July, 2014

July, 2014   ||  Volume 18 No.3



An investigation on the consequential features of Southwest Monsoon-2007 Onset and Super cyclone 'Gonu' using Satellite, Model and Ground-based data

R. Harikumar1*, Hamza Varikoden2, C. A. Babu3, R. Vishnu4, and G. Mohan Kumar5

1ESSO-Indian National Centre for Ocean Information Services, MoES, Govt. of India, Hyderabad-90
2Indian Institute of Tropical Meteorology, MoES, Government of India, Pashan, Pune-08
3Department of Atmospheric Sciences, Cochin University of Science and Technology, Cochin-16
4PG Dept. of Physics, Sree Krishan College, Guruvayur
5Centre for Earth Science Studies, Akkulam, Thiruvananthapuram-31
*Corresponding author E-mail: harikumar@incois.gov.in

Onset features of the Summer monsoon-2007 were analyzed using data from five different sources, namely, the Tropical Rainfall Measuring Mission (TRMM) 3-hourly rainfall, National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) wind reanalysis data set, NOAA Outgoing Longwave Radiation (OLR), cloud imageries from the meteosat satellite,cloud base height and cloud occurrence frequency from a ground-based Vaisala Laser Ceilometer at Thiruvananthapuram. On the day of onset, 33 mm of rainfall was registered by TRMM satellite over south Kerala region with 80% cloud frequency and an averaged cloud base height of 2 km. On the next day, the formation of ‘Gonu’ super cyclone as a consequence of the convergence of monsoon onset surge in the Arabian Sea has caused the dissipation of cloud bands in the Arabian Sea and in the Bay of Bengal, except over the region of the system. This caused a lull situation for about ten days after the India Meteorological Department (IMD) declared monsoon onset. In fact, the remarkable characteristics of onset, such as deepening of westerlies and strengthening of low level jet streams were observed only after two weeks of IMD declared monsoon onset. Another unique behavior of 2007 monsoon onset was that the Arabian Sea branch of monsoon onset surge has advanced faster than the Bay of Bengal branch in the early stage.


Facts about Tsunami: Its origin, earthquake link and prediction: An Opinion

A.B. Roy

INSA Honorary Scientist, Department of Geology, Presidency University, Kolkata 700073
Email: ashitbaranroy@gmail.com

Tsunami occurs when there is a sudden and massive vertical displacement of ocean water because of tectonically induced deformation in the Ocean Crust. In spite of close association, there is no direct cause-and-effect relationship between earthquake and Tsunami. The earthquake waves which possess elastic properties cannot pass through a liquid medium, and hence are ineffective in generating a Tsunami. Tsunami may be generated because of several other non-tectonic reasons. But these are not as devastating as the tectonic types. Prevention of Tsunami is not possible, but warning signals should be seriously considered for mitigating the destruction caused by Tsunami.


Climate variability in Dharamsala - a hill station in Western Himalayas
A. K. Jaswal, Naresh Kumar1 and P. Khare
India Meteorological Department, Shivajinagar, Pune - 411005
1India Meteorological Department, Lodi Road, New Delhi - 110003
Email: jaswal4@gmail.com

Climate change worries the scientific community world over as the surface air temperature increased by 0.74°C during 1906-2005. The impacts of warming in mountainous regions get magnified because of large variations in altitude within small distance. This study focuses on the variability and trends of air temperature and rainfall during 1951-2010 in Dharamsala, a hill station in Himachal Pradesh located in Western Himalaya , India. The results of the trend analysis show a statistically significant increase in monthly mean maximum temperature (January, April, November and December), mean temperature (January), mean diurnal temperature range (January to May, July to December), total monthly rainfall (June) and 24 hour heaviest rainfall (June). Statistically, significant decreasing trends are found in monthly mean minimum temperature (May to October), mean temperature (June), monthly rainfall (January and August) and rainy days (January). Seasonally, significant increasing trends are observed in mean maximum temperature (winter and post monsoon), mean temperature (winter) and diurnal temperature range (all seasons) and significant decreasing trends in minimum temperature for summer, monsoon and post monsoon. Annual mean maximum temperature and mean diurnal temperature range are significantly increasing at a rate +0.018oC/year and +0.033oC/year, respectively ,while annual mean minimum temperature is significantly decreasing by -0.018oC/year. The trend analysis of air temperature and rainfall reveals a tendency of increase in maximum temperature, decrease in minimum temperature and rainfall , which may have impacts on agriculture, water resources, human health and natural environment in Dharamsala and surrounding region.

Delineation of groundwater potential zones along the coastal parts of Kanyakumari district, Tamilnadu
Y. Srinivas1*, D. Hudson Oliver1, A. Stanley Raj2, N. Chandrasekar1
1Centre for GeoTechnology, Manonmaniam Sundaranar University, Tirunelveli, Tamilnadu
2Vel Tech Dr. RR & Dr. SR Technical University, Avadi, Chennai 600 062
Email: drysv@yahoo.co.in

Electrical resistivity method is widely used in groundwater exploration studies because it is a fast and less expensive geophysical tool. The vertical electrical soundings were carried out at 21 sites along the coast of Agastheeswaram taluk between Muttom and Vattakkotai, Kanyakumari district, Tamil Nadu using the Schlumberger configuration. The field data were interpreted using the IPI2win software and the resistivity versus depth models for each location was prepared. Groundwater in this region occurs mainly under semi confined to confined conditions. The study was aimed at improving the success rate of boreholes. The results obtained from the interpreted data indicate three to four geoelectric layers. The thickness of the first and second layers lies between 1 to 4.7m and 1.1 to 13.3m respectively. The sounding locations showing resistivities between 18-100 ohm m are expected to be potential zones with potable water as revealed by TDS value of groundwater from the nearby wells. The areas affected by over exploitation and saline water intrusion into groundwater are also delineated by very low resistivity zones (between 1and 9.6 ohm m) .The geoelectric sections prepared on the basis of VES results clearly delineated the fresh and saline water zones both laterally and vertically. The saline water intrusion can be reduced significantly by construction of barriers to prevent the intrusion of saline water from the nearby estuaries and salt pans. It is also necessary to construct structures to increase the groundwater level through artificial recharge. The saline water intrusion can also be reduced by adopting a suitable pumping pattern. Thus, these studies supported by available litholog data helped in suggesting suitable management techniques to prevent the groundwater degradation.

South Indian Convergence Zone Model: A new approach to seasonal forecasting of summer monsoon rainfall in India Part VI: merits of the model and limitations in seasonal forecasting of rainfall in India
Onkari Prasad, O.P. Singh* and K. Prasad**
43, Ritu Apartments, A-4 Paschim Vihar, New Delhi-110063
*India Meteorological Department, Lodi Road, New Delhi-110003
** D-6, Seema Apartments, Sector 11, Dwarka, New Delhi-110085
Email: prasadonkari123@yahoo.in; singh.op@imd.gov.in; kprasad@rediffmail.com

South Indian Convergence Zone (SICZ) and its role in the development of Indian summer monsoon, forecast of rainfall for India as a whole, in individual meteorological subdivisions of India and districts of the meteorological sub-division of Tamilnadu and Pondicherry, role of intra-seasonal changes in Tropical Pacific Ocean in inter-annual variability of Indian Summer Monsoon Rainfall (ISMR) and relative roles of Equatorial Pacific and Indian Oceans in inter-annual variability of ISMR had been discussed in Part I-V of the paper respectively. SICZ model appears to be a robust one as it has produced reasonably good forecasts, for the past 23 years, for India as a whole and in a number of meteorological subdivisions including the forecast of seasonal rainfall for the districts in the subdivision of Tamilnadu and Pondicherry for the past four years beginning from 2009. SICZ model has several advantages. Merits of SICZ model and limitations in long range forecasting of summer monsoon rainfall, because of large intra-seasonal changes in monsoon circulation system over Indian subcontinent more particularly during the second half of the season in some of the years, have been discussed in this concluding part of the paper. The Indian subcontinent experiences large variability in monsoon rainfall distribution at temporal and spatial scale. Subdivision and district level forecasts of monsoon rainfall available from the model could become an important input in planning of agricultural operations, water management and disaster mitigation strategies.

Horizontal to vertical spectral amplitude ratio of seismic waves as an effective tool for site classification: A study from Chennai, Tamilnadu
P. Prabhakar Prasad*, S.Trupti, P.Pavan Kishore, K.N.S.S.S.Srinivas and T. Seshunarayana
CSIR-National Geophysical Research Institute, Council of Scientific and Industrial Research, Hyderabad-500 007
*E-mail: pvsspp@gmail.com

Passive and active seismic studies were carried out in and around Chennai city to estimate H/V spectral ratio for site classification for use in microzonation. Passive seismic studies included monitoring of ambient seismic noise over a period of time. Active seismic studies carried out using hammer impact as a seismic source to determine the fundamental frequency and the related amplification of soils. The results of the studies conducted at 204 sites in Chennai region revealed good correlation with with different near surface geological data. Hence, we conclude H/V spectral ratio obtained from the short duration data is adequate to classify the sites for the purpose of microzonation of a region.

Conductive heat flow in the Godavari sub-basin (Pranhita-Godavari valley), Indian shield and its significance
Mohan L. Gupta*, S.R. Sharma, and Vijay K. Rao
Formerly with CSIR- National Geophysical Research Institute, Hyderabad – 500 007, India
E-mails: *drmohanlalgupta@yahoo.com; srsharma1946@gmail.com; vijay_k_rao@yahoo.com

The Godavari sub-basin (GSB) is a part of the Gondwana Pranhita – Godavari Valley (PGV) of the Indian Peninsular Shield, which is a major NW-SW lineament where sediments from Neoprotrozoic to Mesozoic are present.
The objective of this paper is three fold viz ; i) an examination and analysis of available measured heat flow values(HFU) of the GSB for hydro-geological perturbations and obtain the most probable true magnitude of conductive heat flow (CHF) value, in cases wherever it is possible, ii) to decipher the thermal characteristics of the GSB through a comparison of its CHF values with the other available heat flow data in its surrounding region of the Indian Shield, and iii) to infer the main deep thermal characteristics of the GSB through an examination of the results so obtained and the inferences from some reported geo-data of the GSB and PGV.
Based on our analysis we obtain; i) that the CHF values at three locations of the NW part of the GSB viz; Indaram, Godavarikhani and Bellampalli areas are 50, 52, and 49 mWm-2 respectively ,and ii) that the average CHF of the GSB is of the same order as the average HFU for the Chandrapur ,a NE sub-basin of the PGV ( 51mWm-2 ) and the Wardha – Yavatmal Deccan Trap region ( Av = 52mWm-2), below which Gondwana sediments, likely extension of the PGV Gondwana rocks ,do occur. The CHF values of the GSB are similar to those that are reported for Proterozoic Bastar Craton, which lies towards NE of GSB and also similar to Mailaram high which is a large outcrop of Archaean- Proterozoic group of rocks in the SE sector of the GSB. Available data on Chemical analysis of thermal waters of the area showed their meteoric origin and association with sedimentary rocks and non-magmatic sources.
Based on these observations, presence of cooling magmatic bodies within the crust of GSB and a shallow Moho below it are strongly ruled out. Available geo-data (geological, gravity, seismic etc.) of GSB are in conformity with these inferences.

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