Arctic Ozone Loss in March 2020 and its Seasonal Prediction in CFSv2: A Comparative Study With the 1997 and 2011 Cases

Abstract

Using reanalysis data, observations, and seasonal forecasts, the March Arctic ozone loss events in 1997, 2011, and 2020 and their predictability are compared. All of the three ozone loss events were accompanied by an extremely strong and cold polar vortex, with the shape and centroid of the ozone loss controlled by the polar vortex. The high autocorrelation of the March Arctic ozone at a lead/lag time of 1-2 months from observations might suggest that a reasonable prediction can be obtained if one initializes 1-2 months in advance. Based on the chemical scheme assessment in CFSv2 and several empirical models using the forecasted metric(s) of the stratospheric polar vortex as predictor(s), the predictability of the 2011 ozone loss event is shown to be longer (1-2 months) than the other two (~1 month), possibly due to a moderate La Niña and quasi-biennial oscillation westerly winds favorable for the formation of a strong polar vortex. However, the overall predictive skills of ozone from empirical models (using a forecasted substitute index to forecast the Arctic ozone) during 1982-2020 are lower than the chemical module assessment in the forecast system, though empirical models have some skill. Contrary to the ozone predictions, the lower tropospheric temperature pattern in March 2011 is less reasonable than in 1997 and 2020. Similar conclusions are also true in other years (2005 versus 2016). Those findings might indicate a weak relationship between the Arctic ozone and the surface climate in the Northern Hemisphere. Plain Language Summary Extremely low ozone concentrations (or an "ozone hole") develop in the Antarctic every austral spring in present-day atmospheric burdens of ozone-depleting substances. However, similar ozone losses are not observed in the Arctic, though in 1997, 2011, and 2020, ozone loss locally approached that in the Antarctic. This study focuses on the meteorological conditions and predictability for those Arctic ozone loss events. All of the three historical ozone loss events were related to a stratospheric circulation system encircling North Pole (i.e., the stratospheric polar vortex). The shape and centroid of the ozone losses were also controlled by the polar vortex: the ozone loss in March 2020 was displaced toward the North American sector, the March 2011 ozone loss was centered over the North Pole, while the 1997 ozone loss was displaced toward the Eurasian sector. Using the chemical scheme in a seasonal forecasting model and/or empirical models, the lead times for forecasting the three ozone loss events are different due to the tropical forcing. The moderate cold state in the tropical Pacific (i.e., La Niña) and westerly winds in the equatorial stratosphere (i.e., westerly QBO) propel the predictability of the 2011 ozone loss event to around 1-2 months, while the 1997 and 2020 March ozone losses can only be forecasted~1 month in advance. Nevertheless, a good prediction of the stratospheric ozone shows little impact on the surface predictability in the Northern Hemisphere.

Robust effects of springtime Arctic ozone depletion on surface climate

“…However, it remains difficult to disentangle the potential downward influence of ozone extremes from extreme dynamical events in the stratosphere, for which a surface impact is well established [17][18][19] . Surface patterns coincident with ozone depletion might be caused entirely by dynamical variability in the lower stratosphere, with ozone simply acting as a passive tracer of such dynamical variability 20,21 . Conversely, some studies based on models and observations conclude that ozone extremes actively influence surface climate 13,14 .…”

The Strong Stratospheric Polar Vortex in March 2020 in Sub‐Seasonal to Seasonal Models: Implications for Empirical Prediction of the Low Arctic Total Ozone Extreme

“…The March 2020 stratospheric polar vortex was extremely strong, nearly persisting its intense state from early January. Such a persistent strong state was not interrupted by a breakdown of the vortex as in most other years since 1979 (see Figure in the supporting information), and the SFW occurred in April (Rao & Garfinkel, 2020). Our focus here is on the predictability of the strong polar vortex in March 2020.…”

“…Considering the potential effect of the ozone loss on the surface, any effort in timely prediction of the ozone loss event may help to provide warnings to society (Calvo et al., 2015; Ivy et al., 2017; Neely et al., 2014; Waugh et al., 2009). We will also use an empirical model developed by Rao and Garfinkel (2020) to compare the predictability of the 2020 major Arctic ozone loss in S2S models.…”

“…(2020a, 2020b). More importantly, this extreme polar vortex is strongly coupled to a low ozone center over the Arctic, which is seldom observed in the Northern Hemisphere due to large planetary wave disturbances and even SSWs preventing long‐lived cold temperatures in the Northern Hemisphere stratosphere (Manney et al., 2011; Rao & Garfinkel, 2020). Different from the ozone hole over the Antarctic observed every October since the 1980s for which heterogeneous chemical processes dominate ozone depletion (Rieder et al., 2014; Solomon, 1999), the Arctic ozone loss is also driven by dynamical processes (Arnone et al., 2012; Manney et al., 2011).…”

“…When the westerly stratospheric polar vortex is strong, the poleward mass transport from the ozone‐rich tropics to the ozone‐poor polar regions is dynamically blocked (Rao & Garfinkel, 2020; Strahan et al., 2013). Hitherto, only three Northern Hemisphere ozone loss events have been observed since 1979 (i.e., March in 1997, 2011, and 2020; Rao & Garfinkel, 2020).…”