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Proceedings Paper

Sensitivity of convectively coupled modes to basic state: implication for the Madden-Julian oscillation under the Walker circulation
Author(s): Masahiro Watanabe
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Paper Abstract

Convectively coupled, tropical low-frequency distrubances are examined by means of eigenanalysis to the linear dynamical operator based on a T21 multilevel primitive model that involves cumulus convetions and surface heat fluxes. With relevant dissipation terms and an adjustment scheme employed to parameterize the convections, no unstable mode emerges while some of the eigenmodes show decay timescale longer than the intrinsic dissipative timescale. Under the zonally unfiorm basic state, one of these less damped modes has a zonal wavenumber 1 structure with the period of 34dy, which may be considered as a prototype of the Madden-Julian Oscillation (MJO). While a forced Kelvin wave prevails on the equator in this mode, frictional convergence in the boundary layer to the east of heating appears crucial in generating the successive convective heating anomally hence slow eastward propagation of the mode. When we incorporate an idealized Walker circulation into the basic state, a similar mode is obtained with longer period and decay timescale but the structure localized over the Indian Ocean to the western Pacific. It is noteworthy that, however, the 2nd MJ mode is traced back, in the eigenspectrum, to a zonally uniform least damped mode but not to the 1st MJ mode identified under the zonal mean basic state. These results may indicate that the origin of the observed MJO resides in a zonally uniform convective mode which is modified by interacting with the mean Walker circulation, but not in zonal wavenumber 1 modes which have been discusssed in previous studies.

Paper Details

Date Published: 14 April 2003
PDF: 9 pages
Proc. SPIE 4899, Atmospheric and Oceanic Processes, Dynamics, and Climate Change, (14 April 2003); doi: 10.1117/12.466585
Show Author Affiliations
Masahiro Watanabe, Hokkaido Univ. (Japan)

Published in SPIE Proceedings Vol. 4899:
Atmospheric and Oceanic Processes, Dynamics, and Climate Change
Zhaobo Sun; Fei-Fei Jin; Toshiki Iwasaki, Editor(s)

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