Low Total Ozone Columns over the North Hemisphere in the Summer of 2020

Abstract:

Record low ozone levels have been observed in the Northern hemisphere midlatitudes during the April-August 2020 period, potentially contributing to higher levels of ultraviolet radiation at the surface. In this work we use a variety of observational records and model simulations to investigate the evolution of the late spring-summer 2020 low ozone values. We use the long-term SBUV total ozone record, dating back to 1970, to establish the exceptionality of this year relative to the long-term record. Vertically resolved ozone observations from Aura MLS and OMPS Limb Profiler are used to determine the vertical evolution of the low total ozone values. We summarize the 2019-2020 severe Arctic ozone loss and investigate its contribution to the persistent low ozone in the mid-latitudes. An unusual quasi-biennial oscillation in the tropics is also likely disrupting the total ozone, as did a similar disruption in 2016. However, separating these compounding factors is complicated. We use the GMI chemistry transport model simulations with and without heterogeneous chemistry to assess the roles of the QBO, transport and depletion in the 2020 low summer ozone. Finally, we show the summer UV time series to assess whether anomalous values resulted from the low ozone during periods of high sun angle at lower latitudes in the summer months.