Signatures of Anomalous Transport in the 2019/2020 Arctic Stratospheric Polar Vortex

The exceptionally strong and long-lived Arctic stratospheric polar vortex in 2019/2020 resulted 23 in large transport anomalies throughout the fall-winter-spring period from vortex development 24 to breakup. These anomalies are studied using Aura MLS long-lived trace gas data for N2O, H2O, 25 and CO, ACE-FTS CH4, and meteorological and trace gas fields from reanalyses. Strongest anoma26 lies are seen throughout the winter in the lower through middle stratosphere (from about 500K 27 through 700K), with record low (high) departures from climatology in N2O and CH4 (H2O). CO 28 also shows extreme high anomalies in midwinter through spring down to about 550K. Exam29 ination of descent rates, vortex confinement, and trace gas distributions in the preceding months 30 indicates that the early-winter anomalies in N2O and H2O arose primarily from entrainment of 31 air with already-anomalous values (which likely resulted from transport linked to an early Jan32 uary sudden stratospheric warming the previous winter during a favorable quasi-biennial oscil33 lation phase) into the vortex as it developed in fall 2019 followed by descent of those anomalies 34 to lower levels within the vortex. Trace gas anomalies in midwinter through the late vortex breakup 35 in spring 2020 arose primarily from inhibition of mixing between vortex and extravortex air be36 cause of the exceptionally strong and persistent vortex. Persistent strong N2O and H2O gradi37 ents across the vortex edge demonstrate that air within the vortex and its remnants remained very 38 strongly confined through late April (mid-May) in the middle (lower) stratosphere.