Measurements from 44 island rain gauge stations in the tropical Pacific ocean over the years 1971- 1990 indicate appreciably enhanced rainfall there, which suggests that the global hydrological cycle is intensifying, which may act as a positive feedback in global warming (1). The area of rainfall enhancement extends from the dateline to about 20° S, 130° W, and is flanked by two smaller areas, north and south respectively, where rainfall decreased slightly. Rainfall enhancement near the equator and reduction poleward from it may indicate an intensified Hadley circulation. Where there was enhancement, there was also a reduction of outgoing longwave radiation, measured by satellite during 1974-1987. More, higher clouds, which have tops which are cold (reducing the radiation to space) yield more convective rainfall. In other words, the raingauge and satellite measurements are consistent
The authors took care to subtract the considerable effects of ENSO events on the rainfall measurements. Their results confirm those of two GCM’s, which show increased rainfalls in the region (i.e. acceleration of the hydrologic cycle), as well as warming of the sea surface.
(1) Morrissey, M.L. & N. E. Graham 1996. Recent trends in rain gauge measurements from the tropical Pacific: evidence for an enhanced hydrologic cycle. Bull. Amer. Meteor. Soc. 77, 1207-19.