Rostami_Zeitlin_2020_2L_Eq_Adjustment.pdf (4.46 MB)
Can geostrophic adjustment of baroclinic disturbances in tropical atmosphere explain MJO events?
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posted on 2020-08-01, 14:01 authored by Masoud RostamiUsing the two-layer moist-convective rotating shallow water model, we study the process of relaxation (adjustment) of localized large-scale pressure anomalies in the lower equatorial troposphere, and show that it engenders coherent structures strongly resembling the Madden Julian Oscillation (MJO) events, as seen in vorticity, pressure, and moisture fields. We demonstrate that baroclinicity and moist convection substantially change the scenario of the quasi-barotropic ``dry'' adjustment, which was established in the framework of one-layer shallow water model and consists, in the long-wave sector, in the emission of equatorial Rossby waves, with dipolar meridional structure, to the West, and of equatorial Kelvin waves, to the East. If moist convection is strong enough, a dipolar cyclonic structure, which appears in the process of adjustment as a Rossby-wave response to the perturbation, transforms into a coherent modon-like structure in the lower layer, which couples with a baroclinic Kelvin wave through a zone of enhanced convection and produces, at initial stages of the process, a self-sustained slowly eastward-propagating zonally- dissymmetrical quadrupolar vorticity pattern. At the same time, a weaker quadrupolar structure of opposite sign arises in the upper layer, the whole picture similar to the active phase of the MJO events. The baroclinic Kelvin wave then detaches from the dipole, which keeps slow eastward motion, and circumnavigates the Equator, catching up and interacting with the dipole.
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- Atmospheric sciences not elsewhere classified
- Atmospheric radiation
- Atmospheric dynamics
- Atmospheric aerosols
- Aboriginal and Torres Strait Islander environmental knowledges
- Climate change processes
- Climatology
- Conservation and biodiversity
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- Ecological applications not elsewhere classified
- Ecological impacts of climate change and ecological adaptation
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Keywords
MJOGeostrophic windGeostrophic adjustmentEquatoria Statebaroclinic tidesBarotropic tidesshallow-watereasterly wind velocityWesterly wind anomaliesatmosphere conditionsatmosphere treatmentsCan geostrophic adjustment of baroclinic disturbances in tropical atmosphere explain MJO events?DOI: 10.1002/qj.3884Atmospheric Sciences not elsewhere classifiedAtmospheric SciencesAtmospheric RadiationAtmospheric DynamicsAtmospheric AerosolsAboriginal and Torres Strait Islander Environmental KnowledgeClimate Change ProcessesClimate ScienceConservation and BiodiversityCloud PhysicsClimatology (excl. Climate Change Processes)Earth Sciences not elsewhere classifiedEcological Applications not elsewhere classifiedEcological Impacts of Climate ChangeGeophysical Fluid DynamicsGeophysicsMeteorologyOceanographyOceanography not elsewhere classified
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