Contribution of mixed-phase boundary layer clouds to the termination of ozone depletion events in the Arctic

During the springtime, ozone depletion events (ODEs) are frequently observed in the Arctic boundary layer. While the chemical reactions associated with the ODEs are understood, the processes responsible for their termination remain unclear. Previous studies proposed that wind shear above the Arctic boundary layer promotes enough vertical mixing to transport ozone-richer air from aloft to the nearly ozone-devoid surface and thus terminates the ODEs. In addition, ozone-richer air masses from mid-latitude regions can migrate to the high Arctic and replenish the Arctic boundary layer with ozone. In the present study, a new mechanism related to mixed-phase boundary layer clouds is proposed as a key contributor to the termination of the ODEs. A single-layer stratocumulus cloud observed over Barrow, Alaska (AK) on April 8, 2008 and its effect on the ODEs is simulated using high-resolution WRF/Chem model. One key finding of this investigation is that the cloud-top radiative cooling can induce strong downdrafts and updrafts. These downdrafts associated with mixed-phase boundary layer clouds can transport ozone-richer air from aloft to the surface, heralding the termination of ODEs.