January, 2012

January, 2012   ||  Volume 16 No.1



South Indian Convergence Zone Model: A new approach to seasonal forecasting of summer monsoon rainfall in India Part II: Forecast for India as a whole

Onkari Prasad and O.P. Singh¹

43, Ritu Apartments, A-4 Paschim Vihar, New Delhi-110 063
¹India Meteorological Department, Lodi Road, New Delhi-110003

Evolution of South Indian Convergence Zone (SICZ) and its close relationship with the activity of southwest monsoon over Indian subcontinent had been discussed in Pt I of this paper by Prasad, Singh and Prasad (2010). This part of the paper aims at developing a technique to use this relationship in seasonal forecasting of summer monsoon rainfall. The method of assigning South Indian Convergence Zone (SICZ) Activity Index (SAI) using mean cloudiness and mean cloud anomalies has been discussed. SAI, ranked from 1 to 20, is inversely related to Indian Summer Monsoon rainfall (ISMR) and it is highly correlated (CC > .9) with it. Linear regression equations between SAI and ISMR, rainfall for India as a whole during monsoon months of June, July, August and September and bi-monthly periods of June+ July, July+ August and August+ September have been developed using data for a period of 25 years (1972-1997, except 1978 when cloud data were not available after 16th March). Data for a period of 13 years (1998-2010) have been used for verification of forecasts. Forecast verification has shown that the model is capable of producing reasonably good forecast of ISMR, rainfall in individual months and bi-monthly periods during southwest monsoon season.


Seismic Hazard Analysis of Low Seismic Regions, Visakhapatnam: Probabilistic Approach
B.V.K Lalith Kumar1, G.V Rama Rao2 and K Srinivasa Rao3
1Research scholar, Civil Engineering Department, Andhra University College of Engineering, Visakhapatnam.
2Prof. G.V Rama Rao, Professor in Civil Engineering, Andhra University College of Engineering, Visakhapatnam.
3Dr. K. Srinivasa Rao, Associate Professor, Andhra University College of Engineering, Visakhapatnam.
E-mail: bvklalitkumar@rediffmail.com

using probabilistic approach. Till 2004, Visakhapatnam is considered as stable region with low intensities. The previous earthquake history of region was considered to generate earthquake recurrence relation. The mean annual rate of exceedance is generated against peak ground acceleration considering study area site conditions. From the present investigation the values of peak ground acceleration varies from 0.004 g to 0.02 g with rate of exceedance 50% and 0.05 g to 0.12g for 10% rate of exceedance.
Keywords: Probabilistic seismic hazard, peak ground acceleration.

Current scenario of crustal deformation and strain distribution around the equatorial Indian Ocean region using GPS-Geodesy

A. Akilan *, S. Balaji**, E.C. Malaimani*, N. Ravikumar* and K. Abilash*
* National Geophysical Research Institute (CSIR), Hyderabad-500606
** Department of Coastal Disaster Management, Pondicherry University, Port Blair-744103
* Email: akilan123@yahoo.com

The crustal dynamics, strain distribution and the cause and effect of the geological processes in the equatorial Indian Ocean region were analysed using the Mahendragiri GPS data along with the network of stations around this region. The Mahendragiri GPS station is in the southern tip of the Indian Peninsula and forms a shorter baseline length with other nearby GPS stations. This has led to provide greater accuracy and lesser errors. The GPS data were processed using the Bernese 5.0 software which revealed that the baseline length changes from station Mahendragiri (MADG) to stations such as Maldives (MALD), Diego Garcia (DGAR), Seychells (SEY1), Cocos (COCO) are 0.0028±0.0009 m/yr, 0.0050±0.0008 m/yr, 0.0352±0.0019 m/yr and -0.0086±0.0.0020 m/yr respectively and the corresponding strain rates per year are 4.41102 x 10-9, 2.76637 x 10-9, 1.25036 x 10-9 and -2.79168 x 10-9 respectively. Further, the horizontal velocity of the MADG station is 0.0418 m/yr, moving towards N53°E.
The baseline length changes in negative values indicated the convergence and the positive values indicated the divergence of plate boundaries. Between Indian and Capricorn plates, north to south slow divergence in the western side of the Capricorn plate and north to south slow convergence in the eastern side are taking place. The propagation of strain rate differs from place to place which may be due to the asymmetry of the spreading rates of Mid-oceanic ridges. Most of the stress generated by the plate driving forces at the Mid-oceanic regions was transferred through the southern India to the northern part of India as evidenced by the visible creation of the Himalayas and the rise of the Himalayas in recent times.
The study has also revealed that there is very less deformation between MALD and MADG and it is not significant. Similarly, very less deformation exists between Chagos ridge and the southern tip GPS station of the Indian Peninsula viz Mahendragiri. The seismicity is varying from west to east in the equatorial Indian Ocean region. The GPS estimated strain rates have a good correlation with the seismicity of the Indian ocean region.  

A Study of Urban/Rural Cooling Rates in Thiruvananthapuram, Kerala
Shareekul Ansar, C.R. Dhanya, George Thomas, Aswathy Chandran1, Liji John1, S. Prasanthi 1, R. Vishnu, and E.J. Zachariah
Atmospheric Sciences Division, Centre for Earth Science Studies, PB 7250, Thuruvikkal P O,
Thiruvananthapuram - 695 031
1Department of Physics, University of Kerala, Kariyavattom, Thiruvananthapuram - 695 681
Email: shareekul@ gmail.com

The inhomogeneous cooling rates in the urban centre and adjoining suburban area and its effect on the Urban Heat Island (UHI) in Thiruvananthapuram city in peninsular South India was investigated. Air temperature variations across the study area were recorded by mobile traverse method. Cooling and warming rates in the urban centre and suburban area were derived from stationary air temperature recorders installed at these locations. The UHI intensity at this location was 2.4oC. Significant difference in the urban and rural cooling rates was observed. The maximum cooling rate in the city centre was 1.5oC/hr and 3.4oC/hr in the rural area.