A Diagnostic Study of the Evolution of the MJO Maintained by Wave Dynamics, Moistening and Convective-Radiative Processes
| Autor: | Ching-Shu Hung, 洪竟書 |
|---|---|
| Rok vydání: | 2016 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 104 The moistening processes for the Madden-Julian Oscillation (MJO) over Indian Ocean and Maritime Continent are investigated through a diagnosis of ECMWF Re-analysis (ERA-Interim) data in November-April, 1982-2011. During this period, 27 MJO events with strong magnitude and clear propagation are identified and further classified as either successive or primary, according to the existence of preceding events. The successive events are analyzed in the current study, whereas the primary events will be explored individually next. A composite of scale-separated lower-tropospheric (1000-700 hPa) moisture (qL) budget is analyzed in four stages: suppressed, cloud developing, convective, and decaying, each corresponding to the MJO Bimodal index phase 567, 81, 2, and 34 for Indian Ocean and 781, 23, 4, 56 for Maritime Continent, respectively. In the suppressed stage, the dominant moisture source over both region is surface evaporation/shallow convection (-Q2). Nonlinear zonal (meridional) advection by synoptic disturbances also has non-negligible contribution over IO (MC). In the cloud developing stage, qL approaches maximum with moistening tendency to its east. This moistening is contributed by the advection of mean moisture by anomalous easterlies associated with downstream Rossby wave response of the dry anomaly and boundary layer frictional moisture convergence. In the convective stage, while the zonal advection of anomalous westerlies and intense precipitation dries the atmosphere, the moistening of meridional advection by downstream Rossby anti-cyclonic gyres leads to the eastward propagation of deep convection. In the decaying stage, the strong westerlies bring in dry air from the west causing widespread drying. Overall, the moisture evolution of MC is consistent with IO except meridional component is more essential in suppressed stage. A column-integrated moist static energy (MSE) budget is also analyzed to further identify the role of radiation and surface turbulent fluxes. The result shows that longwave heating is the dominant term in convective stage and latent heat flux is more prominent in decaying stage when the westerly is strong. The in-phase relation of longwave heating with column-integrated MSE suggests that longwave heating acts to maintain MSE and retard the propagation. Latent heat flux also slows down the propagation due to the phase lag. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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