Density measurement from A1 IX λ385.03/λ392.42 line ratio     

B. N. Dwivedi  A. K. Gupta 《Solar physics》1991,135(2):415-417

A1 IX EUV line ratio 385.03/392.42 has been found to be density sensitive. Using this, an electron density of 3.7 × 10⁸ cm^–9 is found in the quiet, Sun off-limb from Skylab observation reported by Vernazza and Reeves (1978).  相似文献   

AIix emission line ratios in solar flares observed with the S082A spectrograph on board Skylab     

F. P. Keenan  E. S. Conlon  D. A. Bowden  B. N. Dwivedi  K. G. Widing 《Solar physics》1994,149(1):137-142

Theoretical electron-density-sensitive emission line ratios in B-like AIix are presented forR =I(385.01 )/I(392.42 ). A comparison of these with high spectral resolution solar flare data, obtained with the S082A slitless spectrograph on boardSkylab, reveals agreement between theory and observation for those spectra that were observed during the later stages of the flares. These results provide experimental support for the accuracy of the line-ratio calculations, and also resolves discrepancies found previously when the theoretical results were compared with solar observations from the S-055 instrument on boardSkylab. However, the agreement between theory and observation for a spectrum obtained during the early stages of a flare is very poor, which probably indicates that the 392.42 line is blended with a transition arising from a species formed at a very high electron temperature.  相似文献   

Possible Role of mhd Waves in Heating the Solar Corona     

Dwivedi  B.N.  Pandey  V.S. 《Solar physics》2003,216(1-2):59-77

Heating of the solar corona by MHD waves has been investigated. Taking account of dissipation mechanisms self-consistently, a new general dispersion relation has been derived for waves propagating in a homogeneous plasma. Solution of this sixth-order dispersion relation provides information on how the damping of both slow and fast mode waves depends upon the plasma density, temperature, field strength, and angle of propagation relative to the background magnetic field. Wave quantities with and without dissipation are presented. In particular, we consider one of the most important clues from space observations that viscosity of coronal plasma may be orders of magnitude different from its classical value in heating of the corona by MHD waves.  相似文献   

Physics of the sun’s hot atmosphere     

B. N. Dwivedi 《Journal of Astrophysics and Astronomy》2006,27(2-3):125-137

This article briefly overviews the physics of the Sun’s hot atmosphere, using observations from recent solar spacecrafts: Yohkoh, SOHO, TRACE and RHESSI.  相似文献   

A multiwavelength study of an M-class flare and the origin of an associated eruption from NOAA AR 11045     

B.N. Dwivedi  Abhishek K. Srivastava  Mukul Kumar  Pankaj Kumar 《New Astronomy》2012,17(5):542-551

In this paper, we study multiwavelength observations of an M6.4 flare in Active Region NOAA 11045 on 7 February 2010. The space- and ground-based observations from STEREO, SoHO/MDI, EIT, and Nobeyama Radioheliograph were used for the study. This active region rapidly appeared at the north-eastern limb with an unusual emergence of a magnetic field. We find a unique observational signature of the magnetic field configuration at the flare site. Our observations show a change from dipolar to quadrapolar topology. This change in the magnetic field configuration results in its complexity and a build-up of the flare energy. We did not find any signature of magnetic flux cancellation during this process. We interpret the change in the magnetic field configuration as a consequence of the flux emergence and photospheric flows that have opposite vortices around the pair of opposite polarity spots. The negative-polarity spot rotating counterclockwise breaks the positive-polarity spot into two parts. The STEREO-A 195 Å and STEREO-B 171 Å coronal images during the flare reveal that a twisted flux tube expands and erupts resulting in a coronal mass ejection (CME). The formation of co-spatial bipolar radio contours at the same location also reveals the ongoing reconnection process above the flare site and thus the acceleration of non-thermal particles. The reconnection may also be responsible for the detachment of a ring-shaped twisted flux tube that further causes a CME eruption with a maximum speed of 446 km/s in the outer corona.  相似文献   

Hydrologic functioning of the deep critical zone and contributions to streamflow in a high‐elevation catchment: Testing of multiple conceptual models     

Ravindra Dwivedi  Thomas Meixner  Jennifer C. McIntosh  P.A. Ty Ferr  Christopher J. Eastoe  Guo‐Yue Niu  Rebecca L. Minor  Greg A. Barron‐Gafford  Jon Chorover 《水文研究》2019,33(4):476-494

High‐elevation mountain catchments are often subject to large climatic and topographic gradients. Therefore, high‐density hydrogeochemical observations are needed to understand water sources to streamflow and the temporal and spatial behaviour of flow paths. These sources and flow paths vary seasonally, which dictates short‐term storage and the flux of water in the critical zone (CZ) and affect long‐term CZ evolution. This study utilizes multiyear observations of chemical compositions and water residence times from the Santa Catalina Mountains Critical Zone Observatory, Tucson, Arizona to develop and evaluate competing conceptual models of seasonal streamflow generation. These models were tested using endmember mixing analysis, baseflow recession analysis, and tritium model “ages” of various catchment water sources. A conceptual model involving four endmembers (precipitation, soil water, shallow, and deep groundwater) provided the best match to observations. On average, precipitation contributes 39–69% (55 ± 16%), soil water contributes 25–56% (41 ± 16%), shallow groundwater contributes 1–5% (3 ± 2%), and deep groundwater contributes ~0–3% (1 ± 1%) towards annual streamflow. The mixing space comprised two principal planes formed by (a) precipitation‐soil water‐deep groundwater (dry and summer monsoon season samples) and (b) precipitation‐soil water‐shallow groundwater (winter season samples). Groundwater contribution was most important during the wet winter season. During periods of high dynamic groundwater storage and increased hydrologic connectivity (i.e., spring snowmelt), stream water was more geochemically heterogeneous, that is, geochemical heterogeneity of stream water is storage‐dependent. Endmember mixing analysis and ³H model age results indicate that only 1.4 ± 0.3% of the long‐term annual precipitation becomes deep CZ groundwater flux that influences long‐term deep CZ development through both intercatchment and intracatchment deep groundwater flows.  相似文献   

Possible Role of MHD Waves in Heating the Solar Corona     

B. N. Dwivedi  V. S. Pandey 《Solar physics》2009,257(1):215-215

  相似文献   

Forbidden line ratios from Si viii and S x coronal ions     

B. N. Dwivedi 《Solar physics》1991,131(1):49-52

The off-limb spectra, recorded by the NRL Skylab spectrograph, have been used to infer electron densities from theoretical curves of Si viii and S x density-sensitive line ratios. The derived densities are found to be in agreement with those reported by Feldman et al. (1978). Computed line intensities using the Kopp and Orrall (1976) model have also been used to estimate densities in the quite Sun and coronal holes from these curves.  相似文献   

Density dependence of solar emission lines of oxygen-like ions     

P. K. Raju  B. N. Dwivedi 《Solar physics》1978,60(2):269-277

Assuming steady state conditions, the occupation of 9 levels of oxygen-like ions: Ne iii, Mg v, Si vii, S ix, and Ar xi have been computed as a function of electron density and temperature. The following physical processes have been considered: collisional excitations and spontaneous radiative de-excitations for permitted and intercombination transitions; collisional excitations and de-excitations, photo-excitations and spontaneous radiative transitions among the five levels of the ground term. This study indicates that line intensity ratios for oxygen-like ions can be used as a diagnostic in the determination of these two parameters of the solar plasma.Paper presented at the 4th Astronomical Society of India Meeting, held at Radio Astronomy Centre, Ootacamund, India, 7–10 March 1978.  相似文献   

Effects of γ-Rays on Hatching' of the Eggs and Survival Period of Fries of Cyprinus carpio     

R. S. Shrivastava  P. Dwivedi 《洁净——土壤、空气、水》1980,8(4):311-317

The eggs of Cyprinus carpio were irradiated by 5 different strengths: 0.0258, 0.129, 0.258, 0.516 and 1.29 C/kg (100, 500, 1000, 2000 and 5000 R) of γ-rays in the batches of 50 fertilized eggs. The activities of eggs and hatched fries were noted after irradiation doses. The hatching percentages of the eggs were reported for each group. The percentage of hatched eggs of Cyprinus carpio after radiation doses of 0.0258, 0.129, 0.258, 0.516 and 1.29 C/kg (100, 500, 1000, 2000 and 5000 R) was 30%, 24%, 28%, 30%, and 34%, respectively. The 50% mortality period of fries for the above strengths of the γ-rays was 8 days, 7 days, 6 days. 4 days and 4 days, respectively. The survival period of the fries was 11 days, 9 days, 8 days, 7 days and 6 days, respectively. All fries hatched from the eggs irradiated by γ-rays showed early hatching, a higher percentage of mortality, a retarded and abnormal development of the body. A statistical analysis of the results by the correlation coefficient also proved that the hatching percentages of the fries and the survival period of fries are directly proportional to the strength of the γ-rays and inversely proportional to the strength of γ-rays, respectively.  相似文献