Early Spring Arctic Stratospheric Ozone Changes And Stratosphere-troposphere Couplin

Changes in Arctic stratospheric ozone are closely related to stratosphere-troposphere coupling.The total ozone column has shown a decreasing trend year by year in the past decades,and three serious Arctic ozone depletion events occurred in 1997,2011,and 2020 respectively.This paper utilizes re-analysis data and model data to diagnose and analyze the evolution characteristics of ozone before and after the occurrence of Arctic ozone depletion,and also the evolution characteristics of stratosphere-troposphere coupling.Moreover,it further discusses the future trends of Arctic ozone and the changes of stratosphere-troposphere temperature in the 21 st century.The main conclusions of this paper are summarized and shown as following:(1)A comparative analysis is conducted based on the three individual cases of Arctic ozone depletion events in 1997,2011 and 2020.The analysis indicated that the total ozone column over the Arctic continuously reduced month by month in the first period of the Arctic ozone depletion event.Furthermore,the negative anomaly of the total ozone column reaches the annual maximum in March in early spring.It gradually returns to the normal level in the later period of a year.To put it differently,the ozone depletion over the Arctic in March is a result of accumulation from January to February rather than a sudden occurrence.Moreover,it is also found that the interannual variations of 50 h Pa potential height and 50 h Pa temperature in the Arctic oscillate at the same frequency as the interannual variations of ozone.There is a strong cold polar vortex over the Arctic at the time of ozone depletion in all three cases,which aggravates the negative ozone anomaly in the Arctic stratosphere by blocking the Brewer-Dobson circulation.In addition,stratospheric ozone depletion reduces the absorption of solar radiation in the stratosphere,and simultaneously increases the solar radiation reaching the troposphere and the surface.It leads to positive-phase coupling of stratospheric temperature to ozone and anti-phase coupling of tropospheric and surface temperature to ozone.(2)It is synthesized and analyzed separately by using the anomalous values of each physical quantity at the occurrence of the strong polar vortex-ozone loss composite event and the strong polar vortex non-composite event selected from the CESM2-WACCM model.The differences between the synthesis results of the two events are calculated.According to the calculation,strong polar vortex-ozone loss composite events are found to have longer life cycles,stronger positive polarity of stratospheric Northern Hemisphere Annular Mode(NAM),and greater warming effects on the ground compared to strong polar vortex non-composite events.It implies that the coupled dynamical-chemical processes have greater impacts than the dynamical processes alone.Furthermore,it is also found that about 20%-40% of the temperature anomalies in the strong polar vortex-ozone loss composite events can be explained by the ozone content changes,while it is difficult to explain the stratospheric temperature anomalies by solar radiation for the strong polar vortex non-composite events,i.e.,the differences between these two types of events may be concerned with the thermal processes.(3)The paper conducts a univariate linear regression analysis of ozone and stratospheric temperatures over the Northern Hemisphere and the Arctic under four future scenarios of the CESM2-WACCM model.The analysis reveals that the Arctic ozone depletion events identified under current climate conditions are more likely not to occur in the future.Meanwhile,in this premise,the Northern Hemisphere and Arctic ozone will fully recover to1980 levels in the 21 st century,particularly,the extent of recovery of Arctic ozone will be stronger.Moreover,the research highlights that the changes in ozone and the increases in greenhouse gases(GHGs)are the main causes of coupled stratosphere-troposphere temperature changes.The reduction in ozone levels and the rise in GHGs jointly contribute to the trend of stratospheric cooling in the past,while the future temperature changes in each layer will be determined by a combination of future emission pathways and competing effects between ozone recovery and GHGs increases.