The Connection Between Tropical MJO And Stratospheric Wave Activity In The Middle And High Latitudes Of The Northern Hemisphere

The connection between tropical Madden-Julian Oscillation(MJO)and stratospheric wave activity in the middle and high latitudes of the Northern Hemisphere is investigated using the NCEP/NCAR reanalysis dataset,ERA-Interim reanalysis dataset,the interpolated outgoing longwave radiation(OLR)data,MJO indices,Eliassen-Palm(E-P)flux divergence and Whole Atmosphere Community Climate Model(WACCM4).Firstly,the effects of tropical MJO on the stratospheric wave activity at middle and high latitudes in the Northern Hemisphere at different time scales and conditions are analyzed.Based on this,in turn,the response characteristics of tropical MJO after the occurrence of the strong wave activity in the stratosphere at middle and high latitudes in the Northern Hemisphere are given.A complete image of the connection between tropical MJO and stratospheric wave activity at middle and high latitudes in the Northern Hemisphere has been established.The main conclusions are summarized as followings:1.The intraseasonal variability similar to tropical MJO has been found in the wave activity in the extratropical stratosphere.MJO phases 3 and 7 has the most significant influence on wave activity in the extratropical stratosphere as the highest occurrence frequency of MJO phases 3(7)in about two weeks before the weak(strong)wave activity in the extratropical stratosphere,which indicates that MJO phase 3(7)lead to the most weakened(strengthened)wave activity in the extratropical stratosphere in about two weeks.Morever,Quantitative evaluation suggests that tropical MJO can make a 50%contribution to the differences between strong and weak wave activity in the extratropical stratosphere.2.This reanalysis datasets and numerical experiments are used to investigate the influence of the occurrence frequency of the individual phases of the MJO on the interannual variability of stratospheric wave activity in the mid and high latitudes of the Northern Hemisphere during boreal winter.Our analysis reveals that the occurrence frequency of MJO phase 4 in winter is significantly positively correlated with the interannual variability of the E-P flux divergence anomalies in the northern extratropical stratosphere;i.e.,higher(lower)occurrence frequency of MJO phase 4corresponds to weaker(stronger)upward wave fluxes and increased(decreased)E-P flux divergence anomalies in the middle and upper stratosphere at mid to high latitudes,which implies depressed(enhanced)wave activity accompanied by a stronger(weaker)polar vortex in that region.The convection anomalies over the Maritime Continent related to MJO phase 4 excite a Rossby wave train that propagates poleward to mid and high latitudes,and is in anti-phase with the climatological stationary waves of wavenumber 1 at mid and high latitudes.As the spatial distribution of the convection anomalies during MJO phase 7 has an almost opposite,but weaker,pattern to that during MJO phase 4,the occurrence frequency of MJO phase 7 has an opposite and weaker effect on the northern extratropical stratosphere to MJO phase 4.However,the other MJO phases(1,2,3,5,6,and 8)cannot significantly influence the northern extratropical stratosphere because the wave responses in these phases are neither totally in nor out of phase with the background stationary wavenumber 1.3.Bandpass-filtered(20–100 days)OLR variance,across the Indian Ocean and central Pacific,are typically stronger during EQBO winters than WQBO winters.However,just over the central and western Pacific,bandpass-filtered OLR variance is stronger during CENSO winters than WENSO winters.This result implies that intraseasonal convective activity over central and western Pacific tends to stronger during La Ni?a winters,while the intraseasonal convective activity in the almost Indo-Pacific region,from 60~oE to 180~o,tends to be stronger during EQBO winters.More importantly,it is shown that the amplitude and occurrence frequency of the active MJO in the boreal winter is significantly negatively correlated with the stratospheric QBO rather than with ENSO.Morever,in terms of MJO each phase,only the the interanual timeseries of the amplitude of MJO phases 5,6 and 7 is significantly negatively correlated with ENSO.These results suggest that overall intraseasonal convective activity related to MJO,including the amplitude and the occurrence frequency of MJO is highly modulated by the QBO;while only intensity of convective activity over western and central Pacific related to the amplitude of MJO phases 5,6 and 7 is highly modulated by the ENSO.The significant enhancement of the amplitude and frequency of MJO in EQBO winter is related to the decrease of static stability in the upper troposphere and the lower troposphere in the tropics.The enhancement of the amplitude of MJO phases 5,6 and 7 in CENSO winter is related to the increase of sea surface temperature in the central and western Pacific region.4.The paper finally studied the response of tropical MJO to the strong wave activity in the extratropical stratosphere.The results show that during the period of the strong wave activity in the stratosphere in the middle and high latitude,the anomaly of tropical convective activities occur over the equatorial Indian Ocean and then intensify and propagates eastwards to the equatorial central Pacific Ocean.The response characteristics of tropical MJO to the strong wave activity in the middle and high latitudes are as follows:1)the average amplitude of MJO increases gradually within 48 days after the oneset of strong wave activity in the extratropical stratosphere;MJO phases 7 and 8 have the highest occurrence frequency within a month after the oneset of strong wave activity in the extratropical stratosphere.The response characteristics of MJO to strong wave activity events are related to the change of static stability in the upper troposphere and lower stratosphere in the tropics.However,the detailed mechanism of the effects of stratospheric wave activity on MJO is not clear,and needs further study.