July, 2005

July, 2005   ||  Volume 9 No.3

Comparative performance of focused and normal devices
through a numerical study
Rambhatla G. Sastry and Kumar Praveer 1
Department of Earth Sciences, IIT, Roorkee – 247 667
1BG Exploration & Production India Ltd., Ground Floor, MIDAS, Sahar Plaza, Kondivita, Andheri (E), Mumbai – 400 059

E-mail: rgss1fes@iitr.ernet.in / rgssastry@yahoo.com



The superiority of focussed devices over traditional Normal devices has remained a controversy in geophysical literature. A two-dimensional finite-difference scheme for numerical modeling of Normal and Laterlog (LL7) is undertaken to clarify the matters concerned. Spacing for spacing, normal log is better than LL7 for e/AM >1 with Rs=Rm and Rt /Rm £ 500. Unlike the model tank experiment limitations (Roy & Appa Rao, 1976, 1978), in our numerical simulations, we could achieve perfect current focussing and evaluate the performance of existing alternate geometric factors due to Roy (1975) and Moran (1976). The computed Ra/Rm for LL7 was not even close to Ra/Rm under ideal conditions. But a simple two electrode device performs better in comparison to LL7 device provided AM= A1A2. This assertion is valid even for dynamic current ratio settings also.

Moho structure beneath the Eastern Ghat Mobile Belt and adjacent Bastar Craton as deduced from gravity anomalies
I.V.Radhakrishna Murthy, P.Rama Rao, K.S.Sudhakar and S.Bangaru Babu
Department of Geophysics, Andhra University, Visakhapatnam – 530 003
E-mail : ivr_murthy@yahoo.com


A typical gravity profile across Eastern Ghat Mobile Belt (EGMB) and adjacent Bastar Craton was selected from the available Bouguer Gravity Map (NGRI 1975) of India. The Bouguer anomaly map is deceptive as it revealed a low over a background rise of gravity anomaly from the west to the coast. A careful regional-residual separation brought out two prominent highs in place of the frequently quoted low. These highs could be explained by structures at the Moho.

Extreme Weather Events over India in the last 100 years

U.S.De, R.K.Dube1 and G.S.Prakasa Rao2
Visiting faculty Department of Environmental Science/University of Pune, India and
Former Additional Director General of Meteorology (Research), Pune
1Retd.ADGM, Flat No.69, Mausam Apartments, Delhi – 110 034
2India Meteorological Department, National Data Centre, Pune – 411 005



India being mainly an agricultural country the economy and further its growth purely depends on the vagaries of the weather and in particular the extreme weather events. The information on extreme weather events lie scattered in the scientific and technical papers and in the research work of many authors and if put together will help the research community for further analysis.
The authors in this paper present a factual and a brief review of the extreme weather events that occurred in India during the last 100 years (1991-2004). The socio-economic impacts of the extreme weather events such as floods, droughts, cyclones, hail storm, thunderstorm, heat and cold waves have been increasing due to large growth of population and its migration towards urban areas which has led to greater vulnerability. In recent years as per WMO review global losses from such extreme weather events is about US $ 50-100 billion annually with loss of life of about 2,50,000. Thus, greater efforts are needed to improve the forecast skill and use these better forecasts in disaster management.

Study of variations in Columnar Ozone Concentration at Rajkot

Nandita D.Ganguly and K.N.Iyer

Department of Physics, Saurashtra University, Rajkot - 360 005
E.mail: nanditad@icenet.net

The ozone data obtained from Total Ozone Mapping Spectrometer (TOMS) and Solar Back scatter Ultra Violet spectrometer (SBUV) on Nimbus 7 satellite have been used to study the variability of the total column amount of ozone and ozone concentration in different atmospheric layers respectively at Rajkot (22.30N, 70.8 0E) over a period from 1980 –2004. An examination of the monthly mean values obtained from TOMS indicates a marked seasonal variation with a maximum around June and a minimum around December.
The SBUV profile of springtime ozone indicates that the stratospheric ozone concentration at Rajkot has decreased consistently from 1982 to1999. The concentration is found to have increased suddenly in 2000 and further in 2001. Thereafter it decreased in 2002 and again increased in 2003. An insignificant overall downward trend is observed in the total column amount of ozone (0.85%) from 1997 to 2004. Latitudinal variation of ozone from Srinagar to Kanyakumari has also been studied for the year 2003, which indicates an increase in ozone concentration with latitude. The results are discussed in the light of photochemical and dynamical effects.

Thermal Remote Sensing Technique in the Study of Pre-Earthquake Thermal Anomalies

Arun K. Saraf and Swapnamita ChoudhuryDepartment of Earth Sciences, Indian Institute of Technology Roorkee,
Roorkee –247 667
Email: saraffes@iitr.ernet.in

Pressure built-up due to tectonic activities and also associated subsurface degassing might create changes in thermal regime prior to an earthquake event and if by any technique this change is detected, it can provide very important clues about future earthquake activities. Thermal satellite remote sensing which can sense the earth’s surface emissivity at regular interval introduces a new way of analyzing this phenomenon. Using NOAA-AVHRR thermal datasets, few major past earthquakes (Bhuj (India), Boumerdes (Algeria), Bam (Iran) etc.) were analyzed for studying the thermal changes before and after the earthquakes. The study was successful in detecting pre-earthquake thermal anomalies prior to all these earthquakes. Significant thermal anomalies with a rise in temperature of about 5-10°C in the vicinity of the epicenters have been observed. The anomalies disappeared along with the earthquake events. Further, using passive microwave SSM/I sensor datasets from DMSP satellites the occurrence of the phenomenon of pre-earthquake thermal anomalies for few more earthquakes around the world were observed.

Studies On Aberrations In Climate Impacts –
Water Balance Model

A.A.L.N.Sarma, S.Srinivas and A.Karthikeya1
Department of Meteorology & Oceanography, Andhra University,
Visakhapatnam – 530 003
1University of Toledo, Toledo, USA.
E-mail: aalnsarma_met@rediffmail.com

Global climate has been already perturbed due to variations in orbital forcing and man made factors and the footprints of it are traceable in the world climate spectrum (IPCC 1995). It is also evidenced world-wide that man made factors are aggravating the global effects of climate change in terms of triggering extreme weather events. The present paper address critically not only the spatiotemporal variations of moisture and thermal regimes of India through water balance model but also the occurrence of varied degrees of humidness and droughts in moist and dry climates respectively for selected stations that are drawn from its climate spectrum by selecting not less than two stations representing north and south of each of its climate zones. The paper then proceeds in analyzing proneness to varied degrees of droughts on All India basis. Climate stability and the basic water budget elements in extreme climate shifts for the selected stations are also studied. The investigation presents the modulation of basic water budget elements of All India during extreme climate shifts of wetness and dryness in the context of LNSO and ENSO signals and their climate implications are discussed. Finally, trends in All India moisture regime in the context of LNSO and ENSO signals are also reported.

Thermodynamic characteristics over North Bay of Bengal during active and weak monsoon phases of BOBMEX-1999
V.R.Mujumdar, U.V.Bhide, S.G.Nagar, S.P.Ghanekar and P.Seetaramayya

Indian Institute of Tropical Meteorology, Dr. Homi Bhabha Road, Pashan,
Pune –411 008
E-mail : vrmujumdar@hotmail.com

The Bay of Bengal Monsoon Experiment (BOBMEX-99) was carried out during peak monsoon months of July and August, 1999. The surface and the upper air Radiosonde data acquired onboard Ocean Research Vessel (ORV) Sagarkanya, at the stationary position 17.5°N, 89.0°E, during this experiment have been analysed for the periods 28 July to 5 August (Phase I) and 14 to 22 August (Phase II). The analysis of the various parameters over Indian region has shown intra-seasonal fluctuations of active and weak monsoon episodes during these two phases respectively. In addition, day to day variations in the vertical profiles of RH, qe, qes and P in the midtroposphere, at the stationary position of the ship, are observed to be more significant during Phase I than Phase II. The atmosphere near the surface over north Bay of Bengal seems to be conducive to the formation of convection during both the phases. However, over the north bay, three intense synoptic scale disturbances are formed during Phase I while, only a single upper air cyclonic circulation was developed during Phase II.