| Planetary waves are periodic oscillations that mainly exist in the mesosphere and stratosphere.Planetary waves dissipate or break and interact with each other in the propagation process,which constitute the basic characteristics of middle and upper atmosphere dynamics.The nonlinear interactions between planetary waves can cause significant changes in the ionosphere,which closely related to human activities such as aerospace communications,radio broadcasting and radar.Therefore,we conduct an indepth analysis of the properties of eastern and western planetary waves in the northern and southern hemispheres,and the main results are as follows:(1)Statistical analysis of westward quasi-2-day wave events with zonal wavenumbers 4(W4),3(W3)and 2(W2)from 2002 to 2020.It is find that the wave period of W4 varies greatly in the southern hemisphere,and is about 48 hours in the northern hemisphere,and the peak amplitude of W4 is stronger in the northern hemisphere than in the southern hemisphere.The wave period of W3 in both the northern and southern hemispheres is about 48 hours,and the peak amplitude in the southern hemisphere is significantly stronger than that in the northern hemisphere.The wave period of W2 is relatively stable in the northern hemisphere,but varies greatly in the southern hemisphere,and the peak amplitude is slightly stronger in the southern hemisphere than in the northern hemisphere.The W4,W3 and W2 events are mainly concentrated on days 195-210 in the northern hemisphere,and in the southern hemisphere,the occurrence date of the events is delayed with the increase of the zonal wavenumber.The average temperature spatial structure of W4 in the northern and southern hemispheres is bimodal,and the amplitudes are equal.The average temperature spatial structure of W3 is unimodal in the southern hemisphere and bimodal in the northern hemisphere and the amplitude in the southern hemisphere is stronger than that in the northern hemisphere.Through diagnostic analysis,it is find that the instability and background wind of bimodal W3 are stronger than that of unimodal W3.Furthermore,the source activity of bimodal W3 is stronger than that of unimodal W3.This suggests that the instability of the W3 bimodal structure,the background wind and the source activity can provide stronger energy amplification and propagation of W3.It is suggest that the W4 and W3 hemisphere structural changes may be due to the influence of background wind,instability and source activity.The wave period of W4 and W3 increased in the late summer in the northern hemisphere,which is considered to be the influence of the different instability and background wind of W4 and W3 in the three periods before,during and after the northern hemisphere summer.In addition,the difference in the critical layers of large and small periods indicates the selective amplification of different periods by W4 and W3 in the front,middle and back periods.In addition,W3 has a longer wave period than W4 because the phase velocity of the quasi-2-day wave is inversely proportional to its zonal wavenumber and period.(2)To analyze and study the global changes of eastward planetary waves of zonal wavenumbers-1(E1),-2(E2),-3(E3)and-4(E4)in the polar mid-atmosphere in 2019.The eastward planetary waves were find to occur in the winter hemisphere with westward background winds.The peak amplitude of eastward planetary waves is greater in the southern hemisphere than in the northern hemisphere.In addition,with the increase of the zonal wave number,the planetary wave gradually moves to the lower latitude,and the peak amplitude weakens.The wave period of E1 varies from 5 to 3days in both hemispheres,while the wave period of E2 is about 48 hours in the northern hemisphere slightly longer than about 40 hours in the southern hemisphere.The E3 wave period is about 30 hours in both hemispheres,while the E4 period is about 24 hours.The temperature spatial structure of E1,E2,E3 and E4 in the northern and southern hemispheres showed different bimodal structures,and the amplitude of the low peak was larger than that of the peak.The average phase velocities of the eastward planetary waves are relatively stable,and the average phase velocities of E1,E2,E3 and E4 at 70° are 53,58,55 and 52 m/s,respectively.Through diagnostic analysis,it was find that strong instability in the lower Antarctic layer and appropriate background winds may generate enough energy to promote the propagation and amplification of E1 into the upper atmosphere.It shows the effect of background zonal wind and instability of polar mid-atmosphere on eastward planetary wave dynamics.(3)The influence of the quasi-biennial oscillation from 2003 to 2020 on the quasi-2-day wave activities of W4 and W3 was study,and it was find that the temperature fluctuation amplitudes of W4 and W3 in the quasi-biennial oscillationwesterly period in the northern and southern hemispheres were stronger than that during the quasi-biennial oscillation-easterly period.Through diagnostic analysis,it is found that the southern hemisphere W4 has stronger instability,background wind and source activity in the quasi-biennial oscillation-westerly period than the quasi-biennial oscillation-easterly period,while the southern hemisphere W3 is mainly affected by Rossby(3.0),background wind in the mid-layer atmosphere,instabilities,and changes in source activity in the lower atmosphere have limited effects on W3 propagation and amplification.The background wind,instability and source activity of W4 and W3 during the quasi-biennial oscillation-westerly period in the northern hemisphere are stronger than those during the quasi-biennial oscillation-easterly period,indicating the propagation of W4 and W3 in the northern and southern hemispheres during the quasibiennial oscillation-westerly period and amplification is more susceptible to background wind,instability,and source activity. |
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