The Relationship Between The Arctic Stratospheric Ozone Variations And The Climate Anomalies Over The North Pacific

Stratospheric ozone not only protects life on the earth by absorbing harmful solar ultraviolet radiation,but also affects the tropospheric weather and climate through radiation-chemistry-dynamic feedback.Moreover,the tropospheric weather and climate anomalies caused by stratospheric ozone anomalies lag the stratospheric ozone variations by approximate one to several months.Therefore,studies on the impact of stratospheric ozone changes on weather and climate are of great significance for the improvement of the tropospheric extending weather forecasting and short-term climate prediction.Using observational data,reanalysis data and numerical simulations,this paper studies the impacts of Arctic stratospheric ozone change on atmospheric circulation,precipitation,sea surface temperature（SST）and surface ocean current in the North Pacific and corresponding mechanisms.The main results are as follows:Firstly,using observations,reanalysis data and the Community Earth System Model version 1.2.2（CESM1.2.2）,this paper studies the influence of the Arctic stratospheric ozone（referred to as Arctic ozone for simplicity）on the surface ocean current and SST in the North Pacific,as well as the corresponding mechanisms.The results show that when the Arctic stratospheric ozone decreases in March,there are significant northwestward surface ocean current anomalies in the northern North Pacific in April,while significant southward ocean current anomalies occur in the central North Pacific.The surface ocean current anomalies further cause positive Victoria mode（VM）-like SST anomalies.The decreased Arctic stratospheric ozone in March favors an enhancement of Arctic stratospheric polar vortex through radiative processes,which further extends into the troposphere through stratosphere-troposphere dynamical coupling,resulting in the tropospheric positive Arctic Oscillation（+AO）anomaly with easterly anomalies over the midlatitude Asia in late March.The Asian（mainly referring to eastern Asian）easterly anomalies further extend eastward,resulting in easterly anomalies over the midlatitude North Pacific.The North Pacific easterly anomalies induce negative North Pacific Oscillation（–NPO）anomalies through zonal wind shear and the interactions between synoptic eddies and the mean flow in April.The –NPO-related wind anomalies cause the northwestward（southward）surface current anomalies in the northern（central）North Pacific through direct frictions of the wind and the Coriolis force.The modeling results also show that the Arctic stratospheric ozone variations affect the North Pacific surface ocean current by NPO anomalies,supporting the results in the reanalysis data.The above results suggest that the Arctic stratospheric ozone signal in March could be used to predict the variations of the surface ocean currents and SST in the North Pacific.Based on the above results,this paper further explores the impact of Arctic stratospheric ozone change in March on the tropospheric atmospheric circulation and SST in the western North Pacific in early summer（June）.It is found that the decreased Arctic ozone in March favors cyclonic atmospheric circulation anomalies and negative SST anomalies over the western North Pacific in June,and vice versa.The analysis indicates that the reduction of March Arctic ozone favors –NPO-like circulation anomalies and +VM-like SST anomalies in April via strengthening the Arctic stratospheric circulation.The +VM-like SST anomalies persist and a cyclonic circulation anomaly develops over the eastern North Pacific in May through air-sea interactions.This cyclonic circulation anomaly over the eastern North Pacific in May further causes a cyclonic circulation anomaly over the western North Pacific in June by westward-propagating Rossby waves.The northerly anomaly related to the cyclonic circulation anomaly in June favors local –SST anomalies.Numerical simulations also confirm that a decrease of Arctic stratospheric ozone causes –NPO-like circulation anomalies and +VM-like SST anomalies in the North Pacific in April,which further induce a cyclonic circulation anomaly over the eastern North Pacific in May and a cyclonic circulation anomaly over the western North Pacific in June,supporting the mechanism proposed by this paper.The above results suggest that the Arctic stratospheric ozone signal in March has important implications for predicting the atmospheric circulation and SST changes over the western North Pacific in early summer.In addition to the circulation and SST changes,this paper further analyzes the potential impact of Arctic stratospheric ozone change on the North Pacific precipitations.It is found that when the Arctic stratospheric ozone decreases in March,there are significant positive precipitation anomalies over the middle-eastern North Pacific in middle April,while there are significant negative precipitation anomalies over the western and northern North Pacific.In early April,the responses of the North Pacific precipitations to the Arctic ozone changes are relatively weak,and there are weak positive（negative）precipitation anomalies over the middle-eastern（western）North Pacific.The decreased March Arctic ozone tends to induce a–NPO-like anomaly over the North Pacific in April,and the –NPO anomaly reaches its maximum in middle April.Corresponding to the –NPO anomaly,there are cyclonic circulation anomalies over the central North Pacific and anticyclonic circulation anomalies over the northern North Pacific in middle April.A strong northeastward wind anomaly,located over the eastern side of the cyclonic circulation anomalies,transports warm and humid air from the south to the north and thereby induces the increase of local precipitations.The northerly anomalies,located over the western side of the cyclonic circulation anomaly,transport dry air from the north to the south,reducing local precipitations.The ozone-related anticyclonic circulation anomaly over the northern North Pacific is accompanied by a strong northerly anomaly near the Bering Strait,resulting in the reduced local precipitations through dry air advection.On the other hand,the anomalous upward motion over the central North Pacific associated with ozone also favors the increase of local precipitations.And the anomalous downward motions over the western and northern North Pacific favor the negative precipitation anomalies over local regions.These results suggest that the Arctic stratospheric ozone signal in March has important predictive significance for the North Pacific precipitation changes in April.Finally,interdecadal changes in the relationship between the Arctic stratospheric ozone and the North Pacific SST are analyzed.It is found that during 1979–1999,the North Pacific SST variations in April are closely related to the Arctic ozone anomalies in March.However,the relationship between the ozone and SST is significantly weakened during2000–2019.Possible mechanisms responsible for the weakening relationship between the ozone and SST are further analyzed.During 1979–1999,the decreased Arctic ozone favors–NPO-like circulation anomalies and positive Victoria mode-like SST anomalies by influencing stratosphere-troposphere coupling and the interactions between synoptic-scale eddies and the mean flow,leading to the significant relationship between the Arctic ozone in March and Victoria mode-like SST anomalies in April during 1979–1999.However,during2000–2019,the shape of ozone-related +AO anomaly has changed.Firstly,the Arctic negative geopotential height anomaly of the +AO anomaly extends to the high-latitude North Pacific during 2000–2019,and correspondingly,westerly anomalies occur over the midlatitude North Pacific.The westerly anomalies partly offset the easterly anomalies from the midlatitude eastern Asia,making the North Pacific easterly anomalies relatively weak.Secondly,the +AO-related positive geopotential height anomaly over high-latitude Asia is weak during 2000–2019,and the easterly anomalies over the midlatitude Asia are also relatively weak according to the geostrophic wind relations.The weak easterly anomalies propagate to the North Pacific,also leading to weak easterly anomalies over the North Pacific.The North Pacific weak easterly anomalies lead to weak synoptic eddy anomalies and thereby weak geopotential height tendencies and circulation anomalies over the North Pacific,which further force weak SST anomalies.Therefore,the relationship between Arctic ozone in March and the North Pacific SST in April is weakened significantly during2000–2019.These results suggest that when the Arctic ozone signal is used to predict the North Pacific SST variations in April,the shape of the ozone-related tropospheric AO anomaly in March has important effects on the predictions.