Study of two-stage coronal jet associated with a C1.4 class solar flare     

R. Solanki  A. K. Srivastava  B. N. Dwivedi 《Astrophysics and Space Science》2018,363(11):233

We study an active region coronal jet that evolved from southward of a major sunspot of NOAA AR12178 on 04 October 2014. This jet is associated with an onset of the GOES C1.4 flare. We use SDO/AIA, SDO/HMI, GONG \(H\upalpha\) and GOES data for analysing the observed event. We term this jet as a two-stage confined eruption of the plasma. In the first stage, some plasma erupts above the compact flaring region. In the second stage, this eruptive jet plasma and associated magnetic field lines interact with another set of distinct magnetic field lines present in its south-east direction. This creates an X-point region, where the second stage of the jet eruption is deflected above it on a curvilinear path into overlying corona. The lower part of the jet is followed by a cool surge eruption, which is visible only in \(H{\upalpha}\) emissions. The magnetic flux cancellation at the footpoint causes the triggering of C-class flare eruption. This flare energy release further triggers first stage of the coronal jet eruption. The second stage of the jet eruption is a consequence of an interaction of two distinct sets of magnetic field lines in the overlying corona. The first stage of the coronal jet and co-spatial but lagging cool surge may have common origin due to the reconnection generated heating pulses. This complex evolution of the coronal jet involves flare heating induced first stage plasma eruption, guiding of jet’s material above a junction of two distinct sets of field lines in the corona, and intra-relationship with cool surge. In effect, it imposes rigid constraints on the existing jet models.  相似文献   

Lichen as quantitative biomonitors of atmospheric heavy metals deposition in Central India     

Rajesh Bajpai  D. K. Upreti  S. K. Dwivedi  S. Nayaka 《Journal of Atmospheric Chemistry》2009,63(3):235-246

Three different growth forms of lichens belonging to six species; Phaeophyscia hispidula, Parmotrema praesorediosum (foliose); Caloplaca subsoluta, Diploschistes candidissmus (crustose) and Peltula euploca, Phylliscum indicum (squamulose) were studied comparatively for the biomonitoring of Al, Cd, Cr, Cu, Fe, Ni and Zn in Mandav city in central India. Based on the anthropogenic activities three sites were selected for lichen collection. To identify the sources of heavy metal pollution, their concentration was analyzed in thallus as well as in their respective substrates. The thallus of studied lichens showed higher concentration of metals such as Cd, Cr, Ni and Zn, while most of the metals were absent or present in negligible amount in substrates (Fe, Al, Cu), which proves that the accumulated metals were air borne. The foliose lichens (P. hispidula and P. praesorediosum) found highly significant in metal accumulation at each sites followed by crustose and squamulose forms. Lichen samples collected from site 2, adjacent to road side accumulated maximum quantities of Zn, Ni, Cd and Cr whereas the city centre (Site 1) had maximum concentrations of Fe, Cu and Al. The site 3 situated away from the city had lowest amount of all the metals. The analysis of variance and LSD indicated that the metal concentrations among lichen species as well as between substratum is significant at p < 0.05% and P < 0.01% level respectively.  相似文献   

Petrology and geochemistry of metapelites and basic granulites from Sonapahar region of Shillong Meghalaya gneissic complex, North East India     

S. B. Dwivedi  K. Theunuo 《Journal of the Geological Society of India》2013,81(6):755-766

The geochemistry of the metapelites and basic granulite of Sonapahar has been studied in order to assess the nature of the protolith and their likely tectonic environment. Metapelites contains SiO₂ (av. 62.16wt %), K₂O+Na₂O (av. 4.57 wt%), Al₂O₃ (av. 16.69 wt%), MgO (av. 5.31 wt%), Mg# av. 0.60 and low TiO₂ (av. 0.68 wt%) with low Y (av. 23.48 ppm) and Yb (av. 1.6 ppm) which point to their derivation from andesite source. Metapelites show prominent negative europium anomaly (Eu_N/Eu* = 0.38–0.54) and fractionated LREE to HREE pattern (La_N/Lu_N) 17.23 to 56.69. Basic granulites demonstrate low content of SiO₂ (av50.95 wt%), Al₂O₃ (av13.67 wt%), K₂O (av 0.58 wt%) and enriched in Fe₂O₃ ^t (av 11.42 wt%), MgO (av 7.29 wt%), CaO (av 10.60 wt %), Na₂O (av 2.26 wt%), Mg# av. 0.56 and range from calc-alkaline to tholeiitic in nature. The geochemistry of the metapelites and basic granulites advocate that metapelites are derived from arc related andesitic source due to subduction whereas protoliths of basic granulites was originated in rift related volcanism through diapiric movement of hot rising mantle derived basaltic magmas.  相似文献   

The Utility of Day‐and‐Night Observation and Cloud‐Penetration Capability of ERS‐1 SAR Data for Detection of Wetlands     

R. S. Dwivedi  B. R.M. Rao  S. P.S. Kushwaha 《国际地球制图》2013,28(1):7-12

Abstract

The sensitivity of microwave sensors to changes in the complex dielectric constant of soil/water mix with change in water content has been used in several studies for soil moisture estimation and in the detection of wetlands. In the study, reported here, an attempt has been made to delineate various categories of wetlands, namely ‘bils’ (acquaculture ponds), lakes/ponds, creeks, and mangroves through visual interpretation of ERS‐1 SAR images acquired on 29th April, 1993 over part of Sundarban delta, abutting Bay of Bengal. An overall accuracy of 91.2% with respect to delineation of wetlands has been achieved. Further, the cloud penetration and day‐and‐night observation capability of ERS‐1 SAR, though well known, is also illustrated.  相似文献   

Potential fishing zones (PFZ) forecast using satellite data derived biological and physical processes     

H. U. Solanki  R. M. Dwivedi  Shailesh Nayak  D. K. Gulati  M. E. John  V. S. Somvanshi 《Journal of the Indian Society of Remote Sensing》2003,31(2):67-69

  相似文献   

Oblique propagation and dissipation of Alfvén waves in coronal holes     

A. K. Srivastava  B. N. Dwivedi 《Journal of Astrophysics and Astronomy》2007,28(1):1-7

We investigate the effect of viscosity and magnetic diffusivity on the oblique propagation and dissipation of Alfvén waves with respect to the normal outward direction, making use of MHD equations, density, temperature and magnetic field structure in coronal holes and underlying magnetic funnels. We find reduction in the damping length scale, group velocity and energy flux density as the propagation angle of Alfvén waves increases inside the coronal holes. For any propagation angle, the energy flux density and damping length scale also show a decrement in the source region of the solar wind (< 1.05 R_⊙) where these may be one of the primary energy sources, which can convert the inflow of the solar wind into the outflow. In the outer region (> 1.21 R_⊙), for any propagation angle, the energy flux density peaks match with the peaks of MgX 609.78 Å and 624.78 Å linewidths observed from the Coronal Diagnostic Spectrometer (CDS) on SOHO and the non-thermal velocity derived from these observations, justify the observed spectroscopic signature of the Alfvén wave dissipation.  相似文献   

High resolution multispectral satellite data interpretation and limited ground checking: A proxy for geological mapping and uranium exploration in Mahakoshal Fold Belt of Son valley area,Madhya Pradesh     

A. K. Dwivedi  Abhinav Kumar  A. K. Chaturvedi 《Journal of the Geological Society of India》2016,88(2):159-172

This research aims at integrating remote sensing data and field studies to prospect for uranium mineralisation in the Palaeoproterozoic Mahakoshal Group of rocks in the Son valley area, Central India. In present work, a revised geological map of Mahakoshal Fold Belt (MFB) bounded by Son-Narmada north fault (SNNF) and Son-Narmada south fault (SNSF) along Chorhut-Sidhi-Chitrangi sector falling in Sidhi, Rewa and Shahdol districts of Madhya Pradesh has been prepared based on interpretation of digitally enhanced satellite images. The satellite image interpretation is supported by limited field works, radioelemental measurements (eU, eTh and % K) of in-situ rocks by four channel Portable Gamma Ray Spectrometer (PGRS) and existing published geological maps of Geological Survey of India. In search for mineral potential areas, accurate and up-to-date geological maps are essential as it represent the most basic information for carrying out further exploration activities. However, available geological maps of MFB and sedimentary formations ofVindhayan Supergroup along SNNF and Chhotanagpur Granite Gneissic Complex (CGGC) and Gondwana Supergroup along SNSF available in public domain are discontinuous and multi-scaled.  相似文献   

Effect of ion and electron beam on kinetic Alfven wave in an inhomogeneous magnetic field     

A. K. Dwivedi  Sunil Kumar  M. S. Tiwari 《Astrophysics and Space Science》2014,350(2):547-556

Kinetic Alfven waves are examined in the presence of electron and ion beam and an inhomogeneous magnetic field with bi-Maxwellian distribution function. The theory of particle aspect analysis is used to evaluate the trajectories of the charged particles. The expressions for the field-aligned currents, perpendicular currents (with respect to B ₀), dispersion relation and growth/damping rate with marginal instability criteria are derived. The effect of electron and ion beam and inhomogeneity of magnetic field are discussed. The results are interpreted for the space plasma parameter appropriate to the auroral acceleration region of the earth’s magnetoplasma.  相似文献   

Density dependence of solar emission lines of boron-like ions     

B. N. Dwivedi  P. K. Raju 《Solar physics》1980,68(1):111-123

Steady state level density of 20 levels of boron-like ions, Mg viii and Si x, have been computed as a function of electron density and temperature. We have accounted for collisional and spontaneous radiative processes. Photo-excitation between the two levels of the ground term has also been considered. Using the computed level density, line intensities have been obtained as a function of electron density and temperature. In case of Mg viii, line intensity ratio I(430.47)/I(436.62) is found to be electron density sensitive. Likewise other pairs of lines namely, I(75.03)/I(74.86), I(315.02)/I(430.47), and I(315.02)/I(335.23) are also found to be density sensitive. Similar density sensitive line intensity ratios have been found for Si x. Absolute line fluxes from these ions at earth distance have been computed and are found to be comparable with values obtained, using various satellite and rocket measurements.Paper presented at the 5th Astronomical Society of India Meeting, held at Uttar Pradesh State Observatory, Naini Tal, India, 5–9 November, 1979.  相似文献   

Theoretical line intensities from MgVI,SiVIII, and SX coronal ions     

B. N. Dwivedi 《Astrophysics and Space Science》1990,172(1):47-50

Emission line intensities from MgVI, SiVIII, andSX ions of nitrogen sequence have been computed by use of the model atmosphere of Kopp and Orrall (1976) for the quiet Sun and coronal holes and compared with observational data available from rocket and satellite.  相似文献