°W) in Cote-d'Ivoire, another equatorial station, and there is good agreement between the model and observations. The validity of the foE model was also compared with predicted values by IRI-2012 model and good agreement has been observed. The percentage difference, when foE observed compared with IRI-2012 model, was found to be within ±10% for both equinoxes and solstices for the two levels of solar activity.}

7 illus, 4 tables, 23 ref

014533   Feng S;Yu L;Yang Y (NO, Yunnan Key Laboratory of Computer Technology Application/Faculty of In, Kunming-650 500, Email: ynkmfs@science.cn) : Relationship between grouped solar flares and sunspot activity. Bull Astr Soc India 2013, 41(4), 237-46.

Investigate the phase relationship between grouped solar flares (GSFs) and sunspot numbers (SNs) during the time interval from 1965 January to 2008 June. It is found that, (1) from a global point of view, GSFs lead SNs in phase during solar cycles 20, 22 & 23, while the former lags behind the latter in solar cycle 21; (2) the phase relationship between them is not only time-dependent but also frequencydependent. This implies that their relationship is a complex nonlinear relationship, although they are highly correlated with each other.

6 illus, 2 tables, 30 ref

013505   Punyakoti G V;Ramsheshan S (NO, , , Email: punyakoti.gv@gmail.com) : Brazil nuts help unlock the asteroid's boulder mystery. Curr Sci 2014, 107(6), 945-6.

1 illus, 10 ref

013504   Padma K;Selvaraj R S;Boaz B M (NO, Presidency College, Chennai-600 005, Email: padma_manmalai@rediffmail.com ) : Estimation of daily surface ozone using periodic and stochastic modeling in Chennai region. Indian J Radio Space Phys 2014, 43(4-5), 293-302.

The present study deals with the modeling and forecasting of surface ozone time series in an urban area. First, an analysis of the systematic components (periodicity and stochastic components) was performed. Subsequently, prediction model for the daily surface ozone series was developed. In the recent years, there was no permanent measurement of surface ozone at this site, so surface ozone was measured from June 2011 to September 2012 at the urban site Koyembedu, Chennai (the capital of Tamil Nadu), India. Daily cumulative ozone data series was obtained by hourly instantaneous data. It was found, using Mann-Kendall test, that the data series is free of trend. The periodicity of ozone data was analyzed using Fourier Transform method. Stochastic components of ozone data are assumed as residues between observed ozone data and values computed from periodic model. Stochastic model presented in this research is basically a 3rd order autoregressive model. The developed models were validated using correlation coefficient between the predicted values and measured values. The spectrums of series exhibit 100 days period of daily surface ozone and implies that the pattern in the series is repeated every 100 days. The correlation coefficient (R) of this model delivers 0.810 and can provide mean bias error (MBE) = 0.85, and root mean square error (RMSE)=0.83. The result suggests that this approach is good for estimating daily surface ozone with sufficient accuracy.

6 illus, 24 ref

013503   D'ujanga F M;Taabu S D (Physics Dep, Makerere University, Kampala, Uganda, Email: fdujanga@physics.mak.ac.ug) : Study on the occurrence characteristics of VHF and L-band ionospheric scintillations over East Africa. Indian J Radio Space Phys 2014, 43(4-5), 263-73.

A study of the occurrence of ionospheric scintillations at the VHF and L-band frequencies was carried out at two stations in East Africa, viz. University of Nairobi (Geog 1.3°S, 36.8°E; dip -22.9°) and Makerere University (Geog 0.3°N, 32.5°E; dip. -20.6°) during 2011 and 2012, respectively. Observations were made for the nighttime period (1800 to 0600 hrs LT). It was found that pre-sunset scintillations were more frequent from January to March, and after the March equinox, the onset times quickly shifted to pre-midnight and lasted up to pre-dawn hours. Pre-midnight and post-midnight scintillations have been associated with range-type spread-F and frequency-type spread-F, respectively; while pre-sunset scintillations have been linked to the E-region irregularities. The co-existence of both the VHF and L-band frequency scintillations was also observed, but the small scale irregularities responsible for the L-band scintillations could not exist beyond local midnight. Of particular interest to note were the VHF scintillation signatures at the onset, which were highly structured in short duration patches, but having longer duration with reduction in intensity as time progressed.

8 illus, 29 ref

013502   Bisht H;Pande B;Chandra R;Pande S (Physics Dep, MBPG College, Haldwani-263 129, Email: hema.bisht15@yahoo.com) : Statistical study of different solar activity features with total column ozone at two hill stations of Uttarakhan. Indian J Radio Space Phys 2014, 43(4-5), 251-62.

This paper presents a statistical study of different solar activity features (DSAF), viz. sunspot number (SN), solar active prominences (SAP), solar flares (SF) and solar proton events (SPE) with total column ozone (TCO) amount using 28 years (1986-2013) data. The ozone data has been taken for two hill stations of Uttarakhand, viz. Nainital (29°23'N, 79°27'E) and Mussoorie (30°27'N, 78°06'E). The study reveals a positive correlation between yearly averaged TCO and DSAF. The value of linear correlation coefficient (r) for TCO-Nainital with SN, SAP, SF and SPE is found to be 0.51, 0.30, 0.49, and 0.54, respectively and for TCO-Mussoorie with SN, SAP, SF, SPE is found to be 0.45, 0.27, 0.44, and 0.51, respectively. This supports the fact that solar activity features contribute to the production of ozone. Also the trend in TCO over both the stations annually, monthly and seasonally has been studied. A negative trend is observed indicating a decrease in the ozone concentration over these stations in given time period.

8 illus, 5 tables, 26 ref

009468   Suresh Raju C;Antony T;Mathew N;Uma K N; Krishna Moorthy K (Space Physics Laboratory, Vikram Sarabhai Space Centre, ISRO, Thiruvananthapuram-695 022, Email: c_sureshraju@vssc.gov.in ) : MT-MADRAS brightness temperature analysis for terrain characterization and land surface microwave emissivity estimation. Curr Sci 2013, 104(12), 1643-9.

This article reports the potential of the 'MADRAS' payload on-board the Megha-Tropiques satellite for land surface studies. The analysis has been divided into two parts as application of MADRAS data for studying the land surface properties and estimation of microwave emissivity directly from MADRAS brightness temperature (TB) data by applying an in-house developed Microwave Radiative Transfer Computation Code. The derived emissivity is further used to characterize the microwave emissivity of different land surface classes. The polarization difference (PD) parameters, the difference between horizontal (H-) and vertical (V-) polarization of TBs at 18 and 36 GHz clearly discern surface features of different surface classes such as deserts, arid/semi-arid and vegetated regions. Land surface microwave emissivity for MADRAS channels is derived on a global basis. These are inter-compared with the emissivity derived from the operational TRMM Microwave Imager and are in reasonably good agreement. The analysis based on emissivity shows spectral variation for different surface classes.

3 illus, 2 tables, 24 ref

008525   Mishra R K;Pandey A (Mathematics Dep, SLIET Deemed Univ, Longowal-148 106, Email: ravkmishra@yahoo.co.in) : Theory of expanding universe & F-R space of constant curvature. Ultra Scient phys Sci-Sect B 2014, 26(1), 13-18.

Recently Many researchers has given attention on the study of the expanding nature of the universe with variable fundamental constants. It is also believed that the inclusion of vacuum energy term can greatly affect the cosmological theories. The basic purpose of this investigation is to highlight the hidden connection between Finsler Geometry and Riemannian Geometry along with theory of expanding universe.

10 ref

006423   Vemareddy P;Ambastha A;Wiegelmann T (Udaipur Solar Observatory, Physical Research Laboratory, Udaipur, Email: vema@prl.res.in) : Magnetic structure of solar active region NOAA 11158. Bull Astr Soc India 2013, 41(3), 183-93.

Magnetic fields in the solar corona are responsible for a wide range of phenomena. However, any direct measurements of the coronal magnetic fields are very difficult due to lack of suitable spectral lines, weak magnetic fields, and high temperatures. Therefore, one extrapolates photospheric field measurements into the corona. Owing to low coronal plasma β, we can apply a force-free model in lowest order to study the slow evolution of active region (AR) magnetic fields. On applying these models to AR 11158 and compared with coronal plasma tracers, we found that (1) the approximation of potential field to coronal structures over large length scales is a reasonable one, 2) linear force-free (LFF) assumption to AR coronal fields may not be applicable model as it assumes uniform twist over the entire AR, and 3) for modeling fields at sheared, stressed locations where energy release in the form of flares are usually observed, non-linear force free fields (NLFFF) seem to provide a good approximation. The maximum available free-energy profile shows step-wise decrease that is sufficient to power an M-class flare as observed.

3 illus, 20 ref

006422   Tripathi A;Pandey U S;Brijesh Kumar (Physics Dep, Deen Dayal Upadhyaya Gorakhpur Univ, Gorakhpur-273 009, Email: aparatrip@gmail.com) : Photometric study of galactic open cluster NGC 2129, NGC 1502 and king 12. Bull Astr Soc India 2013, 41(3), 209-26.

Presented deep Johnson UBV and Cousins RI CCD photometry of three young open clusters, namely, NGC 2129, NGC 1502 and King 12 reaching down to V <126> 22 mag. For the first time, we have reported optical CCD data for King 12. Fundamental parameters for these clusters have been determined by comparing colour-colour and colour-magnitude diagrams (CMDs) with the theoretical models. The cluster radii have been estimated to be 3.3, 1.7 and 3.9 pc for NGC 2129, NGC 1502 and King 12 respectively. The reddenings E(B-V) have been determined to be 0.77+0.05, 0.68±0.05 and 0.63±0.05 while the corresponding distances have been found to be 2.1±0.1, 1.0±0.1 and 2.5±0.1 kpc respectively. The ages of the clusters have been obtained after fitting theoretical stellar evolutionary rriodels for solar metallicity Z = 0.019 isochrones with the observed CMDs. This gives an age of 10.0±0.1 Myr for all the three clusters. The analysis shows that there is differential interstellar reddening in the direction of all clusters.

13 illus, 2 tables, 27 ref

006421   Sidharth B G (G.P. Birla Observatory & Astronomical Research Centre, B.M. Birla Scie, , Adarsh Nagar, Hyderabad-500 063, Email: birlasc@gmail.com) : Time's arrow as a signature of fuzzy spacetime. Curr Sci 2013, 104(6), 699-700.

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006420   Prabhu K;Rangarajan K E;Ravindra B; Sankarasubramanian K;Selvendran R;Kumaravel P (NO, Indian Institute of Astrophysics, Bengaluru-560 034) : Transit of venus on 2012 june 06: stray light estimation and restoration of ca-k images of twin telescope from kodaikanal observatory. Bull Astr Soc India 2013, 41(3), 227-35.

Observations of the transit of Venus were made from the Kodaikanal Observatory on 2012 June 06 in Ca-K wavelengths. Only half of the event was visible from India. We utilized this unique opportunity to compute the contribution of the scattered light within the Twin Telescope optics at Kodaikanal. The instrumental and atmospheric scattered light are derived from the model point spread function which is a combination of four Gaussians with different widths and weights. The restoration procedure has significantly improved the rms contrast of the images. The rms contrast of the stray light corrected images are almost two fold larger than that those of the unconnected images. The derived network element sizes matches well with previous observations.

15 illus, 23 ref

006419   Nayak A;Sreejith A G;Safonova M;Murthy J (NO, Indian Institute of Astrophysics, Bangalore-560 034, Email: akshata@iiap.res.in) : High-altitude ballooning programme at the Indian institute of astrophysics. Curr Sci 2013, 104(6), 708-13.

Recent advances in balloons and in electronics have made possible scientific payloads at costs accessible to university departments. The primary purpose of high-altitude ballooning programme is to test low-cost ultraviolet payloads for eventual space flight, but to also explore phenomena occurring in the upper atmosphere, including sprites and meteorite impacts, using balloon-borne payloads. This article discusses the results of three tethered balloon experiments carried out at the Centre for Research and Education in Science and Technology (CREST) campus of HA, Hosakote and our plans for the future. Also describe the stages of payload development for these experiments.

5 illus, 1 table, 16 ref

006418   Das R K;Banerjee D P K;Ashok N M;Mondal S (Astrophysics and Cosmology Dep, S N Bose National Centre for Basic Sciences, Salt Lake, Kolkata-700 098, Email: ramkrishna.das@bose.res.in) : Near-infrared spectroscopic and photometric evolution of nova V476 scuti-a nova that formed optically thin dust. Bull Astr Soc India 2013, 41(3), 195-207.

Presented results of near-infrared (near-IR) JHK (1.07 - 2.5 μm) spectro-scopic and photometric observations of Nova V476 Scuti (V476 Sct) which was discovered in outburst in 2005 September. The near-IR observations of the nova presents the evolution of the post-maxima spectra and near-IR light curve. The spectra of V476 Sct, observed on 9 different epochs, show prominent lines due to HI, OI, CI and NI. Based on the IR spectral signatures we independently identify it as a Fe II type of nova, consistent with the same classification obtained from optical spectra. A detailed identification of the observed spectral lines is presented. The near-IR JHK light curve extending for a period of about 59 days after outburst clearly shows the formation of a optically thin dust shell, a phenomenon which is not commonly observed in novae. By fitting black body curves to the spectral energy distributions (SEDs) the temperatures of the dust shell on different epochs have been estimated. Dust formation in V476 Sct is consistent with the presence of lines of elements with low-ionization potential like Na and Mg in the early spectra which had earlier been suggested by us to be potential indicators of dust formation at a later phase in a nova's development.

5 illus, 3 tables, ref

005341   Valarmathi N; (ISRO Satellite Centre, Indian Space Research Organisation, Bangalore-560 017, Email: valar@isac.gov.in) : RISAT-1 spacecraft configuration: architecture, technology and performance. Curr Sci 2013, 104(4), 462-71.

RISAT-1 is the first indigenous active Radar Imaging Satellite launched by Polar Satellite Launch Vehicle (PSLV) in April 2012 from Sriharikota. It carries C-band Synthetic Aperture Radar (SAR) payload which can operate at various values of resolution and swath for various applications. RISAT-1 is the heaviest and high-power satellite with many new technologies to support the SAR payload and the associated elements. RISAT-1 operates at polar sun-synchronous orbit of 536 km altitude with the inclination of 97.554° and it is designed for 5 years lifetime. Performance of the spacecraft system and the SAR payload is satisfactory. This article outlines the architecture, design and on-orbit performance of RISAT-1.

13 illus, 3 tables

005340   Paula A L D;Gama A M;Perotoni M B;De Andrade L A (NO, Institute of Aeronautics and Space Materials Division Sao Jose dos Cam, Brazil, Email: alpaula7@gmail.com) : Complex permittivity and permeability measurements and numerical simulation of carbonyl iron rubber in x-band frequency. Oriental J Chem 2014, 30(2), 419-25.

Recognizing the importance of an adequate characterization of radar absorbing materials (RAM), and consequently their development, the present study aims to contribute for the establishment and validation of experimental determination and numerical simulation of complex permittivity and permeability of electromagnetic materials, using for this a carbonyl iron was seventy percent of the mass concentration. The present work branches out into two related topics. The first one is concerned with the implementation of a computational modeling to predict the behavior of electromagnetic materials in confined environment by using electromagnetic three-dimensional simulation. The second topic re-examines the Nicolson-Ross-Weir mathematical model to retrieve the constitutive parameters (complex permittivity and permeability) of a homogeneous sample (carbonyl iron) from scattering coefficient measurements. The measured and calculated results show a good convergence that guarantees the application of the used methodologies for the characterization of carbonyl iron rubber in x-band frequency.

9 illus, 13 ref

005339   Panchal H (NO, , , Email: hardikpanc87@gmail.com) : Astrosat: a telescope on a satellite. Curr Sci 2013, 104(4), 412.

3 ref

005338   Misra T;Rana S S;Desai N M;Dave D B; Rajeevjoti;Arora R K;Rao C V N;Bakori B V;Neelakantan R;Vachchani J G (Space Applications Centre, Indian Space Research Organisation, Ahmedabad-380 015, Email: misratapan@sac.isro.gov.in) : Synthetic aperture radar payload on-board RISAT-1: configuration, technology and performance. Curr Sci 2013, 104(4), 446-61.

Launch of Radar Imaging Satellite (RISAT-1) marked a new chapter in the remote sensing programme of Indian Space Research Organisation (ISRO). RISAT-1, carrying a multi-mode Synthetic Aperture Radar (SAR) system, will provide complementary imaging capability in microwave along with optical images, being obtained from the well-established IRS class of satellites. RISAT-1 supports a variety of resolution and swath requirements. Both conventional stripmap and scanSAR modes are supported, with dual polarization mode of operation. Additionally a quad polarization stripmap mode is provided for availing additional resource classification. In all these modes, resolutions from 3 to 50 m can be achieved with swath ranging from 25 to 223 km. On experimental basis, a sliding spotlight mode is also available. In all the imaging modes, a novel polarimetry mode called circular or hybrid polarimetry can be exercised seamlessly. The system is capable of imaging on either side of the flight track depending upon prior programming of the satellite. The satellite is placed in a Sun-synchronous orbit with 6 am-6 pm equatorial crossing. This orbit configuration is chosen to maximize solar power availability. The satellite has an on-board-solid state recorder for supporting data acquisition beyond ground station visibility. The payload is based on active antenna array technology. Crucial technology elements like C-band MMICs, TR module and miniaturized power supplies have already been developed in India. A pulsed mode near-field test facility has also been developed in-house in order to characterize the payload in the integration laboratory itself.

22 illus, 8 tables, 14 ref

005337   Maheswari S;Rajagopal K (Botany Dep, Vinayaka Missions Univ, Salem-636 308, Email: darwin_mahe@yahoo.com) : Biodiversity of endophytic fungi in KIgelia pinnata during two different seasons. Curr Sci 2013, 104(4), 515-18.

Endophytic fungi of inner bark and leaf tissue of Kige-lia pinnata (Lam) Benth., also called sausage tree, from South India, have been studied during two different seasons. Four hundred bark and leaf segments were analysed and a total of 732 isolates representing 28 taxa, including 3 morphotypes were isolated. The endophytic fungal population is prevalent during winter on both the tissues and the colonization frequency and isolation frequency were greater in the leaves than bark tissue. Some endophytic fungi were common to both hosts, although more appeared to be tissue-specific.

2 illus, 4 tables, 38 ref

005336   Mahadevan V;Prasad T V S R K;Jain D S; Chowdhury S;Pithamani M;Desai N M (ISRO Satellite Centre, Indian Space Research Organisation, Bangalore-560 017, Email: vm@isac.gov.in) : Ground segment for RISAT-1 SAR mission. Curr Sci 2013, 104(4), 477-89.

RISAT-1 carries a C-band multi-mode Synthetic Aperture Radar (SAR) operating in Stripmap, Scan-SAR and Sliding Spotlight modes and mainly caters to civilian land applications related to agriculture, forestry and disaster management. Considering the multi-resolution and multi-polarization requirements of RISAT-1 SAR, on-board programmability and flexibility in SAR payload as well as fairly autonomous operation have been major mission requirements. The necessary intelligence and sophistication have been built into the on-board SAR subsystems to fulfill these essential requirements, apart from intelligent control and coordination of active antenna of RISAT-1 SAR payload. The complexity and large size of on-board SAR instrument have demanded a matching and equally innovative approach for ground segment operations for RISAT-1 mission. Since the launch of RISAT-1 satellite by PSLV-C19 flight on 26 April 2012, the satellite and SAR payload performances as well as mission and ground segment operations have been found to be nominal and satisfactory. This article highlights the features and achievements of various RISAT-1 ground segment systems and the activities carried out during pre-launch, launch and Early Orbit Phase and normal operating phases of RISAT-1 SAR mission, data reception chain, quick look processing, offline data product generation and dissemination chains.

8 illus

005335   Kunhikrishnan P;Sowmianaryanan L;Nampoothiri M V (PSLV Project, Vikram Sarabhai Space Centre, INdian Space Research Organisation, Thiruvanantapuram-695 022, Email: p-kunhikrishnan@vssc.gov.in) : PSLV-C19/RISAT-1 mission: the launcher aspects. Curr Sci 2013, 104(4), 472-6.

India's Polar Satellite Launch Vehicle (PSLV) precisely placed the indigenous Radar Imaging Satellite (RISAT-1) in the intended orbit successfully on 26 April 2012. This marked the 20th successive success of the launcher. This article gives the special aspects of the 'PSLV-C19/RISAT-1 mission' from the techno-managerial perspective of launch vehicle project. Also given is a summary of the performance of the launch vehicle in this flight.

8 illus, 3 table

005334   Kiran Kumar A S (Space Applications Centre, Indian Space Research Organisation, Ahmedabad-380 015, Email: kiran@sac.isro.gov.in) : Significance of RISAT-1 in ISRO's earth observation programme. Curr Sci 2013, 104(4), 444-5.

005333   Chakraborty M; (Space Applications Centre, Indian Space Research Organisation, Ahmedabad-380 015, Email: manab@sac.isro.gov.in) : Initial results using RISAT-1 C-band SAR data. Curr Sci 2013, 104(4), 490-501.

Imaging radars provide information that is fundamentally different from sensors that operate in the visible and infrared portions of the electromagnetic spectrum. The Indian Space Research Organisation (ISRO) has launched a multi-mode, multi-polarization Synthetic Aperture Radar (SAR) on-board Radar Imaging SATellite-1 (RISAT-1) on 26 April 2012. Various data products from RISAT-1 SAR are now going through calibration-validation (cal-val) phase and soon will be available for the global users for operational and research purposes. In this regard, algorithms are being developed to retrieve various parameters in diverse application areas. This article deals with the in-house algorithm development for studying different resources using initial available data of RISAT-1.

16 illus, 1 table, 56 ref

005332   Behera M D;Dash J (Centre for Oceans, Rivers, Atmosphere and Land Sciences, Indian Institute of Technology Kharagpur, Kharagpur-721 302, Email: mukundbehera@gmail.com) : Terrestrial carbon studies and earth observation data. Curr Sci 2013, 104(4), 413.

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024340   Sreedhar Y H;Rakos K;Hensler G (NO, Institute of Astronomy, Vienna Univ, Austria, Email: yuvrajharsha@gmail.com) : Comparative studies of population synthesis models in the framework of modified stromgren filters. J Astrophys Astr 2014, 35(1), 55-68.

Evolutionary models form a vital part of stellar population research in understanding their evolution, but despite their long history of development, they are often misrepresented and the properties of stellar population observed through broadband and spectroscopic measurements are also misinterpreted. With growing numbers of these synthesis models, model comparison becomes an important analysis to choose a suitable model for understanding stellar populations and model up-gradation. Along with model comparison, we reinvestigate the technique of modified Stromgren photometry to measure reliable parameter-sensitive colours and estimate precise model ages and metallicities. The assessment of Rakos/Schulz models with GALEV and Worthey's Lick/IDS model find smaller colour variation: Δ(UZ - uz) ≤ 0.056, - 26 - Δ(bz - yz) ≤ -0.05 and Δ(uz - yz) ≤ 0.061. The study conveys a good agreement of GALEV models with modified Stromgren colours but with poor UV model predictions and observed globular cluster data, while the spectroscopic models perform badly because of outdated isochrone and stellar spectral libraries with inaccurate/insufficient knowledge of various stellar phases and their treatment. Overall, the assessment finds modified Stromgren photometry well suited to study different types stellar populations by mitigating the effects of age-metallicity degeneracy.

3 illus, 1 table, 70 ref