Studies On The Spatial-temporal Distribution Characteristics And Their Variations Of The Quasi-16-day Atmospheric Waves From The Troposphere To The Lower Thermosphere

Planetary waves,as global-scale atmospheric fluctuations,have a profound impact on atmospheric circulation and climatological changes,and also strongly affect the thermodynamic and dynamic structures and variations of the middle and upper atmosphere.In the classic Rossby wave mode,the quasi-16-day waves(Q16DWs)have the longest period and the smallest phase velocity,making them very sensitive to changes in the background flow and more likely to interact with the background flow or other waves.Therefore,studying the spatiotemporal distribution characteristics of Q16 DWs can deepen our understanding of global-scale dynamic processes and reveal the coupling mechanism between the lower atmosphere and the middle and upper atmosphere.To have a comprehensive understanding of the Q16 DWs and its impact on the basic structure and variations of the atmosphere,this paper utilizes the latest ERA5 reanalysis data and observational data from the Microwave Limb Sounder(MLS)of the Earth Observing System to globally demonstrate the climatological characteristics of Q16 DWs with different zonal wavenumbers in the mesosphere-stratospheretroposphere(MST)region’s wind and temperature fields.The temperature amplitudes obtained from ERA5 reanalysis and MLS observation data are highly consistent,even in very fine spatiotemporal structures.Statistical analysis of temperature and wind amplitudes shows that the Q16 DWs propagating westward with zonal wave number 1(W1)and those propagating eastward with zonal wave numbers 1(E1)and 2(E2)are the dominant wave modes.All three waves show significant intra-annual and interannual variations,with the maximum amplitudes appearing near the stratopause.They exhibit strong,moderate,and weak amplitudes in winter,spring/autumn,and summer.W1 wave activity is stronger in the northern hemisphere winter than in the southern hemisphere winter,while E2 wave activity is the opposite,and E1 wave activity is comparable in the boreal and austral winters.The inter-annual variations of the three waves estimated by peak amplitudes are 1.64-2.50,indicating those are significant but not dramatic.Strong wave activity is always accompanied by a positive squared refractive index.We suggest that the squared refractive index determines the global distribution characteristics of dominant wave modes of Q16 DWs.Compared to E1 and E2 waves,W1 wave in the troposphere are easier to propagate upward into the stratosphere and mesosphere,while intense E1 and E2 waves in the stratosphere and mesosphere may come from higher atmospheric regions or be locally excited.In addition,we studied the climatological characteristics of local Q16 DWs in the mesosphere and lower thermosphere(MLT)region using data from three meteor radar stations along the meridian chain.The study has shown that the activity of Q16 DWs decreases with increasing latitude in zonal winds,while the opposite is true in meridional winds.Regarding seasonal variation,Q16 DWs are most active in winter and weaker in summer.The Q16 DWs at the three stations show clear seasonal and interannual variations and are generally weaker than those in the MST region.Because atmospheric tides are stronger than Q16 DWs in the MLT region,and hence dominates the dynamic processes in this altitude range,we have also studied the climatological characteristics of the diurnal and semidiurnal tides.We find that the amplitude of the diurnal tide decreases with increasing latitude,while that of the semidiurnal tide increases.Their zonal wind amplitudes are higher in winter,while the maximum meridional wind amplitudes mostly occur in summer.Further analysis results,such as the negative correlations in amplitudes,the appearance of corresponding secondary waves,and the Q16DWs’ modulation of semidiurnal tides’ amplitudes,all confirm the the interaction between Q16 DWs and semidiurnal tides.Finally,we also investigate the effect of the equatorial stratospheric quasi-biennial oscillation(QBO)on the Q16DWs’ activity.By calculating the “negative value occurrence rate” of the squared refraction index and the potential vortex gradient,we find that during the boreal winter,under QBOW conditions,The W1/E1 Q16 DWs have better propagation conditions at low and mid/high latitudes.The zonal wind amplitudes of the two waves are generally stronger than those under QBOE conditions.During the austral winter,E1 and E2 Q16 DWs have better propagation conditions at low latitudes under QBOW conditions,and the zonal wind amplitude is also slightly greater than that under QBOE conditions.The amplitude difference of E1 and E2 waves under different QBO conditions may result from the direct modulation by QBO.For all three waves,regardless of the QBO conditions,the Q16 DWs excited by the background flow instability are mostly confined to the local area.The QBO does affect the planetary wave activity at middle and high latitudes.