Sabin, T P; Dr.Babu, C A(Cochin University of Science and Technology, June , 2011)
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Abstract:
The SST convection relation over tropical ocean and its impact on the South Asian monsoon
is the first part of this thesis. Understanding the complicated relation between SST
and convection is important for better prediction of the variability of the Indian monsoon
in subseasonal, seasonal, interannual, and longer time scales. Improved global
data sets from satellite scatterometer observations of SST, precipitation and refined reanalysis
of global wind fields have made it possible to do a comprehensive study of
the SST convection relation. Interaction of the monsoon and Indian ocean has been
discussed. A coupled feedback process between SST and the Active-Break cycle of the
Asian summer monsoon is a central theme of the thesis. The relation between SST and
convection is very important in the field of numerical modeling of tropical rainfall. It is
well known that models generally do very well simulating rainfall in areas of tropical
convergence zones but are found unable to do satisfactory simulation in the monsoon
areas. Thus in this study we critically examined the different mechanisms of generation
of deep convection over these two distinct regions.The study reported in chapter 3 has shown that SST - convection relation over the
warm pool regions of Indian and west Pacific oceans (monsoon areas) is in such a way
that convection increases with SST in the SST range 26-29 C and for SST higher than
29-30 C convection decreases with increase of SST (it is called Waliser type). It is found that convection is induced in areas with SST gradients in the warm pool areas of
Indian and west Pacific oceans. Once deep convection is initiated in the south of the
warmest region of warm pool, the deep tropospheric heating by the latent heat released
in the convective clouds produces strong low level wind fields (Low level Jet - LLJ)
on the equatorward side of the warm pool and both the convection and wind are found
to grow through a positive feedback process. Thus SST through its gradient acts only
as an initiator of convection. The central region of the warm pool has very small SST
gradients and large values of convection are associated with the cyclonic vorticity of the
LLJ in the atmospheric boundary layer. The conditionally unstable atmosphere in the
tropics is favorable for the production of deep convective clouds.
Description:
Department
of Atmospheric Sciences, Cochin University of Science and Technology
Nithin, Viswambharan; Dr.Mohan Kumar, K(Cochin University of Science and Technology, April 23, 2012)
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Abstract:
This thesis entitled southern hemispheric features and their Teleconnection with indian summer monsoon.Southern hemisphere is entirely distinct from the northern hemisphere in many aspects, which is well reflected in atmospheric and oceanic properties.The thesis consists of eight chapters, in which the first chapter contains an overview of southern hemisphere. In this chapter, variability in southern hemisphere is described along with Indian summer monsoon and its teleconnection. The different types of data sets used and various methodologies adopted in the present thesis were described in Chapter 2. The period of climate shift and the magnitude of anomalies after the climate shift, which extended from troposphere to stratopause level, were investigated in detail and presented in chapter 3.
Chapter 4 depicts the recent trend and variability in southern stratosphere. The higher order variability during various months and the frequency of extremity is included in this chapter.Climatology of divergence and convergence after the documented shift is reported in chapter 5.Southern extratropical connection to Indian summer monsoon through the modulation of SAM is presented in Chapter 6.Chapter 7 deals with the modulation of SAM‐Monsoon link through North Atlantic Oscillation.
Description:
Department of Atmospheric Sciences
Cochin University of Science and Technology
Prasanth A, Pillai; Dr.Mohan Kumar, K(Cochin University of Science & Technology, October , 2008)
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Abstract:
The present study illustrates the biennial oscillation in different ocean-atmosphere
parameters associated with interannual variability of Indian summer monsoon rainfall.It also accounts the role of different processes like ENSO, IOD, QBO and ISO in the monsoon variability during the TBO years.
Description:
Department of Atmospheric Sciences,
Cochin University of Science and Technology