The Downward Propagation Of Annular Odel Anomalies In The Northern Hemisphere And Its Relationship With The Ozone

Using the daily ERA-Interim reanalysis dataset,the daily NAMI is calculated by a new improved algorithm defined by Baldwin(2009).By analyzing the daily NAMI,we find that the downward-propagating events contain 12 low NAM index events and 7 high NAM index events.Then the developmental and diagnostic the character of the stratospheric NAM anomalies events,and its relationship with wave-flow interaction and ozone in the stratosphere.The major results are as follow:during the downward-propagating anomalies of NAMI,there are anomalies of the meteorological elements in the stratosphere,which have a downward-propagating trend.There are significant differences in the intensity and duration between the low NAMI events and high NAMI events,especially,in the mid-latitude troposphere.On the item of zonal-mean zonal wind anomalies,during high NAMI,there are two centers of zonal-mean zonal wind anomaly,separately,in the stratosphere and troposphere,and their duration is short;during low NAMI,there is a strong and persistent center of the westerly wind anomaly in the 70° N stratosphere,and zonal-mean zonal wind is even 30m s-1 in the upper stratosphere.On the item of temperature and meridional circulation,during high NAMI,there is obvious center of low temperature in the stratosphere,where the temperature is below 196K.During low NAMI,there are a center of high temperature in the middle stratosphere and the temperature is over 222K above 200hPa.There is obvious a strong updraft in the polar region from the troposphere to the lower stratosphere.Different period of the NAM anomalies downward propagating are closely correlated with the wave activity and the structure of zonal-mean flow,specially 1～2 wave in planetary-scale.During the previous stage,the structure of a zonal mean basic state is in favor of upward-propagating planetary wave from the lower troposphere.During the later stage,it is in favor of the downward-propagating wave from the middle and lower stratosphere in the northern polar regions and the downward-propagating NAM anomalies.The dynamic process is an important mechanism in the transport of the stratospheric ozone.The ozone was transported from the tropics to the high latitudes.In the high latitudes,the amount of the ozone in the lower stratosphere was increased because of the downdrafts.NAMI,at the lOhPa,has a significant negative correlation with the stratospheric ozone in the Arctic region,and the significance test of the 0.01.And,there is a weak positive correlation in the in the Western Europe upper stratosphere.With the decrease of altitude,the center of the positive correlation moves eastward.The mechanism,by which NAM affects the intraseasonal stratospheric zone,is that in the Arctic region,photochemistry effects the features of the ozone in the upper and middle stratosphere,and dynamic effects in the lower stratospheric.During high NAMI,there is a persistent low temperature center in the Arctic region stratosphere.The low temperature enhance rates of the heterogeneous photochemical reaction by which stratospheric ozone was depleted.During low NAMI,the high temperature decreases the rates of the heterogeneous photochemical reaction,and then the amount of the stratospheric ozone is increasing.Meanwhile,polar vortex becomes weak.The circum-polar westeries weaken.The quasi stationary wave propagate from the troposphere to the high latitude stratosphere,and strong meridional circulation transport the ozone to the lower stratosphere.Thus,the amount of ozone becomes increasing.