平流层爆发性增温期间中高层大气行星波研究进展

极区平流层爆发性增温（SSW）是冬季半球最剧烈的大气扰动现象之一. SSW期间温度和风场的剧烈变化被认为是冬季半球中高层大气波动能量异常增强的主要原因.流星雷达是能够稳定连续探测中间层和低热层风场的重要地基探测设备.主要依托国家重大科技基础设施建设项目：“子午工程”,我国已建设了多个流星雷达观测台站,对中间层和低热层风场进行了长期稳定连续的监测,为揭示SSW期间中间层和低热层波动异常变化的物理机制提供了重要的观测资料.本文简述了近年来以我国“子午工程”流星雷达监测数据为核心,SSW期间中高层大气行星波的研究进展和成果;深入讨论了冬季半球中高层大气行星波发生异常变化的主要激发机制.随着“子午工程”二期十个流星雷达台站即将建成,本文对利用“子午工程”流星雷达监测台网进一步研究SSW期间中高层大气波动的变化特性进行了展望.     

2013年平流层爆发性增温期间高纬电离层半日潮汐波研究

基于Sondrestrom站(67°N,51°W)非相干散射雷达观测数据,研究了2013年平流层爆发性增温(SSW)事件发生后高纬地区电离层F层和E层半日潮汐波.同时,对1月非SSW发生期间和不同太阳活动期间高纬电离层中的半日潮汐波进行了统计分析,并和2013年SSW事件发生后的结果进行了比较.研究发现,SSW发生后F...     

平流层爆发性增温期间赤道电集流中太阴潮汐的经度变化统计学研究

本文利用地磁台站和卫星磁场数据,对平流层爆发性增温(Sudden Stratospheric Warming,SSW)期间赤道电集流(Equatorial Electrojet,EEJ)中太阴半日潮汐的经度变化进行了统计学分析.结果显示,SSW期间秘鲁和印度扇区的EEJ中太阴半日潮汐明显增强,且存在显著的经度差异.秘鲁扇区的EEJ中太阴半日潮汐达到峰值的时间要早于印度扇区,进一步分析发现峰值时间的经度差异与太阳活动和准两年振荡相位有关.此外,SSW期间秘鲁扇区EEJ的太阴半日潮汐峰值强度比印度扇区高.对比不同经度带背景磁场的强度与太阴半日潮汐的峰值幅度的关系,可以看出SSW期间EEJ太阴半日潮汐峰值幅度的经度差异与背景磁场强度有关,但也存在其他物理过程的影响.     

中国廊坊(39.4°N,116.7°E)中间层和低热层潮汐的季节变化

本文利用中国廊坊站(39.4°N,116.7°E)流星雷达在2012年4月1日至2013年3月31日期间的水平风场观测数据,分析了廊坊上空中间层和低热层(MLT,80~100 km)大气纬向风、经向风潮汐的季节变化特征.研究表明:廊坊MLT区域周日潮汐和半日潮汐波动比较显著,有明显的季节变化特征.周日潮汐振幅在88 km以下为半年变化,极大值位于2-3月和10月,极小值位于冬、夏季;在88 km以上为周年变化,振幅冬末春初最强,夏季最弱.周日潮汐相位在秋、冬季比春、夏季提前.半日潮汐主要呈现半年变化,在5月和9月最强,冬、夏季最弱.半日潮汐相位在春、夏季比秋、冬季提前.此外,廊坊风场潮汐的观测结果与WACCM4模式模拟结果进行比较,结果表明两者的主要特征相似,在细节上有显著区别.与40°N附近其他站点风场潮汐观测结果的比较结果表明中纬度MLT风场潮汐有显著的随经度变化特性.     

中性风与等离子体行星波的同步振荡

本文是“赤道异常的行星波振荡”的续篇。提供新的事实以说明:由于中层大气的行星波振荡会调制到潮汐风上面,潮汐风上升到E层发电机区域,通过发电机效应产生电场及S_q电流体系的行星波振荡。电场沿磁力线传到F_2层,通过“喷泉效应”引起电离层赤道异常的行星波振荡。所有这些振荡来源相同,所以是同步的。     

高纬地区低层大气行星波的无线电探空仪观测研究

本文通过分析美国阿拉斯加地区三个站点(Nome,64.50°N,165.43°W;McGrath,62.97°N,155.62°W;Fairbanks,64.82°N,147.87°W)无线电探空仪1998～2006年观测数据,研究了北半球高纬地区低层大气行星波特性.通过分析发现行星波主要存在于两个区域,一个在对流层顶附近,一个在冬季极夜急流附近,两个区域的行星波都具有明显的间断性,持续时间一般不超过2个月;三个分量中,温度扰动量的振幅最小,经向风扰动量的振幅最大.对流层顶附近的行星波没有明显的季节变化且谱成分较为复杂,5天波的振幅最小,10天波的振幅略强于16天波.极夜急流附近的行星波主要出现在冬季,波振幅比对流层顶附近小,主要为10天波和16天波,且16天波的振幅强于10天波.由折射指数可以看出,夏季在对流层上方有明显反射层,冬季则较弱甚至消失,很好地解释了平流层行星波主要在冬季出现的原因.对2003/2004年冬季三个站点行星波的细致分析发现对流层区域和极夜急流区域出现明显的准10天波和准16天波,准10天在垂直方向为驻波,温度分量垂直波长约为12km,经向风分量垂直波长大于26km,波自东向西传,纬向...     

中国高层大气与电离层耦合研究进展

近年来,地球高层大气与电离层之间的耦合研究为众多学者所关注.在回顾这一领域国际上若干研究方向进展的基础上,着重介绍了中国学者的近期研究工作与贡献.首先,扼要介绍了中国高层大气观测的新发展,包括激光雷达、FP干涉仪、全天空气辉成像仪等光学探测,MST雷达、全天空流星雷达等无线电探测手段.在高层大气变化特性研究中,介绍了高层大气的气候学及各种大气波动的研究进展.在高层大气与低电离层的耦合研究方面,介绍了突发钠层及低热层钠层的观测研究和钠层模式的研究进展,以及突发E层与大气行星波之间的耦合研究工作.在高层大气波动过程与电离层F2层耦合研究中,着重介绍了电离层四波经度结构与高层大气非迁移潮汐之间的耦合特性与机理研究.在热层与电离层耦合的研究方向上,介绍了热层背景大气风场和重力波对电离层的作用、带电粒子对赤道热层的影响与热层赤道异常的形成机理研究等热层电离层相互耦合工作.综合认为,近年来中国学者在高层大气与电离层耦合的研究领域进行了大量工作,包括实验观测及数据分析、模式化与理论研究等.中国学者取得的研究成果为这一领域近年来的进展与突破做出了重要贡献.     

冬季强、弱平流层增温事件的发生与春季最后增温事件爆发早晚的联系

利用1958~2012年NCEP-NCAR逐日再分析资料,对平流层冬季强、弱爆发性增温事件(SSW)的发生和春季最后增温事件(SFW)爆发的早晚进行了统计、对比和合成分析.结果表明,冬季SSW事件的强、弱以及发生与否,可关系到后期春季SFW事件爆发的早晚.具体地,在发生(未发生)冬季强SSW事件之后的春季,SFW事件的爆发趋于偏晚(早);而在冬季弱SSW事件之后的春季,出现SFW事件爆发早和爆发晚的几率相当.对比冬季强、弱SSW过程中环流以及行星波活动异常的演变发现,在冬季强SSW事件爆发约30天之后,平流层会出现相反的强极涡(强极夜急流)型异常环流,伴随的行星波活动强度的负异常可持续到SSW爆发后约45天;不同的是,冬季弱SSW事件所伴随的环流异常持续时间短,不存在后期的强极涡型环流异常和行星波活动的显著异常.为了进一步证实冬季强SSW事件的发生对春季SFW事件爆发早晚的可能影响,针对冬季强、弱SSW年以及无增温事件发生的普通年份分别进行了合成分析,平均而言,在有强SSW事件(无SSW事件)发生年的冬季月份,热带外平流层行星波活动异常偏强(弱),极夜急流和平流层极涡异常偏弱(强),但在后期的春季月份,行星波活动则异常偏弱(强),平流层极涡异常偏强(弱).在有冬季弱SSW事件发生年的后期春季,平流层极夜急流以及极涡的强度无显著异常,与气候平均状况接近.     

Madden-Julian振荡对北半球冬季中间层影响的动力学过程

本研究揭示了北半球冬季Madden-Julian振荡(MJO)对北半球中间层大气的作用.卫星观测和数值模式模拟的结果表明,北半球高纬度中间层大气在MJO第4相位后约35天显著降温,这一现象滞后MJO引起的高平流层扰动约10天.在中纬度,向上传播的行星波增强还导致了中间层温度在滞后MJO第4相位25天左右时出现1波结构的温度异常. MJO引起的异常行星波可以调制平流层顶-低中间层区域纬向西风在MJO第4相位后约30天减弱.同时,由于重力波的临界层滤波机制,减弱的西风会引起中间层的气候平均西向重力波减弱.受到行星波和重力波变化的共同作用,中间层的经向环流在MJO第4相位滞后约35天显著减弱,并导致极区中间层降温.     

纬向风与赤道异常的行星波同步振荡及其谱分析

本文利用最大熵谱分析方法处理了电离层赤道异常北峰Okinawa站的f₀F₂行星波周期的振荡.比较同一期间相近经度链上的南北半球观测到的低热层中性大气运动,发现较短周期的2-5日波,尤其是在南北半球的夏季期间（北半球7-8月前后,南半球1-2月前后）,其纬向风与赤道异常振荡强弱及周期变化具有良好的同步对应性.对于较长周期的中性风振荡,只要其幅度相当大,也会在赤道异常的振荡中有所对应.从而提供证据说明中性风的行星波振荡是赤道异常的行星波振荡的驱动源.     

Meteor wind radar observations of tidal amplitudes over a low-latitude station Trivandrum (8.5°N, 77°E): Interannual variability and the effect of background wind on diurnal tidal amplitudes

Based on the horizontal winds measured using SKiYMET meteor wind radar during the period of June 2004–May 2007, the seasonal and interannual variability of the diurnal and semidiurnal amplitudes and phases in the mesospheric and lower thermospheric (MLT) region over a low-latitude station Trivandrum (8.5°N) are investigated. The monthly values of amplitudes and phases are calculated using a composite day analysis. The zonal and meridional diurnal tidal amplitudes exhibit both annual and semiannual oscillations. The zonal and meridional components of semidiurnal tide show a significant annual oscillation. The phase values of both diurnal and semidiurnal tides exhibit annual oscillation above 90 km. The effect of background wind in the lower atmosphere on the strength of diurnal tidal amplitudes in the MLT region is studied. The effect of diurnal tides on the background wind in the lower thermosphere is also discussed.     

A possible cause for the generation of unusually strong 20- and 30-hour oscillations in the neutral wind of the lower thermosphere

The harmonic relationship between the diurnal and semidiurnal tides gives rise to an elementary mathematical relationship that has intriguing consequences for secondary waves produced by non-linear interactions between the diurnal tide and planetary waves. A speculative theory is developed which predicts that, under certain conditions, these secondary waves can be amplified by non-linear interaction with the semidiurnal tide. A peculiar feature of dynamics in the MLT region above Bulgaria is the presence of strong oscillations with periods near 20 and 30 h, especially in the zonal wind component. Observational evidence from a meteor radar at Yambol, Bulgaria suggests that the 20- and 30-h signals are produced as the result of non-linear interactions of the type proposed by the novel theory.     

A possible cause for the generation of unusually strong ∼20- and 30-hour oscillations in the neutral wind of the lower thermosphere

The harmonic relationship between the diurnal and semidiurnal tides gives rise to an elementary mathematical relationship that has intriguing consequences for secondary waves produced by non-linear interactions between the diurnal tide and planetary waves. A speculative theory is developed which predicts that, under certain conditions, these secondary waves can be amplified by non-linear interaction with the semidiurnal tide. A peculiar feature of dynamics in the MLT region above Bulgaria is the presence of strong oscillations with periods near 20 and 30 h, especially in the zonal wind component. Observational evidence from a meteor radar at Yambol, Bulgaria suggests that the 20- and 30-h signals are produced as the result of non-linear interactions of the type proposed by the novel theory.     

Evidence for nonlinear coupling of planetary waves and tides in the lower thermosphere over Bulgaria

Analyses of hourly values of zonal and meridional wind near 95 km observed by meteor radar at Yambol (42.5°N, 26.6°E) during January 1991–June 1992 indicate the presence of planetary waves with prevailing periods of 1.5–2.5, 4–6, 9–10 and 16–18 days. About 20% of the whole power of atmospheric motions is connected with these waves, so they play an important role in the dynamics of the mesosphere-lower thermosphere (MLT) region. By dynamic spectral analysis applied to the hourly neutral wind and to the calculated hourly values of tidal amplitudes it has been demonstrated that there is considerable modulation of tidal amplitudes by planetary waves in the neutral wind, as this process is better expressed in the semidiurnal tides. The nonlinear interaction between tides and planetary waves is studied by bispectral analysis. The results of these analyses indicate again that the nonlinear interactions between semidiurnal tides and planetary waves with periods 2–20 days are stronger than those of the diurnal tides and planetary waves. A peculiar feature of dynamics in the MLT region above Bulgaria is the presence of strong oscillations with periods of 20 and 30 h, which indicate significant nonlinear coupling between them.     

Wavelet analysis on transient behaviour of tidal amplitude fluctuations observed by meteor radar in the lower thermosphere above Bulgaria

On the basis of bispectral analysis applied to the hourly data set of neutral wind measured by meteor radar in the MLT region above Bulgaria it was demonstrated that nonlinear processes are frequently and regularly acting in the mesopause region. They contribute significantly to the short-term tidal variability and are apparently responsible for the observed complicated behavior of the tidal characteristics. A Morlet wavelet transform is proposed as a technique for studying nonstationary signals. By simulated data it was revealed that the Morlet wavelet transform is especially convenient for analyzing signals with: (1) a wide range of dominant frequencies which are localized in different time intervals; (2) amplitude and frequency modulated spectral components, and (3) singular, wave-like events, observed in the neutral wind of the MLT region and connected mainly with large-scale disturbances propagated from below. By applying a Morlet wavelet transform to the hourly values of the amplitudes of diurnal and semidiurnal tides the basic oscillations with periods of planetary waves (1.5/20 days), as well as their development in time, are obtained. A cross-wavelet analysis is used to clarify the relation between the tidal and mean neutral wind variability. The results of bispectral analysis indicate which planetary waves participated in the nonlinear coupling with the atmospheric tides, while the results of cross-wavelet analysis outline their time intervals if these interactions are local.     

Seasonal variation of non-migrating semidiurnal tide in the polar MLT region in a general circulation model

Behavior of semidiurnal tides in the north and south polar MLT regions simulated by Middle Atmosphere Circulation Model at Kyushu University is described. Summertime enhancement of westward propagating semidiurnal tide with zonal wavenumber s=1 is found, which is consistent with the observed result at the South Pole (Ann. Geophys. 16 (1998) 828). Additional numerical simulations show that the non-migrating semidiurnal tide is mainly generated by the nonlinear interactions between stationary planetary waves with zonal wavenumber s=1 and the migrating semidiurnal tide in the stratosphere and mesosphere as suggested by Forbes et al. (Geophys. Res. Lett. 22(23) (1995) 3247).     

Global distribution,seasonal, and inter-annual variations of mesospheric semidiurnal tide observed by TIMED TIDI

Based on TIDI mesospheric wind observations, we analyzed the semidiurnal tide westward zonal wavenumber 1 and 2 (SW1 and SW2) component seasonal, inter-annual variations, and possible sudden stratospheric warming (SSW) related changes. Major findings are as follows: (1) The SW1 has a peak near the South Pole during the December solstice and near the North Pole during the March equinox. (2) The SW2 peaks at 60S and 60N mostly during winter solstices. The SW2 also peaks during late summer and early fall in the northern hemisphere. (3) The QBO effect on the semidiurnal tide is much weaker than that on the diurnal tide. The March equinox northern SW1 zonal amplitude appears to be stronger during the westward phase of the QBO, which is opposite of migrating diurnal tide QBO response. (4) Possible SSW event related changes in the semidiurnal tide are significant but not always consistent. Enhancements in the mid-latitude SW2 component during SSWs are observed, which may be related to the increase of total ozone at mid and high latitudes during SSW events. TIDI observations also show a decrease in the SW2 in the opposite hemisphere during a southern SSW event in 2002. Small increases in the high latitude SW1 in both hemispheres during the 2002 southern SSW event were recorded.     

Planetary wave coupling (5–6-day waves) in the low-latitude atmosphere–ionosphere system

Vertical coupling in the low-latitude atmosphere–ionosphere system driven by the 5-day Rossby W1 and 6-day Kelvin E1 waves in the low-latitude MLT region has been investigated. Three different types of data were analysed in order to detect and extract the ∼6-day wave signals. The National Centres for Environmental Prediction (NCEP) geopotential height and zonal wind data at two pressure levels, 30 and 10 hPa, were used to explore the features of the ∼6-day waves present in the stratosphere during the period from 1 July to 31 December 2004. The ∼6-day wave activity was identified in the neutral MLT winds by radar measurements located at four equatorial and three tropical stations. The ∼6-day variations in the ionospheric electric currents (registered by perturbations in the geomagnetic field) were detected in the data from 26 magnetometer stations situated at low latitudes. The analysis shows that the global ∼6-day Kelvin E1 and ∼6-day Rossby W1 waves observed in the low-latitude MLT region are most probably vertically propagating from the stratosphere. The global ∼6-day W1 and E1 waves seen in the ionospheric electric currents are caused by the simultaneous ∼6-day wave activity in the MLT region. The main forcing agent in the equatorial MLT region seems to be the waves themselves, whereas in the tropical MLT region the modulated tides are also of importance.     

High-altitude data assimilation system experiments for the northern summer mesosphere season of 2007

A global numerical weather prediction system is extended to the mesosphere and lower thermosphere (MLT) and used to assimilate high-altitude satellite measurements of temperature, water vapor and ozone from MLS and SABER during May–July 2007. Assimilated temperature and humidity from 100 to 0.001 hPa show minimal biases compared to satellite data and existing analysis fields. Saturation ratios derived diagnostically from these assimilated temperature and water vapor fields at PMC altitudes and latitudes compare well with seasonal variations in PMC frequency measured from the aeronomy of ice in the mesosphere (AIM) satellite. Synoptic maps of these diagnostic saturation ratios correlate geographically with three independent transient mesospheric cloud events observed at midlatitudes by SHIMMER on STPSat-1 and by ground observers during June 2007. Assimilated temperatures and winds reveal broadly realistic amplitudes of the quasi 5-day wave and migrating tides as a function of latitude and height. For example, analyzed winds capture the dominant semidiurnal MLT wind patterns at 55°N in June 2007 measured independently by a meteor radar. The 5-day wave and migrating diurnal tide also modulate water vapor mixing ratios in the polar summer MLT. Possible origins of this variability are discussed.     

External impact on wind in the mesosphere/lower thermosphere region

Regular measurements of the velocity and direction of the horizontal wind in the mesosphere/lower thermosphere (MLT) region at a height of ∼95 km have been conducted since 1975 over Eastern Siberia (Badary observatory near Irkutsk), using the spaced-diversity reception method in the LF range. The accumulated database of measurement results (for more than 20 years, from 1974 to 1996) makes it possible to get information on the impact on wind in the MLT region from both below (stratospheric warmings) and above (geomagnetic storms as a consequence of magnetospheric disturbances) with sufficient statistical reliability. Effects of stratospheric warmings and strong geomagnetic storms in the prevailing wind and amplitude of the semidiurnal tide are evaluated by the superposed epoch method. It is shown that the effects of stratospheric warmings depend on the type (intensity) of stratospheric warming and on the phase of quasi-biennial oscillations of the wind in the equatorial stratosphere at the 30 hPa level. The response of MLT winds to external impacts is different for the 21st and 22nd cycles of solar activity. Effects of geomagnetic storms (A _p > 100) are manifested in the decrease in the eastward prevailing wind and increase in the semidiurnal tide amplitude.