Ionospheric effects of transient celestial X-ray and gamma-ray events

The paper presents the results on investigations of the ionospheric effects arising out of the transient celestial events at X-ray and gamma-ray energies such as that from X-ray novae and cosmic gamma-ray bursts. The VLF data recorded at Ahmedabad corresponding to the 164 kHz transmission from Tashkent are examined to see whether there are any observable effects time coincident with the transit of the X-ray novae Cen X-4 and Cet X-2 around their intensity maxima. Besides, the VLF data have also been examined in relation to the cosmic gamma-ray bursts detected by Vela, IMP-6 and OSO-7 satellites.Theoretical computations are carried out for estimating electron density enhancements using the available data on intensities and energy spectra for these events. Further, the observational resutls are explained in terms of these theoretical calculations.Presently at Indian Space Research Organization, Bangalore, India.Paper presented at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975.     

RARE GASES IN BANSUR,UDAIPUR AND MADHIPURA CHONDRITES

We have analysed three Indian meteorites — Bansur, Udaipur and Madhipura — for the elemental and isotopic composition of Ne, Ar, Kr and Xe and determined their radiation and gas-retention ages. It is found that Udaipur belongs to the group of unequilibrated ordinary chondrites and Madhipura probably belongs to the group of shocked hypersthene chondrites.     

Landscape analysis for pedo-geomorphological characterization in part of basaltic terrain,central India using remote sensing and GIS

In the present study, an attempt has been made to analyse IRS-ID LISS-III satellite data in conjunction with field observations for geomorphological mapping and pedo-geomorphological characterisation in Mohgaon area of Nagpur district, Maharashtra. Analysis of satellite data reveals distint geomorphological units viz., plateau top, isolated mounds, linear ridges, escarpments, plateau spurs, subdued plateau, rolling plains, pediments, narrow valleys and main valley floor. Soil profiles, studied on different identified landforms, showed variation in site and morphological charactaristics. Moderate soil erosion occurs on plateau top, isolated mouds, plateau spurs, rollinmg plains and pediments. Severe erosion was identified on escarpments and subdued plateau and narrow valleys suffer very slight erosional hazards. Moderately well drained soils were found on rolling plains, pediments, narrow valleys and main valley floor. Well drained soils were noticed on plateau top and plateau spurs. Very shallow soils were found on the plateau top and isolated mounds. Shallow soils are found in linear ridges, escarpments, plateau spurs and rolling plains. Moderately deep and deep soils are found on subdued plateau, pediments and main valley floor. The landform-soil relatioinship reveals that the soils on the plateau top and isolated mounds are very shallow, well drained, clay textured. The soils on the narrow valleys and main valley floor are deep, moderatly well drained, and clayey in texture. It also indicates that landform-soil processes are governed by physiographic position, drainage, slope and erosion conditions of the area. The present study reveals that the analysis of remotely sensed data in conjunction with field observations in GIS will be of immense help in geomorphology mapping, analysis of landform-soil relationships and generation of their geo-spatial database.     

Behaviour of masonry structures during the Bhuj earthquake of january 2001

A variety of masonry structures suffered damage during the recent Bhuj earthquake. Some of the traditional masonry structures had no earthquake resistant features and suffered considerable damage. This paper attempts to evaluate the behaviour of masonry structures based on the type of masonry used in places like Bhuj, Anjar, Bhachau, Morbi, Samakhyali and several other places. Quite a few masonry buildings had used earthquake resistant features like lintel bands and corner reinforcements. The cracking and failure patterns of such buildings have also been examined. The paper concludes with a discussion on the relevance of the current codal provisions for earthquake resistance of masonry structures and the direction of further research in the area.     

The Indian summer monsoon as revealed by the NCMRWF system

In this study, we present the mean seasonal features of the Indian summer monsoon circulation in the National Centre for Medium Range Weather Forecasting (NCMRWF) global data assimilation and forecast system. The large-scale budgets of heat and moisture are examined in the analyzed and model atmosphere. The daily operational analyses and forecasts (day 1 through day 5) produced for the summer seasons comprising June, July and August of 1995 and 1993 have been considered for the purpose. The principal aim of the study is two-fold. Primarily, to comprehend the influence of the systematic errors over the Indian summer monsoon, secondarily, to analyze the performance of the model in capturing the interseasonal variability. The heat and moisture balances show reduction in the influx of heat and moisture in the model forecasts compared to the analyzed atmosphere over the monsoon domain. Consequently, the diabatic heating also indicates reducing trend with increase in the forecast period. In effect, the strength of Indian summer monsoon, which essentially depends on these parameters, weakens considerably in the model forecasts. Despite producing feeble monsoon circulation, the model captures interseasonal variability realistically. Although, 1995 and 1993 are fairly normal monsoon seasons, the former received more rainfall compared to the latter in certain pockets of the monsoon domain. This is clearly indicated by the analyzed and model atmosphere in terms of energetics.     

Mitigation of Flooding and Cyclone Hazard in Orissa, India

Storm surges generated by the strong tangential wind stressesand normal atmospheric pressure gradients at the sea surface due to tropical cyclones (TC'S)have been studied with the goal of detecting any significant and systematic changes due to climatechange. Cyclone and storm surge data for the 19th and 20th centuries for the Bay of Bengalcoast of the state of Orissa in India are available to varying degrees of quality and detail,the data being more scientific since the advent of the India Meteorological Department in 1875.Based on more precise data for the period 1971 to 2000, statistical projections have been madeon the probable intensities of tropical cyclones for various return periods. The super cyclone ofOctober 29, 1999 (SC1999) appears to have a return period of about 50 years. The cyclones of1831, 1885 and possibly the one in 1895 could have been super cyclones. During the 19th century,there were 72 flooding events associated with cyclones, whereas in the 20th century therewere only 56 events. There was no observational evidence to suggest that there was an increaseeither in the frequency or intensity of cyclones or storm surges on the coast of Orissa. However,the impact of cyclones and surges is on the increase due to increase of population and coastalinfrastructure.     

Geomagnetic activity control on VHF scintillations over an Indian low latitude station, Waltair (17.7‡N, 83.3‡E, 20‡N dip)

Using the data of amplitude scintillations recorded at 244 MHz from the geostationary satellite, FLEETSAT (73‡E) at a low latitude station, Waltair (17.7‡N, 83.3‡E, 20‡N dip), during the increasing sunspot activity period of 1997–2000, the effect of the geomagnetic storms on the occurrence of ionospheric scintillations has been studied. A total of 60 SC storms studied during this period, following the Aarons’ criterion, reveals that the local time of onset of the recovery phase of the geomagnetic storms play an important role in the generation or inhibition of the ionospheric irregularities. Out of the 60 storms studied, nearly 60 to 70% satisfied the categories I, II and III of Aarons’ criteria. However, in the remaining 30 to 40% of the cases, no consistent results were observed. Thus, there is a necessity for further investigation of the effect of geomagnetic storms on ionospheric irregularities, particularly with reference to the altitude variations of the F-layer (h’F) relating to the changes in the local electric fields.