Ground-based observations of noctilucent clouds with a northern hemisphere network of automatic digital cameras

For the first time we present an analysis of observations of noctilucent clouds obtained with a network of automatic digital cameras located at opposite sides of the northern hemisphere. The advantage of this network is that the cameras are located along the same latitude circle producing comparable measurements. We find that there is an indication of the 2-day planetary wave propagation influencing the occurrence frequency, geographical distribution and brightness variations of noctilucent clouds. The 5-day planetary wave has much less effect on noctilucent clouds than that of the 2-day wave, at least for the summers of 2006 and 2007. At the same time, bright noctilucent clouds tend to occur every successive night during short periods of 3–5 nights.     

夜光云内小尺度重力波对冰晶粒径谱的影响规律研究

本文利用AIM卫星搭载的CIPS云图反照率和冰晶粒径数据,从中提取了2007/08南半球和2008年北半球共6489个小尺度重力波活动(波长5~150km范围)个例,对重力波区域与背景云层冰晶粒径谱进行对比分析,从而研究重力波对冰晶平均半径和谱宽的影响规律.结果表明,北半球重力波区域冰晶的平均半径和谱宽分别比背景云层小2.5nm和6.1nm,南半球则分别减小1.1nm和7.9nm.在随纬度的分布上,小于80°时,南北半球的平均半径扰动值均为负值,绝对值随纬度增大而减小,而大于80°时,负扰动转变为正扰动,且绝对值增加;谱宽扰动的绝对值也随着纬度增加而减小,但均为负值.在季节内随时间的分布上,南北半球重力波对冰晶平均半径和谱宽的扰动在始末阶段以负值为主,且绝对值较大,而在中期阶段正负值相当,且绝对值较小.这一特征与重力波引起冰晶粒径变化的振幅在纬度和时间上的分布趋势一致.重力波的波长均随纬度升高而减小,在季节的始末阶段较大,中期小,且南半球的平均波长和变化幅度都要明显大于北半球的,粒径扰动振幅随波长的变化率为南半球0.207nm·km-1,北半球的0.163nm·km-1.根据分析推断,重力波自身的扰动振幅应与其影响区域内的谱参数相对于背景云层的变化量有直接关系,且振幅越大,平均半径和谱宽的负扰动就越大.     

Long-term changes of (polar) mesosphere summer echoes

Strong VHF radar echoes have been observed not only during summer months at polar latitudes (polar mesosphere summer echoes, PMSE) but also at middle latitudes (mesosphere summer echoes, MSE). These echoes are closely connected with small ice particles, thus containing information about mesospheric temperature and water vapour content. But the (P)MSE also depend on the ionisation due to solar wave radiation and precipitating high energetic particles. Observations with VHF radars at Andenes (69.3°N; 16.0°E) since 1994 and at Kühlungsborn (54.6°N; 11.8°E) since 1998 are used for investigations of the solar and geomagnetic control of the (P)MSE as well as of possible long-term changes. The (P)MSE are positively correlated with the solar Lyman α radiation and the geomagnetic activity and have slightly positive trends. Due to the limited measuring period, the significance levels of the detected (P)MSE trends are small. Positive trends in noctilucent clouds (NLC) and polar mesospheric clouds (PMC) are in general agreement with (P)MSE trends.     

Interhemispheric comparison of mesospheric ice layers from the LIMA model

The new LIMA/ice model is used to study interhemispheric temperature differences at the summer upper mesosphere and their impact on the morphology of ice particle related phenomena such as noctilucent clouds (NLC), polar mesosphere clouds (PMC), and polar mesosphere summer echoes (PMSE). LIMA/ice nicely reproduces the mean characteristics of observed ice layers, for example their variation with season, altitude, and latitude. The southern hemisphere (SH) is slightly warmer compared to the NH but the difference is less than 3 K at NLC/PMC/PMSE altitudes and poleward of 70N/S. This is consistent with in situ temperature measurements by falling spheres performed at 69N and 68S. Earth's eccentricity leads to a SH mesosphere being warmer compared to the NH by up to approximately 85 km and fairly independent of latitude. In general, NH/SH temperature differences in LIMA increase with decreasing latitude and reach at 50. The latitudinal variation of NH/SH temperature differences is presumably caused by dynamical forcing and explains why PMSE are basically absent at midlatitudes in the SH whereas they are still rather common at similar colatitudes in the NH. The occurrence frequency and brightness of NLC and PMC are larger in the NH but the differences decrease with increasing latitude. Summer conditions in the SH terminate earlier compared to NH, leading to an earlier weakening and end of the ice layer season. The NLC altitude in the SH is slightly higher by 0.6–1 km, whereas the NLC altitudes itself depend on season in both hemispheres. Compared to other models LIMA/ice shows smaller interhemispheric temperature differences but still generates the observed NH/SH differences in ice layer characteristics. This emphasizes the importance of temperature controlling the existence and morphology of ice particles. Interhemispheric differences in NLC/PMC/PMSE characteristics deduced from LIMA/ice basically agree with observations from lidars, satellites, and radars.     

Approximation of the infra-red radiation flux in an atmosphere with cloud

Summary A three-stream infra-red radiation scheme for use particularly in boundary layer models is described. Local uniformity of the atmosphere (i.e. a generalization of the cooling to space approximation in clear air) is assumed, and the radiation equation is solved by simple collocation rather than by the full discrete ordinate method. In clear air the scheme corresponds to the usual approximation, which incorporates the Elsasser factor in the transmission function to account for diffuse radiation. The band models of Goody for water vapour and Elsasser for carbon dioxide are used for the band averaging of the transmission functions. Consistent with this, the band averaging of the radiation flux in cloud is undertaken by replacing the rapidly varying absorption coefficients for the gases by the actual band-averaged values of those coefficients. The band averaging is precise in the limits of strong and weak gaseous absorption.     

Earthquake Research Advances(ERA) opens a new era in earthquake research

正In May 2021, two strong earthquakes occurred in west and southwest China, causing ground cracks, building damages, along with human injuries. These events remind us again, that earthquakes and earthquakeinduced disasters always intertwine with human history. Reducing the losses caused by earthquakes and subsequent hazards (e.g., landslides,tsunamis) is one of the primary goals that geoscientists keep striving for.     

Tracing magnetic helicity from the solar corona to the interplanetary space

On October 14, 1995, a C1.6 long duration event (LDE) started in active region (AR) NOAA 7912 at approximately 5:00 UT and lasted for about 15 h. On October 18, 1995, the Solar Wind Experiment and the Magnetic Field Instrument (MFI) on board the Wind spacecraft registered a magnetic cloud (MC) at 1 AU, which was followed by a strong geomagnetic storm. We identify the solar source of this phenomenon as AR 7912. We use magnetograms obtained by the Imaging Vector Magnetograph at Mees Solar Observatory, as boundary conditions to the linear force-free model of the coronal field, and, we determine the model in which the field lines best fit the loops observed by the Soft X-ray Telescope on board Yohkoh. The computations are done before and after the ejection accompanying the LDE. We deduce the loss of magnetic helicity from AR 7912. We also estimate the magnetic helicity of the MC from in situ observations and force-free models. We find the same sign of magnetic helicity in the MC and in its solar source. Furthermore, the helicity values turn out to be quite similar considering the large errors that could be present. Our results are a first step towards a quantitative confirmation of the link between solar and interplanetary phenomena through the study of magnetic helicity.     

Radiative properties of cirrus clouds in NOAA 4 VTPR channels: Some explorations of cloud scenes from satellites

A one-dimensional spectral infrared radiative transfer model has been developed for atmospheres containing cirrus clouds and absorbing gases above, below and within the cloud. The transfer model takes into consideration the inhomogeneity of the cloudy atmosphere, the gaseous absorption in scattering cloud layers and the wavenumber dependence of radiative transfer. In addition, the cirrus cloud is further divided into a number of sub-layers to account for the non-isothermal and inhomogeneous cloud characteristics. Single-scattering properties for ice crystals are calculated assuming ice cylinders 200 and 60 m in lenght and width, respectively, randomly oriented in a horizontal plane. The spectral infrared transfer program is applied to VTPR channels of the NOAA 4 satellite to simulate upward radiances in cirrus cloud conditions.Comparisons between satellite observed and theoretically simulated upward radiances are carried out for selected cirrus cloud cases. Incorporating atmospheric profiles obtained from radiosonde and the observed cloud information into the spectral transfer program, we show a systematic agreement between observed and computed upward radiances. Systematic reduction patterns of the upward radiance caused by the increase of the cloud ice content are clearly demonstrated for VTPR channels employing tropical and midlatitude atmospheric profiles. Having the quantitative relationships between upward radiances and ice contents, procedures are described for the inference of the cloud ice content and cloud amount. The proposed method has been successfully applied to the three cirrus cloud cases.     

The role of sodium bicarbonate in the nucleation of noctilucent clouds

It is proposed that a component of meteoric smoke, sodium bicarbonate (NaHCO₃), provides particularly effective condensation nuclei for noctilucent clouds. This assertion is based on three conditions being met. The first is that NaHCO₃ is present at sufficient concentration (10⁴ cm^–3) in the upper mesosphere between 80 and 90 km. It is demonstrated that there is strong evidence for this based on recent laboratory measurements coupled with atmospheric modelling. The second condition is that the thermodynamics of NaHCO₃(H₂O)_n cluster formation allow spontaneous nucleation to occur under mesospheric conditions at temperatures below 140 K. The Gibbs free energy changes for forming clusters with n = 1 and 2 were computed from quantum calculations using hybrid density functional/Hartree-Fock (B3LYP) theory and a large basis set with added polarization and diffuse functions. The results were then extrapolated to higher n using an established dependence of the free energy on cluster size and the free energy for the sublimation of H₂O to bulk ice. A 1-dimensional model of sodium chemistry was then employed to show that spontaneous nucleation to form ice particles (n > 100) should occur between 84 and 89 km in the high-latitude summer mesosphere. The third condition is that other metallic components of meteoric smoke are less effective condensation nuclei, so that the total number of potential nuclei is small relative to the amount of available H₂O. Quantum calculations indicate that this is probably the case for major constituents such as Fe(OH)₂, FeO₃ and MgCO₃.     

原子磁力仪研究进展

原子磁力仪是利用量子理论并结合光学方法技术的一种磁力仪.由于它具备高灵敏度,无需低温条件,可小型化等诸多优点,成为人们高度关注的新型磁力仪.本文从主要量子磁力仪的概况出发,列表介绍了包括原子磁力仪在内的磁力仪名称,工作原理及灵敏度,进而对原子磁力仪的原理,国内外研究现状进行了综述,最后简要描述了原子磁力仪的应用前景,着...     

The isotopic signature of monsoon conditions,cloud modes,and rainfall type

This work provides a comprehensive physically based framework for the interpretation of the north Australian rainfall stable isotope record (δ¹⁸O and δ²H). Until now, interpretations mainly relied on statistical relationships between rainfall amount and isotopic values on monthly timescales. Here, we use multiseason daily rainfall stable isotope and high resolution (10 min) ground‐based C‐band polarimetric radar data and show that the five weather types (monsoon regimes) that constitute the Australian wet season each have a characteristic isotope ratio. The data suggest that this is not only due to changes in regional rainfall amount during these regimes but, more importantly, is due to different rain and cloud types that are associated with the large scale circulation regimes. Negative (positive) isotope anomalies occurred when stratiform rainfall fractions were large (small) and the horizontal extent of raining areas were largest (smallest). Intense, yet isolated, convective conditions were associated with enriched isotope values whereas more depleted isotope values were observed when convection was widespread but less intense. This means that isotopic proxy records may record the frequency of which these typical wet season regimes occur. Positive anomalies in paleoclimatic records are most likely associated with periods where continental convection dominates and convection is sea‐breeze forced. Negative anomalies may be interpreted as periods when the monsoon trough is active, convection is of the oceanic type, less electric, and stratiform areas are wide spread. This connection between variability of rainfall isotope anomalies and the intrinsic properties of convection and its large‐scale environment has important implications for all fields of research that use rainfall stable isotopes.     

Recent Results from Studies of Electric Discharges in the Mesosphere

The paper reviews recent advances in studies of electric discharges in the stratosphere and mesosphere above thunderstorms, and their effects on the atmosphere. The primary focus is on the sprite discharge occurring in the mesosphere, which is the most commonly observed high altitude discharge by imaging cameras from the ground, but effects on the upper atmosphere by electromagnetic radiation from lightning are also considered. During the past few years, co-ordinated observations over Southern Europe have been made of a wide range of parameters related to sprites and their causative thunderstorms. Observations have been complemented by the modelling of processes ranging from the electric discharge to perturbations of trace gas concentrations in the upper atmosphere. Observations point to significant energy deposition by sprites in the neutral atmosphere as observed by infrasound waves detected at up to 1000 km distance, whereas elves and lightning have been shown significantly to affect ionization and heating of the lower ionosphere/mesosphere. Studies of the thunderstorm systems powering high altitude discharges show the important role of intracloud (IC) lightning in sprite generation as seen by the first simultaneous observations of IC activity, sprite activity and broadband, electromagnetic radiation in the VLF range. Simulations of sprite ignition suggest that, under certain conditions, energetic electrons in the runaway regime are generated in streamer discharges. Such electrons may be the source of X- and Gamma-rays observed in lightning, thunderstorms and the so-called Terrestrial Gamma-ray Flashes (TGFs) observed from space over thunderstorm regions. Model estimates of sprite perturbations to the global atmospheric electric circuit, trace gas concentrations and atmospheric dynamics suggest significant local perturbations, and possibly significant meso-scale effects, but negligible global effects.     

Global pattern of trends in the upper atmosphere and ionosphere: Recent progress

The global pattern of long-term trends and changes in the upper atmosphere and ionosphere has been presented by Laštovička et al. [2006a. Global change in the upper atmosphere. Science 314 (5803), 1253–1254]. Trends in the mesospheric temperature, electron concentration in the lower ionosphere, electron concentration and height of its maximum in the E-region, electron concentration in the F1-region maximum, thermospheric neutral density and F-region ion temperature qualitatively agree with consequences of the enhanced greenhouse effect and form a consistent pattern of global change in the upper atmosphere. Three groups of parameters were identified as not-fitting this global pattern, the F2-region ionosphere, mesospheric water vapour, and the mesosphere/upper thermosphere dynamics. The paper reports progress in development of the global pattern of trends with emphasis to these three open problems. There are several other factors contributing to long-term trends, namely the stratospheric ozone depletion, mesospheric water vapour concentration changes, long-term changes of geomagnetic activity and of the Earth's magnetic field.     

Mesospheric bore events in the equatorial middle atmosphere

An all-sky CCD imager designed to measure wave structure of the OH, O₂b(0,1) and OI557.7 nm airglow emission layers in the mesosphere and lower thermosphere (MLT) region has been operated near the equatorial region at São João do Cariri (Cariri), Brazil, (7.5°S, 36.5°W). A large number of gravity wave was observed from September 2000 to September 2002 and among them 64 wave events were identified as mesospheric bores. The bore front shows a horizontal extension greater than 1000 km, and observed in the airglow layers as a complementary brilliance between the three emissions. At the first time mesospheric bore events were observed and analyzed in the equatorial region. Their predominant characteristics, occurrence, local time dependency, morphology and propagation direction will be presented and discussed.     

Solar response in the temperature over the equatorial middle atmosphere

One of the longest temperature records available for the equatorial region is provided by Rocketsonde from Thumba (8°N, 77°E), India during the period 1971–1993. In recent times, these data sets are reanalyzed using the up-to-date regression models, which take care of several corrections and parameters, not accounted for in earlier analyses and hence affecting the conclusions. In this paper, annual mean solar response in this data set along with the seasonal solar coefficient is quantitatively estimated now with improved confidence. A negative solar response in the stratosphere (1–2 K/100 solar flux unit, sfu) and a positive response for the mesosphere (0.5–3 K/100 sfu) are found. The negative stratospheric solar response is in contrast to the solar coefficient reported for low latitudes by earlier workers for other stations.     

中间层与低热层二氧化碳体积混合比的年际变化特征研究

利用17年的SABER(Sounding of the Atmosphere using Broadband Emission Radiometry)Level2C数据研究了中间层与低热层大气(MLT, Mesosphere and Lower Thermosphere) CO₂ VMR(Volume Mixing Ratio)的年际变化特征.使用多元线性回归模型对双月平均时间序列拟合,定量地提取各变化特征.结果表明,SABER CO₂ VMR长期趋势在中间层保持在5.5%/decade左右,在中间层顶和低热层降低至4.5%/decade左右;结果与模式预测在统计意义上相符.长期趋势没有显著的纬度差异,但在各纬度上都具有明显的季节依赖,MLT CO₂ VMR长期趋势的季节性改变源自低层大气长期趋势季节性改变.SABER CO₂ VMR对QBO (Quasi-Biannual Oscillation)和ENSO (El Ni1o-Southern Oscillation)在绝大多数区域没有统计显著的响...     

中国空间天气研究进展

空间天气指太阳、行星际空间和地球空间(地球磁层、电离层、热层和中高层大气)的状态及其变化,它能够影响到天基和地基技术系统的运行和可靠性,危及人类的生存.空间天气计划包括观测和资料分析,研究和数值建模,预报和服务.本文评述了近十年来我国空间天气研究中的一些重要成果.     

The effect of intensity of turbulence in umbrella cloud on tephra dispersion during explosive volcanic eruptions: Experimental and numerical approaches

During an explosive volcanic eruption, tephra fall out from the umbrella region of the eruption cloud to the ground surface. We investigated the effect of the intensity of turbulence in the umbrella cloud on dispersion and sedimentation of tephra by performing a series of laboratory experiments and three dimensional (3-D) numerical simulations. In the laboratory experiments, spherical glass-bead particles are mixed in stirred water with various intensities of turbulence, and the spatial distribution and the temporal evolution of the particle concentration are measured. The experimental results show that, when the root-mean-square of velocity fluctuation in the fluid (W_rms) is much greater than the particle terminal velocity (v_t), the particles are homogeneously distributed in the fluid, and settle at their terminal velocities at the base of the fluid where turbulence diminishes. On the other hand, when W_rms is as small as or smaller than v_t, the particle concentration increases toward the base of the fluid during settling, which substantially increases the rate of particle settling. The results of the 3-D simulations of eruption cloud indicate that W_rms is up to 40 m/s in most of the umbrella cloud even during a large scale plinian eruption with a magma discharge rate of 10⁹ kg/s. These results suggest that relatively coarse pyroclasts (more than a few mm in diameter) tend to concentrate around the base of the umbrella cloud, whereas fine pyroclasts (less than 1/8 mm in diameter) may be distributed homogeneously throughout the umbrella cloud during tephra dispersion. The effect of the gradient of particle concentration in the umbrella cloud explains the granulometric data of the Pinatubo 1991 plinian deposits.     

The structure of the equatorial mesosphere at Thumba

The structure of the equatorial mesosphere is being investigated at Thumba by rocket borne ultraviolet absorption photometry as well as by the meteorological M-100 rocket launching programme. Whereas the meteorological M-100 rocket luanching programme has been regular, the UV absorption studies have been few in number and sporadic in nature. In this paper an attempt is made to consolidate the results so far obtained from both these investigations.