Baode Chen

The Origin of Monsoons

Abstract The monsoon is interpreted as an intertropical convergence zone (ITCZ) substantially away (more than 10°) from the equator and the existence of the ITCZ does not have to rely on land–sea contrast. Land–sea contrast can provide a favorable longitudinal location for the ITCZ but this role can be replaced by sea surface temperature contrast in the longitudinal direction. Thus, the interpretation of the monsoon presented herein differs from the long-held fundamental belief that its basic cause is land–sea thermal contrast on the continental scale in the sense that the existence of landmass is not considered a necessary condition for monsoons. Through general circulation model experiments, support has been found for this interpretation. The Asian and Australian summer monsoon circulations are largely intact in an experiment in which Asia, maritime continent, and Australia are replaced by ocean with sea surface temperature (SST) taken from that of the surrounding oceans. Thus, in these areas land–sea c...

Multiple Quasi Equilibria of the ITCZ and the Origin of Monsoon Onset. Part II: Rotational ITCZ Attractors

Abstract Chaos numerical and theoretical work on multiple quasi equilibria of the intertropical convergence zone (ITCZ) and the origin of monsoon onset is extended to solve two additional puzzles. One is the highly nonlinear dependence on latitude of the “force” acting on the ITCZ due to the earths rotation, which makes the multiple quasi equilibria of the ITCZ and monsoon onset possible. The other is the dramatic difference in such dependence when different cumulus parameterization schemes are used in a model. Such a difference can lead to a switch between a single ITCZ at the equator and a double ITCZ, when a different cumulus parameterization scheme is used. Sometimes one of the double ITCZ can diminish and only the other remains strong, but still this can mean different latitudinal locations for the single ITCZ. A single idea based on two off-equator attractors for the ITCZ symmetric with respect to the equator, due to the earths rotation, and the dependence of the strength and size of these attrac...

The Role of Surface Friction in Tropical Intraseasonal Oscillation

Abstract The role of surface friction in the tropical intraseasonal oscillation, or the Madden–Julian oscillation (MJO), is investigated by comparing two 4-yr integrations with the Goddard atmospheric general circulation model: one with the original model design with one added feature to enhance the intensity of the MJO and the other is identical but with surface friction in the Tropics replaced by its zonal mean value. This comparison indicates that in the second experiment the MJO not only still exists but also exists with similar intensity. The oft-cited frictional wave-CISK (FWC) interpretation for the origin of the MJO, which emphasizes the role of frictionally induced convergence in the surface layer, is reassessed in light of these experiments. The possibility of the MJO in the second experiment being forced by the middle latitudes is excluded by a third experiment. These experiments do not support one of the central ideas in FWC that surface friction plays an instability-enhancing role.