The Origins of ITCZ, Monsoon and Monsoon Onset
Dr. Winston C. Chao
The intertropical convergence zone (ITCZ), monsoons and monsoon onset
are among the most prominent features of the atmospheric general
circulation. Understanding their origins is fundamental to a full
understanding of the atmospheric general circulation, and has
challenged meteorologists for a very long time. There have been some
important advances in recent years in understanding these origins,
however. In this presentation, these advances, including the
speaker's own contributions, will be reviewed.
These advances are: 1) land-sea thermal contrast is not necessary for
monsoons to arise; 2) the ITCZ and the monsoon are not two separate
phenomena as often thought; 3) monsoon onset is a sudden poleward jump
of the ITCZ during its annual cycle of latitudinal movement; and 4)
the SST latitudinal maximum is not a predominant, or even a necessary,
factor in the formation of the ITCZ.
The monsoon is an ITCZ located more than 10 degrees away from the
equator and its associated circulation field. A monsoon, in fact, is
an ITCZ after its poleward jump. Therefore, ITCZs and monsoons should
be studied together. Finally, there are other important, if not more
important, factors than the SST latitudinal maximum in the formation
of the ITCZ. These other factors are the interaction between
convection and surface fluxes, the interaction between convection and
radiation, and the earth's rotation.
Chao, W. C., and B. Chen, 2004: Single and double ITCZ in an
aqua-planet model with constant SST and solar angle. Climate Dynamics,
Chao, W. C., and B. Chen, 2001: The origin of
monsoons. J. Atmos. Sci., 58, 3497-3507.