| The transition between the middle atmosphere and the thermosphere is the so called MLT region.Atmospheric tide and planetary wave are both mainly perturbations in MLT.These perturbations are founded in atmospheric wind,temperature,airglow,etc.tide and planetary wave can change background wind fields in the region and may interact with other waves,affecting the magnitude and period of the amplitude of other waves,which play an important role in dynamics and energetic transfer in MLT region.Investigations on seasonal variability,interannual variability,spatial distribution,interaction,potential source,propagation and model research contributes to describe the dynamics and energetic transfer more extensively and further.In the present study,meteor radar and medium frequency radar are primarily observational equipment used to observe the MLT region.In this paper,the data measured by meteor radar at Andes(30.3°S,70.7°W)from 1 Jan 2010 to 21 march 2014 were used to investigate the seasonal characteristics and spatial distribution of background wind fields,diurnal tide,semidiurnal tide,quasi-16-day planetary wave and quasi-2-day.Regarding tide,background wind fields and tide are studied and compare with the results of HWM-07 and GSWM-00,respectively.Combining with the result of bispectral,we also investigated interactions between diurnal tide and planetary waves in this paper.Regarding planetary wave,the results of reanalysis data of horizontal wind fields were used to complement the results of data observed by meteor radar to more fully describe the seasonal characteristics and spatial distribution of quasi-16-day planetary wave.Combining with zonal background wind fields,we also investigated the influence of background wind fields on planetary wave.Finally,outgoing longwave radiation and ultra-violet radiation were used to discuss the source of planetary wave.Main results and discussion are outlined as follows.1.The horizontal wind fields at MLT region over Andes.Meridional wind are southward from May to August at 80 to 100 km,The maximum of velocity of northward wind observed by meteor radar are about 11 m · s-1 in June.Meridional wind are almost northward from October to February,The maximum values of the northward wind observed by meteor radar are about 13 m · s-1.The observed monthly mean zonal wind usually is eastward all the year,except only few months at several altitudes.that of-20 m · s-1-37 m·s-1 from HWM-07.The variational range of monthly mean meridional wind is about-4 m·s-1-6 m·s-1 and The variational range of monthly mean zonal wind is about-20 m ·s-1-37 m ·s-1.The results of HWM-07 and observations have similar seasonal variations and spatial distribution,but they are not the same,such as,the seasonal variations of northward wind above 95 km,the altitude at which northward wind reach maximum,the temporal and spatial distribution of westward wind fields,the variational range of horizontal wind.The Lomb-Scargle spectrograms of horizontal wind fields indicated that diurnal tide is most prominent perturbation.Besides,we also found there exist semidiurnal tide,terdiurnal tide,quasi-2-day wave.2.The tide at MLT region over Andes.Regarding diurnal tide,observation indicated the diurnal tide propagate upward vertically.The amplitude of diurnal tide exhibits two peaks in the time-height section,the monthly mean amplitude of meridional wind component reachs maximum at 96 km in March,its value is about 51 m·s-1.Another peak appear at 93 km in September,its value is about 40 m · s-1;The monthly mean amplitude of zonal wind component reachs maximum at 94 km in March,its value is about 44 m · s-1.Another peak appear at 93 km in September,its value is about 37 m· s-1.Both the observations and GSWM-00 show that the diurnal tide exhibits two peaks in the time-height section of its monthly mean amplitudes.There are differences between the result of observation and model,for instance,the month in which peaks appear,the altitude at which peaks appear,etc.Regarding semidiurnal tide,the amplitude of meridional component of semidiurnal tide is strongest in summer and weakest in winter;the amplitude of meridional component of semidiurnal tide is rather large in autumn and winter,and is rather small in spring and summer.The amplitude of zonal and meridional component of semidiurnal tide are generally increase with height.The largest amplitude of zonal component of semidiurnal tide is obviously larger than the largest amplitude of meridional component of semidiurnal tide.The observational result suggested that the largest amplitude of meridional component of semidiurnal tide appear in January at 98 km,and its value is about 22 m·s-1.The largest amplitude of zonal component of semidiurnal tide appear in September at 100 km,and its value is about 31 m·s-1.3.The planetary wave at MLT region over Andes.We first describe the quasi-16-day planetary wave.The result observed by meteor radar shows the amplitude of meridional component of quasi-16-day planetary wave is smaller than the amplitude of zonal component of quasi-16-day planetary wave,and there are some differences between the temporal and spatial distribution of amplitude of meridional and zonal component.We mainly compare the observational results in 2010 and 2012.Both the amplitude of meridional component of quasi-16-day planetary wave in 2010 and 2012 reach their peak value in July to August at 80 km;Both the amplitude of zonal component of quasi-16-day planetary wave in 2010 and 2012 reach maximum amplitude in May at 85 to 90 km.The largest amplitude of quasi-16-day planetary wave generally appear in April to September,and the height variability of amplitude is irregular.While the observational results in 2010 and 2012 show most of largest amplitude of quasi-16-day planetary wave appear at 80 to 90 km.The results estimated from ECWMF data indicate that the amplitude of zonal component of quasi-16-day planetary wave is smaller than the amplitude of meridional component of quasi-16-day planetary wave;There are a number of similarities between the temporal and spatial distribution of zonal and meridional amplitude.The time profiles at 225 to 250 hpa level show both of the amplitude of zonal and meridional component are significantly larger,and the amplitude in low-pressure areas also significantly larger in June to September.Except for 2013,the area in which quasi-16-day planetary wave reachs largest amplitude is completely opposite.Besides,the observational results show the interannual variabilities of amplitude of zonal and meridional component of quasi-16-day planetary wave is in reverse.Refer to background wind fields,background wind fields affected the strength of amplitude of quasi-16-day planetary wave.The amplitude of quasi-16-day planetary wave is obviously weaker in some areas related to westward wind.After comparing the results derived from surface ultra-violet radiation and outgoing longwave radiation,surface ultra-violet radiation has greater impact on the amplitude of quasi-16-day planetary wave.While the amplitude estimated from surface ultra-violet radiation attain maximum amplitude,the amplitude of quasi-16-day planetary wave may significantly strengthen in the meantime.Finally,we discuss about quasi-2-day planetary wave.The results observed by meteor radar indicate the amplitude of meridional component of quasi-2-day planetary wave is generally larger than the amplitude of zonal component of quasi-2-day planetary wave,and the maximum amplitude in late January is larger than the maximum amplitude in late December.The amplitude of meridional component of quasi-2-day planetary wave is found to attain maximum amplitude at 93 km in January,its value is about 45m·s-1.The amplitude of zonal component of quasi-2-day planetary wave is found to attain maximum amplitude at 99 km in January,its value is about 18 m·S-1.There are some differences between the temporal and spatial distribution of amplitude of zonal and meridional component.The amplitude of zonal component is significantly strengthen in June,but the phenomenon did not appear in meridional component. |
PDF Full Text Request