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dc.contributor.advisorJai, Sukhatme
dc.contributor.authorMonteiro, Joy Merwin
dc.date.accessioned2017-11-29T17:30:54Z
dc.date.accessioned2018-07-31T05:25:46Z
dc.date.available2017-11-29T17:30:54Z
dc.date.available2018-07-31T05:25:46Z
dc.date.issued2017-11-29
dc.date.submitted2016
dc.identifier.urihttp://etd.iisc.ac.in/handle/2005/2836
dc.identifier.abstracthttp://etd.iisc.ac.in/static/etd/abstracts/3687/G27248-Abs.pdfen_US
dc.description.abstractThe effects of a non-zero background state on atmospheric dynamics is explored through simple models and observations. Firstly, we examine the effects of moisture gradients on the stability and propagation of Rossby waves in a mid-latitude -plane. We begin by a consistent derivation of the forced quasi-geostrophic equations on a -plane to understand the constraints placed by geostrophy on the time scale of condensation. We see that the presence of meridional gradients of moisture results in a slowdown of the waves. On the introduction of zonal gradients of moisture, the waves become unstable, and for certain parameters which are representative of the real atmosphere, they propagate eastward and mature on an intra-seasonal timescale. The mechanism of the in hence of moisture on waves is understood by thinking of condensation as providing an \equivalent" potential vorticity (PV) gradient which opposes the dynamical PV gradient. Secondly, we look at the effects of a mean background ow on the Matsuno-Gill response in the spherical shallow water system. The mean ow is prescribed to resemble the climatological upper tropospheric zonal wind structure in the atmosphere. As the strength of the ow increases, the equatorially trapped Matsuno-Gill response rst transforms into a poleward propagating Rossby wavetrain. As the strength of the mean ow reaches values similar to that observed in the atmosphere, the stationary wave response becomes a zonally oriented quadrupole structure. This structure bears a striking resemblance to the observed upper level structure of the Madden-Julian oscillation (MJO). The time evolution of this quadrupole structure is quick enough to be relevant on MJO timescales, and the structure is quite robust across a range of values for the drag coefficient. Finally, we look at the role played by low frequency variability in the Pacific in the recent expansion of the Hadley cell. We find that the dominant effect of the low frequency variability is a stationary dispersive Rossby wavetrain extending from the tropical Paci. We further find that most of the observed expansion of the Hadley cell can be accounted for by this low frequency variability. We nd that large scale changes such as the changes in the equator-pole temperature gradient or midlatitude static stability need not be invoked to understand the observed expansion.en_US
dc.language.isoen_USen_US
dc.relation.ispartofseriesG27248en_US
dc.subjectMoisture Gradientsen_US
dc.subjectMadden-Julian Oscillation (MJO)en_US
dc.subjectAtmospheric Dynamicsen_US
dc.subjectRossby Wavesen_US
dc.subjectPotential Vorticity Gradienten_US
dc.subjectPV Gradienten_US
dc.subjectMatsuno-Gill Responseen_US
dc.subjectEl Nino Southern Oscillation (ENSO)en_US
dc.subject.classificationAtmospheric and Oceanic Sciencesen_US
dc.titleA Tale of Two Gradients : Atmospheric Dynamics in an Inhomogeneous Backgrounden_US
dc.typeThesisen_US
dc.degree.namePhDen_US
dc.degree.levelDoctoralen_US
dc.degree.disciplineFaculty of Engineeringen_US


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