018304   Ambastha A (Udaipur Solar Observatory, Physical Research Laboratory, , Udaipur-313 001, Email: ambastha@prl.ernet.in) : Helioseismic effects of energetic transients. J Astrophys Astr 2008, 29(1-2), 93-101.

Photospheric and chromospheric signatures related to large, energetic transients such as flares and CMEs, have been extensively reported during the last several years. In addition, energetic solar transients are expected to cause helioseismic effects. Some of the recent results are reviewed here; in particular, the helioseismic effects of the powerful flares in superactive region, NOAA 10486, including the 4B/X17 superflare of October 28, 2003. We also examine the temporal variations of power in low-l modes during the period May 1995-October 2005, and compare with daily, disk-integrated flare- and CME-indices to infer the effect of transients on the scale of whole solar disk.

6 illus, 33 ref

018303   Aggarwal M;Jain R;Mishra A P;Kulkarni P G; Vyas C;Sharma R;Gupta M (NO, Physical Rersearch Laboratory, Navrangpura, Ahmedabad-380 009) : X-ray emission characteristics of flares associated with CMEs. J Astrophys Astr 2008, 29(1-2), 195-205.

Present the study of 20 solar flares observed by "Solar X-ray Spectrometer (SOXS)" mission during November 2003 to December 2006 and found associated with coronal mass ejections (CMEs) seen by LASCO/SOHO mission. In this investigation, X-ray emission characteristics of solar flares and their relationship with the dynamics of CMEs have been presented. We found that the fast moving CMEs, i.e., positive acceleration are better associated with short rise time (< 150 s) flares. However, the velocity of CMEs increases as a function of duration of the flares in both 4.1-10 and 10-20 keV bands. This indicates that the possibility of association of CMEs with larger speeds exists with long duration flare events. We observed that CMEs decelerate with increasing rise time, decay time and duration of the associated X-ray flares. A total 10 out of 20 CMEs under current investigation showed positive acceleration, and 5 of them whose speed did not exceed 589 km/s were associated with short rise time (< 150s) and short duration (< 1300s) flares. The other 5 CMEs were associated with long duration or large rise time flare events. The unusual feature of all these positive accelerating CMEs was their low linear speed ranging between 176 and 775 km/s. We do not find any significant correlation between X-ray peak intensity of the flares with linear speed as well as acceleration of the associated CMEs. Based on the onset time of flares and associated CMEs within the observing cadence of CMEs by LASCO, we found that in 16 cases CME preceded the flare by 23 to 1786 s, while in 4 cases flare occurred before the CME by 47 to 685 s. We argue that both events are closely associated with each other and are integral parts of one energy release system.

6 illus, 1 table, 27 ref

017326   Sankaran A V (NO, , No.10, P and T Colony, Ist, Cross, II Block, R.T. Nagar, Bangalore-560 032, Email: av.sankaran@gmail.com) : Galactic triggering of geologic events in earth's history. Curr Sci 2008, 95(6), 714-16.

1 illus, 15 ref

010976   Rastogi R G;Chandra H (NO, Physical Research Laboratory, Ahmedabad-380 009) : Space disturbance effect on equatorial sporadic-E during sunrise. Indian J Radio Space Phys 2009, 38(2), 105-11.

The space weather event of 25 September 1998 and its effect in the E-region near magnetic equator has been studied. The geomagnetic H field variations recorded at low latitudes was normal on 24 and 26 September 1998 but there was a geomagnetic storm on 25 September with sudden commencement at 0445 hrs LT (75° EMT). There was a strong counter electrojet after sunrise associated with the magnetic storm. Solar wind speed and ion density and the interplanetary magnetic field (IMF) data show the IMF BZ turning towards south in the morning on 25 September 1998 and solar wind velocity was 850 kms^-1. Quarter hourly ionograms at Thumba, located close to the dip equator were examined during morning hours on 24-26 September 1998. On 24 and 26 September 1998, E-region irregularities (E_s-q) were first generated about an hour after the appearance of fresh E-region ionization following sunrise and by the time ΔH at Trivandrum started increasing above the corresponding value at Alibag. On the disturbed day, 25 September 1998, E_s-q appeared later due to occurrence of counter electrojet after sunrise. This is caused by electric field changes associated with the magnetic storm rather than the late reversal of the electric field in the morning.

006090   Sunil Krishna M V;Vir Singh (Physics Dep, Indian Institute of Technology Roorkee, Roorkee-247 667, Email: virphfph@iitr.ernet.in) : Testing of Solar2000 EUV flux model in 900-1350 Å wavelength range using greenline dayglow emission. Indian J Radio Space Phys 2009, 38(1), 37-41.

The contribution of photodissociation of molecular oxygen to the total volume emission rate of greenline dayglow emission at 5577 Å is modelled in the study. The Solar EUV radiation fluxes for modelling are obtained from the Solar2000 V 2.25 model. The modelling has been done in the altitude range 92-105 km, where photodissociation and three body recombination are main contributing processes to greenline dayglow emission. The present results are discussed in the light of Wind Imaging Interferometer (WINDII) observations of greenline dayglow emission in the altitude range 92-105 km. It is found that the Solar2000 V2.25 flux model gives better agreement with the WINDII observations especially in the range 92-96 km where earlier models predicted a very low emission rate. In the mesospheric emission peak region, present results are higher than the measurements and this discrepancy may possibly be attributed to higher values of solar fluxes for those spectral lines which are main sources of production of greenline dayglow emission. The present study suggests the re-examination of Solar2000 flux model at least for those spectral lines which are the main sources of greenline dayglow emission in mesospheric emission peak region.

006089   Shukla A K;Shinghal P;Sivaraman M R; Bandyopadhyay K (NO, SATCOM & IT Applications Area, Space Applications Centre, ISRO, Ahmedabad-380015, Email: ashishs@sac.isro.gov.in) : Comparative analysis of the effect of ionospheric delay on user position accuracy using single and dual frequency GPS receivers over Indian region. Indian J Radio Space Phys 2009, 38(1), 57-61.

The ionosphere acts as a prominent source of range errors for users of Global Positioning System (GPS) satellite signals requiring accurate position determination. Various models and mathematical formulations have been devised to calculate the absolute range error caused due to ionospheric delay. The present study aims at comparing two methods for calculating delay due to ionosphere: (i) using grid based model at L1 carrier frequency with bilinear interpolation technique; and (ii) using pseudo-range measurements at both L1 and L2 carrier frequency. For analyzing the effect of ionospheric delay on the seasonal behaviour of positional accuracy, a quantitative analysis has been done for all quiet days (Ap index < 50) in 2005 using GPS data for International GNSS Service (IGS) Bangalore (IISc) receiver in January, March and June. Various corrections such as satellite clock bias, transit time, ionospheric delay corrections, etc. are applied to pseudo-ranges to calculate the user coordinates. For single frequency (L1) receivers, ionospheric delay corrections have been applied using IGS total electron content data derived from grid based ionospheric model; and for the dual frequency receivers, pseudo-range measurements at L1 and L2 carrier frequencies have been used. It has been observed that there is an improvement of 1-4 m in the standard deviation of position errors when the ionospheric delay correction is applied using pseudo-range measurements at L1 and L2 frequencies (dual frequency receiver) as compared to L1 frequency only. It has also been observed that some residual errors still remain in the estimated user position even after using dual frequency receivers.

006088   Pan C J;Brahmanandam P S (Institute of Space Science, National Central University, Chung-Li 32054, Taiwan, R.O.C, Email: cjpan@jupiter.ss.ncu.edu.tw) : Range rate variation studies of the low-altitude quasi-periodic radar echoes during SEEK-2 campaign. Indian J Radio Space Phys 2009, 38(1), 50-6.

The first experimental evidence on range rate reversal of lowaltitude quasi-periodic (LQP) echoes from nighttime midlatitude sporadic E region with systematic characteristics in their occurrences for the echoes observed during SEEK- 2 (Sporadic-E Experiment over Kyushu) campaign with 24.515 MHz frequency agile radar located at Tanegashima in southern Japan (30.75°N, 130.03°E, geomagnetic latitude 20.97°N, dip angle 43.2°N) is presented. Four reversal cases of LQP echoes are found during the observation period. The reversal times of these echoes from positive QP to negative QP are found between 2000 and 2400 hrs LT and negative QP to positive QP around 0200 hrs LT. Besides, Doppler velocities associated with these echoes show preferential directions meaning that they are consistent with the sign of range rate of QP echoes in most cases. As the backscatter echoes studied are confined to the collision dominated lower E region and semi-diurnal tide is most pronounced at latitude higher than 30°, large-period neutral winds such as tidal and planetary waves in addition to atmospheric gravity waves play a role in the generation and control of these backscatter echoes.

006087   Kazimirovsky E S;Vergasova G V (NO, Institute of Solar-Terrestrial Physics, Russian Academy of Sciences (, Post Box 4026, 664033, Irkutsk, Russia, Email: ekazimirovsky@yandex.ru) : Mesospheric, lower thermospheric dynamics and external forcing effects: a review. Indian J Radio Space Phys 2009, 38(1), 7-36.

Presents some of the most important experimental results and models obtained by international scientific community during last decade for the mesospheric and lower thermospheric dynamics (mean winds, planetary waves, tides and internal gravity waves). In addition to climatological features, the external forcing - the coupling from below (stratosphere) and possible influence of solar and geomagnetic activity on the dynamical processes at this region are presented.

006086   Brahmanandam P S;Pan C J;Lee C C;Tsai W C (Institute of Space Science, National Central University, Chung- Li 32054, Taiwan, Email: cjpan@jupiter.ss.ncu.edu.tw) : E-region irregularity observed by the Tanegashima Frequency Agile Radar during SEEK-2 campaign. Indian J Radio Space Phys 2009, 38(1), 42-9.

Reports the nighttime field-aligned plasma irregularity (FAI) at 6.1 m in E-region during SEEK-2 (Sporadic E Experiment over Kyushu) campaign during July-August 2002 using Tanegashima (30.75°N, 131.03°E, geomagnetic 20.97°N, dip 43.2°N) Frequency Agile Radar (FAR) operated at 24.515 MHz. According to the characteristics of radar echo, the echoes are classified into four types: negative quasi-periodic (NQP) echo; positive quasi-periodic (PQP) echo; continuous echo; and undefined echo. A study shows that FAI appear generally at 80-110 km altitudes during 1800-0400 hrs LT, and FAI occur most frequently at 2200 hrs LT. Further, among the four different echo types, the occurrence probability of NQP is greater than other types.

004125   Dwivedi B N (Applied Physics Dep, Institute of Technology, Banaras Hindu university, Varanasi-221 005, Email: bholadwivedi@gmail.com) : Hinode probes the sun's mysteries. Curr Sci 2008, 94(5), 562-4.

Investigating the interaction of the Sun's magnetic field with its outer atmosphere, the Hinode spacecraft, with three telescopes on-board, is probing some of the Sun's outstanding riddles; Why a hot corona exists and how it is heated? What drives explosive events such as solar flares and coronal mass ejections; What creates the Sun's magnetic field? Hinode's 'detection of Alfven waves' opens a new era in unlocking the secrets of the Sun.

^ssc5 illus, 9 ref

002085   Sharaf M A;Sharaf A A (Astronomy Dep, Faculty of Science, King Abdul Aziz Univ, Jeddah, Saudi Arabia) : Data analysis of the mean atmospheric co₂ 1959-2005. Bull pure appl Sci-Sect D 2008, 27(1), 37-46.

An accurate and full data analysis of the monthly mean atmospheric CO₂ since 1959 to 2005 was devolved. The results show that, there is no any doubt that the atmospheric CO, increases with the time. so our planet is getting warmer. The precision criteria of the analysis are very satisfactory and was support graphically and computationally by many tests.

5 illus, 3 tables, 6 ref

002084   Namboodiri P M S (NO, Indian Institute of Astrophysics, Bangalore-560 034, Email: pmsn@iiap.res.in) : Some properties of merger remnants of interacting galaxies modeled as n = 4 polytrope. Bull Astr Soc India 2008, 36(1), 65-76.

Galaxies interact in a multitude of ways with their environment. Such interactions can alter the morphological type of galaxies, trigger star formation and even produce active galactic nuclei. One of the important parameter in a galaxy collision is the impact parameter. Numerical simulations have been performed to study the effect of changing the impact parameter in a galactic collision. The initial density distribution in the galaxy corresponds that of a polytrope of index n = 4. The galaxy model does not include the dark matter halo component and therefore is not expected to mimic all properties of a real galaxy. Both merging and non-merging collisions of equal mass galaxies have been studied to see where the transition occurs between these two processes. Merging occurs when the closest approach distance of the galaxies is less than three times its half-mass radius. The merging time increases with the distance of closest approach. The density profiles of the merger remnants follow a r^1/4 law in the inner parts and deviate from it in the outer regions. Distant encounters do not result in merging and the galaxies remain almost intact with only negligible change in its mass and internal energy.

4 illus, 1 table, 25 ref

002083   Mahdi B (NO, Inter Univ Center for Astronomy & Astrophysics, Post Bag 4, Ganeshkhind, Pune-411 007, Email: mahdi@iucaa.ernet.in) : Automated classification of ELODIE stellar spectral library using probabilistic articial neural networks. Bull Astr Soc India 2008, 36(1), 1-54.

A Probabilistic Neural Network model has been used for auto-mated classification of ELODIE stellar spectral library consisting of about 2000 spectra into 158 known spectro-luminosity classes. The full spectra with 561 flux bins and a PCA reduced set of 57, 26 and 16 components have been used for the training and test sessions. The results show a spectral type classification accuracy of 3.2 sub-spectral type and luminosity class accuracy of 2.7 for the full spectra and an accuracy of 3.1 and 2.6 respectively with the PCA set. This technique will be useful for future upcoming large databases and their rapid classification.

5 illus, 7 tables, 14 ref

002082   Chandra S;Shinde S V (School of Physical Sciences, S.R.T.M. Univ, Nanded-431 006) : Anomalous absorption in rhomboidal SiC₃ molecules. Bull Astr Soc India 2008, 36(1), 55-63.

Laboratory detection of two isomers of cyclic SiC₃ molecule have been reported by McCarthy et al. (1999a, 1999b) and Apponi et al. (1999b). Seven transitions of the isomer-I have been detected in IRC+10216 by Apponi et al. (1999a). However, to date, the second isomer is not detected in the interstellar space. Proposes identification of isomer-I through the transition 4₂₂ - 4₂₃ at 0.2 GHz and of isomer-II through the transitions 2₂₀-2₂₁ at 4.44 GHz and 4₄₀-4₄₁ at 2.16 GHz, in absorption against the cosmic microwave background (CMB). In absence of the availability of the collisional rates, we have used scaled values for them. Checkes the sensitivity of the lines on the rates by enhancing the rates for transitions with Δk_a = 0 by a factor of 10 and the results are not found sensitive.

4 illus, 11 ref

002081   Aggarwal P C;Sreekantan B V;Bhandari N (NO, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai-400 012, Email: pagrawal@tifr.res.in) : Space astronomy and interplanetary exploration. Curr Sci 2007, 93(12), 1767-78.

Brief overview of Indian contributions to space astronomy and planetary studies, mainly through the satellite-borne experiments is presented. Some important results obtained in X-ray and low energy gamma-ray astronomy are summarized. Highlights of the salient results from lunar explorations are discussed. Important features of the Indian multi-wave length astronomy satellite, Astrosat and expected science from it are described. Details of the Chandrayaan-1 mission and studies initiated by the Indian Space Research Organizartion aimed at various aspects of lunar science are presented.

6 illus, 2 tables, 31 ref

001040   Santosh Kumar;Simranjit Kaur (Physics and Electronics Dep, Rani Durgawati University, Jabalpur-482 001, Email: s_kumar123@rediffmail.com) : Geo-effective transients and their solar causes during solar cycle 23. Indian J Radio Space Phys 2008, 37(6), 379-85.

During nine-year period of the current solar cycle 23 from July 1996 to January 2005, geomagnetic storms (GMSs) of Intense if (Dst < -100nT), Major if (-50nT ≥ Dst ≥ -100nT) and Minor if (-20nT ≥ Dst ≥ -50nT) have been investigated. It is observed that maximum number of GMSs are associated with coronal mass ejections (CMEs) followed by individual Hα and X-ray solar flare events. When accumulated effect of Hα and X-ray solar flare events are considered, these solar flares are better associated with GMSs than CMEs. A significant decline in the number of Intense and Minor GMSs have been observed from 1998 to 1999, however, there is an increase in Major GMSs. On the contrary, during 1997-98, Intense and Minor GMSs have increased with the ascending phase of solar activity and Major GMSs have decreased. It is observed that an overall northern bias apparently prevails for solar flares and active prominences and disappearing filaments. Hα and X-ray solar flares occurring over the western limb of the solar disk cause larger disturbances in magnetosphere leading to occurrence of Intense GMSs, whereas, solar flares occurring on eastern limb of the solar disk lead to occurrence of Major and Minor GMSs. It is observed that coronal intensity (CI) is maximum for Minor GMSs followed by Major and Intense GMSs, whereas, mean CI is maximum for Intense GMSs followed by Major and Minor GMSs. The results show that the product of solar wind velocity (Vsw) with minimum Bz component (Bz_min) of interplanetary magnetic field (Vsw.Bz_min), product of linear velocity of CMEs (Vcme) with Bz_min (Vcme.Bz_min) along with minimum Dst of the sudden storm commencement day are the reliable indicators of intensity of GMSs.

001039   Sanalkumaran Nair V;Prabhakaran Nayar S R (Physics Dep, V T M N S S College, Dhanuvachapuram, Thiruvananthapuram-695 503, Email: sanalkumar.nair@yahoo.co.in) : North-South asymmetry in solar wind & geomagnetic activity and its solar cycle evolution. Indian J Radio Space Phys 2008, 37(6), 391-5.

The unequal distribution of various aspects of solar activity between the north and south hemisphere of the Sun is well known for over a century. Analysis of solar wind data observed during 1964 - 2004 showed that solar wind velocity (V_sw), interplanetary magnetic field (IMF) B_z component and geomagnetic activity index (A_p) exhibit a clear heliospheric north-south asymmetry. In general, amplitude of the north-south asymmetry is maximum during the minimum phase of solar cycle. For V_sw and IMF B_z component, amplitude of the asymmetry is greater during even cycles 20 and 22 compared to the odd cycles 21 and 23. The phase of the asymmetry of IMF B_z reverses every cycle with a northern dominance in even cycles and southern dominance in odd cycles. The asymmetry of V_sw has a northern dominance during cycles 20 and 23 and southern dominance during cycles 21 and 22. Thus, for V_sw, the amplitude of the asymmetry and IMF B_z, both the amplitude and phase exhibit a 22-year period. The asymmetry of A_p index appears similar to that of solar wind velocity. The asymmetry in solar wind velocity and geomagnetic activity may be due to the existence of a relic solar magnetic field in the solar convection zone.

001038   Pande S;Pande B;Uddin W;Pandey K (Physics Dep, DSB Campus, Kumaun University, Nainital-263 002, Email: pandebimal@yahoo.co.in) : Hα, EUV and UV analysis of an eruptive 3B/X1.2 flare. Indian J Radio Space Phys 2008, 37(6), 386-90.

The observational results of an extremely energetic eruptive flare 3B/X1.2 from superactive region NOAA 10486. The observations were taken on 26 October 2003 with 15 cm Solar Tower Telescope at Aryabhatta Research Institute of Observational Sciences (ARIES). Hα observations of the flare show long multi ribbon eruptions along a large twisted (sigmoid) filament in a high gradient (~90°) magnetic field and shear. The evolution pattern of this flare is similar in EUV and UV. Four eruptive centers or kernels in Hα have been chosen, wherein K₁ shows two prominent peaks while K₃ exhibits only one prominent peak with gradual decay. The analysis shows that this is a classical long duration event (LDE). The results have been discussed in the light of existing theories.

000114   Senovilla J M M (Fisica Teorica, Universidad del Pais Vasco, Apartado 644, 48080 Bilbao, Spain) : A singularity theorem based on spatial averages. Pramana J Phys 2007, 69(1), 31-47.

Inspired by Raychaudhuri's work, and using the equation named after him as a basic ingredient, a new singularity theorem is proved. Open non-rotating Universes, expanding everywhere with a non-vanishing spatial average of the matter variables, show severe geodesic incompletness in the past. Another way of stating the result is that, under the same conditions, any singularity-free model must have a vanishing spatial average of the energy density (and other physical variables). This is very satisfactory and provides a clear decisive difference between singular and non-singular cosmologies.

53 ref

000113   Pandya M R;Singh R P;Chaudhari K N;Murali K R;Kirankumar A S;Dadhwal V K;Parihar J S (Space Applications Centre, Indian Space Research Organication, Ahmedabad-380 015, Email: mrpandya@sac.isro.gov.in) : Spectral characteristics of sensors onboard IRS-1D and P6 satellites: estimation and their influence on surface reflectance and NDVI. J Indian Soc Remote Sens 2007, 35(4), 333-50.

Reports the results of a modeling study carried out with two objectives, (1) to estimate and compare effective spectral characteristics (central wavelength, bandwidth and bandpass exo-atmospheric solar irradiance E₀) of various spectral channels of LISS-II1, WiFS, LISS-III*, LISS-IV and AWiFS onboard Indian Remote Sensing Satellites IRS-1D and P6 using moment method based on the laboratory measurements of sensor spectral response, and (2) to quantify the influence of varying sensor spectral response on reflectance and Normalized Difference Vegetation Index (NDVI) measurements using surface reflectance spectra corresponding to different leaf area index conditions of crop target obtained through field experiment. Significant deviation of 4 to 14 nm in central wavelength and 1.6 to 14.07 nm in spectral width was observed for the corresponding channel of IRS sensors. Coefficient of variation of the order of 0.1 to 1.11% was noticed in E₀ among various IRS sensors, which could induce a difference of 0.72 to 3.35% in the estimation of top of atmosphere reflectance for crop target. The variation in spectral response of IRS sensors implied a relative difference of the order of 0.91 to 3.38% in surface reflectance and NDVI measurements. Polynomial approximations are also provided for spectral correction that can be utilized for normalizing the artifacts introduced due to differences in spectral characteristics among IRS sensors.

9 illus, 5 tables, 28 ref

000112   Mukku C ;Mahajan S M;Bambah B A (NO, International Institute of Information Technology, Hyderabad-500 032) : On a Raychaudhuri equation for hot gravitating fluids. Pramana J Phys 2007, 69(1), 137-45.

Generalises- the Raychaudhuri equation for the evolution of a self gravitating fluid to include an Abelian and non-Abelian hybrid magneto fluid at a finite temperªature. The aim is to utilise this equation for investigating the dynamics of astrophysical high temperature Abelian and non-Abelian plasmas.

9 ref

000111   Kar S;Sengupta S (Physics and Centre for Theoretical Studies Dep, Indian Institute of Technology, Kharagpur-721 302) : Raychaudhuri equations: a brief review. Pramana J Phys 2007, 69(1), 49-76.

Bbrief review on the Raychaudhuri equations has been presented. Beginning with a summary of the essential features of the original article by Raychaudhuri and subsequent work of numerous authors, are moved on to a discussion of the equations in the context of alternate non-Riemannian space times as well as other theories of gravity, with a special mention on the equations in space times with torsion (Einstein-Cartan-Sciama-Kibble theory). Finally, gives an overview of some recent applications of these equations in general relativity, quantum field theory, string theory and the theory of relativisitic membranes.

89 ref

000110   Gupta K K;Gupta R (Instrumentation Group, B.I.T.S., Pilani-333 031, Email: kgupta@bits-pilani.ac.in) : Algorithm for road enhancement in sar images using wavelet transform. J Indian Soc Remote Sens 2007, 35(4), 361-7.

^ssc3 illus, 2 tables, 14 ref

000109   Ellis G F R (Mathematics Dep, University of Cape Town, Rondebosch, Cape Town, South Africa, Email: Ellis@MATHS.uct.ac.za) : On the raychaudhuri equation. Pramana J Phys 2007, 69(1), 15-22.

The Raychaudhuri equation is central to the understanding of gravitational attraction in astrophysics and cosmology, and in particular underlies the famous singularity theorems of general relativity theory. Reviews the derivation of the equation, and its significance in cosmology.

11 ref

000108   Dadhich N (NO, Inter-University Centre for Astronomy and Astrophysics, Post Bag 4, Pune-411 007, Email: nkd@iucaa.ernet.in) : Singularity: Raychaudhuri equation once again. Pramana J Phys 2007, 69(1), 23-9.

Recounts Raychaudhuri's deep involvement with the singularity problem in general relativity. Argues that precisely the same situation has arisen today in loop quantum cosmology as obtained when Raychaudhuri discovered his celebrated equation. A new analogue of the Raychaudhuri equation in quantum gravity is needed.

30 ref