An Analysis Of The Spatial-Temporal Variations Of The Stratospheric Trace Gases And Its Impact Factors

Stratospheric trace gases play an important role in the global radiation budget,energy balance and stratospheric chemistry.Focused on some hot topics of the stratospheric trace gases,an analysis of the spatial-temporal variations of the stratospheric trace gases and its impact factors is carried by using several satellite observations,renalaysis data and a chemical transport model.The specific topics are the long-term trends of stratospheric water vapor and its impact factors for the period1990-2015,the uncorrelated relationship between stratospheric water vapor anomalies and the tropical tropopause temperature anomalies in 1996 and 1999,attribution of the hemispheric asymmetries in trends of stratospheric trace gases for the period2004-2012 and the causes of large anomaly of northern hemisphere stratospheric trace gases during 2010/2011.The main conclusions are as following:?1?Using SWOOSH observation data and ERA-Interim reanalysis together with a SLIMCAT model simulation from 1990 to 2015,the spatial-temporal variations of the stratospheric water vapor and the key factors of the long term trends of stratospheric water vapor are analyzed.It is found that there is the significant positive trend of stratospheric water vapor for the period 1990-2015.Specifically,stratospheric water vapor increased significantly from 1990 to 2000,decreased significantly from2000 to 2005 and began to increase again from 2006 to 2015.The factors affecting the trend of stratospheric water vapor are different in those three time periods.The increased methane emissions and enhanced deep convective activity in 1990-2000 are the main factors affecting the increase in stratospheric water vapor during this period.The enhanced tropical upwelling after 2000 results in colder tropopause temperature,and further in lower water vapor during 2000-2005.During 2006-2015,the increased stratospheric water vapor was mainly contributed by the warmer tropopause temperature.?2?There are the uncorrelated relationship between stratospheric water vapor anomalies and the tropical tropopause temperature anomalies in 1996 and 1999.Further analysis of the reasons for the poor correlation between temperature and water vapor in these two years shows that the key factor responsible for the poor correlation between tropical tropopause temperature and stratospheric water vapor in 1996 is the anomalously enhanced deep convective activity.The instantaneous intensity of four short periods of deep convective activity is greater during the‘mismatched'months.Thus,water vapor is transported from the lower troposphere to the lower stratosphere through a strong deep convective activity,leading to an increase in stratospheric water vapor.Meanwhile,deep convective activity can lift the tropopause and cool the tropopause temperature.The instantaneous intensity of four short periods of deep convective activity is mainly caused by strong surface cyclones and high sea surface temperatures.In addition,an anomalously strong residual circulation in 1996 brings more water vapor into the stratosphere,and this exacerbates the poor correlation between temperature and water vapor.A strong rate of increase in tropical cold-point tropopause temperature?CPTT?in 1999 is the key factor impacting the poor correlation between temperature and water vapor during this year.The transformation of the east phase of the Quasi-Biennial Oscillation?QBO?is a key influence on the warming of the tropopause,which leads to the subsidence of tropopausea and then a warmer tropopause.MLR analysis shows that this east-west phase transition in the QBO can contribute up to 50%of the explained variance in the large rate of increase in tropopause warming in 1999.?3?Using Microwave Limb Sounder?MLS?satellite observations,ERA-Interim reanalysis dataset and a SLIMCAT model simulation,we analyze and investigate the causes of the asymmetric hemispheric trends of N₂O,HCl and CH₄ in the stratosphere during the period 2004 to 2012.Our analysis confirms previous findings that significant hemispheric asymmetry exists in the trends of trace gases in the mid-latitude middle and lower stratosphere.There are the positive trend of N₂O and CH₄ in the northern lower stratosphere and the negative trends in the southern middle stratosphere.The trends of HCl are opposite with N₂O and CH₄.We find that a positive net influx of air masses between 70-10 hPa at northern hemisphere mid-latitudes is mainly due to weakened downward transport of air out of this region by the residual circulation during the period 2004-2012.In contrast,more air is transported upward from the lower stratosphere and poleward across the mid-latitudes,hence causing a positive net inflow anomaly of air masses in the southern hemisphere middle stratosphere during this period.In addition,the southward shift of upwelling of the residual circulation in the recent decades can partly explain trace gas trends above 20 hPa.The changes in the eddy mixing process have an opposite effect to that of the residual circulation changes on the trends of trace gases in the low-latitude lower stratosphere.In the southern hemisphere high latitude,the changes in the eddy mixing process play an opposite role in the trace gases.?4?Finally,using MLS satellite observations and ERA-Interim reanalysis dataset,we analyze and investigate the causes of the large anomaly of HCl,N₂O and H₂O concentrations in the Northern Hemisphere during 2010/2011.We found that the concentrations of these three trace gases in the mid-latitude stratosphere in the northern hemisphere during 2010/2011 are obviously abnormal compared with their climate averages.The main reason for this large anomaly of HCl,N₂O and H₂O concentrations is the QBO easterly phase in the upper stratosphere,La Ni?a event in the tropical Pacific and strong polar vortex in the stratosphere.On the one hand,the QBO easterly phase in the upper stratosphere and strong polar vortex result in an enhanced deep branch of the residual circulation,hence accelebrating the air with high concentration of HCl/H₂O?low concentration of N₂O?being transported from upper stratosphere to lower stratosphere.On the other hand,La Ni?a event results in a weakend shallow branch of the residual circulation,hence slowing the air with high concentration of HCl/H₂O?low concentration of N₂O?being transported out of the lower stratosphere.Those two processes contribute to the increase of HCl/H₂O and decrease of N₂O during 2010/2011.