Quasi-6-day waves in the mesosphere and lower thermosphere region and their possible coupling with the QBO and solar 27-day rotation

By using atmospheric wind data in the mesopause and lower thermosphere(MLT)region,features of seasonal variations in the quasi-6-day wave(6DW)at different latitudes are analyzed,and modulation of the 6DW by the diurnal tide and solar 27-day period is discussed.The data used in the analysis are extracted from a wind dataset collected by a meteor radar chain from December 2008 to November 2017.The meteor radar chain includes four stations,in Mohe,Beijing,Wuhan,and Sanya.Features of seasonal variations in the 6DW indicate that in summer the 6DW is usually strongest during July and August,followed by stronger variations in January and April.At certain altitudes over Wuhan and Sanya,the 6DW is slightly different in different years and altitudes.In our analysis of seasonal variations in the 6DW,we find that it is generally affected by annual oscillations and semiannual oscillations.The annual oscillations of the 6DW in the mid-low latitudes are modulated by the quasibiennial oscillation in the diurnal tide,resulting in seasonal features that are different from those at other latitudes.In addition,the 6DW amplitude at mid-high latitudes has a significant 27-day solar rotation variation,which was prominent in 2016.

Characteristics of the quasi-16-day wave in the mesosphere and lower thermosphere region as revealed by meteor radar,Aura satellite,and MERRA2 reanalysis data from 2008 to 2017

This study presents an analysis of the quasi-16-day wave(Q16DW)at three stations in the middle latitudes by using a meteor radar chain in conjunction with Aura Microwave Limb Sounder temperature data and MERRA2(Modern-Era Retrospective Analysis for Research and Applications,Version 2)reanalysis data from 2008 to 2017.The radar chain consists of three meteor radar stations located at Mohe(MH,53.5°N,122.3°E),Beijing(BJ,40.3°N,116.2°E),and Wuhan(WH,30.5°N,114.6°E).The Q16DW wave exhibits similar seasonal variation in the neutral wind and temperature,and the Q16DW amplitude is generally strong during winter and weak around summer.The Q16DW at BJ was found to have secondary enhancement around September in the zonal wind,which is rarely reported at similar latitudes.The latitudinal variations of the Q16DW in the neutral wind and temperature are quite different.The Q16DW at BJ is the most prominent in both neutral wind components among the three stations and the Q16DW amplitudes at MH and WH are comparable,whereas the wave amplitude in temperature decreases with decreasing latitude.The quasi-geostrophic refractive index squared at the three stations in the period from 2008 to 2017 was revealed.The results indicate that the Q16DW in the mesosphere and lower thermosphere(MLT)at MH has a limited contribution from the lower atmosphere.Around March and October,the Q16DW in the troposphere at BJ can propagate upward into the MLT region,whereas at WH,the contribution to the Q16DW in the MLT region is largely from the mesosphere.

Nonlinear Interactions between the Quasi 5-day Wave and Tides Based on Meteor Radar Observations at Maui

Nonlinear interactions between the quasi 5-day wave and tides based on meteor radar observation in the Mesosphere and Lower Thermosphere(MLT) at Maui are studied in this paper.Strong sum interaction between quasi 5-day wave and diurnal tide,and evident difference interaction between quasi 5-day wave and semidiurnal tide are observed during the time of attention.However,their difference and sum counterparts are clearly weaker.The secondary waves generated from those interactions beat with the tide and show intense modulation at the period of 5 days which confirms the existence of their interactions.Additionally,correlation coefficients among these waves are calculated to further explore their interactions and find that they can persist for several days although they are highly intermittent.The energy exchange among these waves can be reversible during the observational time.The periods when the significant difference interaction between the quasi 5-day wave and semidiurnal tide occur are much shorter than those when the significant sum interaction between the quasi 5-day wave and diurnal tide occur.Moreover,these two strong interactions can take place simultaneously.In generally,this study provides the proof of nonlinear interactions between quasi 5-day wave and tides which were seldom reported before.

Nonlinear Three-Wave Interaction among Barotropic Rossby Waves in a Large-scale Forced Barotropic Flow

In this paper. the coupling equations describing nonlinear three-wave interaction amongRossby waves including the forcing of an external vorticity source are obtained. Under certainconditions, the coupling equations with a constant amplitude forcing, the stability analysis indicates that when the amplitude of the external forcing increases to a certain extent, a pitchforkbifurcation occurs. Also. it is shown fi-o m numerical results that the bifurcation can lead to chaoticbehavior of' strange' attractor. For the obtained three-variable equation, when the amplitude ofmodulated external forcing gradually increases, a Period-doubling bifurcation is found to lead tochaotic behavior. Thus, in a nonlinear three-wave coupling model in the large-scale forcedbarotropic atmospheric flow, chaotic behavior can be observed. This chaotic behavior can explainin part 30-60-day low-flequency oscillations observed in mid-high latitudes.

北京上空电离层8小时潮汐波对2018年SSW的响应研究

本文利用北京中国科学院地质与地球物理研究所站和北京怀柔站的电离层TEC数据以及由全球导航卫星服务系统(IGS)提供的全球电离层地图(GIM)数据,研究了2018年2月极区平流层爆发性增温(SSW)期间北京上空电离层8小时潮汐波的变化过程.研究结果表明,SSW发生后电离层8小时潮汐波振幅有较长时间的明显增强,且增强分量主要为8小时迁移潮汐波.同时,SSW发生后北京站上空电离层增强的8小时潮汐波也呈现出周期约为6.5天的振荡.通过分析同一时期北京站流星雷达观测到的风场数据,我们发现SSW爆发后低层大气中也存在着异常增强的6.5天波.这表明电离层中调制8小时潮汐波的6.5天振荡很可能与SSW期间低层大气所激发的6.5天波有关.

Long-term variation of Arctic Sudden Stratospheric Warmings(SSW)and potential causes

Utilizing the European Centre for Medium-Range Weather Forecast(ECMWF)Reanalysis v5(ERA5),for the first time,we have confirmed close links among Sudden Stratospheric Warmings(SSWs)in the Northern Hemisphere(NH),the polar vortices,and stratospheric Planetary Waves(PWs)by analyzing and comparing their trends.Interestingly,within overall increasing trends,the duration and strength of SSWs exhibit increasing and decreasing trends before and after the winter of 2002,respectively.To reveal possible physical mechanisms driving these trends,we analyzed the long-term trends of the winter(from December to February)polar vortices and of stratospheric PWs with zonal wave number 1.Notably,our results show that in all three time periods(the entire period of 41winters,1980 to 2020,and the two subperiods—1980-2002 and 2002-2020)enhancing SSWs were always accompanied by weakening winter polar vortices and strengthening polar PWs like Stationary Planetary Waves(SPWs)and 16-day waves,and vice versa.This is the first proof,based on ERA5 long-term trend data,that weakening polar vortices and enhancing stratospheric PWs(especially SPWs)could cause an increase in SSWs.