Water vapor control at the tropopause by equatorial Kelvin waves observed over the Galapagos

Soundings of frost-point hygrometers, ozonesondes, and radiosondes at San C ristobal Island (0.9 degreesS, 89.6 degreesW) in September 1998 provide an observational evidence that equatorial Kelvin waves around the tropopause a ct as a dehydration pump for the stratosphere. During the downward-displace ment phase of a Kelvin wave, dry and ozone-rich stratospheric air is transp orted into the upper troposphere. During the upward-displacement phase, on the other hand, higher specific-humidity air moves up in the tropopause reg ion, but at the same time, this upward motion causes cooling of the air tha t limits the water vapor amount entering the stratosphere. Also, wave break ing contributes to the irreversible transport of ozone across the tropopaus e. Considering their omnipresence at the equatorial tropopause, we suggest that Kelvin waves may be one of the important agents for maintaining the dr yness of the tropical lower stratosphere.