Measurement of mesopause temperature from hydroxyl nightglow at Kolhapur (16.8°N, 74.2°E), India

The paper reports the nightglow observations of hydroxyl (8–3), (7–2) and (6–2) Meinel band carried out at a low latitude station Kolhapur (16.8°N, 74.2°E, dip latitude 10.6°N), India during November 2002 to May 2005 with the objective of investigating mesopause dynamics based on derived OH rotational temperature. Overall, 132 nights of quality data were collected using filter-tilting photometer and an all-sky scanning photometer. The mean mesopause temperature observed at Kolhapur is 195 ± 11, 196 ± 9 and 195 ± 7 K from OH (8–3), (7–2) and (6–2) band emissions, respectively, using transition probabilities given by Langhoff et al. [Langhoff, S.R., Werner, H.J., Rosmus, P. Theoretical transition probabilities for the OH Meinel system. Journal of Molecular Spectroscopy 118, 507–529, 1986]. Small wave-like variations (periodicities ∼ few hours) existing over long period variations in derived temperatures are also present. A steady decrease of emission intensities from evening to dawn hours has been observed in approximately 59% of nights. No significant change of nightly mean temperatures has been noted. Furthermore, about 62% of observed nightly mean temperatures lie within one error bar of MSISE-90 model predictions.     

Connection between winter mesopause region temperatures and diurnal LF reflection height variations measured at Collm

Scale height, H, estimates are calculated from the decrease/increase of ionospheric virtual reflection heights of low-frequency (LF) radio waves at oblique incidence in suitably defined morning intervals around sunrise during winter months. The day-to-day variations of H qualitatively agree with daily mean temperature variations around 90 km from meteor radar measurements. Since mesospheric long-period temperature variations are generally accepted to be the signature of atmospheric planetary waves, this shows that LF reflection height measurements can be used for monitoring the dynamics of the upper middle atmosphere. The long-term variations of monthly mean H estimates have also been analysed. There is no significant trend, which is in agreement with other measurements of mesopause region temperature trends.     

Sodium lidar measurements of mesopause region temperatures at 23° S

A sodium lidar, capable of measuring temperature in the 80–100 km region, has been in operation at São José dos Campos (23° S, 46 W) since March 2007. Good quality data have been obtained for late autumn, winter and spring, but weather conditions make it extremely difficult to make measurements from mid-November to mid- February. We find the temperature structure to be strongly modulated by tides and gravity waves, but average profiles typically show a primary mesopause height close to 100 km with temperatures around 180 K, and a tendency for a secondary minimum of about 185 K to occur close to 90 km. Vertical temperature gradients greater than 50 K/km are sometimes seen even on profiles averaged over several hours. The strongest gradients are always positive and are frequently associated with strong gradients in sodium concentration. On the other hand, we frequently see rapid changes in the temperature profile, suggesting that models and non-local temperature measurements, as made by satellite radiometers, for example, are of little use in applications such as the analysis of gravity wave propagation seen in airglow images.     

Investigation of infrasound signatures from microbaroms using OH airglow and ground-based microbarometers

In the frame of the European H2020 project ARISE, a short wave infrared (SWIR) InGaAs camera has been operated at the Haute-Provence Observatory, during a night that corresponds to the peak of Geminid meteor shower to investigate infrasound associated with meteor arrivals. This camera allows continuous observations during clear-sky nighttime of the OH airglow layer centered at 87 km. These observations were collocated with Rayleigh lidar measurements providing vertical temperature profiles from the lower stratosphere to the altitude of the OH layer around the mesopause. Spectral analysis of OH images did not allow to detect infrasound associated with meteor trails, however it reveals a peak corresponding to infrasound signals in the frequency band of those produced by ocean swell. Infrasound wave activity observed from ground-based microbarometers as well as the OH camera, appear to be modified with the presence of a temperature inversion described by Rayleigh lidar. Indeed, there is a difference in energy related to infrasonic activity between the first part of the night during the temperature inversion and after the inversion.     

Gravity waves and wind-shear in the MLT at 23°S

We have used the technique suggested by Hocking [Hocking, W. A new approach to momentum flux determinations using SKiYMET meteor radars. Ann. Geophys. 23, 2005.] to derive short period wind variances in the 80–100 km region from meteor radar data. We find that these fluctuating winds, assumed to correspond to gravity waves and turbulence, are closely correlated with the vertical shear of the horizontal tidal winds. This close correlation suggests that in situ wind shear may be a major source of gravity waves and turbulence in the MLT. If this is the case, gravity waves generated in the troposphere and propagating up to the MLT region, generally assumed to constitute an important influence on the climatology of the region, may be a less important source of energy and momentum in the 80–100 km region than has been hitherto believed.     

Long-period meteor radar temperature variations over Collm (51°N, 13°E) and Kazan (56°N, 49°E)

We have estimated temperatures from meteor radar measurements using the gradient method and the full width at half maximum method over Kazan (56°N 49°E) and Collm (51°N, 13°E). The time series cover the period 2016–2019. The temperature gradient model is constructed from SABER temperature observations. We demonstrate that annual mean, amplitudes and phases of the annual and semiannual oscillations of the radar temperatures are close to those of the MLS and SABER temperatures. The annual mean temperatures over Kazan and Collm differ non-significantly. The seasonal variability of the radar temperature is mostly due to the annual cycle which tends to grow with latitude. The gradient method produces temperatures which agree with the SABER temperatures better than with the MLS ones. The harmonics of the annual oscillations from periods of 73 days up to periods of about 40 days are the most significant day-to-day temperature oscillations and have zonal wavenumber zero. Their periods and phases are in good correspondence with those of the MLS and SABER ones. We also show some results which demonstrate that at 56°N the FWHM method is not as robust as the gradient method.     

基于钠激光雷达观测数据的中间层顶大气温度分布特性研究

作为中间层和热层的边界层,中间层顶存在多种能量交换方式,是大气能量耦合的重要区域。本文利用部署于中国科学院廊坊临近空间大气探测站的钠荧光多普勒激光雷达2013年的观测数据,研究了廊坊上空中间层顶区域大气温度的年度和季节分布特性,并分析了影响温度分布的多种因素。年平均温度廓线图显示,中间层顶位于约97.5 km高度处,温度约191.2 K。受放热化学反应的影响,年平均温度廓线91 km高度处出现了一个198 K的相对温度高点。中间层顶区域大气温度的季节分布受太阳辐射和大气动力学因素综合影响,夏季在大气动力学影响下,中间层顶高度较低,位于88 km高度处,温度也较低,约177 K;冬季太阳辐射起主导作用,中间层顶位于99 km高度处,温度为181 K。通过拟合月平均温度分析了中间层顶区域大气温度年变化和半年变化的振幅和相位特征。结果显示,中间层顶区域上部温度分布主要受太阳辐射的影响;在中间层顶区域下部,大气波动主导了温度分布。      

TIMED卫星探测的全球大气温度分布及其与经验模式的比较

利用TIMED卫星遥感探测的全球温度分布与NRLMSISE-00大气经验模式进行了对比研究.研究表明,在中间层下部以下的高度范围内,经验模式与卫星探测的大气温度分布有很好的一致性.但是比较发现,在中层顶区域,经验模式的计算结果与实测结果有较大的差异.卫星探测表明,在春分季节的低纬地区中层顶区存在稳定的逆温层,但是经验模式不能给出低纬地区春分季节中间层逆温层的分布特征.卫星观测表明在全球范围内中层顶有两个非常不同的高度,一个处于100km附近,另一个处于85km附近,但是经验模式不能给出这一中层顶高度的分布特征.同时在低热层,经验模式计算的温度分布与卫星遥感的探测结果有很大的差异.      

Model calculations of middle atmospheric wind and temperature fields

The zonally-averaged circulation of the middle atmosphere between 10 and 110 km is calculated from a two-dimensional grid point model for steady solstice conditions. Using the temperatures of CIRA 72 in a diagnostic study of the vertical-meridional circulation we have investigated the influence of a latitude dependent static stability and the consequences of meridional temperature advection. In the summer mesopause region we found an area of subsidence which is located near the equatorward boundary of the noctilucent cloud region. In a self-consistent dynamical study we have assumed an empirical momentum source in the lower summer thermosphere in addition to the well-known Rayleigh friction to obtain an eastward zonal flow in this region.     

Reduced meteoric smoke particle density at the summer pole – Implications for mesospheric ice particle nucleation

Noctilucent clouds (NLC) and polar mesospheric summer echoes (PMSE) are phenomena that occur in the summertime polar regions due to the presence of ice particles around the mesopause. That ice particles are able to form in a region with such low water vapour concentration as the mesopause is noteworthy. Even though the summer mesopause is the coldest region on Earth, temperatures are generally not low enough for homogeneous nucleation to occur, which necessitates the presence of pre-existing condensation nuclei. The nature of these nuclei has long puzzled the scientific community and many candidates have been suggested, such as particles of meteoric origin, ion clusters, sodium bi-carbonate, sulfate aerosols and soot particles. Out of these the so-called “smoke particles”, i.e. particles re-condensed from ablated meteoritic material, have long been considered the most likely. Generally, it has been believed that these particles exist in numbers of the order of thousands per cubic centimetre at the mesopause. This belief is based on 1-dimensional studies of meteoric material. A recent 2-dimensional model study, which includes the atmospheric circulation from summer to winter pole however, suggests much lower number densities at the summer mesopause. We here investigate the implications of low number densities for the formation of ice particles. We find that even though resulting ice particle distribution may produce typical NLC brightness, the number density of ice particles is not consistent with what is expected for NLC and PMSE. In particular, it is much lower than the ice particle concentration (>1000 cm⁻³) typically expected to explain the “electron bite-outs” that are frequently observed in the vicinity of PMSE’s. We therefore re-examine the assumptions and parameters that determine the smoke distribution. We show that even though the number of condensation nuclei at the polar summer mesopause can be increased within the uncertainties, the results in most scenarios remain insufficient. We show that charged particles, perhaps in combination with significant deviations from the mean mesospheric state, may be necessary for condensation of ice particles in the polar summer mesosphere. Hence, we raise the question whether the conventional ideas of nucleation on meteoric smoke, which are used in current mesospheric ice models, are correct.     

SATI image processing and mesopause temperature determination

The Spectral Airglow Temperature Imager (SATI) instrument registers airglow coming from an annular mesopause segment. The temperatures of various points of this segment are retrieved by sectors of the registered images containing spectral information. A stage of SATI spectrogram processing connected with deriving spectral information from images and the determination of the rotational temperature of oxygen molecules emitting at the altitude of the mesopause is considered.     

Variations of mesopause temperatures in Europe

Mesopause temperatures were derived from ground measurements of the near infrared OH1 spectrum. Preliminary data are presented. Seasonal variations at Wuppertal (51° N, 7° E) are well represented if the Cole and Kantor (1978) model [1] is raised by 10 K and shifted by about 18 days. Latitudinal variations from 68° N to 51° N are found much smaller than the model variations. During a stratospheric warming, mesopause and stratosphere temperatures were found to be in anticorrelation only if a substantial longitudinal shift is introduced.     

Directional Filtering Due to Mesospheric Wind Shear on the Propagation of Acoustic-gravity Waves

Gravity waves with periods close to the Brunt-V?is?l? period of the upper troposphere are often observed at mesopause altitudes as short period, quasi-monochromatic waves. The assumption that these short period waves originate in the troposphere may be problematic because their upward propagation to the mesosphere and lower thermosphere region could be significantly impeded due to an extended region of strong evanescence above the stratopause. To reconcile this apparent paradox, an alternative explanation is proposed in this paper. The inclusion of mean winds and their vertical shears is sufficient to allow certain short period waves to remain internal above the stratopause and to propagate efficiently to higher altitudes. A time-dependent numerical model is used to demonstrate the feasibility of this and to determine the circumstances under which the mesospheric wind shears play a role in the removal and directional filtering of short period gravity waves. Finally this paper concludes that the combination of the height-dependent mean winds and the mean temperature structure probably explains the existence of short period, quasi-monochromatic structures observed in airglow images of mesopause region.      

Ozone chemical equilibrium in the extended mesopause under the nighttime conditions

For retrieval of atomic oxygen and atomic hydrogen via ozone observations in the extended mesopause region (～70–100?km) under nighttime conditions, an assumption on photochemical equilibrium of ozone is often used in research. In this work, an assumption on chemical equilibrium of ozone near mesopause region during nighttime is proofed. We examine 3D chemistry-transport model (CTM) annual calculations and determine the ratio between the correct (modeled) distributions of the O₃ density and its equilibrium values depending on the altitude, latitude, and season.The results show that the retrieval of atomic oxygen and atomic hydrogen distributions using an assumption on ozone chemical equilibrium may lead to large errors below ～81–87?km. We give simple and clear semi-empirical criterion for practical utilization of the lower boundary of the area with ozone’s chemical equilibrium near mesopause.     

用武汉流星雷达观测象限仪座流星雨期间的流星速度

利用武汉流星雷达,首次成功地观测了象限仪座流星雨及流星雨期间的流星速度,讨论了利用单站全天空流星雷达观测流星雨的相关问题.从观测结果可以发现此次象限仪座流星雨发生在2004年1月4日的0000-0800LT,其中流星峰值出现在0400LT,而且通过流星雷达观测到的流星雨期间的流星回波平面推测得到的流星雨辐射点也与该流星雨的理论辐射点位置对应非常好.利用流星回波振幅的Fresnel振荡方法计算了此次流星雨期间观测到的流星的速度,分析了该流星速度的分布,这次流星雨期间观测到的流星速度主要集中在10-30 km/s,可以看出这种速度分布是由流星雨进入地球大气的初始速度和流星在大气中的减速过程共同决定的.最后研究了流星速度随高度的变化,并且由此讨论了地球大气对于流星体的减速作用.      

The characteristics of the semi-diurnal tides in mesosphere/low-thermosphere (MLT) during 2002 at Wuhan (30.6°N, 114.4°E) – using canonical correlation analysis technique

In this paper, we use canonical correlation analysis (CCA) method to investigate the semi-diurnal tidal winds in mesosphere and low thermosphere (MLT) region, observed by a newly installed meteor radar at Wuhan (30.6°N, 114.4°E), during the year 2002. In general, 4(3) effective semi-diurnal tidal pairs of patterns are obtained, which represent ∼2/3 total variances of the origin data set. These patterns are expected to be corresponding to the atmospheric oscillations within the semi-diurnal frequency band excited or modulated by different sources, i.e., the seasonal variations, the modulations by the planetary wave oscillations or the solar 27-day activity. Among all the patterns, the 1st pattern, which represents ∼1/3 of total variances, is the most notable. Its amplitudes show maximum values in spring and autumn, and the vertical wavelengths are longer in summer and shorter in winter, which is in line with the results obtained from traditional harmonic analysis. The vertical wavelengths of the higher order patterns (∼50 km) suggest the classic semi-tidal mode S(2, 4)/S(2, 5) is dominant.     

Plasma and electromagnetic wave simulations of meteors

Every day billions of meteoroids impact and disintegrate in the Earth’s atmosphere. Current estimates for this global meteor flux vary from 2000 to 200,000 tons per year, and estimates for the average velocity range between 10 km/s and 70 km/s. The basic properties of this global meteor flux, such as the average mass, velocity, and chemical composition remain poorly constrained. We believe much of the mystery surrounding the basic parameters of the interplanetary meteor flux exists for the following reason, the unknown sampling characteristics of different radar meteor observation techniques, which are used to derive or constrain most models. We believe this arises due to poorly understood radio scattering characteristics of the meteor plasma, especially in light of recent work showing that plasma turbulence and instability greatly influences meteor trail properties at every stage of evolution. We present our results on meteor plasmas simulations of head echoes using particle in cell (PIC) ions, which show that electric fields strongly influence early stage meteor plasma evolution, by accelerating ions away from the meteoroid body. We also present the results of finite difference time domain electromagnetic simulations (FDTD), which can calculate the radar cross section of the simulated meteor plasmas. These simulations have shown that the radar cross section depends in a complex manner on a number of parameters. These include the angle between radar and meteor entry, a large dependence on radar frequency, which shows that for a given meteor plasma size and density, the reflectivity as a function of probing radar frequency varies, but typically peaks below 100 MHz.     

Tidal associated temperature disturbances observed at the middle atmosphere (30–65 km) by a Rayleigh lidar at 23°S

A lidar has been operated in São José dos Campos, Brazil (23.2°S, 45.8°W) since 1972, mainly dedicated to the study of mesospheric sodium at the 589 nm resonant line. The molecular Rayleigh scattering can also be used provided we limit the height to ∼75 km where the sodium scattering begins. Nevertheless, the weak signal obtained only permits the determination of density and temperature profiles by accumulating a large number of shots giving only nocturnal average profiles. Temporal variations in density and temperature on the scale of hours can however, be obtained by performing a superposed epoch analysis for a given time interval and covering a period of several days. In this way we obtained hourly mean profiles grouped by months, seasons and overall, with data acquired from 1993 to 2004. The difference between the hourly temperatures and the nocturnal means shows for some months, with enough data coverage, downward propagating structures that apparently have tidal origin. The seasonal averages show a recurrent feature with high temperatures before and low temperatures after midnight above 50 km. Some similarity is found with the GSWM model, but the observed temperature amplitudes are twice of that for the model.     

Cometary/meteor coupling: structure of young streams.

Information on atmospheric parameters, properties and processes above 70 km are mainly based upon meteor data. An important problem of such data systematization is to single out the meteor streams associated with a series of extreme phenomena. The forecasting of these phenomena requires a physical model of meteor streams at the early stage of their occurrence. A direct coupling with comets is assumed for most of the streams. This paper analyses the structure simulation of cometary nucleus desintegration. The D-criterion is used as the orbital community criterion. Giacobini-Zinner comet in its ten appearances (1900-1979) is considered. Determination of stream location and its detailed structural characteristics is essential for long space missions.     

人为活动对高平流层,中间层大气的影响

利用一维光化、辐射耦合模式研究了人为活动所排放出的废弃物ＣＨ４、Ｎ２Ｏ和ＣＯ２含量增加对高平流层，中间层大气的影响。结果指出，对流层中这些气体增加一倍将导致上中层大气水汽、Ｏ３和温度的明显变化。ＣＯ２含量增加将使上中层温度降低约１０Ｋ；而ＣＨ４含量的加倍不仅使中层顶附近水汽含量增加５０％以上，也使其温度有更明显的下降，这将更有利于於光云的形成。