THE DRY STRATOSPHERE - A LIMIT ON COMETARY WATER INFLUX

The stratosphere accumulates the bulk of meteoric and cometary materia l that impacts the Earth and provides a measure of that flux. Recent m odels and measurements of the effective age of stratospheric air demon strate our ability to simulate this buildup. Current observations of H 2O in the stratosphere and mesosphere are consistent with an extraterr estrial source of H2O, but limit its influx to less than 2 Tg/yr. Such a flux is consistent with standard estimates but is 100 times less th an the small-comet hypothesis.