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Document Type:Latin Dissertation
Language of Document:English
Record Number:54199
Doc. No:TL24153
Call number:‭3273676‬
Main Entry:Thaned Rojsiraphisal
Title & Author:A study of variability in the North Indian OceanThaned Rojsiraphisal
College:University of Colorado at Boulder
Date:2007
Degree:Ph.D.
student score:2007
Page No:169
Abstract:The Indian Ocean is one of the three principal ocean basins in the world, yet it is the least explored. It is unique in that it is not connected directly to the Arctic and is forced by seasonally reversing monsoons, which play a very important role in its variability. Previous studies of its circulation are based on sparse, incomplete data collected sporadically at different locations and times and/or satellite data, which only observe properties near the sea surface. In this study, a primitive equation-based, data-assimilative model has therefore been applied to overcome this problem and provide data needed for a systematic study of the variability in the North Indian Ocean. The University of Colorado version of the fully nonlinear sigma-coordinate Princeton Ocean Model (CUPOM) has been applied to the North Indian Ocean. This is the first study that runs the model with data assimilation in hindcast mode at a relatively high 1/4° horizontal resolution. Unlike other ocean models that have been used to study the Indian Ocean, the present model produces an estimate of the oceanic state, and is able to resolve various meso-scale features occurring in the North Indian Ocean for 13 years covering the period from 1993 to 2005. The resulting comprehensive 3-D data set can be used for improving our understanding of the variability and look at the dynamical processes causing the variability in the North Indian Ocean. This study also makes it possible to setup an operational nowcast/forcast system for the region. Hindcast results are first validated with available observations and other available numerical models to ensure that the hindcast has reliable skill. The data are then analyzed with mathematical/statistical methods. Principal Component Analysis, Wavelet analysis and Multi-Taper Method-Singular Value Decomposition analysis (MTM-SVD) have been applied to the model output in order to understand the variability in the circulation of the North Indian Ocean. The principal component analysis used in this study identifies uncorrelated interannual variability. It also provides principal component time series associated with each spatial pattern, which are analyzed by wavelet analysis in order to localize the time when those patterns occur. The MTM-SVD is a combination of two techniques: Multiple-Taper spectrum, which yields information in the frequency domain, and Singular Value Decomposition method. The combination of these two techniques can consistently reveal an oscillatory signal, both its spatial structure and narrowband frequency-domain structure. It can be used to identify frequencies where a large variance occurs and also to reconstruct the time history and spatial pattern associated with the frequency of interest. MTM-SVD has been applied to the near surface hindcast data to study the variability in the North Indian Ocean. We next investigate the evolution of meso-scale features in the western boundary current, the Arabian Sea and the Bay of Bengal using currents at 30 m and SSH as identifiers of the existence, development and evolution of the meso-scale features. We also investigate the highly anomalous events of 1994 and 1997-98 which are evident in the zonal wind, sea surface height, sea surface temperature, and zonal surface current. Lastly, the oceanic heat transport and the heat budget of the North Indian Ocean are examined using the 13-year hindcast. This study should provide a better understanding of the variability and oceanic heat transport in the North Indian Ocean. It should be of help in understanding the monsoons, which impact more than a billion people dependent on the monsoons for sustenance. Knowledge of the currents and their variability should also be of help in offshore exploration and production activities as well as marine transportation activities.
Subject:Earth sciences; Indian Ocean; Monsoons; Ocean circulation; Ocean variability; Oceanography; 0415:Oceanography
Added Entry:L. J. Kantha, Keith
Added Entry:University of Colorado at Boulder