Global features of sea-level pressure distribution in April and July associated with contrasting situations of Indian summer monsoon

Global sea-level pressure distribution has been analysed for the months of April and July for 5 years of contrasting situations of Indian summer monsoon, comprising of two drought years (1972 and 1974), a flood year (1975) and two normal monsoon years (1970 and 1973). Mean monthly sea-level pressure data at about 400 stations have been used in the study. Prominent features of pressure departures from long-term normals have also been noted. It is observed that the month of April shows more prominent contrasting features than July. In April, the high pressure centres over USSR and the North Pacific move considerably eastward during poor monsoon years, while a breakaway cell of Icelandic Low goes deep south. Both the high pressure areas over south Indian Ocean and Australia are stronger in good monsoon years. In July, the subtropical high pressure zone over the southern Indian Ocean is stronger and the Australian high is more eastward, in good monsoon years.     

Search for Spatial Variability in the Solar Acoustic Spectrum

Motivated by the various examples of spatial variability in the power of the acoustic spectrum, we attempted to look for spatial variability in the peak frequency of the spectrum. However, the determination of this peak frequency on a spatial scale of a single pixel (8 arc sec for the GONG data) is limited by the stochastic variations in the power spectrum presumably caused by the stochastic nature of the excitation process. Averaging over a large number of spectra (100 spectra from a 10 × 10 pixel area) produced stabler spectra. The peak frequencies of 130 such locations were found to be distributed with a FWHM of about 130 Hz. A map of the spatial variation of this peak frequency did not show any strong feature with statistically significant deviation from the mean of the distribution. Likewise, the scatter in the peak frequencies masked the detection of magnetic-field-induced changes in the peak frequency. On a much larger scale, the N latitudes showed a slightly lower value of the peak frequency as compared to the S latitudes, although the difference (25 Hz) is barely larger than the r.m.s. spread (20 Hz).     

Detection of crustal motion using spaceborne laser ranging systems

The spaceborne laser ranging (or lasering) system provides a method of precise positioning of a large number of points on the earth's surface in a short period of time. That is, a measure of the relative location of geodetic markers from a space platform can maintain horizontal and vertical control to 2 to 5 cm. At this level of control, small earth surface crustal motions should be detectable. Development of a model for the strain field can be constructed. Furthermore, the spaceborne lasering system can survey an area in a very short period of time (one to two weeks) and resurvey the area as required. System design parameters are now being established by NASA for a possible test flight aboard the Shuttle in 1982. These include design specifications of economical corner cubes for ground retroreflectors coupled with the evolution of engineering model to flight model development. If the experiment of the Shuttle proves to be successful, it is hoped to put the laser in a free flight satellite. This paper presents the results of a simulated analysis for this latter case. The system is conceived as an orbiting ranging device with a ground base grid of reflectors or transponders (spacing 10 to 30 km), which are projected to be of low cost (maintenance-free and unattended) and which will permit the saturation of a local area to obtain data useful to monitor crustal movements. The test network includes 75 stations with roughly half of them on either side of the San Andreas fault zone. Critical study comparatively evaluates various observational schemes and statistically analyzed crustal motion recovery. The study considers laser radar as the main ranging system pending final selection from many possible candidates. The satellite orbit is inclined at 110° and slightly eccentric (e=0.04) with orbital altitudes varying from 370 km to 930 km. The results indicate that the geometric mode (simultaneous ranging) with a minimum of five grid and three distant (fundamental) stations and mixed ranging to satellite and airplane seems to be most promising. The fundamental stations are distinguished from the grid station in their location and this location should be “distant” enough from the area of crustal movement so that they can be considered stationary over the time span of the motion involved. Presented at the 1977 I.A.G. International Symposia on Satellite Geodesy, Budapest, Hungary, June 28–July 1, and on Recent Crustal Movements, Palo Alto, California, USA, July 25–30.     

Habitat range of two alpine medicinal plants in a trans-Himalayan dry valley, Central Nepal

Understanding of the habitat range of threatened Himalayan medicinal plants which are declining in their abundance due to high anthropogenic disturbances is essential for developing conservation strategies and agrotechnologies for cultivation. In this communication, we have discussed the habitat range of two alpine medicinal plants, Aconitum naviculare （Bruehl） Stapf and Neopicrorhiza scrophulariiflora （Pennel） Hong in a trans-Himalayan dry valley of central Nepal, Manang district. They are the most prioritized medicinal plants of the study area in terms of ethnomedicinal uses. A. naviculare occurs on warm and dry south facing slopes between 4090-4650 m asl along with sclerophyllous and thorny alpine scrubs, while N. scrophulariiflora is exclusively found on cool and moist north facing slope between 4000 and 4400 m asl where adequate water is available from snow melt to create a suitable habitat for this wetland dependent species. The soil in rooting zone of the two plants differs significantly in organic carbon （OC）, organic matter （OM）, total nitrogen （N） and carbon to nitrogen （C/N） ratio. Due to cool and moist condition of N. scrophulariiflora habitat, accumulation of soil OC is higher, but soil N content is lower probably due to slow release from litter, higher leaching loss and greater retention in perennial live biomass of the plant. The C/N ratio of soil is more suitable in A. navuculare habitat than that of N scrophulariiflora for N supply. Warm and sunny site with N rich soil can be suitable for cultivation ofA. naviculare, while moist and cool site with organic soil for N. scrophulariiflora. The populations of both the plants are fragmented and small. Due to collection by human and trampling damage by livestock, the population of A. naviculare was found absent in open areas in five of the six sampling sites and it was confined only within the bushes of alpine scrubs. For N. serophulariiflora, high probability of complete receding of small glaeiers may be a new threat in future to its habitat. The information about habitat conditions, together with the information from other areas, ean be useful to identify potential habitats and plan for cultivation or domestication of the two medieinal plants.     

Modeling of local ionospheric time varying characteristics based on singular value decomposition over low-latitude GPS stations

Singular Value Decomposition (SVD) model is implemented to recognize the Total Electron Content (TEC) time series of daily, temporal as well as seasonal characteristics throughout the 24th solar cycle period of the year 2015 in the study. The Vertical (vTEC) analysis has been carried out with Global Positioning System (GPS) data sets collected from five stations from India namely GNT, Guntur (16.44^° N, 80.62^° E), and IISC, Bangalore (12.97^° N, 77.59^° E), LCK2, Lucknow (26.76^° N, 80.88^° E), one station from Thailand namely AITB, Bangkok (14.07^° N, 100.61^° E), and one station from South Andaman Island namely PBR, Port Blair (11.43^° N, 92.43^° E), located in low latitude region. The first five singular value modes constitute about 98% of the total variance, which are linearly transformed from the observed TEC data sets. So it is viable to decrease the number of modeling parameters. The Fourier Series Analysis (FSA) is carried out to characterize the solar-cycle, annual and semi-annual dependences through modulating the first three singular values by the solar (F10.7) and geomagnetic (Ap) indices. The positive correlation coefficient (0.75) of daily averaged GPS–TEC with daily averaged F10.7 strongly supports the temporal variations of the ionospheric features depends on the solar activity. Further, the significance and reliability of the SVD model is evaluated by comparing it with GPS–TEC data and the standard global model (Standard Plasma-Spherical Ionospheric Model, SPIM and International Reference Ionosphere, IRI 2016).     

Rainfall variability and indices of extreme rainfall-analysis and perception study for two stations over Central Himalaya,India

The analysis of rainfall pattern and indices of extreme rainfall events is performed for two meteorological stations located in the Central Himalayan Region which is highly vulnerable to rain-induced hazards. The records of these rain-induced disasters suggest that such events are generally observed in later part of monsoon season, when soil is saturated after monsoon rains. An attempt is made here to test trends of 19 different extreme rainfall indices that have been widely used in the literature, using daily rainfall data for two urban centres (Nainital and Almora) over the period 1992–2005. We have used statistical tools such as Sen’s method and Mann–Kendall test for detection of trend in annual rainfall, monsoon rainfall, number of rainy days and 1-day extreme rainfall. Principal component analysis gives the correlation between different extreme rainfall indices. Time series of principal components are representing the trends of extreme indices, their variation and interrelation between different indices. The perception study conducted in the same sites indicates that extreme rainfall events and change in rainfall amount and timing are well perceived by the local people.     

Dump slope stability analysis – A case study

In opencast mining operation, the stability of waste materials stands at high priority from the safety and economic perspective. Poor management of overburden (OB) dump results the instability of slope in an opencast mine. The present paper deals with the stability analysis of dump material of an opencast coal mine at Talcher coal field, Angul district, Odisha, by means of different geotechnical parameters and mineralogical composition affecting the dump slope. The prolonged rainfall in the mining area causes dump failure and loss of valuable life and property. A recent dump failure that occurred in 2013 at Basundhara mines of Mahanadi Coalfields Limited (MCL), Odisha, took 14 lives, and created problems for the mining industry. Most of the dump failure that occurs in the study area are mainly due to increase in pore water pressure as a result of rainfall infiltration. The stability of the waste dump was investigated using the limit equilibrium analysis to suggest an economical, sustainable and safe disposal of the dump in the study area.