The Remarkably Strong Arctic Stratospheric Polar Vortex of Winter 2020:
Links to Record-Breaking Arctic Oscillation and Ozone Loss
The Northern Hemisphere (NH) polar winter stratosphere of 2019/2020
featured an exceptionally strong and cold stratospheric polar vortex.
Wave activity from the troposphere during December-February was
unusually low, which allowed the polar vortex to remain relatively
undisturbed. Several transient wave pulses nonetheless served to help
create a reflective configuration of the stratospheric circulation by
disturbing the vortex in the upper stratosphere. Subsequently, multiple
downward wave coupling events took place, which aided in dynamically
cooling and strengthening the polar vortex. The persistent strength of
the stratospheric polar vortex was accompanied by an unprecedentedly
positive phase of the Arctic Oscillation in the troposphere during
January-March, which was consistent with large portions of observed
surface temperature and precipitation anomalies during the season.
Similarly, conditions within the strong polar vortex were ripe for
allowing substantial ozone loss: The undisturbed vortex was a strong
transport barrier, and temperatures were low enough to form polar
stratospheric clouds for over four months into late March. Total column
ozone amounts in the NH polar cap decreased, and were the lowest ever
observed in the February-April period. The unique confluence of
conditions and multiple broken records makes the 2019/2020 winter and
early spring a particularly extreme example of two-way coupling between
the troposphere and stratosphere.