Evaluating the Ozone Valley over the Tibetan Plateau in CMIP6 Models

Total column ozone(TCO)over the Tibetan Plateau(TP)is lower than that over other regions at the same latitude,particularly in summer.This feature is known as the“TP ozone valley”.This study evaluates long-term changes in TCO and the ozone valley over the TP from 1984 to 2100 using Coupled Model Intercomparison Project Phase 6(CMIP6).The TP ozone valley consists of two low centers,one is located in the upper troposphere and lower stratosphere(UTLS),and the other is in the middle and upper stratosphere.Overall,the CMIP6 models simulate the low ozone center in the UTLS well and capture the spatial characteristics and seasonal cycle of the TP ozone valley,with spatial correlation coefficients between the modeled TCO and the Multi Sensor Reanalysis version 2(MSR2)TCO observations greater than 0.8 for all CMIP6 models.Further analysis reveals that models which use fully coupled and online stratospheric chemistry schemes simulate the anticorrelation between the 150 hPa geopotential height and zonal anomaly of TCO over the TP better than models without interactive chemistry schemes.This suggests that coupled chemical-radiative-dynamical processes play a key role in the simulation of the TP ozone valley.Most CMIP6 models underestimate the low center in the middle and upper stratosphere when compared with the Microwave Limb Sounder(MLS)observations.However,the bias in the middle and upper stratospheric ozone simulations has a marginal effect on the simulation of the TP ozone valley.Most CMIP6 models predict the TP ozone valley in summer will deepen in the future.

Responses of Arctic sea ice to stratospheric ozone depletion

The Arctic has experienced several extreme springtime stratospheric ozone depletion events over the past four decades,particularly in 1997,2011 and 2020.However,the impact of this stratospheric ozone depletion on the climate system remains poorly understood.Here we show that the stratospheric ozone depletion causes significant reductions in the sea ice concentration(SIC)and the sea ice thickness(SIT)over the Kara Sea,Laptev Sea and East Siberian Sea from spring to summer.This is partially caused by enhanced ice transport from Barents-Kara Sea and East Siberian Sea to the Fram Strait,which is induced by a strengthened and longer lived polar vortex associated with stratospheric ozone depletion.Additionally,cloud longwave radiation and surface albedo feedbacks enhance the melting of Arctic sea ice,particularly along the coast of the Eurasian continent.This study highlights the need for realistic representation of stratosphere-troposphere interactions in order to accurately predict Arctic sea ice loss.