022110   Choudhury I;Chakraborty M;Santra S C;Parihar J S (Space Applications Centre, ISRO, , Ahmedabad-380 015) : Characterization of agroecosystem based on land utilization indices using remote sensing and GIS. J Indian Soc Remote Sens 2006, 34(1), 23-37.

Information on various agricultural resource parameters at various levels is essential for proper management and efficient resource allocation for sustainable agricultural development. Limitations in ground-based method have encouraged the use of satellite data coupled with geographical information system (GIS) in providing spatial as well as temporal information over large and inaccessible areas. An attempt has been made to generate raster maps using remote sensing and GIS techniques to characterize the agroecosystem of South 24 Paraganas district of West Bengal, based on land utilization indices. Information on multi-season landcover derived from the analysis of the multi-temporal RADARSAT-1 SAR and IRS-1D LISS III data as well as other ancillary information in GIS environment are the basic inputs used in the study. The analysis shows that northern and northwestern parts are more diverse in terms of agricultural intensification as compared to the southern and northeastern parts whereas the central parts show moderate density. In terms of carrying capacity, the high carrying capacity has been observed in the southern to northeastern parts whereas the northwestern and central parts show moderate and northern parts show low carrying capacity. Overall, the characterization of agroecosystem using land utilization indices can be identified as major input to formulate a management plan for sustainable agriculture with concerns for the environment.

3 tables, 4 illus, 26 ref

022109   Chenna Reddy K;Phani Kumar D V;Yellaiah G (Department of Astronomy, Osmania University, Hyderabad-500 007) : Visual observations of Geminid meteor shower 2004. Bull Astr Soc India 2006, 34(2), 225-33.

Based on 19 hours of effective visual observations with a group of 5 observers, authors detected a total of 2352 Geminid meteors from Japal-Rangapur Observatory, a low latitude station. From three days observations of Geminid meteor shower during 11-14 december, 2004, authors observed that the peak activity of the shower occurred at 20:30 hrs UT on 13 December with a maximum rate of 257 meteors per hour. The Geminid meteor shower activity produced more number of faint meteors compared to bright meteors on the peak day. The population index value is also high on the peak day of the activity leading to a conclusion that the shower contains more number of small size particles at the centre of the stream. Here authors present an analysis of the activity profile of the shower, the magnitude and directional variation of the shower. The luminosity class distribution of the shower is also presented and discussed.

4 illus, 2 tables, 19 ref

021180   Zhang H (NO, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100 012, China) : Observational study of solar magnetic active phenomena. J Astrophys Astr 2006, 27(2-3), 305-14.

Electric current separated into two parts reflected the quantative properties of heterogeneity and chirality of magnetic field, and defined them as the shear and twist components of current. Analyzes the basic configuration and evolution of superactive region NOAA 6580-6619-6659. It is found that the contribution of the twist component of current cannot be reflected in the normal analysis of the magnetic shear and gradient of the active regions. The observational evidence of kink magnetic ropes generated from the subatmosphere cannot be found completely in some super delta active regions.

6 illus, 16 ref

021179   Verma S R (Physics Dep, DBS (PG) College, Dehradun-248 001, Email: srvastro@rediffmail.com) : Mechanisms of coronal heating. J Astrophys Astr 2006, 27(2-3), 113-14.

The Sun is a mysterious star. The high temperature of the chromosphere and corona present one of the most puzzling problems of solar physics. Observations show that the solar coronal heating problem is highly complex with many different facts. It is likely that different heating mechanisms are at work in solar corona. Recent observations show that Magnetic Carpet is a potential candidate for solar coronal heating.

8 ref

021178   Vats H O (NO, Physical Research Laboratory, Navrangpura, Ahmedabad-380 009, Email: vats@prl.ernet.in) : Geo-effectiveness of solar wind extremes. J Astrophys Astr 2006, 27(2-3), 227-35.

Examples of extreme events of solar wind and their effect on geomagnetic conditions are discussed here. It is found that there are two regimes of high speed solar wind streams with a threshold of <126> 850 km s^-1. Geomagnetic activity enhancement rate (GAER) is defined as an average increase in Ap value per unit average increase in the peak solar wind velocity (Vp) during the stream. GAER was found to be different in the two regimes of high speed streams with +ve and -ve IME GAER is 0.73 and 0.53 for solar wind streams with +ve and -ve IMF respectively for the extremely high speed streams (<60> 850 kms s^-1). This indicates that streams above the threshold speed with +ve IMF are 1.4 times more effective in enhancing geomagnetic activity than those with -ve IMF. However, the high speed streams below the threshold with -ve IMF are 1.1 times more effective in enhancing geomagnetic activity than those with +ve IME. The violent solar activity period (October-November 2003) of cycle 23 presents a very special case during which many severe and strong effects were seen in the environment of the Earth and other planets; however, the z-component of IMF (Bz) is mostly positive during this period. The most severe geomagnetic storm of this cycle occurred when Bz was positive.

6 illus, 19 ref

021177   Uddin W;Chandra R;Ali S S (NO, Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital-263 129, Email: wahab@upso.ernet.in) : Extremely energetic 4B/X17.2 flare and associated phenomena. J Astrophys Astr 2006, 27(2-3), 267-76.

Observed B/X 17.2 flare in Hα from super-active region NOAA 10486 at ARIES, Nainital. This is one of the largest flares of current solar cycle 23, which occurred near the Sun's center and produced extremely energetic emission almost at all wavelengths from γ-ray to radiowaves. The flare is associated with a bright/fast full-halo earth directed CME, strong type II, type III and type IV radio bursts, an intense proton event and GLE. This flare is well observed by SOHO, RHESSI and TRACE. The Hα observations show the stretching/de-twisting and eruption of helically twisted S shaped (sigmoid) filament in the south-west direction of the active region with bright shock front followed by rapid increase in intensity and area of the gigantic flare. The flare shows almost similar evolution in Hα, EUV and UV. Measures the speed of Hα ribbon separation and the mean value is <126> 70 km s^-1. This is used together with photospheric magnetic field to infer a magnetic reconnection rate at three HXR sourced at the flare maximum. Also discusses the energetics of active region filament, flare and associated CME.

5 illus, 26 ref

021176   Srivastava N (NO, Udaipur Solar Observatory, P.O. Box 198, Badi Road, Udaipur-313 001, Email: nandita@prl.res.in) : Challenge of predicting the occurrence of intense storms. J Astrophys Astr 2006, 27(2-3), 237-42.

Geomagnetic super-storms of October and November 2003 are compared in order to identify solar and interplanetary variables that influence the magnitude of geomagnetic storms. Although these superstorms (D_ST 60> -300 nT) are associated with high speed CMEs, their D_ST indices show large variation. The most intense storm of November 20, 2003 (D_ST <126> -472 nT) had its source in a comparatively small active region and was associated with a relatively weaker, M-class flare, while the others had their origins in large active regions and were associated with strong X-class flares. An attempt has been made to implement a logistic regression model for the prediction of the occurrence of intense/superintense geomagnetic storms. The model parameters (regression coefficients) were estimated from a training data-set extracted from a data-set of 64 geo-effective CMEs observed during 1996-2002. The results indicate that logistic regression models can be effectively used for predicting the occurrence of major geomagnetic storms from a set of solar and interplanetary factors. The model validation shows that 100% of the intense storms (-200nT 60> D_ST 60> - 100 nT) and only 50% of the super-intense (D_ST -200 nT) storms could be correctly predicted.

2 illus, 1 table, 9 ref

021175   Srivastava A K;Dwivedi B N (Applied Physics Dep, Institute of Technology, Banaras Hindu University, Varanasi-221 005, Email: aks.astro.itbhu@gmail.com) : Magnetosonic waveguide model of solar wind flow tubes. J Astrophys Astr 2006, 27(2-3), 353-9.

Considers solar wind flow tubes as a magnetosonic wave-guide. Assuming a symmetric expansion in edges of slab-modelled wave-guide, studied the propagation characteristics of magnetosonic wave in the solar wind flow tubes. Presents the preliminary results and discuss their implications.

5 illus, 10 ref

021174   Singh Y P;Munendra Sing;Badruddin (Physics Dep, Aligarh Muslim University, Aligarh-202 002, Email: badr_phys@yahoo.co.in) : Analysis of plasma and field conditions during some intensely geo-effective transient solar/interplanetary distrubances of soalr cycle 23. J Astrophys Astr 2006, 27(2-3), 361-6.

Problem of solar wind-magnetosphere coupling is investigated for intense geomagnetic storms (Dst ≤ -100 nT) that occurred during solar cycle 23. For this purpose interplanetary plasma and field data during some intensely geo-effective transient solar/interplanetary disturbances have been analysed. A geomagnetic index that represents the intensity of planetary magnetic activity at subaurorallatitude and the other that measures the ring current magnetic field, together with solar plasma and field parameters (V, B, Bz, σ_B, N, and T) and their various derivatives (BV, -BVz, BV², -BzV², B²V, Bz²V, NV²) have been analysed in an attempt to study mechanism and the cause of geo-effectiveness of interplanetary manifestations of transient solar events. Several functions of solar wind plasma and field parameters are tested for their ability to predict the magnitude of geomagnetic storm.

3 illus, 2 tables, 13 ref

021173   Singh K A P (Applied Physics Dep, Institute of Technology, Banaras Hindu University, Varanasi-221 005, Email: kaps_bhul@yahoo.co.in) : Spatial damping of linear compressional magnetoacoustic waves in quiescent prominences. J Astrophys Astr 2006, 27(2-3), 321-6.

Studies the spatial damping of magnetoacoutic waves in an unbounded quiescent prominence invoking the technique of MHD seismology. Considers Newtonian radiation in the energy equation and derive a fourth order general dispersion relation in terms of wavenumber k. Numerical solution of dispersion relation suggests that slow mode is more affected by radiation. The high frequency waves have been found to be highly damped. The uncertainty in the radiative relaxation time, however, does not allow us to conclude if the radiation is a dominant damping mechanism in quiescent prominence.

2 illus, 13 ref

021172   Shelke R (NO, Ram Meghe Institute of Technology and Research, Badnera, Amravati-444 607) : Evolving coronal holes and interplanetary erupting stream disturbances. J Astrophys Astr 2006, 27(2-3), 101-12.

Coronal holes and interplanetary disturbances are important aspects of the physics of the Sun and heliosphere. Interplanetary disturbances are identified as an increase in the density turbulence compared with the ambient solar wind. Erupting stream disturbances are transient large-scale structures of enhanced density turbulence in the interplanetary medium driven by the high-speed flows of low-density plasma trailing behind for several days. An attempt has been made to investigate the solar cause of erupting stream disturbances, mapped by Hewish & Bravo (1986) from interplanetary scintillation (IPS) measurements made between August 1978 and August 1979 at 81.5 MHz. The position of the sources of 68 erupting stream disturbances on the solar disk has been compared with the locations of newborn coronal holes and/or the areas that have been coronal holes previously. It is found that the occurrence of erupting stream disturbances is linked to the emergence of new coronal holes at the eruption site on the solar disk. A coronal hole is indicative of a radial magnetic field of a predominant magnetic polarity. The newborn coronal hole emerges on the Sun. owing to the changes in magnetic field configuration leading to the opening of closed magnetic structure into the corona. The fundamental activity for the onset of an erupting stream seems to be a transient opening of pre-existing closed magnetic structures into a new coronal hole, which can support highspeed flow trailing behind the compression zone of the erupting stream for several days.

11 illus, 11 ref

021171   Shah A B et al (NO, Physical Research Laboratory, Navarangpura, Ahmedabad-380 009, Email: abshah@prl.res.in) : Data acquisition, control, communication and computation system of soalr X-ray spectrometer (SOXS) mission. J Astrophys Astr 2006, 27(2-3), 299-304.

Solar X-ray Spectrometer (SOXS) mission on board GSAT-2 Indian Spacecraft was launched on 08 May 2003 using GSLV-D2 rocket by Indian Space Research Organization (ISRO). SOXS aims to study solar flares, which are the most violent and energetic phenomena in the solar system, in the energy range of 4-56 keV with high spectral and temporal resolution. SOXS employs state-of-the-art semiconductor devices, viz., Si-Pin and CZT detectors to achieve sub-keV energy resolution requirements. Presents an overview of data acquisition, control, communication and computation of low energy payload of the SOXS mission.

1 illus, 9 ref

021170   Pecker J C;Narlikar J V (NO, College de France, 3 re d'Ulm, FR-75005 Paris, France, Email: jvn@iucaa.ernet.in) : Stellar and extragalactic radiation at the earth's surface. J Astrophys Astr 2006, 27(1), 1-6.

Reviving a calculation made by Eddington in the I 920s, and using the most recent and comprehensive databases available on stars and galaxies, including more than 2,500,000 stars and around 20,000 galaxies authors have computed their total radiation received at the Earth just outside its atmosphere. This radiation density, if thermalized, would be equivalent to a temperature of 4.212 K. The comparability of this temperature to that of the cosmic microwave background (2.723 K) may either be a pure coincidence or may hold a key to some as yet unknown, aspect of the universe.

5 ref

021169   Pant P (NO, Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital-263 129, Email: ppant@aries.ernet.in) : Research facilities for soalr astronomy at ARIES. J Astrophys Astr 2006, 27(2-3), 293-7.

Solar observational facilities at ARIES (erstwhile V.P. State Observatory, UPSO), Nainital, began in the sixties with the acquisition of two moderate sized (25 cm, f/66 off-axis Skew Cassegrain and 15 cm, f/15 refractor) telescopes. Both these systems receive sunlight through a 45 cm and 25 cm coelostat respectively. The backend instruments to these systems comprised of a single pass grating spectrograph for spectroscopic study of the Sun and a Bernhard-Halle Hα filter, coupled with a Robot recorder camera for solar patrolling in Hα respectively. With the advancement in solar observing techniques with high temporal and spatial resolution in Hα and other wavelengths, it became inevitable to acquire sophisticated instrumentation for data acquisition. In view of that, the above facilities were upgraded, owing to which the conventional photographic techniques were replaced by the CCD camera systems attached with two 15 cm, f/15 Coude refractor telescopes. These CCD systems include the Peltier cooled CCD camera and photometries PXL high speed modular CCD camera which provide high temporal and spatial resolution of <126> 25 ms and' <126> 1.3 arcsec respectively.

2 illus, 11 ref

021168   Omar A;Dwarakanath K S (NO, Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital-263 129, Email: aomar@aries.ernet.in) : Tully-fisher relations of the eridanus group of galaxies. J Astrophys Astr 2006, 27(1), 7-23.

The Tully-Fisher (TF) or the luminosity-linewidth relations of the galaxies in the Eridanus group are constructed using the HI rotation curves and the luminosities in the optical and in the near-infrared bands. The slopes of the TF relations (absolute magnitude vs log 2 V_ftat) are -8.6 ± 1.1, -10.0 ± 1.5, -10.7 ± 2.1, and -9.7 ± 1.3 in the R, J, H, and K bands respectively for galaxies having flat HI rotation curves. These values of the slopes are consistent with those obtained from studies of other groups and clusters. The scatter in the TF relations is in the range 0.5-1.1 mag in different bands. This scatter is considerably larger compared to those observed in other groups and clusters. It is suggested that the larger scatter in the TF relations for the Eridanus group is related to the loose structure of the group. If the TF relations are constructed using the baryonic mass (stellar + HI + Helium mass) instead of the stellar luminosity, nearly identical slopes are obtained in the R and in the near-infrared bands. The baryonic TF (baryonic mass vs log 2 V_ftat) slope is in the range 3.5-4.1.

021167   Narain U;Pandey K (NO, Astrophysics Research Group, Meerut College, Meerut, Email: uditnarain@yahoo.co.in) : Nanoflares and heating of the solar corona. J Astrophys Astr 2006, 27(2-3), 93-100.

Coronal heating by nanoflares is presented by using observaªtional, analytical, numerical simulation and statistical results. Numerical simulations show the formation of numerous current sheets if the magªnetic field is sheared and bipoles have unequal pole strengths. This fact supports the generation of nanoflares and heating by them. The occurrence frequency of transients such as flares, nano/microflares, on the Sun exhibits a power-law distribution with exponent α varying between 1.4 and 3.3. For nanoflares heating α must be greater than 2. It is likely that the nanoflare heating can be reproduced by dissipating Alfven waves. Only observations from future space missions such as Solar-B, to be launched in 2006, can shed further light on whether Alfven waves or nanoflares. heat the solar corona.

1 illus, 1 table, 29 ref

021166   Mukherjee U;Paul B (NO, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai-400 005) : Luminosity dependent study of the high mass X-ray binary pulsar A4 0114 + 65 with ASCA. J Astrophys Astr 2006, 27(1), 37-45.

Reports the spectral characteristics of the high and low states of the pulsar 4U 0114 + 65 and examine the change in the paraªmeters of the spectral model. A power law and a photoelectric absorption by material along the line of sight together with a high energy cut-off suffice to describe the continuum spectrum in both the states. A fluorescence iron line at <126> 6.4 keV is present in the high as well as in the low state, though it is less intense in the latter. The photon index, cut-off energy and e-folding energy values hardly show any discernible change over the states. Compares these spectral characteristics as observed with ASCA with those of other satellites. Also compare the spectral characteristics of 4U 0114 + 650 with other X-ray sources which show intensity variation at different time scales.

4 illus, 2 tables, 23 ref

021165   Mukherjee U;Bapna S;Raichur H;Paul B;Jaaffrey S N A (NO, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai-400 005) : Variable quasi periodic oscillations during an outburst of the transient X-ray pulser XTE J1858 + 034. J Astrophys Astr 2006, 27(1), 25-35.

Investigates the Quasi Periodic Oscillation (QPO) properties of the transient accreting X-ray pulsar XTE Jl858 + 034 during the second outburst of this source in April-May 2004. Authors have used observations made with the Proportional Counter Array (PCA) of the Rossi X-ray Timing Explorer (RXTE) during May 14-18,2004, in the declining phase of the outburst. Detected the presence of low frequency QPOs in the frequency range of 140-185 mHz in all the RXTE-PCA observations. Reports evolution of the QPO parameters with the time, X-ray flux, and X-ray photon energy. Though a correlation between the QPO centroid frequency and the instantaneous X-ray flux is not very clear from the data, authors point out that the QPO frequency and the one day averaged X-ray flux decreased with time during these observations. Obtained a clear energy dependence of the RMS variation in the QPOs, increasing from about 3% at 3 keV to 6% at 25 keV. The X-ray pulse profile is a single peaked sinusoidal, with pulse fraction increasing from 20% at 3 keV to 45% at 30 keV. Authors have found that, similar to the previous outburst, the energy spectrum is well fitted with a model consisting of a cut-off power law along with an iron emission line.

8 illus, 15 ref

021164   Kariyappa R;Dame L;Hiremath K M (NO, Indian Institute of Astrophysics, Bangalore-560 034, Email: rkari@iiap.res.in) : Observational searches for chromospheric g-Mode oscillations from CaII H-line observations. J Astrophys Astr 2006, 27(2-3), 327-31.

Uses a high spatial and temporal resolution of long time sequence of spectra in Call H-line obtained at the Vacuum Tower Telescope (VTT) of the Sacramento Peak Observatory on a quiet region at the center of the solar disk over a large number of bright points and network elements to search for atmospheric (chromospheric) g-mode oscillations. An important parameter of the H-line profile. intensity at H_2v (I_H2v), has been derived from a large number of line profiles. Derives the light curves of all the bright points and network elements. The light curves represent the main pulse with large intensity amplitude and followed by several follower pulses with lower intensity amplitudes. The light curves of these bright points would give an impression that one can as well draw curves towards and away from the highest peak (main pulse) showing an exponential growth and decay of the amplitudes. An exponential decaying function has been fitted for all the light curves of the bright points to determine the damping time of the modes that are more or less the same, and one value of the coefficient of exponent can represent reasonably well the decay for all the cases. The FFT analysis of temporal variation of both the bright points and the network elements indicates around I0-min periodicity. Speculates that this longer period of oscillation may be related to chromospheric g-mode oscillations.

2 illus, 1 table, 8 ref

021163   Joshi B;Pant P;Manoharan P K (NO, Aryabhatta Research Institute of Observational Sciences, Nainital-263 129, Email: bhuwan@aries.ernet.in) : North-south distribution of solar flares during cycle 23. J Astrophys Astr 2006, 27(2-3), 151-7.

Investigates the spatial distribution of solar flares in the northern and southern hemispheres of the Sun that occurred during the period 1996 to 2003. This period of investigation includes the ascending phase, the maximum and part of the descending phase of solar cycle 23. It is revealed that the flare activity during this cycle is low compared to the previous solar cycle, indicating the violation of Gnevyshev-Ohl rule. The distribution of flares with respect to heliographic latitudes shows a significant asymmetry between northern and southern hemisphere which is maximum during the minimum phase of the solar cycle. The study indicates that the activity dominates the northern hemisphere in genªeral during the rising phase of the cycle (1997-2000). The dominance of northern hemisphere shifted towards the southern hemisphere after the solar maximum in 2000 and remained there in the successive years. Although the annual variations in the asymmetry time series during cycle 23 are quite different from cycle 22, they are comparable to cycle 21.

2 illus, 21 ref

021162   Jassur D M Z;Khodadadi A (Faculty of Physics, Tabriz University, Tabriz, Iran) : Photometric modelling of close binary star CN And. J Astrophys Astr 2006, 27(1), 47-56.

Results of two color photometry of active close binary CN And are presented and analyzed. The light curves of the system are obviously asymmetric, with the primary maximum brighter than the secondary maximum, which is known as the O'Conell effect. The most plausible explanation of the asymmetry is expected to be due to spot activity of the primary component. For the determination of physical and geometrical parameters, the most new version of W-D code was used, but the presence of asymmetry prevented the convergence of the method when the whole light curves were used. The solutions were obtained by applying mode 3 of W-D code to the first half of the light curves, assuming synchronous rotation and zero eccentricity. Absolute parameters of the system were obtained from combining the photometric solution with spectroscopic data obtained from radial velocity curve analysis. The results indicate the poor thermal contact of the components and transit primary minimum. Finally the O-C diagram was analyzed. It was found that the orbital period of the system is changing with a rate of d P / dt = -2.2(6) X 10^-10 which corresponds to mass transfer from more massive component to less massive with the rate of dM /dt <126> 4.82 x 10^-8 M_sun/year.

11 illus, 5 tables, 18 ref

021161   Janardhan P (NO, Physical Research Laboratory, Ahmedabad-380 009, Email: jerry@prl.res.in) : Enigmatic solar wind disappearance events - Do we understand them?. J Astrophys Astr 2006, 27(2-3), 201-7.

At the Sun-Earth distance of one astronomical unit (I AU), the solar wind is known to be strongly supersonic and super Alfvenic with Mach and Alfven numbers being on average 12 and 9 respectively. Also, solar wind densities (average <126> 10 cm^-3) and velocities (average <126> 450 km s^-1) at 1 AU. are known to be inversely correlated with low velocities having higher than average densities and vice versa. However, on May 11 and 12 1999 the Earth was engulfed by an unusually low density (<60> 0.1 cm^-3) and low velocity (<60> 350 km s^-1) solar wind with an Alfven Mach number significantly less than 1. This was a unique low-velocity, low-density, sub-Alfvcnic solar wind flow which spacecraft observations have shown lasted more than 24 hours. One consequence of this extremely tenuous solar wind was a spectacular expansion of the Earth' s magnetosphere and bow shock. The expanding bow shock was observed by several spacecraft and reached record upstream distances of nearly 60 Earth radii, the lunar orbit. The event was so dramatic that it has come to be known as the solar wind disappearance event. Though extensive studies of this event were made by many authors in the past, it has only been recently shown that the unusual solar wind flows characterizing this event originated from a small coronal hole in the vicinity of a large active region on the Sun. These recent results have put to rest speculation that such events are associated with global phenomenon like the periodic solar polar field reversal that occurs at the maximum of each solar cycle. Revisits the 11 May 1999 event, look at other disappearance events that have occurred in the past, examine the reaªsons why speculations about the association of such events with global phenomena like solar polar field reversals were made and also examine the role of transient coronal holes as a possible solar source for such events.

1 illus, 1 table, 19 ref

021160   Jain R;Joshi V;Hanaoka Y;Sakurai T;Upadhyay N (NO, Physical Research Laboratory, Navarangpura, Ahmedabad-380 009, Email: rajmal@prl.res.in) : Microflares through SOXS mission. J Astrophys Astr 2006, 27(2-3), 339-46.

Presents a study of 10 microflares observed in 4-30keV by SOXS mission simultaneously with Hα observations made at NAOJ, Japan during the interval between February and August 2004. The X-ray and Hα light curves showed that the lifetime of microflares varies between 4 and 25 min. Finds that the X-ray emission in all microflares under study in the dynamic energy range of 4-30 keV can be fitted by thermal plus non-thermal components. The thermal spectrum appeared to start from almost 4keV, low level discriminator (LLD) of both Si and CZT detectors, however it ends below 8 ke V. Also observed the Fe line complex features at 6.7 keV in some microflares and attempted to fit this line by isothermal temperature assumption. The temperature of isothermal plasma of microflares varies in the range between 8.6 and 10.1 MK while emission measure between 0.5 and 2 x 10⁴⁹ cm^-3. Non-thermal (NT) emission appeared in the energy range 7-15 keV with exponent -6.8 ≤ γ ≤ -4.8. The study of microflares that had occurred on 25 February 2004 showed that sometimes a given active region produces recurrent microfiarc activity of a similar nature. Concludes from X-ray and simultaneous Hα observations that the microflares are perhaps the result of the interaction of low lying loops. It appears that the electrons that accelerated during reconnection heat the ambient coronal plasma as well as interact with material while moving down along the loops and thereby produce Hα bright kernels.

3 illus, 1 table, 15 ref

021159   Jagdev Singh;Sakurai T;Ichimoto K;Muneer S (NO, Indian Institute of Astrophysics, Koramangala, Bangalore-560 034) : Spectroscopic studies of solar corona VI: trend in line-width variation of coronal emission lines with height independent of the structure of coronal loops. J Astrophys Astr 2006, 27(2-3), 115-24.

Obtaines spectroscopic observations in coronal emission lines by choosing two lines simultaneously, one [Fe x] 6374 Angstrom and the other [Fe XI] 7892 Angstrom or [Fe XIII] 10747 Angstrom or [Fe XIV] 5303 Angstrom. Founds that in 95 per cent of the coronal loops observed in 6374 Angstrom. the FWHM of the emission line increases with height above the limb irrespective of the size, shape and orientation of the loop and that in case of 5303 Angstrom line decreases with height in about 89 percent of the coronal loops. The FWHM of 7892 A and 10747 Angstrom emission lines show intermediate behavior. The increase in the FWHM of 6374 Angstrom line with height is the steepest among these four lines. Also studied the intensity ratio and ratio of FWHM of these lines with respect to those of 6374 Angstrom as a function height above the limb. Found that the intensity ratio of 7892 Angstrom and 10747 Angstrom lines with respect to 6374 Angstrom line increases with height and that of 5303 Angstrom to 6374 Angstrom decreases with height above the limb. This implies that temperature in coronal loops will appear to increase with height in the intensity ratio plots of 7892 Angstrom and 6374 Angstrom; and 10747 Angstrom and 6374 Angstrom whereas it will appear to decrease with height in intensity ratio of 5303 Angstrom to 6374 Angstrom line versus height plot. These findings are up to a height of about 200 arcsec above the limb. The varying ratios with height indicate that relatively hotter and colder plasma in coronal loops interact with each other. Therefore. the observed increase in FWHM with height above the limb of coronal emission lines associated with plasma at about I MK may not be due to increase in non-thermal motions caused by coronal waves but due to interaction with the relatively hotter plasma. These findings also do not support the existing coronal loop models, which predict an increase in temperature of the loop with height above the limb.

8 illus, 25 ref

021158   Iyer K N;Jadav R M;Jadeja A K;Manoharan P K (Physics Dep, Saurashtra University, Rajkot-360 005, Email: iyerkn@yahoo.com) : Spaced weather effects of coronal mass ejection. J Astrophys Astr 2006, 27(2-3), 219-26.

Describes the space weather effects of a major CME which was accompanied by extremely violent events on the Sun. The signatures of the event in the interplanetary medium (IPM) sensed by Ooty Radio Telescope, the solar observations by LASCO coronagraph onboard SOHO, GOES X-ray measurements, satellite measurements of the interplanetary parameters, GPS based ionospheric measurements, the geomagnetic storm parameter Dst and ground based ionosonde data are used in the study to understand the space weather effects in the different regions of the solar-terrestrial environment. The effects of this event are compared and possible explanations attempted.

7 illus, 6 ref

021157   Hiremath K M;Lovely M R;Kariyappa R (NO, Indian Institute of Astrophysics, Bangalore-560 034, Email: hiremath@iiap.res.in) : Extreme solar activity during October-November 2003. J Astrophys Astr 2006, 27(2-3), 333-8.

Positional measurements of sunspots from the Kodaikanal Observatory and Solar Geophysical data are used to study the association between occurrence of the abnormal activities of big sunspot groups that were observed during the period of October-November 2003 and occurªrence of the flares. During the evolution of the sunspot groups, investigated the temporal variations in areas; rotation rates; longitudinal extents; and number of small spots produced in a sunspot group. Among all these activity variations, it found that the spot groups that experience abnormal rotation rates during their evolutionary phases eventually trigger the flares.

4 illus, 14 ref

021156   Hiremath K M (NO, Indian Institute of Astrophysics, Bangalore-560 034, Email: hiremath@iiap.res.in) : Influence of solar activity on the rainfall over India: cycle-to-cycle variations. J Astrophys Astr 2006, 27(2-3), 367-72.

Uses 130 years data for studying correlative effects due to solar cycle and activity phenomena on the occurrence of rainfall over India. For the period of different solar cycles, it computes the correlation coefficients and significance of correlation coefficients for the seasonal months of Jan-Feb (JF), Mar-May (MAM), June-Sept (JJAS) and Oct-Dec (OND) and, annual mean data. Finds that with a moderate-to-high significance, Indian rainfall is correlated with the sunspot activity and there is an overall trend that during the period of low sunspot activity, occurrence of rainfall is high compared to the period of high sunspot activity. Speculates a possible physical connection between the occurrence of the rainfall and the sunspot activities and, the flux of galactic cosmic rays. Some of the negative correlations between the occurrences of the sunspot and rainfall activities obtained for different solar cycle periods are interpreted as effects of aerosols on the rain forming clouds due to either intermittent volcanic eruptions or due to intrusion of interstellar dust particles in the Earth's atmosphere.

1 illus, 1 table, 9 ref

021155   Hiremath K M (NO, Indian Institute of Astrophysics, Bangalore-560 034, Email: hiremath@iiap.res.in) : Flares associated with the dynamics of the sunspots. J Astrophys Astr 2006, 27(2-3), 277-84.

Study considers six years data of spot groups that have well developed leading and following spots obtained from the Kodaikanal Observatory white light pictures and occurrence of Hα flares. From the daily observations, computes the variations in rotation rates, meridional velocity, the areas and longitudinal separations. Finds that among all these variations, the occurrence of abnormal rotation rates (the rotation rates that have greater than 1 σ) and longitudinal minimum separation during the course of their evolution eventually lead to triggering of flares. Also finds that the events of abnormal rotation rates, longitudinal minimum separation and the flares occur mainly during the 50-80% of the sunspots' life span indicating magnetic reconnection probably below (0.935 R_Θ) the solar surface. Relevance of these results with the conventional theory of magnetic reconnection is briefly discussed.

4 illus, 29 ref

021154   Gupta S K;Mathew S K;Venkatakrishnan P (NO, Udaipur Observatory, P.O. Box 198, Badi Road, Udaipur-313 001, Email: sudhir@prl.res.in) : Development of soalr scintillometer. J Astrophys Astr 2006, 27(2-3), 315-20.

Index of scintillation measurement is a good parameter to compare different sites for image quality or `seeing'. 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. Also 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). Discusses the instrumentation and present the initial results.

3 illus, 5 ref

021153   Gosain S;Venkatakrishnan;Venugopalan K (NO, Udaipur Solar Observatory, P.O. Box 198, Dewali, Bari Road, Udaipur-313 001, Email: sgosain@prl.res.in) : Design and status of solar vector magnetograph (SVM-I) at Udaipur Solar Observatory. J Astrophys Astr 2006, 27(2-3), 285-92.

Presents the status of the instrument called Solar Vector Magnetograph Phase-I (SVM-I) currently being developed at Udaipur Solar Observatory. SVM-I is an instrument which aims to determine the magnetic field vector in the solar atmosphere by measuring Zeeman induced polarization across the spectral line. The instrument is currently in a preliminary development stage, with all components under an evaluation process. The integration of components is being done. The integrated performance of the system on a tracking mount and its control software is being tested. Some test observations of sunspots has been carried out. Gives a technical description of the hardware and software elements of the instrument and present the polarized images obtained during test observations.

5 illus, 8 ref

021152   Gopalswamy N (NO, NASA Goddard Space Flight Centre, Greenbelt, MD 20771, USA, Email: gopals@ssedmail.gsfc.nasa.gov) : Coronal mass ejections of soalr cycle 23. J Astrophys Astr 2006, 27(2-3), 243-54.

Summarize the statistical, physical, and morphological properties of coronal mass ejections (CMEs) of solar cycle 23, as observed by the Solar and Heliospheric Observatory (SOHO) mission. The SOHO data is by far the most extensive data, which made it possible to fully establish the properties of CMEs as a phenomenon of utmost importance to Sun-Earth connection as well as to the heliosphere. It also discusses various subsets of CMEs that are of primary importance for their impact on Earth.

6 illus, 30 ref

021151   Choudhuri A R (Physics Dep, Indian Institute of Science, Bangalore-560 012, Email: arnab@physics.iisc.ernet.in) : Some recent developments in solar dynamo theory. J Astrophys Astr 2006, 27(2-3), 79-85.

Discusses the current status of solar dynamo theory and describe the dynamo model developed by the group. The toroidal magnetic field is generated in the tachocline by the strong differential rotation and rises to the solar surface due to magnetic buoyancy to create active regions. The decay of these active regions at the surface gives rise to the poloidal magnetic field by the Babcock-Leighton mechanism. This poloidal field is advected by the meridional circulation first to high latitudes and then down below to the tachoc1ine. Dynamo models based on these ideas match different aspects of observational data reasonably well.

2 illus, 32 ref

021150   Chatterjee P (Physics Dep, Indian Institute of Science, Bangalore-560 012, Email: piyali@physics.iisc.ernet.in) : Helicity of solar active regions from a dynamo model. J Astrophys Astr 2006, 27(2-3), 87-91.

Calculates helicities of solar active regions based on the idea that poloidal flux lines get wrapped around a toroidal flux tube rising through the convection zone, thereby giving rise to the helicity. Uses the solar dynamo model based on the Babcock-Leighton α-effect to study how helicity varies with latitude and time.

3 illus, 13 ref

021149   Bhatnagar A (NO, Udaipur Solar Observatory, Physical Research Laboratory, Udaipur-313 001, Email: arvind@prl.ernet.in ) : Why study the Sun?. J Astrophys Astr 2006, 27(2-3), 59-78.

Describes the Sun through large number of illustrations and pictures of the Sun taken from early times to the present day space missions. The importance of the study of the Sun is emphasized as it is the nearest star which presents unparallelled views of surface details and numerous phenomena. Our Sun offers a unique celestial laboratory where a large variety of phenomena take place, ranging in temporal domain from a few milliseconds to several decades, in spatial domain from a few hundred kilometers to thousands of kilometers, and in the temperature domain from a few thousand degrees to several million degrees. Its mass motion ranges from thousandths to thousands of kilometers per second. Such an object provides us with a unique laboratory to study the state of matter in the Universe. The existing solar ground-based and space missions have already revealed several mysteries of the outer environment of our Sun and much more is going to come in the near future from planned new sophisticated ground-based solar telescopes and Space missions. The new technique of helioseismology has unravelled many secrets of the solar interior and has put the Standard Solar Model (SSM) on firm footing. The long-standing problem of solar neutrinos has been recently sorted out, and even the `back side' view of the Sun can be seen using the technique of holographic helioseismology.

24 illus, 3 ref

021148   Barauddin (Physics Dep, Algarh Muslim University, Aligarh-202 002, Email: badr_phys@yahoo.co.in) : Transient perturbations and their effects in the heliosphere, the geo-magnetosphere, and the earth's atmosphere: space wealth perspective. J Astrophys Astr 2006, 27(2-3), 209-17.

Discusses the effects of certain dynamic features of space environment in the heliosphere, the geo-magnetosphere, and the earth's atmosphere. In particular, transient perturbations in solar wind plasma, interplanetary magnetic field, and energetic charged particle (cosmic ray) fluxes near I AU in the heliosphere have been discussed. Transient variations in magnetic activity in geo-magnetosphere and solar modulation effects in the heliosphere have also been studied. Emphasis is on certain feaªtures of transient perturbations related to space weather effects. Relationships between geomagnetic storms and transient modulations in cosmic ray intensity (Forbush decreases), especially those caused by shock-associated interplanetary disturbances, have been studied in detail. Aanalysed the cosmic ray, geomagnetic and interplanetary plasma/field data to understand the physical mechanisms of two phenomena namely, Forbush decrease and geomagnetic storms, and to search for precursors to Forbush decrease (and geomagnetic storms) that can be used as a signature to forecast space weather. It is shown that the use of cosmic ray records has practical application for space weather predictions. Enhanced diurnal anisotropy and intensity deficit of cosmic rays have been identified as precursors to Forbush decreases in cosmic ray intensity. It is found that precursor to smaller (less than 5%) amplitude Forbush decrease due to weaker interplanetary shock is enhanced diurnal anisotropy. However, larger amplitude (greater than 5%) Forbush decrease due to stronger interplanetary shock shows loss cone type intensity deficit as precursor in ground based intensity record. These precursors can be used as inputs for space weather forecast.

4 illus, 21 ref

021147   Asai A;Yokoyama T;Shimojo M;Masuda S;Shibata K (NO, Nobeyama Solar Radio Observatory, Minamisaku, Nagano, 384-1305, Japan, Email: asai@nro.nao.ac.jp) : Flare ribbon expansion and energy release. J Astrophys Astr 2006, 27(2-3), 167-73.

Reports a detailed examination about the relationship between the evolution of the Hα flare ribbons and the released magnetic energy during the April 10 2001 flare. In the Hα images, several bright kernels are observed in the flare ribbons. Identified the conjugated footpoints, by analyzing the lightcurves at each Hα kernels, and showed their connectivities during the flare. Then, based on the magnetic reconnection model, calculated quantitatively the released energy by using the photospheric magnetic field strengths and separation speeds of the Hα flare ribbons. Finally, examined the downward motions which are observed at the Hα kernels. Founds that the stronger the red-asymmetry tends to be associated with the brighter the Hα kernel.

4 illus, 14 ref

021146   Ambastha A (NO, Udaipur Solar Observatory, Physical Research Laboratory, Udaipur-313 001, Email: ambastha@prl.res.in ) : Photospheric, chromospheric and helioseismic signatures of large flare in super-active region NOAA 10486. J Astrophys Astr 2006, 27(2-3), 255-65.

NOAA 10486 produced several powerful flares, including the 4B/X 17.2 superflare of October 28, 2003/ 11: l0 UT. This flare was extensively covered by the Hα and GONG instruments operated at the Udaipur Solar Observatory (USO). The central location of the active region on October 28. 2003 was well-suited for the ring diagram analysis to obtain the 3-D power spectra and search for helioseismic response of this large flare on the amplitude, frequency and width of the p-modes. Further, using USO observations, identified the sites of new flux emergences, large proper motions and line-of-sight velocity flows in the active region and their relationship with the flare.

7 illus, 50 ref

021145   Ali S S;Uddin W;Chandra R (NO, Aryabhatta Research Institute of Observational Sciences (ARIES), Manora Peak, Nainital-263 129, Email: salman@aries.ernet.in) : Large helical eruptive prominence associated with double CME on 21 April 2001. J Astrophys Astr 2006, 27(2-3), 347-52.

Presents a preliminary analysis of a helical eruptive prominence at the east limb of the Sun on 21 April 200 I. Unusually this eruption is associated with a double CME. Tried to study the morphology of the event, energy budget of the prominence and associated CMEs. The analysis shows that the prominence and first CME started simultaneously from the limb and prominence carries sufficient energy to feed both the CMEs. Moreover, it is also concluded that CMEs are magnetically driven and internally powered.

3 illus, 12 ref

020184   Papadopoulos N J;Caranicolas N D (Phys Dep, Sect of Astrophys, Astronomy and Mechanics, Univ of Thessaloniki, 541 24, Thessaloniki, Greece, Email: caranic@astro.auth.gr) : Report on the dynamical evolution of an axially symmetric quasar model. J Astrophys Astr 2006, 27(4), 389-97.

The role of the angular momentum in the regular or chaotic character of motion in an axially symmetric quasar model is examined. It is found that, for a given value of the critical angular momentum Lzc, there are two values of the mass of the nucleus Mn for which transition from regular to chaotic motion occurs. The [Lzc-Mn] relationship shows a linear dependence for the time independent model and an exponential dependence for the evolving model. Both cases are explained using theoretical arguments together with some numerical evidence. The evolution of the orbits is studied, as mass is transported from the disk to the nucleus. The results are compared with the outcomes derived for galactic models with massive nuclei.

7 illus, 10 ref

020183   Oza S R;Singh R P;Dadhwal V K;Desai P S (Space Applications Centre (ISRO), , Ahmedabad-380 015, Email: Sandipoza@sac.isro.gov.in) : Large area soil moisture estimation and mapping using space-borne multi-frequency passive microwave data. J Indian Soc Remote Sens 2006, 34(4), 343-50.

Reports the estimation of surface soil moisture (SM) using surface wetness Index (SWI) retrieved from multi-frequency passive microwave radiometer. A change detection algorithm was followed which transforms SWI variations in to SM variations using per pixel soil property of field capacity and air-dry status. Estimated soil moisture was compared with the point measurements made at the Monmouth and De Kalb sites of Illinois (USA) for the validation. Sensitivity of the SWI to the variations of rainfall at various. vegetation fractions is analyzed. RMS error of volumetric soil moisture is found to be in the range of 6.35 to 8.85%. The method works well up to the vegetation fraction of 40%. Applications of the technique are demonstrated by the spatio-temporal analysis of estimated soil moisture maps for India. Characteristic increase in soil moisture was observed with the progress of monsoon from 25 to 32 week in northern India and 46 to 52 week in the costal parts of Tamil Nadu in south.

4 illus, 19 ref

020182   Mukherjee U;Raichur H;Paul B;Naik S;Bhatt N (NO, Tata Inst of Fundamental Res, Homi Bhabha Road, Colaba, Mumbai-400 005, Email: uddipan@mailhost.tifr.res.in) : Orbital evolution and orbital phase resolved spectroscopy of the HMXB pulsar 5U 1538-52 with RXTE-PCA and BeppoSAX. J Astrophys Astr 2006, 27(4), 411-23.

Reports results from detailed timing and spectral studies of the high mass X-ray binary pulsar 4U 1538-52 over several binary periªods using observations made with the Rossi X-ray Timing Explorer (RXTE) and BeppoSAX satellites. Pulse timing analysis .with the 2003 RXTE data over two binary orbits confirms an eccentric orbit of the system. Combining the orbital parameters determined from this observation with the earlier measurements we did not find any evidence of orbital decay in this X-ray binary. Carried out orbital phase resolved spectroscopy to meaªsure changes in the spectral parameters with orbital phase, particularly the absorption column" density and the iron line flux. The RXTE-PCA spectra in the 3-20 keV energy range were fitted with a power law and a high energy cut-off alongwith a Gaussian line at <126> 6.4 keV, whereas the BeppoSAX spectra needed only a power law and Gaussian emission line at <126> 6.4 ke V in the restricted energy range of 0.3-10.0 ke V. An absorption along the line of sight was included for both the RXTE and BeppoSAX data. The variation of the free spectral parameters over the binary orbit was investigated and we found that the variation of the column density of absorbing material in the line of sight with orbital phase is in reasonable agreement with a simple model of a spherically symmetric stellar wind from the companion star.

7 illus, 31 ref

020181   Jain P;Sarala S (Phys Dep, Indian Inst of Technol, Kanpur-208 016) : Interpretation of the global anisotropy in the Radio Polarizations of Cosmologically distant sources. J Astrophys Astr 2006, 27(4), 443-54.

Presents a detailed statistical study of the observed anisotropy in radio polarizations from distant extragalactic objects. This anisotropy was earlier found by Birch (1982) and reconfirmed by Jain and Ralston (1999) in a larger data set. A very strong signal was seen after imposing the cut <157> R M - R M <157> <62> 6 rad/m<^>2, where RM is the rotation measure and R M its mean value. Show that there are several indications that this anisotropy cannot be attributed to bias in the data. Also finds that a generalized statistic shows a very strong signal in the entire data without imposing the R M dependent cut. Finally argues that an anisotropic background pseudoscalar field can explain the observations.