Electron impact polarization of resonance lines from Lithium-like ions

The Oppenheimer-Penney theory, as developed by Percival and Seaton (1958), is applied to calculate the polarization of resonance lines from Li-like ions. Two laws for the pitch-angle distribution of electrons around the magnetic field are accounted. The degrees of polarization are averaged over the energy of non-thermal electrons generated during the initial phase of solar flares. It is found that for the full space pitch-angle distribution, as adopted by Chandra and Joshi (1984), the degrees of polarization are nearly independent of the atomic number of ion. Whereas for the forward-come distribution used by Haug (1981), they depend on the choice of the free parameterE ₀. The polarization of the resonance lines from Li-like ions is two times larger than that of the L radiations from H-like ions. Hence, under favourable conditions, it may be detected during solar flares.     

On the quiet-time Pc 5 pulsation events (Spacequakes)

A quiet-time Pc 5 event (designated Spacequake) of March 18, 1974, first noted on the Fort Churchill magnetopram, was studied using global data. Its amplitude was found to be largest in the northern part of the auroral zone and its period seemed to increase with latitude. The clockwise polarization of the event noted at Baker Lake and higher latitudes changed to counterclockwise at Fort Churchill in X-Y, X-Z and Y-Z planes. The resonance of a field line (L ? 10) excited due to an instability of the Kelvin-Helmholtz type may have given rise to the observed event. It is conjectured that the cause of instability at this high altitude was internal convection of the magnetosphere. Similar quiet-time events from four Canadian observatories were selected from approximately 11 years of magnetograms and their statistical analysis revealed that (i) occurrences maximized near dawn and dusk (ii) the amplitude-latitude profile peaked at Great Whale River (L ? 6.67), (iii) periods increased with increasing geomagnetic latitudes, (iv) a large number of events occurred in January, February and March every year, and (v) frequency of occurrence increased with increasing sunspot numbers. Comparison of these results with those available in the literature from analyses of satellite data clearly indicate that quiet-time Pc 5 events (Spacequakes) originate in the outer magnetosphere.     

Hypsometric analysis of the micro-watersheds with different management practices located on Shivalik foothills

In this paper, the hypsometric curves and integrals of four neighboring micro-watersheds draining into Patiala-Ki-Rao stream which is situated in the Shivalik foothills of district SAS Nagar in the Punjab state (India) has been presented to access and compare the erosion regimes under different management practices. Area-elevation ratio method has been used to compute hypsometric curve and integral values for each micro-watershed through ArcGIS 10.3 and Microsoft Excel. The 9-year data of runoff and sediment yield for all these micro-watersheds under different management practices has been analyzed for their effect on land cover and soil quality. Thus, the results of present study are very useful for comparing, planning, implementing, and controlling soil erosion in similar watersheds.     

Decumbent development: Urban sprawl in the Guwahati Metropolitan Area,India

Urban sprawl has become a global phenomenon as an outcome of growing population and rapid urbanization. Previous studies have addressed the rising incidence of uncontrollable urban development, particularly in peri-urban areas of cities, leading to chronic urban sprawl. The city of Guwahati, a million city in north east India, has expanded significantly in recent years. In this article, the links between population and growth of built-up areas were examined using geo-spatial techniques and remotely sensed datasets. The results indicate that the sprawl has accentuated in recent years. The intensity of land use remained uneven due to marked variations in the distribution of built-up areas, plausibly an outcome of unplanned urban growth. If current trends are anything to go by, future urban sprawl could pose serious threats to the vulnerable eco-sensitive and peri-urban areas of Guwahati. Secondary cities have unfortunately received scant attention in urban policy research, and Guwahati, epitomizes urban woes in a developing country.     

A multiwavelength view of a classical T Tauri star CV Cha

Using long-term optical, ultraviolet(UV) and X-ray data, we present a study of a classical T Tauri star CV Cha. The V-band light curve obtained from the All Sky Automated Survey(ASAS) shows short as well as long-term variability. The short-term variability could be due to rotational modulation of CV Cha. We derive the rotational period of 3.714 ± 0.001 d for CV Cha. UV light curves obtained from Swift also show the variations. X-ray light curves from XMM-Newton and Swift do not show any significant short as well as long-term variability. However, the light curve from Chandra appears to be variable, which could be due to the emergence of flaring activities. X-ray spectra from all observations are explained well by the single temperature plasma of 0.95 keV with X-ray luminosity of 1030.4erg s-1in the 0.5–7.5 keV energy band. It appears that variability in optical and UV bands could be due to the presence of both hot and cool spots on the surface, while X-ray emission is dominated by magnetic processes.     

SporadicE ionization associated with meteor events

Two meteor events which were sighted in the Gujarat skies of India, were accompained by the visibility of sporadicE ionization on the ionograms recorded at Ahmedabad (Geog. Lat. 23·2°N, long. 72·30°E). The first event was the Dhajala fireball which flashed into the geoatmosphere along an E-N to W-S trail at about 20·40 h IST on 28 January 1976; the closest distance of the ground projection of meteor trail from Ahmedabad was 50km. The other event was a possible meteor group sighted over Ahmedabad on 28 May 1978, at about 21·10 h IST. This work describes the nature of the sporadicE ionization observed on Ahmedabad ionograms during the two events. Features of theEs echo during the Dhajala event which indicate that it could be of meteoric origin are discussed. Meteor theory is used to relate the observed ionization with the physical dimensions of the Dhajala meteorite as obtained by other workers.     

Denudation History of South China Block and Sediment Supply to Northern Margin of the South China Sea

On the basis of apatite fission track (AFT) analyses,this article aims to provide a quantitative overview of Cenozoic morphotectonic evolution and sediment supply to the northern margin of the South China Sea (SCS).Seventeen granite samples were collected from the coast to the inland of the South China block.Plots of AFT age against sample location with respect to the coastline show a general trend of youngling age away from the coast,which implies more prolonged erosion and sediment contribution at the inland of the South China Sea during post break-up evolution.Two-stage fast erosion process,Early Tertiary and Middle Miocene,is deduced from simulated cooling histories.The first fast cooling and denudation during Early Tertiary are recorded by the samples along the coast (between 70 and 60 Ma) and the inland (between 50 and 30 Mu),respectively.This suggests initial local erosion and deposition in the northern margin of the SCS during Early Tertiary.Fast erosion along the coast ceased since ca.50 Ma,while it had lasted until ca.30 Ma inland,indicating that the erosion was transferred from the local coastal zone initially toward the continental interior with unified subsidence of the northern margin,which resulted in the formation of a south-dipping topography of the continental margin.The thermal stosis in the South China block since ca.30 Mu must det'me the time at which the northern margin became dynamically disconnected from the active rifting and stretching that was taking place to the south.The lower erosion rate is inconsistent with higher sedimentary rate in the Pearl River Mouth basin during Late Oligocene (ca.25 Ma).This indicates that the increased sedimentation in the basin is not due to the erosion of the granite belt of the South China block,but perhaps points to the westward propagation of the paleo-Pearl River drainage related to the uplift of the eastern margin of Tibet plateau and southward jumping of spreading axis of the South China Sea.The socond erosion acceleration rate of the Middle Miocene (ca.14 Ma) cooling could have been linked to the long-distance effect of uplift of the Tibet plateau or due to the enhanced East Asian monsoon.     

Detecting groundwater contamination of a river in Georgia, USA using baseflow sampling

Algal blooms and fish kills were reported on a river in coastal Georgia (USA) downstream of a poultry-processing plant, prompting officials to conclude the problems resulted from overland flow associated with over-application of wastewater at the plant’s land application system (LAS). An investigation was undertaken to test the hypothesis that contaminated groundwater was also playing a significant role. Weekly samples were collected over a 12-month period along an 18 km reach of the river and key tributaries. Results showed elevated nitrogen concentrations in tributaries draining the plant and a tenfold increase in nitrate in the river between the tributary inputs. Because ammonia concentrations were low in this reach, it was concluded that nitrate was entering via groundwater discharge. Data from detailed river sampling and direct groundwater samples from springs and boreholes were used to isolate the entry point of the contaminant plume. Analysis showed two separate plumes, one associated with the plant’s unlined wastewater lagoon and another with its LAS spray fields. The continuous discharge of contaminated groundwater during summer low-flow conditions was found to have a more profound impact on river-water quality than periodic inputs by overland flow and tributary runoff.