April, 2006

April, 2006   ||  Volume 10 No.2

Declination effects on magnetospheric ring current over the magnetic equator

Physical Research Laboratory, Ahmedabad - 380 009
E-mail: profrgrastogi@yahoo.com, parvs@prl.ernet.in

It has been shown that the magnetospheric ring current has a very significant effect on the storm time variations of the Eastward component (Y) besides the horizontal component (H) at ground magnetic observatories. The storm time variation of H is a depression at low and middle latitude at any of the longitudes, roughly following the variations of Dst index. The storm time variation of the Y at equatorial electrojet region shows a large depression in East Brazil longitudes and a large increase in East African longitudes, and only small changes in the Pacific longitudes. These changes are shown to be related to the index sin-1 (y - D) where y and D are the dipole and dip declination at the stations. At equatorial stations the ionospheric Sq current flows along the dip equator while the disturbance ring current flows along the dipole equator.

Tsunami warning systems for the hyperbolic (Pacific), parabolic (Atlantic) and elliptic (Indian) oceans


T.S.Murty, A.D.Rao1*, N.Nirupama2 and I.Nistor1

Department of Civil Engineering, University of Ottawa, Ottawa, Canada
E-mail: smurty@hotmail.com, nistor@genie.uottawa.ca
1Centre for Atmospheric Sciences, Indian Institute of Technology, New Delhi, India.

E-mail: adrao@cas.iitd.ernet.in
2Applied Disaster & Emergency Studies, Brandon University, Brandon, Canada.

*Corresponding author

It is shown that the Pacific, Atlantic and Indian Oceans have very different tsunami characteristics. Hence the numerical modelling of tsunamis in these three oceans has to be quite different, with particular relevance for the tsunami warning system. The Pacific and Indian Oceans generate ocean-wide tsunamis, but with one major difference. The Indian Ocean, being much smaller in geographical extent than the Pacific Ocean, has shorter tsunami travel times and in the Indian Ocean, reflected waves from the coast lines can interact with subsequent tsunami waves. Hence to determine the maximum tsunami amplitudes in the Indian Ocean, boundary reflections must be taken into account. In the much larger Pacific Ocean, the influence of boundary conditions is somewhat minimal. In the Atlantic Ocean, unlike in the Pacific and Indian Oceans, there are no converging tectonic plates, where tsunamigenic earthquakes could be generated. The mid-Atlantic Ridge is a diverging plate boundary. In the Atlantic Ocean, there are tsunamis only in the marginal seas at the edges. Since tsunamis travel slower in shallow water, Atlantic tsunamis are slow moving, somewhat like a diffusion or a Parabolic process. On the other hand, Pacific tsunamis, which are more influenced by initial conditions, are a Hyperbolic process. Indian Ocean tsunamis, which are strongly influenced by the boundary conditions, have to be modelled as an Elliptic process.

Analysis of Triple Collocation Method for validation of model predicted significant wave height data


G.Muraleedharan, A.D.Rao, Mourani Sinha and D.K.Mahapatra
Centre for Atmospheric Sciences, Indian Institute of Technology, Delhi, Hauz Khas,

New Delhi -110 016.
E-mail: muralg@yahoo.com

The validation of the model (Wam, Swan and Nested-Swan) predicted significant wave height data using the new triple collocated statistical method suggests that the predicted values are sufficiently accurate when compared with the buoy measurements. The Wam and Nested-Swan significant wave height estimations give significant positive correlation with deep and shallow water buoy measurements respectively. The linear regression (LR) method is inconsistent and the new method (Functional Relationship, FR) paves way for estimating the variances of the errors in measuring and predicting the physical truth (here significant wave height). The larger the random errors, the larger are the deviations between FR and LR lines. The FR model lines align with the best fit-line (x=y) while comparing the model results and buoy measurements. Also the deviations of the data from the FR model lines are a minimum. Thus we can say FR model as compared to LR model is more realistic when inherent error exists in both cases, measurement by instruments and model predictions.

Sensitivity of Oceanic Mixed Layer to Different Model Resolutions in Response to Indian Ocean Cyclone

A.A.Deo, D.W.Ganer and P.S.Salvekar

Indian Institute of Tropical Meteorology, Dr.Homi Bhabha Road, Pashan,

Pune - 411 008
E-mail: aad@tropmet.res.in

Present work deals with the numerical investigation of the oceanic upper mixed layer response to Indian Ocean cyclones by changing different model parameters such as horizontal resolution, vertical temperature gradient in a simple 1½-layer wind driven reduced gravity ocean model. The sensitivity experiments are performed for a cyclone moving along a northward track, initially. Cyclones in the Arabian Sea and Bay of Bengal during the year 2004 are chosen. The sensitivity of ocean response to model resolution is examined by increasing the model resolution from ½° x ½° to 1/8 x 1/8° and 1/12° x 1/12°. Further, the sensitivity to initial vertical temperature gradient is also studied. The model simulated SSTs are compared with the observed SSTs during cyclone period. It is found that the cooling in model SSTs is in agreement with that in the observed SSTs for each case.

Heat storage variability in the Indian Ocean using Topex/Poseidon Altimeter Data

B.H.Vaid, C.Gnanaseelan*, B.Thompson, Ayantika De and P.S.Salvekar

Indian Institute of Tropical Meteorology, Dr.Homi Bhabha Road, Pashan,

Pune – 411 008
*E-mail: seelan@tropmet.res.in, pss@tropmet.res.in

Sea surface height anomalies (SSHA) derived from the Topex/Poseidon (T/P) satellite are used for computing heat storage anomalies (HSA) and heat storage rates (HSR) over the north Indian Ocean [20oS – 25oN and 35oE – 115oE] for a period of 10 years (1993-2002). In normal years during September to November positive HSA and HSR were observed in the region 10oS - Equator, 90oE -110oE. But during the years 1994 and 1997 negative HSA and HSR were observed in this region, this interannual variability has recently been addressed as Indian Ocean Dipole (IOD). The heat content anomaly clearly showed the existence of the dipole like structure in the equatorial Indian Ocean (IO) in 1994 and 1997. The T/P measurement showed large SSHA in the western equatorial Indian Ocean during 1994-1995 and 1997 -1998 IOD events that represent the oceanic response to the surface wind forcing. These anomalies in turn played an important role in forming the sea surface temperature anomalies (SSTA). The 1997 Dipole mode structure was observed to be stronger than 1994 and that can be clearly seen in calculated HSA, HSR, T/P SSH anomalies, thermocline depth (D20) anomaly derived from Simple Ocean Data Assimilation (SODA) and in HADISST anomaly. The Rossby wave propagation is found to have a good correlation with the heat content anomaly derived from Topex/Poseidon sea surface height anomalies. During the dipole years 1994-95 and 1997-98 the anomalous westward propagation of SSHA and HSA were clearly observed especially in the region south of 7oS and strengthened in 80 - 90oE belt. Wind stress curl anomalies play an important role in strengthening this propagation in 80-90oE and hence warming the west Indian Ocean in the early months of 1998. It was seen that positive and negative dipole years are inversely correlated in the southeastern equatorial Indian Ocean (10oS - Equator, 90oE -110oE). To understand the interannual variability of upper ocean SSHA, Complex Empirical Orthogonal Function (CEOF) has been applied to T/P SSHA and HSA. IOD has been shown to be the leading mode of the interannual variability of the upper ocean SSHA and HSA. The westward propagation of the phase is in agreement with the sea saw thermocline variability observed in the equatorial Indian Ocean.


Hydraulic potentials due to finite-length line source over an anisotropic aquifer system with inclined bedding planes

Mathew K.Jose and Rambhatla G.Sastry1
National Institute of Hydrology, Jalvigyan Bhawan, Roorkee -247 667
E-mail: mjose@nih.ernet.in
1Department of Earth Sciences, I.I.T, Roorkee-247667, India
E-mail: rgss1fes@iitr.ernet.in / rgssastry@yahoo.com

Water resources planning and management require estimation of seepage losses from surface water bodies like streams, rivers and canals to aquifer systems or recharge characteristics of aquifer systems. In such cases, numerical groundwater flow models are not quite capable of simulating flow in anisotropic aquifer systems with inclined planes of stratification. However, analytical results can be useful for simulating hydraulic heads/ flow in such systems. An analytical procedure for computing hydraulic heads in such a homogeneous anisotropic aquifer system due to a finite-length surface water source is presented. The procedure has been demonstrated using numerical experiments with the results as equipotential plots. Different coefficients of anisotropy, and orientation of bedding planes have been considered for the illustrations.


A semi-analytical procedure for the computation of hydraulic
heads and streamlines in multi-layered aquifer systems

Rambhatla G.Sastry and Mathew K.Jose1
Department of Earth Sciences, IIT, Roorkee-247 667
E-mail: rgss1fes@iitr.ernet.in / rgssastry@yahoo.com
1National Institute of Hydrology, Jalvigyan Bhawan, Roorkee-247 667
E-mail: mjose@.nih.ernet.in

Analytical solutions are presented for the computation of steady-state hydraulic heads and streamlines in multi-layered aquifer systems. Considering the analogy between direct-current electrical flow and groundwater flow, the proposed methodology, point source over n-layer (NLPNT) invokes the geoelectric sounding principles. Numerical examples for the cases of a 3, 4, and 5-layered aquifer system are presented. Comparison of NLPNT solutions with the corresponding solutions obtained from popular MODFLOW indicate that the NLPNT is quite cost-effective in computing hydraulic heads and streamlines.


Modelling and prediction of rainfall using artificial neural network and ARIMA techniques

V.K.Somvanshi, O.P.Pandey, P.K.Agrawal, N.V.Kalanker1, M.Ravi Prakash and Ramesh Chand
National Geophysical Research Institute, Hyderabad -500 007
2Swami Ramanand Teerth Marathwada University Nanded – 431 602

Climate and rainfall are highly non-linear and complicated phenomena, which require sophisticated computer modelling and simulation for accurate prediction. An artificial intelligence technology allows knowledge processing and can be used .as forecasting tool. For example, the application of Artificial Neural Networks (ANN), to predict the behaviors of nonlinear systems has become an attractive alternative to traditional statistical methods. In this paper, we present tools for modeling and predicting the behavioral pattern in rainfall phenomena based on past observations. The paper introduces two fundamentally different approaches for designing a model, the statistical method based on autoregressive integrated moving average (ARIMA) and the emerging computationally powerful techniques based on ANN. In order to evaluate the prediction efficiency, we made use of 104 years of mean annual rainfall data from year 1901 to 2003 of Hyderabad region (India). The models were trained with 93 years of mean annual rainfall data. The ANN and the ARIMA approaches are applied to the data to derive the weights and the regression coefficients respectively. The performance of the model was evaluated by using remaining 10 years of data. The study reveals that ANN model can be used as an appropriate forecasting tool to predict the rainfall, which out performs the ARIMA model