The generally held assumption, that the bulk of tropical rain over the oceans is generated where the sea is warmer than the air, is being largely verified in this article with the new tool of satellite cloudiness mapping. The discussion focuses on the satellite-observed variable position of the boundary between the west Pacific equatorial rain clouds over warm ocean water and the east Pacific aridity along the equator over cool upwelling water. The often quite abrupt changes between these two regimes in the mid-Pacific are known from an eighteen-year sequence of ocean and atmosphere data at Canton Island. This article describes the same phenomena delineated by satellite television data recorded during 1962–67, and adds features of the geographic cloudiness distribution not obtainable from the widely spaced fixed points of observation.

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* Goddard Space Flight Center, Greenbelt.

** USAF Environmental Technical Applications Center, Washington, D. C., Air Weather Service member temporarily attached to Goddard Space Flight Center.

*** Environmental Data Service, ESSA, Silver Spring, Md.

**** On leave from the Free University of Berlin, Germany, as National Academy of Science-National Research Council Senior Postdoctoral Resident Research Associate with the Goddard Space Flight Center.