| Planetary waves(PWs)are large-scale atmospheric waves that affect the atmospheric structure and circulation.The periods of PWs are generally 2 to 20 days,and their wavenumbers are from 1 to 5.PWs can be analyzed from the atmospheric parameters obtained from satellite,radar,and other detecting instruments.PWs are generally excited in the lower atmosphere and propagate upward to the stratosphere and the mesosphere.They play important roles in the energy coupling and transport process.The interaction between PWs that propagate upward from below and the polar vortex is considered to be an important mechanism for generating sudden stratospheric warmings(SSWs).Thus,investigations on the characteristic of PWs and their contribution to SSWs are important for us to understand the atmospheric dynamics.In this paper,the seasonal,altitude,and inter-annual variations of eastward/westward propagating quasi 16-day planetary waves at high latitudes are analyzed based on the temperature data between December 2004 and September 2018 obtained from Aura/MLS satellite.The temperature,wind,geopotential height,Ertel potential vorticity data from MERRA2 reanalysis data is used in this study to investigate the association between the quasi 16-day planetary waves and the SSWs.The main results are summarized as follows:1.Long-term variations of the quasi 16-day planetary wave at high latitudesThe quasi 16-day planetary waves are strong at high latitudes of the northern and southern hemispheres.The amplitude of the quasi 16-day planetary waves exhibits clear seasonal variations.The amplitude is the strongest in winter and its magnitude reaches up to8 K.In the southern hemisphere(SH),the eastward propagating waves dominate the westward propagating waves.In the northern hemisphere(NH),the quasi 16-day waves with wavenumber 1(E1 wave,W1 wave)are much stronger than the waves with wavenumber 2(E2 wave,W2 wave).When comparing the results between the two hemispheres,it can be found that the amplitudes of the westward propagating modes(W1 wave,W2 wave)in the NH are much stronger than in the SH,while the amplitudes of the eastward propagating modes(E1 wave,E2 wave)in both hemispheres are comparable.The quasi 16-day waves are strong but not at all interested pressure levels.The amplitudes of the quasi 16-day waves are very weak around 1 h Pa(?50 km)that near the stratopause region while the amplitudes above and below this region are strong.All of the quasi 16-day propagating modes exhibit a strong annual oscillation(AO)in both hemispheres.The AO amplitudes in the NH are generally 0.5 K larger than in the SH.2.Statistical analysis(2005-2018)of the quasi 16-day planetary waves during SSWsTo further understand the variations of the quasi 16-day planetary wave activities during multiple major/minor and polar vortex displacement/split(PVD/PVS)SSWs,a statistical analysis of the four propagating quasi 16-day waves with wavenumbers 1 and 2 during SSW events from 2005 to 2018 is presented based on the Aura/MLS temperature and MERRA2 reanalysis data.The amplitudes of the quasi 16-day waves exhibit a clear enhancement before the commencement of the SSWs,reaching to the maximums around the onset date and then decrease.The total wave power of the eastward and westward waves(Wave E/W)during major/minor SSW is calculated in this paper.The results revealed that the sharp deceleration of the eastward background wind is likely associated with the quick amplification of the westward propagating waves.Based on the Ertel potential vorticity(EPV)from the MERRA2 reanalysis data,the evolution of the polar vortex is exhibited in this study.The EP flux of the quasi 16-day waves is calculated to reveal the magnitude and direction of the energy propagation during the SSWs.The results of the EPV evolution and EP flux indicate that the quasi 16-day waves with wavenumber 1 are associated with the formation of the displaced vortex while quasi 16-day waves with wavenumber 2(mainly W2)contribute on the split of the polar vortex. |
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