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dc.contributor.authorRupp, Philip
dc.date.accessioned2019-04-29T12:21:17Z
dc.date.available2019-04-29T12:21:17Z
dc.date.issued2019-05-18
dc.date.submitted2018-09-20
dc.identifier.urihttps://www.repository.cam.ac.uk/handle/1810/292068
dc.description.abstractThe Asian summer monsoon circulation has been the subject of continuous research for several decades. Much emphasis has been given to the lower level cyclone, but while various models and mechanisms have been proposed to explain certain features of the upper level anticyclone, like the zonal scale or time dependence, a comprehensive theory combining these characteristics is still lacking. We re-visited the steady and linear 2D monsoon model proposed by Gill and Matsuno, which potentially captures the time-mean response of the flow, but fails to account for any kind of temporal evolution and requires a strong mechanical friction throughout the atmosphere, which is a questionable assumption for the upper troposphere/lower stratosphere region. We then re-modelled the monsoon flow as a response to a localised heat source using a numerical model that is able to capture the time dependence, non-linearity and three-dimensional nature of the system, which we see as necessary to successfully model the monsoon anticyclone. In addition to the explicit heating driving the monsoon we included a simple representation of mid-latitude dynamics into the model by imposing a relaxation towards a baroclinically unstable state. The simulated flow therefore includes mid-latitude westerly jets and baroclinic eddies. We then explored the parameter space by varying for example the forcing magnitude or the meridional temperature gradient of the basic state and investigated changes of the response. This way it was possible to identify various parameter combinations for which the response shows similar structures and behaviours to what has been observed in re-analysis data in relation to the monsoon anticyclone. This includes a finite zonal length scale of the response, as well as temporal evolution in the form of east- and westward shedding of eddies. Many characteristics of the behaviour of the upper level monsoon anticyclone can potentially be investigated by considering the dynamical evolution of a single fluid layer forced by a steady mass source. Such a single-layer model can be used to perform more in-depth studies than are possible in a 3D model. Using this approach we explained a variety of phenomena related to westward eddy shedding from the monsoon anticyclone as a consequence of an absolute instability of the flow field. By performing a comprehensive spatial stability analysis of an idealised representation of the system we were able to develop a theory for the transition between different shedding states. Adapting a simple analytic theory based on a centre-of-mass approach further allowed us to explain the near-steady propagation of the eddies shed from the monsoon. We also showed that the eddy propagation in our system is not modified by the fact that eddies are not well-separated and shed as a series of vortices, in contrast to findings of previous authors. By extending the theory and including a zonal background wind we were further able to explain some aspects of the changes due to thermal damping and the interaction of the flow with a zonal mean background wind like the mid-latitude jet. The presented study covers various observed features and behaviours of the Asian monsoon anticyclone and shows how they arise in simple dynamical models for certain ranges of values of external parameters.
dc.description.sponsorshipThe European project StratoClim (7th Framework Programme, project no. 603557), the ACCI project of the European Research Council (project no. 267760), as well as the Cambridge Philosophical Society and the Queens' College Cambridge
dc.language.isoen
dc.rightsAll rights reserved
dc.rightsAll Rights Reserveden
dc.rights.urihttps://www.rioxx.net/licenses/all-rights-reserved/en
dc.subjectmonsoon
dc.subjectAsian monsoon
dc.subjectstratosphere
dc.subjectstrat-trop-coupling
dc.subjectdynamics
dc.subjectatmosphere
dc.subjectanticyclone
dc.subjectshedding
dc.subjectvortices
dc.subjecteddies
dc.subjectlocalisation
dc.subjectweastward
dc.subjecteastward
dc.subjectinstability
dc.subjectabsolute
dc.subjectconvective
dc.subjectvertical extent
dc.subjecttropopause
dc.subjecttransition
dc.subjecttrop-strat
dc.subjecttropics
dc.subjectsub-tropics
dc.subjectcirculation
dc.subjectfriction
dc.subjectidealised
dc.subjectmodelling
dc.subjectre-analysis
dc.subjectGCM
dc.subjectPV
dc.subjectshallow water
dc.subjectheating
dc.subjectbaroclinic instability
dc.subjectmid-latitude dynamics
dc.subjectjet
dc.titleOn the structure and dynamics of the Asian monsoon anticyclone
dc.typeThesis
dc.type.qualificationlevelDoctoral
dc.type.qualificationnameDoctor of Philosophy (PhD)
dc.publisher.institutionUniversity of Cambridge
dc.publisher.departmentDepartment of applied mathenmatics and theoretical physics
dc.date.updated2019-04-29T07:46:11Z
dc.identifier.doi10.17863/CAM.39223
dc.publisher.collegeQueens'
dc.type.qualificationtitlePhD in applied mathematics
cam.supervisorHaynes, Peter
cam.thesis.fundingfalse


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