Effects Of ENSO On Stratospheric Water Vapor And Its Mechanism

Water vapor in the stratosphere makes a significant contribution to global climate change by altering the radiative energy budget of the Earth's climate system.Researching stratospheric water vapor trends and factors impacting or controlling stratospheric water vapor changes have great reference values for further study of stratospheric-tropospheric exchange.ENSO has a distinct effect on stratospheric water vapor due to its intense ocean-atmosphere coupling.Using ERA-Interim reanalysis and MERRA-2 reanalysis data,combined with SWOOSH satellite observations,the distribution and variation of stratospheric water vapor,the seasonal evolution of ENSO impacts on lower stratospheric water vapor and the influence of extreme El Ni(?)o on water vapor in the stratosphere were systematically analyzed and studied.Summarizes the primary coverage which this article studies as follows to show:(1)Water vapor in the stratosphere has a distinct vertical structure.From 150 h Pa to1 h Pa,the content of water vapor in the stratosphere first decreases and then increases,and there is a minimum value area near 80 h Pa in the tropics.In addition,the stratospheric water vapor in different latitudes has a discrepancy in different altitudes.Near the tropopause,the content of water vapor in the tropics is significantly higher than that in the northern and southern hemispheres,while in the middle and upper stratosphere,it is always lower than that in the northern and southern hemispheres.What's more,there are obvious seasonal and interannual variations of stratospheric water vapor.The seasonal variation of water vapor in the lower stratosphere is the strongest,while that in the middle and upper stratosphere is weaker.From the change tendency,the trend of water vapor in the lower stratosphere is contrary to water vapor in the upper stratosphere.(2)The effect of the ENSO on the tropical lower stratospheric water vapor shows a distinct seasonal evolution that is hysteresis impacts.From winter to spring,El Ni(?)o events moisten the lower stratosphere in winter and increase the water vapor content in spring,La Ni(?)a events dry the tropical lower stratosphere in both winter and spring,but this moistening/dehydration effect is more pronounced in spring.(3)The delayed warming/cooling in the lower stratosphere during El Ni(?)o/ La Ni(?)a springs lead to the seasonal evolution of the effects of ENSO events on the water vapor in lower stratosphere.The enhanced planetary wave activity induced by El Ni(?)o leads to the strengthening of Brewer–Dobson circulation,and the enhanced Brewer–Dobson circulation leads to anomalous cooling in the lower stratosphere,but this effect peaks in El Ni(?)o winter and decays in the following spring.Therefore,the content of water vapor in the tropical lower stratosphere increases during El Ni(?)o spring.(4)The influence of extreme El Ni(?)o events on water vapor in the tropical lower stratosphere is more robust compared with moderate El Ni(?)o events.This is because the abnormal change of SST caused by extreme El Ni(?)o is more intense,and the corresponding convection activity in the tropics is more vigorous,which leads to the drastic change of the tropical tropopause temperature,so the content of water vapor entering the tropical lower stratosphere increases.From the perspective of time evolution,the effect of moderate El Ni(?)o events on the tropical lower stratospheric water vapor shows distinct seasonal evolution,that is,the tropical lower stratosphere is wetter in spring than in winter,while the extreme El Ni(?)o events makes the tropical lower stratosphere strongly wetter in almost all seasons.(5)The 2015/16 extreme El Ni(?)o had a more significant impact on tropical lower stratospheric water vapor content than 1982/83 and 1997/98.In the 2015/16 El Ni(?)o,the position of the maximum warm SST anomaly moved westward compared with the previous two events,leading to the westward movement of convective activities in the Central and Eastern Pacific,and the corresponding the cold anomaly center of tropopause temperature in the Central and Eastern Pacific region was also more westward,crossing the solar boundary.The 2015/16 extreme El Ni(?)o activity almost warmed the whole tropical tropopause,resulting in dramatic humidification of the lower stratosphere.