Global structure,seasonal and interannual variability of the eastward propagating tides seen in the SABER/TIMED temperatures (2002–2007)

The present paper is focused on the global spatial (altitude and latitude) structure, seasonal and interannual variability of the most stable in amplitude and phase eastward propagating diurnal and semidiurnal tides with zonal wavenumbers 2 and 3 derived from the SABER/TIMED temperatures for full 6 years (January 2002–December 2007). The tidal results are obtained by an analysis method where the tides (migrating and nonmigrating) and the planetary waves (zonally travelling, zonally symmetric and stationary) are simultaneously extracted from the satellite data. It has been found that the structures of the eastward propagating diurnal tides with zonal wavenumbers 3 and 2 change from antisymmetric with respect to the equator below ∼85 km height, to more symmetric above ∼95 km. The seasonal behavior of the DE3 is dominated by annual variation with maximum in August–September reaching average (2002–2007) amplitude of ∼15 K, while that of the DE2 by semiannual variation with solstice maxima and with average amplitude of ∼8 K. These tides revealed some interannual variability with a period of quasi-2 years. The seasonal behavior of the eastward propagating semidiurnal tide with zonal wavenumber 2 in the southern hemisphere (SH) is dominated by annual variation with maximum in the austral summer (November–January) while that in the northern hemisphere (NH) by semiannual variation with equinoctial maxima. The SE2 maximizes near 115 km height and at latitude of ∼30° reaching an average amplitude of ∼6 K. The seasonal behavior of the eastward propagating semidiurnal tide with zonal wavenumber 3 in both hemispheres indicates a main maximum during June solstice and a secondary one during December solstice. The tide maximizes near 110–115 km height and at a latitude of ∼30° reaching an average amplitude of ∼4.8 K in the SH and ∼4 K in the NH. The tidal structures of the two eastward propagating semidiurnal tides are predominantly antisymmetric about the equator.     

Response of quasi-10-day waves in the MLT region to the sudden stratospheric warming in March 2020

We present an analysis of the response of quasi-10-day waves (Q10DWs) to the sudden stratospheric warming (SSW) event which occurred on March 23, 2020. The Q10DWs are observed in the mesosphere and lower thermosphere (MLT) region by three meteor radars, which are located at middle latitudes along the 120°E meridian from Mohe (MH, 53.5°N, 122.3°E), Beijing (BJ, 40.3°N, 116.2°E), to Wuhan (WH, 30.5°N, 114.6°E). The Q10DWs reveal similar temporal and altitudinal variations during the SSW in the MLT region at the three stations. The activities of Q10DWs are also captured in the temperature measurements from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite in the MLT region. Further analysis of the Q10DW phases indicates that the Q10DWs might be in situ generated due to mesospheric instabilities at higher latitudes around MH and then propagate southward to lower latitudes at BJ and WH. The atmospheric instabilities are not directly responsible for the excitations of Q10DWs at lower latitudes, while the observed equatorward propagation of the Q10DWs is important. Our result provides the observational evidence for latitudinal couplings in the MLT region after the SSW onset, which is achieved by southward propagating planetary waves in the MLT region.     

Stratosphere-mesosphere coupling during stratospheric sudden warming events

In this review article we summarize recent results in the coupling of the stratosphere–mesosphere during stratospheric sudden warming (SSW) events. We focus on the role of planetary and gravity waves in driving the middle atmosphere circulation and illustrate the stratosphere–mesosphere coupling during undisturbed wintertime circulation, during an SSW event, and after an SSW event during the formation of an elevated stratopause using simulations of past Arctic and Antarctic winters from the Specified Dynamics version of the Whole Atmosphere Community Climate Model (SD-WACCM). We illustrate the transition of the polar stratopause from being a gravity wave driven phenomena to a planetary wave driven phenomena during SSW events and its subsequent reestablishment and control by gravity waves. We also examine the synoptic structure of the stratosphere, mesosphere, and lower thermosphere using SD-WACCM data fields that show the structure of the vortex during specific dynamical events in both hemispheres. We illustrate the longitudinal asymmetry in the thermal structure in the stratosphere and mesosphere driven by differences in circulation over the polar cap regions during an SSW event. We complement this analysis of the middle atmosphere circulation with a classification of both the Arctic and Antarctic winters since 1979 into major, minor, elevated stratopause or quiet winters based on the level of disturbance using the Modern Era-Retrospective Analysis for Research and Applications (MERRA) reanalysis data. From the MERRA data we find that the combined occurrences of both major and minor warmings in the Arctic have remained constant over the past three decades while we find a minor increase in their occurrences in the Antarctic.     

武汉上空中层和低热层大气潮汐的流星雷达观测

武汉流星雷达是2002年元月建成的我国第一部全天空流星雷达，本文对2002年2月19日到7月31日流星雷达观测的潮汐的讨论表明，武汉中层顶以周日潮汐为潮汐运动的主要分量，它的强度远大于半日潮汐，周日潮汐和半日潮汐的波源都在80km以下．周日潮汐分量在3、4月份最强，并且经向分量略强于纬向分量．两个分量的峰值在约95km处出现，分别达到44m／s和60m／s．半日潮的最大值24m／s出现在4月初约93km处．周日潮汐和半日潮汐的振幅和相位随时间呈现出拟周期变化的特征，这可能是潮汐与行星波非线形相互作用的结果．观测结果与GSWM模型的比较表明，GSWM模型在相位随高度变化趋势上与观测结果一致，但模型的周日潮相位比观测约超前1—2h，半日潮相位约滞后1—4h．在周日潮汐较强的月份，模型与观测有较大的差异，观测的幅度通常在95km附近有极大值，而模型并没有极大值．GSWM模型对半日潮的幅度的估计通常过小，观测的半日潮汐幅度有时甚至超过模型值的一倍以上．     

Response of the extratropical middle atmosphere to the September 2002 major stratospheric sudden warming

The effects of a major stratospheric sudden warming (SSW) at extratropical latitudes have been investigated with wind and temperature observations over a Brazilian station, Cachoeira Paulista (22.7°S, 45°W) during September–October 2002. In response to the warming at polar latitudes a corresponding cooling at tropical and extratropical latitudes is prominent in the stratosphere. A conspicuous signature of latitudinal propagation of a planetary wave of zonal wavenumbers 1 and 2 from polar to low latitude has been observed during the warming period. The polar vortex which split into two parts of different size is found to travel considerably low latitude. Significant air mass mixing between low and high latitudes is caused by planetary wave breaking. The meridional wind exhibits oscillations of period 2–4 days during the warming period in the stratosphere. No wave feature is evident in the mesosphere during the warming period, although a 12–14 day periodicity is observed after 2 weeks of the warming event, indicating close resemblance to the results of other simultaneous investigations carried out from high latitude Antarctic stations. Convective activity over the present extratropical station diminishes remarkably during the warming period. This behavior is possibly due to destabilization and shift of equatorial convective active regions towards the opposite hemisphere in response to changes in the mean meridional circulation in concert with the SSW.     

Atmospheric tides below 80 km

Measurements and theory of diurnal and semidiurnal tidal oscillations between about 25 and 80 km are reviewed. At latitudes greater than about 30°, meridional (N-S) wind components are consistently in quadrature with and similar to the zonal (E-W) components. The tidal structures are interpreted as a superposition of quasi-steady higher-order modes excited in the troposphere by sources of limited extent (1,000–10,000 km). At latitudes less than about 30°, steady or quasi-steady diurnal and semidiurnal components are not necessarily the dominant components of the daily variation. At high latitudes diurnal phases generally show little change with height in comparison with observations at lower latitudes, in accord with the latitudinal properties of diurnal modes with positive and negative equivalent depths.     

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.      

北京上空冬季潮汐波活动特征全天时激光雷达探测研究

利用北京延庆子午工程激光雷达对北京上空钠层进行长期连续观测，分析研究钠层及其相关参数的周日变化.提取钠层各个高度上的相位信息，与同时段经向风潮汐信息进行比较发现:在各个高度上，二者周日相位数值基本一致.半日相位对比结果表明，虽然存在差异，但整体仍保持较好的一致性.此外，从2014年至2016年每年10月到第二年1月共4个月的钠层连续观测数据中提取钠层周日和半日的振幅和相位，探究北京上空冬季的潮汐特征.结果显示:周日潮的相位自上向下传播，且无明显的季节变化特征，其垂直波长在40～50km的范围；周日潮较强，半日潮较弱.      

Application of ERA5 Reanalysis to the Construction of Initial Conditions for WACCM Simulations

This study uses ECMWF fifth-generation reanalysis, ERA5, which extends to the mesopause, to construct the Initial Conditions (IC) for WACCM (Whole Atmosphere Community Climate Model) simulations. Because the biases between ERA5 and Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) temperature data are within ±5 K below the lower mesosphere, ERA5 reanalysis is used to construct IC in the lower atmosphere. Four experiments are performed to simulate a Stratospheric Sudden Warming (SSW) event from 5 to 15 February 2016. The simulation using the WACCM default climatic IC cannot represent the sharp meteorological variation during SSW. In contrast, the 0~4 d forecast results driven by ERA5-constructed IC is consistent with ERA5 reanalysis below the middle mesosphere. Comparing with WACCM climatology ICs scheme, the ICs constructing method based on ERA5 reanalysis can obtain 67%, 40%, 22%, 4% and 6% reduction of temperature forecast RMSE at 10 hPa, 1 hPa, 0.1 hPa, 0.01 hPa and 0.001 hPa respectively. However, such improvement is not shown in the lower thermosphere.      

Structure of the migrating diurnal tide in the Whole Atmosphere Community Climate Model (WACCM)

As part of an ongoing effort to understand the migrating diurnal tide generated by the NCAR Whole Atmosphere Community Climate Model, version 3 (WACCM3), we compare the WACCM3 migrating diurnal tide in the horizontal wind and temperature fields to similar results from the Global Scale Wave Model (GSWM). The WACCM3 diurnal tidal wind fields are also compared to tropical radar measurements at Kauai (22°N, 200.2°E) and Rarotonga (21.3°S, 199.7°E). The large-scale features of the WACCM3 results, such as the global spatial structure and the semiannual amplitude variation are in general agreement with past tidal studies; however, several differences do exist. WACCM3 exhibits a much higher degree of hemispheric asymmetry, lower overall amplitudes around the equinoxes, and peaks which are more confined in latitude when compared with the GSWM. Factors which may contribute to such differences between WACCM3 and GSWM are the solar heating profiles from ozone and water vapor, dissipation, and the zonal mean zonal winds. We find that the internally generated heating in WACCM3 and eddy dissipation values are both smaller than the values specified in the GSWM; the eddy dissipation fields and zonal mean zonal winds of the two models also display measurable differences in spatial structure. Comparisons with radar data show several differences in spatial and seasonal structure. In particular, the diurnal tide zonal winds in WACCM3 above Kauai are considerably larger in amplitude than those observed in the radar data, due to contributions from nonmigrating tidal components including wave numbers eastward 1 through 3, westward 2, and stationary components, which interfere constructively with the migrating component around equinox in WACCM3.     

Middle-atmosphere tides: Recent advances in theory and observation

Recent progress in the theoretical and observational investigation of middle atmosphere tides is reviewed. Theoretical advances include development of more realistic thermal excitation and numerical simulation models, investigation of seasonal — latitudinal and longitudinal variations in tidal structures, and the origin and effects of ‘unsteadiness’ in tidal oscillations over periods of days. Recent analyses of middle latitude radar data between 80 Km and 130 Km delineate consistent seasonal phase patterns in this region. Analyses of rocket data show stratosphere and lower mesosphere tides to be characterized by smaller amplitudes, shorter vertical scales, greater unsteadiness, and greater spatial variability than exhibited in the upper mesosphere and above. Results from the first two ATMAP (Atmospheric Tides Middle Atmosphere Program) campaigns are also discussed.     

Interannual and seasonal variations of diurnal tide,gravity wave,ozone, and water vapor as observed by MLS during 1991–1994

The diurnal tide in the mesosphere and lower thermosphere (MLT) shows large seasonal and interannual variations. Despite recent modeling investigations, the underlying physical mechanisms for causing these variations remain unclear. This paper provides further observational constraints to tide-sensitive variables (H₂O, O₃, and gravity wave variances) used by the models, which are obtained simultaneously by upper atmosphere research satellite microwave limb sounder at altitudes below the MLT region. The strong quasi biannual oscillation and semiannual oscillation variations in these measurements reveal good correlations between the diurnal tide with other tide-sensitive variables, which should be taken into account for further modeling studies.     

Early winter meteor wind over Bologna (45°N, 11°E)

The Bologna meteor radar was operational during two winter campaigns, from 6 January 1982 to 1 February 1982 and from 10 December 1982 to 2 February 1983. As occurrence of minor stratospheric warmings has been reported for these intervals, possible effects on meteor wind over Bologna related to this kind of warming are pointed out. Zonal and meridional prevailing winds are found to exhibit the maximum peak to peak value in their oscillations when a minor stratospheric warming reaches such an intensity that ΔT_{(90°N–60°N)} at 10 mbar is reversed. Diurnal and semidiurnal tides exhibit usual amplitude variations, but the semidiurnal tide has a noticeable phase shift at the time of a minor warming occurrence, while a similar shift is less evident in the diurnal tide phase.     

Horizontal winds in the mesosphere at high latitudes

A total of 146 meteorological rocket flights applying the ‘falling sphere’ technique are used to obtain horizontal winds in the mesosphere at polar latitudes, namely at the Andøya Rocket Range (69°N, 125 flights), at Spitsbergen (78°N, 10 flights), and at Rothera (68°S, 11 January flights only). Nearly all flights took place around noon or midnight, i.e., in the same phase of the semidiurnal tide. Meridional winds at 69°N show a clear diurnal tidal variation which is not observed in the zonal winds. The zonal wind climatology shows a transition from summer to winter conditions with the zero wind line propagating upward from 40 km (end of August) to 80 km (end of September). Zonal winds are smaller at Spitsbergen compared to Andøya which is in line with a common angular velocity at both stations. Meridional winds at noon are of similar magnitude at all three stations and are directed towards the north and south pole, respectively. Horizontal and meridional winds generally agree with empirical models, except for the zonal winds at Antarctica which are similar to the NH, whereas there is a significant SH/NH difference in CIRA-1986.     

Moderate geomagnetic storms of January 22–25, 2012 and their influences on the wave components in ionosphere and upper stratosphere-mesosphere regions

Moderate geomagnetic storms occurred during January 22–25, 2012 period. The geomagnetic storms are characterized by different indices and parameters. The SYM-H value on January 22 increased abruptly to 67 nT at sudden storm commencement (SSC), followed by a sharp decrease to −87 nT. A second SSC on January 24 followed by a shock on January 25 was also observed. These SSCs before the main storms and the short recovery periods imply the geomagnetic storms are CME  -driven. The sudden jump of solar wind dynamic pressure and IMF _Bz$B_z$ are also consistent with occurrence of CMEs. This is also reflected in the change in total electron content (TEC) during the storm relative to quiet days globally. The response of the ionospheric to geomagnetic storms can also be detected from wave components that account for the majority of TEC variance during the period. The dominant coherent modes of TEC variability are diurnal and semidiurnal signals which account upto 83% and 30% of the total TEC variance over fairly exclusive ionospheric regions respectively. Comparison of TEC anomalies attributed to diurnal (DW1) and semidiurnal (SW2) tides, as well as stationary planetary waves (SPW1) at 12 UTC shows enhancement in the positive anomalies following the storm. Moreover, the impact of the geomagnetic storms are distinctly marked in the daily time series of amplitudes of DW1, SW2 and SPW1. The abrupt changes in amplitudes of DW1 (5 TECU) and SW2 (2 TECU) are observed within 20°S–20°N latitude band and along 20°N respectively while that of SPW1 is about 3 TECU. Coherent oscillation with a period of 2.4 days between interplanetary magnetic field and TEC was detected during the storm. This oscillation is also detected in the amplitudes of DW1 over EIA regions in both hemispheres. Eventhough upward coupling of quasi two day wave (QTDWs) of the same periodicity, known to have caused such oscillation, are detected in both ionosphere and upper stratosphere, this one can likely be attributed to the geomagnetic storm as it happens after the storm commencement. Moreover, further analysis has indicated that QTDWs in the ionosphere are strengthened as a result of coherent oscillation of interplanetary magnetic field with the same frequency as QTDWs. On the otherhand, occurrences of minor SSW and geomagnetic storms in quick succession complicated clear demarcation of attribution of the respective events to variability of QTDWs amplitudes over upper stratosphere.     

基于WACCM+DART的临近空间SABER和MLS温度观测资料同化试验

基于WACCM+DART（Whole Atmosphere Community Climate Model，Data Assimilation Research Test-Bed）临近空间资料同化预报系统，以2016年2月的一次平流层爆发性增温（SSW）事件为例，开展了临近空间SABER（Sounding of the Atmosphere using Broadband Emission Radiometry）和MLS（Microwave Limb Sounder）温度观测资料集合滤波同化试验.结果表明:同化SABER和MLS温度观测资料可显著降低WACCM模式在中间层和平流层中上部（0.001～10hPa）大气温度场的预报误差，改善CR试验在SSW发生时中间层变冷现象偏强、纬向风场首次发生反转的层次偏低以及增温恢复阶段0.1～10hPa的东风层提前消退、纬向风速偏大、平流层顶位置偏高等现象.基于ERA5（The Fifth Generation of ECMWF Reanalyses）再分析资料的检验表明:同化SABER和MLS温度资料明显有利于减小北半球高纬度地区（60°-90°N）平流层中上层和下中间层（0.1～14hPa）纬向风场以及平流层和中间层中下层（0.01～100hPa）温度场的分析误差；同化低层大气观测也有利于减小0.1～14hPa纬向风场和0.01～100hPa温度场的分析误差，但是不如同化SABER和MLS温度资料对临近空间纬向风场和温度场分析误差的改善效果显著.      

中纬度冬季低热层潮汐非线性相互作用的MF雷达观测

采用武汉(30°N,114°E)MF雷达在2001年冬季的风场观测数据研究中纬度低热层大气潮汐之间的二阶非线性相互作用.经向风场的Lomb-Scargle归一化振幅谱表明,周日、半日和8 h潮汐是中纬冬季中层顶区域占优势的大气扰动;此外6 h潮汐也清晰可见.双相干谱分析揭示大多数显著的双相干谱峰代表潮汐谐振分量之间的相位互相关或单个潮汐分量的自相关.对随时间变化的潮汐垂直波长的比较发现,实际观测的8h潮汐垂直波长与假定的由观测的24 h潮汐和12 h潮汐非线性相互作用产生的8 h潮汐的理论垂直波长具有明显的一致性.在94.0～98.0km高度范围,周日、半日和8h潮汐之间不仅存在明显的相位相关和垂直波数相关,且它们的振幅随时间变化也显示出振荡幅值相近、振荡相位同步或反相的相关性,表明它们之间已经发生了二阶非线性相互作用.但是在94.0 km以下,三个潮汐分量之间的各种相关性随高度的下降变得越来越弱,因此潮汐二阶相互作用更可能是一种局地和暂态的现象.      

Nonlinear Interactions between the Quasi 5-day Wave and Tides Based on Meteor Radar Observations at Maui

Nonlinear interactions between the quasi 5-day wave and tides based on meteor radar observation in the Mesosphere and Lower Thermosphere(MLT) at Maui are studied in this paper.Strong sum interaction between quasi 5-day wave and diurnal tide,and evident difference interaction between quasi 5-day wave and semidiurnal tide are observed during the time of attention.However,their difference and sum counterparts are clearly weaker.The secondary waves generated from those interactions beat with the tide and show intense modulation at the period of 5 days which confirms the existence of their interactions.Additionally,correlation coefficients among these waves are calculated to further explore their interactions and find that they can persist for several days although they are highly intermittent.The energy exchange among these waves can be reversible during the observational time.The periods when the significant difference interaction between the quasi 5-day wave and semidiurnal tide occur are much shorter than those when the significant sum interaction between the quasi 5-day wave and diurnal tide occur.Moreover,these two strong interactions can take place simultaneously.In generally,this study provides the proof of nonlinear interactions between quasi 5-day wave and tides which were seldom reported before.     

极区夏季中间层半日潮汐的VHF雷达观测

采用德国SOUSYVHF雷达观测数据,研究了极区夏季中间层半日潮汐的结构和变化特征.纬向和经向风的动态Lomb-Scargle谱表明,半日潮是中间层高度上占支配地位的波动,其谱峰对应的频率一般与1/12c·h-1有偏离,说明它们经常处在被扰动状态.稳定的半日潮振幅随高度增加而迅速增长,在87.9km高度附近达到饱和;经向分量的相位一般比纬向分量的相位超前π/4-π/2,从而水平扰动速度矢量端点随时间变化的轨迹显示出顺时针方向旋转的特征.半日潮汐特征参量在纬向和经向风中随时间的变化在基本趋势一致的基础上显示出一定程度的各向异性.      

Longitudinal MLT wind structure at higher mid-latitudes as seen by meteor radars at central and Eastern Europe (13°E/49°E)

The mid-latitude mesosphere and lower thermosphere (MLT) wind speeds measured by two SKiYMET meteor radars (MRs) at Collm (51°N, 13°E) and Kazan (56°N, 49°E) during 2016–2017 were analyzed to study longitudinal wind structures. The differences between monthly mean prevailing wind speeds and tidal amplitudes were compared with the corresponding differences obtained from TIMED/TIDI satellite winds and gradient wind speeds from the AURA/MLS instrument. It is shown that the MR wind difference between the two sites is statistically significant. The difference of the horizontal prevailing winds can be explained by a superposition of the background zonal flow, which is different at the two latitudes, with stationary planetary waves of different origin. Non-migrating tides contribute significantly to the difference of the semidiurnal tidal winds between the two sites.