April, 2007

April, 2007   ||  Volume 11 No.2

On the intriguing relationship between seawater salinity and d18O of Globigerina bulloides at higher latitudes

N.Khare, Rajeev Saraswat and S.K.Chaturvedi1

National Centre for Antarctic and Ocean Research

(Ministry of Earth Sciences), Headland Sada, Vasco-da-Gama, Goa- 403 804
1Shanmugha Arts, Science, Technology and Research Academy
SASTRA University, Tirumalaisamudram, Thanjavur - 613 402
E.mail : nkhare@ncaor.org

The δ18O variation in planktic foraminifera Globigerina bulloides from nineteen surface sediment samples, collected onboard ORV Sagar Kanya between 1.92°S and 55.01°S latitude in the Indian Ocean sector of Southern Ocean, have been analyzed to understand the relationship between oxygen isotopic fractionation and near surface seawater salinity. The initial intriguing results indicate that up to ~31°S latitude, salinity may influence the oxygen isotopic composition of the foraminiferal tests. However, beyond 31°S (further south) latitude, salinity does not appear to influence the G.bulloides oxygen isotopic composition significantly.


Groundwater Exploration in Hard Rock Areas of Vizianagaram District, Andhra Pradesh, India
S.N.Das, N.C.Mondal1 and V.S.Singh1
Action For Food Production (AFPRO), Hyderabad-500 007
1 National Geophysical Research Institute, Hyderabad-500 007
E-mail: surendra_n_das@rediffmail.com / ncmngri@yahoo.co.in

Identifying a good site for groundwater exploration in hard rock terrain is a challenging task. In hard rocks, groundwater occurs in secondary porosity developed due to weathering, fracturing, faulting, etc., which is highly variable and varies sharply within very short distances, contributing to near-surface inhomogeneity. In such situations topographic, hydrogeological and geomorphological features provide useful clues for the selection of suitable sites.
Initially based on the satellite imageries, topographical, geomorphological and hydrogeological inference promising zones were demarcated in hard rock areas of three Mandals (Seethanagaram, Salur and Pachipenta) of Vizianagaram District, Andhra Pradesh, India, an area of about 750 km2 to identify good locations for groundwater exploration. Total 100 Vertical Electrical Soundings (VES) were carried out using Wenner electrode configuration and an interactive interpretation of the VES data sharpened the information inferred from geomorphological and hydrogeological reconnaissance. Out of them 42 sites were recommended for drilling. Drilling with Down-The-Hole hammer (DTH) drill method was carried out for drilling in the recommended sites. 42 bore wells are drilled down to 50 to 80 m depths. The interpreted VES results are also correlated with the drilled bore well lithologs, showing good agreement with them. The yields of these bore wells vary from 1500 to 8000 lph, which are obtained from step draw down pumping test.

Rainfall and soil wetness response to ENSO and soil wetness estimation from remote sensing data

A.A.L.N.Sarma and T.V.Lakshmi Kumar
Dept of Meteorology & Oceanography, Andhra University, Visakhapatnam – 530 003
E.mail :aalnsarma_met@rediffmail.com & lkumar@ausi.com

Studies on water budget elements are of great importance in the context of geo-hydrological scenario. The estimation and analysis of soil wetness for a particular region is helpful in understanding the various mechanisms involved in the land surface hydrology. The present study attempts to understand the daily rainfall and soil wetness variations with respect to the geophysical indices of ENSO phases such as NINO 3 sea surface temperature and Southern Oscillation Index. The parameter soil wetness is derived from the water balance model on a daily basis. The study has been performed for the monsoon seasons of 1999 to 2002 over selected stations of Andhra Pradesh (120-200N; 760-860E). The study then proceeds in estimating the soil wetness using the brightness temperature data of Multichannel Scanning Microwave Radiometer of IRS-P4. As the study region consists of different types of soils such as medium black, redloam and laterite soils, the investigation makes use of the brightness temperature variations with reference to soil category in relation to soil wetness.

Variability of sea surface temperature field over Indian Ocean during 2002 and 2004
U.S.De and Medha Khole1
Visiting Faculty, Dept. of Environmental Sciences, University of Pune
1India Meteorological Department, Pune - 411 005

The role of Indian Ocean in climate variability has been extensively documented in the literature. During 1997, the year that witnessed the strongest El-Nino of 20th Century, significant warming was observed also over the Indian Ocean [Medha Khole (2000)]. There exist complex and interesting inter-relationships between Sea Surface Temerature (SST) over the Pacific and Indian Ocean basins and All India Summer Monsoon Rainfall (AISMR) [Medha Khole & De (2001), Rejeevan, Medha Khole & De (2000)]. In recent times, 2002 was the first all-India drought year, ranking fifth of the most severe droughts over India, after a continuous spell of 14 good monsoons which followed the previous all-India drought year of 1987. The seasonal rainfall (June-September) for the country as a whole, during 2002, was 19% below normal with 29% area of India experiencing drought conditions. The month of July reported the worst rainfall deficiency of 49% (IMD 2004). The rainfall of 1997, in spite of a major El Nino and considerable warming in the Indian Ocean, since January 1997 till December 1998, has been near normal. The inverse relationship between EI-Nino and AISMR, though, not one-to-one and has been weakening in recent years, remains one of the important parameters controlling the variability of AISMR. During 2002, the values of anomalies of SSTs over Nino 3 (5° N-5°S, 150° W- 90° W), Nino (5° N-5° S, 160° W-150° W) and Nino 1 + 2 (0-10° , 90° W- 80° W) regions of the Pacific Ocean exhibited warming during the Indian Summer monsoon season (June-July-August-September), however, the SSTs over Nino 1+2 region of the Pacific were colder than normal during this period. This warming pattern over Pacific Ocean is, thus, anomalous in nature. It was, therefore, considered interesting to analyse the variability of SST field over Indian Ocean during the phase of warm SSTs over the Pacific Ocean. With this backdrop, the cycle of evolution of SSTs over Indian Ocean (20° S - 25° N, 50° E - 100° E), during the period January 2001 to December 2003, has been analysed in this paper. Its relationship with the deficiency of AISMR during 2002 has also been assessed. It has been observed that the SST over Arabian Sea (5° N - 20° N, 50° E - 80° E) was colder than normal during June and September, 2002 while it was warmer than normal during July and August, 2002. The further details of SST variability are extensively discussed in the paper.



Comparison of drop size distribution between stations in Eastern and Western coasts of India
R.Harikumar, V.Sasi Kumar, S.Sampath and P.V.S.S.K.Vinayak

Atmospheric Sciences Division, Centre for Earth Science Studies, Thiruvananthapuram - 695 031
Email :harikumarraj@yahoo.com

A Joss-Waldvogel type disdrometer was installed at Thiruvananthapuram, Kochi, and Sreeharikotta (SHAR) during various periods. This paper presents results from the analysis of the data.
Drop Size Distribution (DSD) and rainfall rate for each minute were computed from the disdrometer data, and the entire data for each month were sorted by rainfall rate. The data were then divided into different ranges of rainfall rate and DSD computed for each. The average DSD for each range was fitted with a lognormal distribution function of the form
N(D) = (a0/D) exp (-0.5(ln( D)-a1)/a2)2
where D = drop diameter, N(D) = number of drops/m3/mm interval.
The results show the following: For the lowest rainfall intensity, the distribution is narrow and is dominated by small drops. With increase in intensity, the distribution spreads out and more larger drops appear. However, in some cases, the data does not follow the lognormal distribution.
The total number of drops, NT, geometric mean diameter, Dg and standard geometric deviation, s was derived from the ai. NT showed a tendency to increase slightly with rainfall rate. Dg followed a simple power relationship of the form Dg = b0Rb1. The standard geometric deviation did not show any significant dependence on rainfall rate.
The characteristics of rainfall in terms of the three parameters for coastal stations on the west coast are similar. The rate of increase of NT is higher at SHAR than at Kochi. NT is higher at SHAR than at Kochi for any particular rainfall rate, indicating that, unlike Kochi and other stations on the western coast, rainfall at SHAR is made up of more number of smaller drops.




Turbulent kinetic energy and its dissipation rate of the Indonesian throughflow region via Lombok and Savu Straits
Vivek Kumar Pandey and Avinash Chandra Pandey
K.Banerjee Centre of Atmospheric and Ocean Studies, Institute of Interdisciplinary -Studies,
University of Allahabad, Allahabad – 211 002.
E-mail: vivekkpandey@rediffmail.com

Turbulent kinetic energy (TKE) and its dissipation rate are estimated at Lombok (115° 50’E, 8° 30’ S) and Savu (122°E, 9° 30’ S) strait of Indonesian Throughflow (ITF), in the upper and middle layers. It is the region having most complicated geometry of the world ocean. TKE is of the order of 10-3 m2s-2 in the upper layer whereas it is 10-4 m2s-2 in the middle layer. Corresponding values of TKE dissipation rate are of the order of 10-6 m2s-3 and 10-8m2s-3.




Impact of barren island volcanic eruptions on climatic conditions over Port Blair
P.S.Kannan and Vijay Kumar Soni1
Regional Meteorological Centre, IMD, Chennai - 600 006
1Meteorological Office, Pune - 411 005
Email: kannan_imd@yahoo.com

The impact on climate parameters, direct radiation, sunshine duration, precipitation chemistry and turbidity coefficient over Port Blair are examined using 31 years of data during major volcanic eruptions of Barren Island volcano. A fall of about 0.8oC to 1oC in mean maximum and minimum temperature is observed during the period of volcanism (Mar-Oct, 1991 and Dec, 1994 –May, 1995). However there is no evidence of winter warming during this period. Though there is no significant reduction in mean annual bright sunshine duration, a drop of the order of 0.8 to 1.2 hours is noticed during the concerned months with respect to volcanically quiescent period. Measurements on cloudless days showed significant changes in solar radiation during 1991. An increase in diffuse sky total radiation and a concomitant decrease in total radiation were observed. Extreme perturbations in turbidity values are noticed during the major volcanic eruptions.