Tidally-modulated high frequency internal waves in Gautami-Godavari estuary, East coast of India

1695-1707<span style="font-size:9.0pt;line-height: 150%;font-family:" times="" new="" roman";mso-fareast-font-family:calibri;mso-bidi-font-family:="" "times="" roman";mso-ansi-language:en-us;mso-fareast-language:en-us;="" mso-bidi-language:ar-sa"="" lang="EN-US">Time series temperature and salinity (at 1 hour interval) and currents data (10 min interval) at surface (3 m) and bottom (14 m), collected in the   Gautami-Godavari estuary during 25-27 September 2008 were utilized to document the characteristics of Internal waves (IWs) and to infer their generation mechanism.  Based on the stability criteria, two High Frequency (HF) significant modes in the Internal Wave (IW) field at frequencies 96.67 cph (10 m depth) and 71.15 cph (14 m depth) have been identified. At these modes, IW parameters viz., wave length (L), wave number (κ), potential energy (PE), baroclinic potential energy (BPE) and phase speed (ci)  and displacement function (η(z,t)) have been computed (with salinity and currents data) objectively by adopting well known harmonic technique through Principal Component Analysis (PCA). Results revealed that (1) first mode: IW was found to move with a phase speed of 0.13 m s-1 and wave length of 0.0056 km (wave number=178.64 cycles km-1) having energies of 0.0006 J m-2 (potential) and 0.0027 J m-2 (baroclinic) whereas (2) second mode:  0.09 m s-1, 0.0076 km, 131.48 cycles km-1, 0.0055 J m-2, 0.020 J m-2 and 0.094 m s-1 for L, κ, PE, BPE and ci respectively. η(z,t) was found to be positive (elevation-type IWs) and negative values (oscillation-type) during IW propagation of two modes respectively wherein  mode 2 is more energetic (8 times) than mode 1. Tidally-modulated force may be the possible mechanism to generate HF IWs under ebb period.</span

Utility of natural generalised inverse technique in the interpretation of dyke structures

285-298Forward and Inverse methods of magnetic interpretation have been used to estimate the parameters of dyke like intrusion over the eastern continental shelf of India. In the forward problem, the tentative parameters of the causative source are assumed and anomalies are calculated using the anomaly equation, while inverse problem refers to methods of tracing the boundaries or outlines of anomalous bodies using an iterative approach. While solving the inverse problem, data kernel has been generated through the model (i.e. partial derivatives of magnetic anomaly function with respect to model parameters at each station forming the kernel). In solving the coupled eigenvalue problem of covariance matrices of data kernel, Singular Value Decomposition (SVD) has been performed to build Generalised Inverse Operator (GIO). This GIO is operated on the observed anomaly (with reference to the calculated) to yield improved model parameters. Data and model resolution matrices are computed to check the correctness of the solution and further analysis. The marine magnetic total field anomaly of continental shelf of Visakhapatnam is interpreted using GI technique, which revealed the causative source of the anomaly as a dyke model at a depth of 120 m below seabed