Mesospheric intrusion and anomalous chemistry during and after a major stratospheric sudden warming

Several major stratospheric sudden warmings (SSWs) characterized by a rapid vertical displacement of the winter polar stratopause are simulated in the National Center for Atmospheric Research's Whole Atmosphere Community Climate Model. The stratopause descends into the mid-stratosphere at the onset of the SSW, and then abruptly reforms near 70 km. The SSWs are accompanied by a strong equatorward and downward residual circulation between 40 and 60 km. The descent occurs mainly through the core of the highly displaced vortex, and is accompanied by an intrusion of air rich in carbon monoxide (CO) from the mesosphere into the mid-stratosphere. Around the periods when the stratopause undergoes rapid vertical displacement, the simulation shows that the air of mesospheric origin is being cut off and remains distinct from surrounding stratospheric air masses for at least a month after SSW onset. Such mesospheric cut-off intrusion of CO-rich appears to be a defining signature of winters with major SSWs. Due to its strong temperature dependency, the secondary ozone maximum (between 90 and 110 km) abruptly decreases in amplitude at the time of the high-altitude stratopause reformation that influences the thermal structure at these altitudes. The vertical location of the tertiary ozone maximum (between 70 and 75 km) shows significant variations in response to the changing vertical motion during SSW.

► A stratospheric sudden warming is simulated in WACCM.
► It is accompanied by abrupt reformation of the polar stratopause at mesospheric altitudes.
► An intrusion is peeled off the mesosphere as the vortex collapses.
► Both the secondary and tertiary ozone maxima are affected in amplitude or altitude.