Above-mentioned theoretical considerations suggest strongly the importance of diurnal cycle in particular along coastlines in the equatorial region. The equatorial rainfall 2,000 mm/year maintaining the earth's climate is concentrated around coastlines, and that the largest regional rainfall and the convection center pumping atmosphere from the surface to the stratosphere appear over the maritime continent with the longest coastlines on the earth. Therefore the temporal and horizontal resolutions of observations and numerical models must be higher than the scales of the diurnally-reversing sea-land breeze circulations. Such high-resolution observations by satellites (e.g., Mori et al., 2004; Sakurai et al., 2005) and a radar-profiler network called HARIMAU (Hydrometeorological Array for Interaseasonal Variation-Monsoon Automonitoring) (e.g., Yamanaka et al., 2008; Wu et al., 2007; Sakurai et al., 2009) have been promoted over the maritime continent.
Similarly the monsoon circulation across the equator between the both hemispheres is concentrated in the Eurasian Continent-Indian Ocean sector including the maritime continent as the eastern boundary, which looks similar to the simplified case considered theoretically here. Because the actual coastline is in the northern hemisphere apart from the equator, there are also intraseasonal variations resulting from the aqua-planet-like situation (Hayashi and Sumi, 1986; Miura et al., 2005). Those variations between diurnal and annual periodicities with nonzero zonal wavenumbers may be interacted with the diurnal and annual cycles in the maritime continent and other coastal regions of the Indian Ocean, which can be studied by wave dynamics as mentioned here. An overview of observational results is shown from this viewpoint.