The Evolutions and Large-scale Mechanisms of Summer Stratospheric Ozone
Intrusion across Global Hotspots
Abstract
Stratospheric ozone intrusions have a significant impact on surface
ozone levels. Especially in summer, intrusions can contribute to extreme
ozone events because of preexisting high ozone levels near the surface
and cause serious health issues. Considering the increasing trend of
surface ozone level, an understanding of stratospheric ozone intrusion
is necessary. Previous studies mainly focused on the case studies, and
general knowledge of the spatial structure and large-scale dynamics
underlying these intrusions is lacking. Thus, based on the Whole
Atmosphere Community Climate Model, version 6 (WACCM6) simulation and a
stratospheric origin ozone tracer, we identify the global hotspots of
stratospheric intrusions: North America, Africa, the Mediterranean, and
the Middle East, and investigate the underlying large-scale mechanisms.
From the trajectory analysis, we find that the upper-level jet drives
isentropic mixing near the jet axis and initiates stratospheric ozone
intrusion. Subsequently, climatological descent at the lower troposphere
brings the ozone down to the surface, which explains the spatial
preference of summertime stratospheric intrusion events. Apart from
others, the Middle East shows a relatively fast descent, likely related
to the Asian summer monsoon circulation.