Changes in the amount of stratospheric water vapor can affect both the chemistry and
climate in the stratosphere and troposphere. Convectively lofted ice near and above the
tropopause can evaporate and contribute to stratospheric water vapor. Here we conduct
several experiments using a trajectory model driven by two chemistry-climate models
(CCMs) to study the contribution of lofted ice to stratospheric water vapor. We show
that the largest amount of evaporation of convectively lofted ice occurs in the Tropical
Tropopause Layer (TTL) and above the Lagrangian cold point, and we find two key regions
for lofted ice evaporation: the Asian monsoon region during JJA (June, July, and
August) and the tropical western Pacific during DJF (December, January, and February),
regions where convection frequently occurs and the evaporation rate of lofted ice is high.
The distribution of net contribution is mainly determined by the degree of subsaturation in
the TTL, and the net contribution of lofted ice is then transported to the rest of the stratosphere
by the general circulation. Over the 21st century, an increase of subsaturation leads
both the lofted ice evaporation rate and the net contribution to increase. It explains part of
the increase of stratospheric water vapor over the 21st century
