平流层冬季增温及大气中的行星波

本文利用NIMBUS-7SAMS资料分析了东经100度子午线上的两个站点(67.5°N和42.5°N)在10mb和0.0827mb高度上从1978年底至1982年间的大气温度,获得几年的平流层冬季增温结果.在1978/1979年和1981年初的冬季,高纬站点几天内出现的平流层增温最大幅度可达65K.对平流层增温的谱分析结果指出,在高纬冬季平流层有很强的16天、32夭、21天周期的行星波。中纬冬季平流层增温幅度较小,约为20K.中纬的中间层高度上整年存在有5天、8天和16天的行星波。分析研究、南、北半球不同纬度的温度随经度的分布,得出高纬冬季平流层、中间层大气温度随经度有明显的变化。波数1和波数2的波有大的幅度(主要是波数1),从高纬到低纬,波幅逐渐减小在冬季的平流层和中间层大气中,波数1和波数2的行星波在短期内可强烈增强,引起平流层冬季增温。      

平流层爆发性增温事件中大气准16日行星波

2014年1月上中旬高纬平流层发生弱增温事件,增温幅度约25K,纬向西风减弱并于2月初转向.行星波在平流层爆发性增温（SSW）事件产生中具有重要作用.利用北半球近东经120°链上中低纬5个流星雷达探测的风场数据,研究了此SSW事件发生前和发生期间中间层和低热层区（MLT）大气风场的行星波状况.结果显示,极区平流层增温前MLT区大气呈现出明显增强的准16日波动,增温达到最大时,16日波也最强,表明中低纬MLT区的行星波变化与SSW事件存在耦合关系.进一步利用欧洲中心平流层再分析资料数据,分析SSW期间北半球平流层的波动和零风线状况,发现平流层准16日波和零风线随时间由低纬向高纬移动,反映出16日波与SSW之间存在某种动力学联系.      

2009年冬季平流层爆发性增温期间行星波活动特征

利用2008年12月至2009年4月的MERRA再分析数据资料,对2009年1月下旬北半球高纬平流层发生的强增温事件以及与之相关的行星波活动进行了研究.谱分析发现,SSW发生前后极区平流层内准16天行星波活动显著.利用二维谐波拟合法分别拟合温度场准16天波4个波模（W1,W2,E1,E2）的振幅和相位,结果表明:背景西风减弱时四个波模的振幅均有不同程度的增大,且都在50°-80°N范围内的平流层中上层达到最大值;准16天W2波的增幅最大且辐合最强烈,其引起的背景流最大西风减速超过4m·-1·d-1,说明准16天W2波在该次增温事件中占主导地位;行星波传播与零风线移动关系密切,准16天W2波在中高纬地区垂直向上传播并近似呈现经向驻波结构,然后分别向极点和赤道两个方向传播,这表明中高纬地区可能是行星波的一个源区.      

用全球原始方程半谱模式研究QBO对行星波传播的影响

本文建立了一个全球原始方程半谱模式,模拟了赤道上空风场准两年振荡(QBO)及其相应的副热带急流大小对冬季半球行星波向上传播及平流层突然增温的影响。结果表明,波数1的行星波在QBO东风相比西风相更易向上传播,平流层增温更快更强。波数2则相反。QBO对低纬对流层里的行星波上传的影响限制在低纬低平流层,对中高纬影响不大。     

对流层特大暴雨天气对电离层变化的影响

研究气象活动对电离层变化的影响．利用时序叠加方法，通过对1958-1998年期间发生在武汉的5次特大暴雨天气事件对武汉上空电离层变化的影响进行分析，发现：(1)特大暴雨能够引起低电离层，fbEs和，f0Es参量较明显地减小；(2)特大暴雨对电离层F区寻常波描迹的最低虚高h′F和电离层等效峰高hpF的参量也有一定影响，且随着雨量的增大这种影响作用也会增加；(3)特大暴雨对电离层其他参量影响甚弱或没有影响．本文认为，特大暴雨天气事件对电离层的影响主要来自于动力过程，特别是特大暴雨激发的或相伴的大气重力波、潮汐波和行星波等长周期大尺度过程的作用．     

大气行星波影响低频电波吸收变化的机制

本文根据冬季中低纬低电离层中、低频（ＬＦ）电波振幅扰动与高纬平流层中大气行昨波活动密切相关的观测事实，分析研究了可能引起低电离层对ＬＦ电波吸收变化诸因素的作用后，提出了一种能较好地解释观测现象的物理机制，大气行星波可通过两种方式改变大气离化率ｑ，因而引起低电离层中电子密度Ｎ扰动，进而改变由Ｎ大小决定的电离层电波吸收值，结果导致ＬＦ电波振幅发生相应变化。文中给出了描述这一物理计算公式和某些计算结果。     

地形对低平流层突然增温的可能影响

本文用Nimbus7 SAM卫星观测的温度资料,分析了突然增温事例中地面地形不同的四个子午圈剖面内的温度分布及变化过程。结果表明,高山地区、平原和海面上空的行星波加热和低平流层突然增温有很大的差别。地形的影响是明显的。      

2009年1月平流层爆发性增温期间全球电离层响应的研究

2009年1月平流层爆发性增温(Stratospheric Sudden Warming, SSW)事件是有记录以来最强、持续时间最长的一次主增温事件(Major Warming Event, MWE), 期间太阳活动和地磁活动均处于较低的水平, 因此非常有利于研究电离层对平流层增温事件的响应情况. 本文利用COSMIC (Constellation Observing System for Meteorology, Ionosphere, and Climate)系统提供的掩星数据, 使用Kriging方法分别构建了此次SSW期间及平静期的电离层N_mF₂, h_mF₂和110～750km高度范围的垂直积分TEC (简称VTEC)地图, 同时从全球定位导航卫星系统服务组织(International GNSS Service, IGS)发布的全球电离层TEC地图(Global Ionospheric Maps, GIMs)中提取了日固坐标系(Sun-fixed, 地磁纬度和地方时)下全球TEC地图. 通过对比发现, SSW期间与平静期相比, 地磁纬度中低纬电离层参数存在早晨上升, 下午和夜间下降的现象. 利用OSTM/JASON-2卫星高度计观测值进行验证后的结果显示, 此前研究均未有提及的夜间时段电离层参数N_mF₂, h_mF₂和TEC (VTEC和IGS TEC)的下降现象的确存在.      

赤道异常的行星波振荡

利用日本及印度垂测站的电离层月报表资料,分析出电离层赤道异常具有行星波周期的振荡.振荡周期一般在2天到5天之间.也观测到15—20天周期的振荡.      

基于MST雷达数据的中纬对流层和低平流层大气行星波研究

通过分析中国河北香河站MST (Mesosphere-Stratosphere-Troposphere)雷达 2012-2014年的水平风场数据, 研究了北半球中纬地区对流层和低平流层 (Troposphere and Lower Stratosphere, TLS)区域大气行星波的特性. 谱分 析发现, 在这一区域准16天波和准10天波占据主导地位, 准16天波更为显著. 在 对流层区域, 行星波具有丰富的频谱成分, 活动具有间断性, 持续时间一般不 超过三个月, 并没有明显的季节性变化特征, 其中纬向分量的振幅大于经向分量. 在 平流层区域(高度17km以上), 行星波一般出现在冬季, 并且主要在纬向分量中. 通常平流层区域的振幅要小于对流层区域. 结合MERRA再分析资料分 析了强行星波传播特性, 结果表明: 2014年2-3月纬向分量中的准16天波垂 直向上传播, 垂直波长约为64km, 纬圈波数约为2, 纬向传播方向自西向东, 水平波长约为15324.7km, 对应的相速度为11.1m·s-1 (向东为正); 2014年5月纬向分量中的准10天波在10~18km高度范围内向下传播, 垂直波长约为50km, 纬圈波数约为1, 传播方向自西向东, 水平波长约为 30649.4km, 对应相速为35.5m·s-1.      

Dissipation of temperature perturbations in the middle atmosphere

It is often observed that the stratospheric and mesospheric temperature structure undergoes transient disturbances from its averaged steady-state behavior. The causes may be traceable to gravity waves, planetary waves, solar proton and relativistic electron precipitation, etc. We examine the theoretical time behavior of the atmospheric temperature following the cessation of such heating phenomena as it relaxes toward its quiescent steady-state value. We also study the time-dependent response during a model stratospheric-warming/mesospheric-cooling event. In particular, we investigate the roles of eddy heat conduction, non-LTE cooling in the 15μm CO₂ band, and an ambient vertical wind, and their relative importance as they depend upon altitude and time, in modifying temperature changes in this region.     

Temperature variability in the tropical mesosphere during the northern hemisphere winter

Temperature observations at 20–90 km height and 5°N–15°N during the period of December 1992–March 1993 from the WINDII and MLS experiments on the UARS satellite are analysed together with MF radar winds and UKMO assimilated fields of temperature and zonal and meridional winds. The correlation between the different datasets at the tropics and zonal mean wind data at mid latitudes is examined for period February–March 1993, when series of stratospheric warming events were observed at middle and high latitudes. Wavelet analysis is applied to investigate coupling between stationary and travelling planetary waves in the stratosphere and the upper mesosphere. Planetary waves m = 1 with periods of 4–7 days, 8–12 days and 13–18 days are found to dominate the period. Westward 7- and 16–18 day waves at the tropics appear enhanced by stationary planetary waves during sudden stratospheric warming events.     

Height-latitude structure of stationary planetary waves in the stratosphere and lower mesosphere

Daily UK Met Office stratospheric assimilated data for the Northern and Southern Hemispheres, accumulated for the period from 2004 to 2012 and pressure range of 1000–0.1 hPa, are used in this paper. The paper presents and thoroughly discusses spatial–temporal distributions of stationary planetary wave (SPW) amplitudes and phases, calculated on the basis of geopotential height, temperature, zonal and meridional wind data for zonal wave numbers 1 and 2 (SPW1 and SPW2). The climatological planetary wave amplitudes and phases are calculated by extracting waves from three types of data: daily, monthly mean and climatological monthly mean. It has been established that magnitude of amplitudes and height-latitude distribution of amplitudes of SPW1 and SPW2 depend on data processing method for all parameters. It has also been established that height-latitude distribution amplitudes and phases significantly differ for geopotential height, temperature, zonal and meridional wind and depend on wave number and hemisphere. However, height-latitude distributions of phases are little different from each other for the used methods of data processing.     

Multi-year high latitude mesospheric neutral wind observations using a Fabry–Perot interferometer

From 1995 to 1999, a Fabry–Perot Interferometer was stationed at Resolute Bay, Canada (75°N, 95°W) to measure the mesospheric neutral winds in the polar cap from the OH nightglow emission during winter seasons. A 12-h wave is the most prominent feature in the neutral winds. The wave amplitude has large day-to-day variations and inter-annual variability, whereas the phase of the wave appears to be largely consistent for year to year. Small phase shift from early winter to later winter was noticed during most of the seasons when early winter data were available. The 12-h wave showed stronger variability during the 1995/1996 winter season, which may be related to nonlinear interactions with planetary waves. Large negative zonal winds were observed during stratospheric sudden warming events.     

The day-to-day variability in the mesosphere and lower thermosphere in low latitudes: A study using MF radar

This study presents the analysis of planetary waves (PWs) using daily mean wind velocities for four years (August 2013 to July 2017) of continuous measurements using MF radar over the low latitude Indian region Kolhapur (16.8° N; 74.2° E). The MF radar at Kolhapur was upgraded in 2013. These are the first results of PWs after the upgradation of MF radar. The seasonal and intra-seasonal variabilities of East-West (EW) traveling PWs in the MLT region have been studied. In the present work, the data was analyzed to study the waves with various periodicities (e.g. 3–4, 5–8, 15–17, and 30–60 days). The 3.5 day [Ultra-Fast Kelvin (UFK)] wave shows semiannual variability with burst like wave activity observed during the summer months and December solstice. In addition, it is observed to be stronger in the spring equinoctial period. A strong semiannual oscillation (SAO) has been observed in a 6.5-day wave with peaks near the equinoxes. Similar to SAO over the low latitude MLT region, the wave activity is stronger in April/May than in September/October. The 6.5-day waves are observed to be stronger when the background mean wind is westward. From the analysis, it has been seen that the period before and after the equinoctial period is favorable for the 6.5-day wave propagation. The 16-day wave has no significant seasonal dependence; instead, the waves spread to almost all seasons. The Madden-Julian Oscillations (MJOs) have been observed to be propagating with an average wind speed of ～ 5 m/s when the background mean wind is eastward. The occurrence of MJO is observed during the summer and winter months. These results are the first of their kind in two aspects: first, they show the PWs with enhanced altitude coverage covering up to 110 km, and second, they show the PWs not contaminated due to equatorial electro jet influence.     

Some features of the day-to-day MLT wind variability in winter 2017–2018 as seen with a European/Siberian meteor radar network

We present results of wind measurements near the mesopause carried out with meteor radars (MRs) at Collm (51°N, 13°E), Obninsk (55°N, 37°E), Kazan (56°N, 49°E), Angarsk (52°N, 104°E) and Anadyr (65°N, 178°E) from October 1, 2017 till March 31, 2018. The Collm and Kazan MRs are SKiYMET radars with vertical transmission and radio echo height finding, while the other radars operate with horizontal transmission and without height finding. We paid particular attention to the meridional wind variability with periods of 4–6 days and 9–11 days. The waves with these periods are seen as spots of the wave activity in the wavelet spectra and include oscillations with different periods and different discrete zonal wavenumbers. These wave packets successively propagate as a group of waves from one site to another one in such a way that they are observed at one site and almost disappear at the previous one. The 4–6 wave group includes planetary-scale oscillations (individual spectral components) which have eastward phase velocities and mostly zonal wavenumbers 2 and 3, and the vertical wavelength exceeds 70 km at middle latitudes. The source of the oscillations is the polar jet instability. The wave group itself propagates westward, and the amplitudes of wind oscillations are approximately 5–6 m/s as obtained from the wind data averaged over the meteor zone. The 9–11 day wave set propagates westward as a group and mainly consists of spectral components which have westward phase velocity and zonal wavenumber 1. Amplitudes of these wind perturbations strongly vary from station to station and can reach, approximately, 8 m/s. The vertical wavenumber is 0.014 km⁻¹ as taken from the Kazan and 0.05 km⁻¹ according to the Collm data. We obtained a global view on the waves by using the AURA MLS geopotential data. We found a good correspondence between wave features obtained from the MR wind measurements and the MLS data. To our knowledge, such a wave propagation of planetary wave in the mesosphere/lower thermosphere (MLT) region has so far not obtained much attention.