Oceanic Influence on Continental Rainfall Observed From Space

A method has been developed and validated to estimate moisture transport integrated over the depth of the atmosphere (Q) over the ocean, using both spaceborne scatterometers and microwave radiometers. The divergence of Q compares well with the fresh water flux into the ocean as estimated from separate estimates of evaporation and precipitation, and it is related to the long term variation of in situ salinity measurements. For major land masses over the world under the influence of monsoons, Q normal to the coastlines have been computed and compared with continental rainfall measured by the Tropical Rain Measureing Mission for four years, starting 1999. During the summer. moisture is observed to be transported from the Arabian Sea across the west coast of the Indian Subcontinent, and out to the Bay of Bengal across the east coast. The temporal variation of the net Q agrees, and is in phase with, the changes of rainfall integrated over the subcontinent. However, the onset of moisture moving out the subcontinent into the Bay of Bengal is earlier than the onset of moisture transport into the subcontinent from the Arabian Sea. The variation of rainfall over China and Indochina agrees very well, and is in phase with, the total transport from the Bay of Bengal and Indian Ocean but out-of-phase with moisture advection from the Pacific coastline. The variation of rainfall in the Amazon is dominated by, and is in phase with Q from the Atlantic, particularly in the intra-seasonal time scales