Holocene climatic changes over northwest India: An appraisal

Multidisciplinary studies of the climatic conditions of the present-day arid regions of the northwest Indian region indicate phases of distinct change during the recent post-glacial period. In view of the topical importance of the subject, and the sources of information being scattered throughout multidiscipli-nary research journals, an attempt has been made to summarize and present a coherent picture of the climate of the present-day desert regions of northwest India for the Holocene period. The present-day climatology and physiography of the region is presented as introductory material. The important studies which throw some light on the glacial arid phase, the wet phase, coinciding with the Harappan civilization, and the present-day arid phase are reviewed.     

Mapping of tropical dry deciduous forest and landuse in part of Vindhyan range using satellite remote sensing

Forest vegetation of Vindhyan range located in the north of G.B. Pant Sagar (dam) has been subjected to degradation due to high biotic pressure caused by the installation of thermal power plants, coal mining, heavy cattle grazing etc. In the present study Landsat TM FCC of 1∶250,000 scale was visually analysed with respect to forest vegetation types, crown density and structure along with other landuse/land cover classes. ExceptShorea robusta (Sal) andLagerstroemia parviflora (Lendia) all forest vegetation types show higher percentage of degradation and under-stocked condition with respect to their areal extent under study. Overall classification accuracy of the forest types has been found to be 88.94%. This indicates that for obtaining reliable mapping accuracy in dry deciduous areas, satellite remote sensing data of appropriate season is essential.

     

Some features of the arid area variations over India: 1871–1984

Spatial variability of the annual rainfall over drier regions of India is studied by examining the variations in the arid areas. A long period (1871–1984) arid area series has been prepared for the entire country, including the two broad subregions of North India and Peninsular India, using annual rainfall data from 306 well distributed stations. Following an objectively determined criterion based on rainfall amount alone, the yearly area under arid conditions is obtained by totalling areas which received annual rainfall totals less than 560 mm. The interannual variability of the arid area series is large and its distribution is highly right-skewed, demonstrating large spatial variations in the annual rainfall over India. Statistical tests do not suggest any significant long-term trend in the arid area series, but persistently low values of the arid area after 1941 are noteworthy. Implications for the study of risk analysis and assessment of drought and desertification processes are discussed.     

On coda waves of earthquakes

Summary Coda waves viz. the tail portion of an earthquake record have been observed and analysed byCarder, Macelwane and others. They showed that the periods of such waves increase with the increase of epicentral distances.Carder observed that these waves have very little transverse component so that these may be considered as of the type of Rayleigh waves. RecentlyOmote showed that the Coda waves contain three periodsT ₁,T ₂,T ₃ of whichT ₁ increases with epi-central distances as observed by previous observers. ButT ₂,T ₃ remain constant for all earthquakes from different epicentral distances.Omote tried to explain this phenomenon by considering that the surface of the earth consists of several layers andT ₂,T ₃ are free oscillation periods of the surface layers.T ₁ period has been explained bySezawa and also byJeffreys which has been shown byGutenberg. The author has attempted to explain the periodsT ₂,T ₃ by considering passage of cracks at the focal region. The Rayleigh wave character of Coda waves and low velocity of such waves have been explained.     

Electron-probe check of fe-distribution in sphalerite grains of the Nagybörzsöny hydrothermal ore deposits,Hungary

Micron-scale iron-distribution patterns in sphalerite grains derived from two contrasting mineral assemblages of the Nagybörzsöny hydrothermal ore deposits (high temperature stockwork and low temperature veins), were determined with electron microprobe, pointcounter and continuous chart-recorder measurements along radial profiles. A significant oscillation of iron-content ranging from 8.1 to 18 per cent for stockwork and 4.3 to 15.8 per cent for veins took place during crystal growth. Homogeneous crystal cores are characteristic for vein-filling, while replacement occurring in deeper levels of the stockwork results in mosaic cores. Frequent oscillation of iron content is relevant to top-sections of the ore bodies, copious supply being recorded in recurring shells, whereas scanty, unilateral ones produce crescents arranged in onion-like structure.

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Zusammenfassung Bestimmungen der Eisenverteilung wurden an Zinkblendekörnern aus zwei verschiedenen Mineralparagenesen (Hochtemperatur-Stockwerk und Gangfüllungen niederiger Bildungstemperatur) der hydrothermalen Erzlagerstätte Nagybörzsöny im Mikronbereich durch Elektronen-Mikrosonde-Messungen (Punktzählung und kontinuierliche Band-Registrierung) entlang radialer Profile vorgenommen. Bedeutende Schwankungen des Eisengehaltes (8,1–18% für das Stockwerk und 4,3–15,8% für die Gänge) wurden registriert. Homogene Kristallkerne kennzeichnen die Gangfüllungen, wogegen in tieferen Horizonten des Stockwerks Verdrängungen zur Bildung von Kristallen mit Mosaik-Kernen führen. Allgemein ist in den Gipfel-Partien der Erzkörper Fluktuation des Eisengehaltes häufig. Gleichmäßiger Nachschub während des Kristallwachstums führte zu ringförmigen Zonen gleicher Eisengehalte, spärlicher oder einseitiger dagegen zu halbmondförmigen Hüllen mit Zwiebelstruktur.

     

Electromagnetic scattering due to deformed inhomogeneous bodies (Part I: Sphere)

Summary The potential technique of the perturbation has been employed to find the analytical expressions for the response of conducting bodies of irregular shapes. In Part I spherical bodies and in Part II cylindrical ones are considered. The conductivities are assumed to be finite and radially varying. The deformation of the boundaries in both the cases are considered to be of the typek _p =r ₀[1++f ₁(, )] where is the perturbation parameter. Calculations have been made for uniform as well as non-uniform excitation fields. Since the models represent the geological ore-formation more closely, the results will find application in preparing type curves for induction prospecting.N.G.R.I. Contribution No. 70-194.     

The solar and lunar daily geomagnetic variation of declination at Trevandrum, 1853–1869

Summary The eye readings of easterly declination at Trevandrum observatory have been analysed to determine solar and lunar daily vatiations. Hourly readings during February 1853 to February 1865 are analysed by Chapman-Miller method. The 8 values read at unequidistant day-time hours during March 1865 to December 1869 are analysed to compute the amplitude and phase of the semimonthly wave at each of the hours separately. The semi-monthly lunar wave obtained from the hourly readings shows a considerable night-time variation. A brief discussion of the results is also given.Contributions from the Earth Physics Branch, No. 323     

Waves and stresses produced in an elastic medium due to impulsive radial forces and twist on the surface of a spherical cavity

Summary Displacements and stresses produced by impulsive radial pressure and by impulsive twists have been determined. In the former case total flow of energy across a spherical boundary has been obtained.     

Influence of forest fire episodes on the distribution of gaseous air pollutants over Uttarakhand,India

ABSTRACT

Widespread forest fire events occurred in the foothills of North Western Himalaya during 24 April to 2 May 2016 (Event-1) and 20–30 May 2018 (Event-2). Their impacts were investigated on the distribution of pollutant gases ozone (O₃), carbon monoxide (CO), and oxides of nitrogen (NOx) over Uttarakhand using simulations of Weather Research and Forecasting model coupled with chemistry (WRF-Chem) and in-situ observations of these gases over Dehradun, the capital of Uttarakhand. During Event-1, the observed CO mixing ratio over Dehradun increased from 25 April 2016 onwards, attained maximum (705.8 ± 258 ppbv) on 2 May 2016 and subsequently decreased. The rate of increase of daily baseline CO was 29 ppbv/day during HFAP (High Fire Activity Period). During Event-2, daily average concentrations of CO, O₃, and NOx showed systematic increase over Dehradun during HFAP period. The rate of increase of CO was 9 ppbv/day, while it was very small for NOx and O₃. To quantitatively estimate the influence of forest fire emissions, two WRF-Chem simulations were made: one with biomass burning (BB) emissions and other without BB emissions. These simulations showed 52% (34%) enhancement in CO, 52% (32%) enhancement in NOx, and 11% (9%) enhancement in O₃ during HFAP for Event-1 (Event-2). A clear positive correlation (r = 0.89 for Event-1, r = 0.69 for Event-2) was found between ?O₃ (O_{3with BB} minus O_{3without BB}) and ?CO (CO_{with BB} minus CO_{without BB}), indicating rapid production of ozone in the fire plumes. For both the events, the vertical distribution of ?O₃, ?CO, and ?NOx showed that forest fire emissions influenced the air quality upto 6.5 km altitude. Peaks in ?O₃, ?CO, and ?NOx during different days suggested the role of varying dispersion and horizontal mixing of fire plumes.