火星电离层电子密度对太阳辐射变化的响应

太阳辐射是火星电离层变化的重要控制因素.利用火星全球勘探者号(Mars Global Surveyor,MGS)电离层掩星探测数据,并结合一个火星电离层总电子含量(Total Electron Content,TEC)经验模型,研究了火星北半球高纬地区电离层电子密度对太阳辐射变化的响应特性.在考虑了火星掩星数据中电离层电子密度对太阳天顶角的依赖关系后,发现随着太阳辐射增强,火星电离层M₂层峰值密度增大,但增长偏离线性趋势,而M₂层峰值高度和大气标高没有很明显的变化趋势.从100~200 km高度区域掩星电子密度剖面积分得到的TEC及底部和顶部TEC也随太阳辐射增大而增大,但增长率有所减小,表明火星电离层可能存在类似地球电离层的饱和特征.MGS掩星TEC及其底部和顶部剖面的TEC与经验模型TEC的比值均与太阳辐射强度变化呈反相关特性,表明在强太阳辐射情形下200 km以上电子含量在TEC中占比增大.这一特性意味着太阳活动增强,在火星顶部电离层区域,动力学过程对电离层的控制逐渐超过光化学过程.

     

释放化学物质耗空电离层电子密度的研究

电离层作为电波传播的主要通道和载体,影响着无线电通信的质量,因此人工电离层扰动具有广阔的应用前景.在电离层中释放具有较强电子亲和力的化学物质可以耗空电离层F区的电子密度,是人工电离层扰动的有效手段之一.本文通过对CO2和SF6气体在电离层中的扩散和离子化学反应过程的分析,理论计算了在我国北京地区上空释放这两种气体后电离层电子密度的时空演变过程.结果表明:(1)在电离层高度上释放100 kg的CO2或SF6气体后,电离层电子密度迅速减少,释放点周围局部区域的电子密度被耗空,能够形成一定尺度的电离层空洞,上述现象能够维持数小时之久;(2)与CO2气体相比,SF6气体具有扩散慢且化学反应快的优点,对电离层的影响较大,具有更好的电离层扰动效果.     

极区电离层F2层峰值电子浓度对太阳活动依赖性的共轭研究

本文利用南极中山站(ZHS),以及北极与其地理共轭的Tromso站(TRO)、地磁共轭的Longyearbyen站(LYB)各自约一个太阳活动周的观测数据,对比分析了极区电离层F₂层峰值电子浓度(N_mF₂)对太阳活动的依赖性.结果表明,三个台站N_mF₂月中值随修正太阳10.7 cm通量指数F_10.7P(简称P)增大在总体上呈线性增长,这说明在这三个台站,太阳辐射仍是其F₂层主要电离源.其中TRO站N_mF₂与P线性关系最好,ZHS站的次之,LYB站的最差.在日变化中,TRO站N_mF₂对太阳活动响应最为敏感的时刻出现在地方时中午附近,LYB站出现在磁中午,ZHS站则出现在地方时中午和磁地方时中午之间.这主要是由地理/地磁纬度差异引起的不同强度的光致电离与极区等离子体对流共同作用的结果.在年变化中,TRO站N_mF₂随太阳活动变化上升最快的季节出现在冬季,夏季上升最慢.在ZHS站与LYB站,N_mF₂对太阳活动变化的响应都在两分季最为敏感.这种季节上的差异则是由于三个台站光致电离与中性大气成分R[O/N₂]的不同所致.     

电离层电场的半年变化对F2区峰值电子浓度的影响

利用一个电离层理论模式,模拟了太阳活动低年、地磁宁静情况下,中低纬和赤道地区电离层F2区峰值电子浓度(NmF2)的半年变化规律,重点讨论了电离层电场对NmF2半年变化的影响.模拟结果表明,当输入的电场没有周年和半年变化时,磁赤道地区电离层NmF2本身就具有一定的半年变化特征,而在稍高的纬度上,NmF2半年变化的强度较弱.当输入的电场具有一定的半年变化时,电离层NmF2的半年变化强度有明显的改变,且这种改变随地方时和地磁纬度不同有明显的差别.在地磁赤道附近的电离层赤道槽地区,从上午到午夜的时间内,具有半年变化的电场对电离层NmF2半年变化的强度是减弱的作用,在其他的时间内,电场对电离层NmF2半年变化强度是加强的作用.而在稍高纬度的电离层驼峰地区,情况明显不同.从上午一直到翌日日出前,具有半年变化的电场对电离层NmF2半年变化的幅度都是加强的作用.在其他的时间内,电场对电离层NmF2半年变化的幅度是减弱的作用.同时,研究表明电离层电场对NmF2半年变化的作用和“赤道喷泉”现象强烈相关.     

电离层斜测数据集

电离层斜测数据集包括F₂层临界频率数据和最大电子密度空间分布图,来源于中国地震电离层监测试验网观测数据。2008年汶川地震后,中国地震局地震预测研究所和中国电子科技集团第22研究所,在国防科技工业电波环境观测站网原有的稀疏发射站网基础上,根据地震重点监测区带分布和区域数据覆盖能力的双重需要,利用电离层对地基发射信号的反射特性,在华北5个电离层垂测发射站的基础上,建立了20个电离层斜测接收站,形成100条发射—接收链路,达到以经济手段取得电离层加密监测的效果。数据由接收台站接收后,汇聚到北京数据中心,并建立Oracle数据库,将数据入库。通过人工判读,生成可应用的电离层斜测观测数据。此数据集通过数据共享网站提供数据共享服务,可为地震系统内部各省地震局和研究所进行地震监测预测研究以及系统外部科研机构和院校电离层观测研究提供基础数据。     

Demeter观测的电离层非震变化特征研究

利用法国电磁卫星Demeter装载的ICE(电场探针)及IAP(等离子体分析仪)探测数据,分析研究2006年不同季节、不同地方时顶部电离层电场及各等离子参量的全球空间分布特征,结果发现,电场x分量及H+离子浓度、O+离子浓度、He+离子浓度、等离子体温度具有显著的季节变化和地方时变化,而电场y分量及z分量全球分布的季节...     

普洱地震前电离层电子密度扰动变化研究

挑选普洱地震前邻近地震震中的3条轨道的电子密度（Ne)数据,分析其1年内的所有重访轨道,并提取了这次地震前的Ne前兆异常. 结果表明：① 夜间电离层Ne存在明显的季节变化,4个季节呈现了各自不同的变化形态;② Ne的主要变化形态有3种,即单峰、马鞍和平缓状,这些形态在各个季节都可能出现,但每个季节有相对集中的形态;③ Ne空间图象在震前30天内在震中区附近形成高值,异常信息在空间和时间上都与地震分布有很好的相关性,反映空间出现的异常信息确与本次地震有关;④ Ne重访轨道曲线形态有一定的相似性,可以为识别判定地震异常提供背景信息.     

川滇地区电离层多参量异常监测系统的设计与实现

介绍了川滇地区电离层多参量异常监测系统的设计思路与功能实现,并将该系统应用于2019年6月17日四川长宁MS6.0地震的监测试验.结果表明:该系统实现了全球和中国区域垂直总电子含量VTEC、站点VTEC和F2层临界频率foF2异常变化的实时监测,有助于开展示范性地震电离层异常监测工作,其图形及数据结果可为地震-电离层异...     

电离层日变化特性研究简述

电离层具有非常鲜明的日变化特性.?电离层日变化特性是认识包括逐日变化等众多电离层现象的出发点,也是电离层经验模型需要呈现的最基本特性.?本文简要介绍了有关电离层日变化的一些研究工作,重点关注以电场为核心的电离层日出变化、电离层午时咬失现象、电离层夜间增强,特别是以威德海异常为典型代表的中纬电离层夏季夜间异常变化.?评述...     

F子夜均值逐日差空间异常变化与地震的关系研究

利用2010年1月1日至2014年4月30日我国地磁台网100多个台站的地磁总强度F子夜均值数据,逐一分析了F子夜均值逐日差的空间变化趋势。结果表明,在此期间有18次小区域的异常变化,其中16次异常与其后几天到半年时间内该区域发生的地震有很好的对应关系,另外两次新近的异常有待后续进一步验证。我国西北部地区地磁台站稀疏,布局不合理,限制了对新疆、青海、西藏等地震多发区震磁关系的研究,建议这些地区进一步加密台站建设,优化布局。     

Modelling F2-layer seasonal trends and day-to-day variability driven by coupling with the lower atmosphere

This paper presents results from the TIME-GCM-CCM3 thermosphere–ionosphere–lower atmosphere flux-coupled model, and investigates how well the model simulates known F2-layer day/night and seasonal behaviour and patterns of day-to-day variability at seven ionosonde stations. Of the many possible contributors to F2-layer variability, the present work includes only the influence of ‘meteorological’ disturbances transmitted from lower levels in the atmosphere, solar and geomagnetic conditions being held at constant levels throughout a model year.In comparison to ionosonde data, TIME-GCM-CCM3 models the peak electron density (NmF2) quite well, except for overemphasizing the daytime summer/winter anomaly in both hemispheres and seriously underestimating night NmF2 in summer. The peak height hmF2 is satisfactorily modelled by day, except that the model does not reproduce its observed semiannual variation. Nighttime values of hmF2 are much too low, thus causing low model values of night NmF2. Comparison of the variations of NmF2 and the neutral [O/N₂] ratio supports the idea that both annual and semiannual variations of F2-layer electron density are largely caused by changes of neutral composition, which in turn are driven by the global thermospheric circulation.Finally, the paper describes and discusses the characteristics of the F2-layer response to the imposed ‘meteorological’ disturbances. The ionospheric response is evaluated as the standard deviations of five ionospheric parameters for each station within 11-day blocks of data. At any one station, the patterns of variability show some coherence between different parameters, such as peak electron density and the neutral atomic/molecular ratio. Coherence between stations is found only between the closest pairs, some 2500 km apart, which is presumably related to the scale size of the ‘meteorological’ disturbances. The F2-layer day-to-day variability appears to be related more to variations in winds than to variations of thermospheric composition.     

基于Swarm卫星GPS/TEC观测的顶部电离层三维电子密度分布的层析法研究

利用两颗伴飞的Swarm A/C卫星搭载的双频GPS接收机获取的TEC数据,在两个卫星轨道平面同时对顶部电离层电子密度进行层析成像,实现对顶部电离层电子密度的三维观测.为了能够重现扰动期间电离层电子密度的空间变化特征,在正则化求解过程中,我们引入了水平矩阵H和垂直矩阵V刻画电子密度的空间变化特征,引入整体约束矩阵C以调节不同空间对电子密度相对变化的权重.数值验证结果表明我们的算法对常见的观测误差具有较强的包容性,反演计算出的电子密度平均偏差优于10%.在不同地磁活动条件下,与第三方观测数据的对比,验证了本文反演算法的可靠性.实测数据反演结果表明我们的算法不仅能够较好地重现顶部电离层子午向百公里级别的不规则结构,还能有效分辨纬向相隔~150 km的两个卫星轨道平面的电子密度差异.     

Using geostatistics and spectral analysis to study spatial patterns in the topography of southeastern Washington State,U.S.A.

Topography for four areas in the Palouse region of southeastern Washington State having different patterns and encompassing areas of about 900 ha each were quantitatively compared and described using two-dimensional semi-variograms and periodograms. The four areas studied were from the Garfield, La Crosse, Thornton, and Wilcox quadrangle topographic maps. Semivariance of elevation residuals were modelled using a combination of spherical, periodic, or linear semivariogram models. The range of the spherical component was interpreted as a relatively short-range scale of correlation which was not periodic. For each of the study areas a model was developed to describe the variation in range with orientation. Values for the range from this model reached maximum values of from about 700 m to 800 m at an orientation of from 35° to 55° (approximately northeast) in each study area. This orientation was interpreted as the dominant direction of non-periodic small-scale landscape features. The wavelength and amplitude of the periodic semivariogram component, which were highly correlated, were interpreted in terms of parallel northeast-trending ridges having relatively long scales of periodic correlation varying in size from about 1350 m to 2100 m. This attempt to identify the dominant orientation of periodic landscape features using models for the wavelength and amplitude was, however, not completely definitive. Two-dimensional spectral analysis provided significantly more detail concerning orientation and wavelengths of the periodic topographic patterns than the semivariogram analysis. In the Garfield study area, spectral analysis identified north-trending ridge systems separated by a wavelength of 1494 m and northeast-trending systems with a wavelength of 747 m. In the La Crosse study area, both north and northeast-trending patterns were identified having periodic spacings of 980 and 735 m. North-trending ridges separated by wavelengths of 996 m and northeast-trending ridges separated by wavelengths of 747 or 996 m were the predominant periodic features of topography in the Thornton study area. In the Wilcox study area, northeast-trending ridge systems separated by wavelengths of 373, 498, or 996 m were detected. A comparison of the results from geostatistical and spectral analysis of these complex topographic surfaces shows that each approach had significant strengths and weaknesses. Two-dimensional analysis with semivariograms was the only method which could be used for identifying the correlation scale and orientation of relatively small non-periodic landscape features. Two-dimensional spectral analysis accurately identified the predominant orientation of relatively large periodic features in topography, whereas semivariogram analysis was somewhat inconclusive. Also, semivariograms were generally unable to detect the presence of multiple or harmonic periodicities operating at different wavelengths along a given orientation.     

fCO2 variability in the Bay of Biscay during ECO cruises

The Bay of Biscay is part of the North Atlantic Ocean, the most important sink of CO₂, and a subduction zone of mode waters that favours the entry of carbon to the ocean interior. To investigate the seasonal and interannual variability of CO₂ uptake, continuous underway measurements of the partial pressure of CO₂ at sea surface were performed along a commercial route between Vigo (Spain) and St. Nazaire (France). An unattended measuring system of CO₂ fugacity (fCO₂), with meteorological station, and temperature, salinity, oxygen and fluorescence sensors, was installed on board of ships of opportunity (RO-RO L’Audace and RO-RO Surprise).     

Predicting new snow density in the Italian Alps: A variability analysis based on 10 years of measurements

Despite its strong impact on the time evolution of the snowpack, current estimation of new snow density (ρ_hn) is usually accomplished either by using local empirical techniques or by assuming a constant snow density. Faced with the lack of an estimation model of ρ_hn valid for a wide spatial scale and supported by a suitable number of observations, this study aims to develop simple monthly linear regression models at scale of the entire Italian Alpine chain based on 12,112 snowfall observations at 122 stations, using only air temperature as predictor. Moreover, the remaining variance is investigated in both time and space, also considering some qualitative features of the snowfall events. The daily ρ_hn measurements present a mean value of 115 kg m^?3 (105 and 159 kg m^?3 for dry and wet conditions, respectively). The mean air temperature of the 24 hr preceding the snowfall event has been found to be the best predictor of the ρ_hn, within 31% of uncertainty. The analysis of associated residues allows supporting the idea that the adoption of a more local approach than the one analysed here is not able to substantially increase the predictive capabilities of the model. In fact, the main factor explaining the remaining variance over the air temperature is the wind, but in a complex orography, as mountain regions are, supplying realistic local wind fields is particularly challenging. Therefore, we conclude that using only the daily mean temperature as predictor is a good choice for estimating daily new snow density at scale of Italian Alpine chain, as well as at more regional scale.     

降水过程对断层CO2气体异常排放响应的个例分析

为了从观测事实的角度揭示岩石圈的热异常对大气圈的影响,本文利用怀来后郝窑测点的断层气CO₂排放观测数据和中国752站降水的逐日观测资料,分析了断层气CO₂异常排放与降水事件的时空演变联系.个例分析结果表明,断层气CO₂的异常排放会导致局地降水的增多.以1991年为例,伴随着断层气CO₂排放的异常增加,在大范围降水负异常的背景下,CO₂排放点周边区域出现显著的降水正异常（降水距平百分率大于零）区.同时,CO₂异常幅度较大的时段,相应的降水正异常区的中心值也较大.此外,分析降水响应断层气CO₂排放异常的时间还发现,断层气CO₂异常排放对其后10天内的降水过程影响最为显著.     

A comparative study of winds and tidal variability in the mesosphere/lower-thermosphere region over Bulgaria and the UK

Meteor radars located in Bulgaria and the UK have been used to simultaneously measure winds in the mesosphere/lower-thermosphere region near 42.5°N, 26.6°E and 54.5°N, 3.9°W, respectively, over the period January 1991 to June 1992. The data have been used to investigate planetary waves and diurnal and semidiurnal tidal variability over the two sites. The tidal amplitudes at each site exhibit fluctuations as large as 300% on time scales from a few days to the intra-seasonal, with most of the variability being at intra-seasonal scales. Spectral and cross-wavelet analysis reveals closely related tidal variability over the two sites, indicating that the variability occurs on spatial scales large compared to the spacing between the two radars. In some, but not all, cases, periodic variability of tidal amplitudes is associated with simultaneously present planetary waves of similar period, suggesting the variability is a consequence of non-linear interaction. Calculation of the zonal wave number of a number of large amplitude planetary waves suggests that during summer 1991 the 2-day wave had a zonal wave number of 3, but that during January/February 1991 it had a zonal wave number of 4.     

Spatial variability of N2O concentrations and of denitrification-related factors in the surficial groundwater of a catchment in Northern Germany

N₂O concentrations and denitrification-related factors (NO₃, SO₄, dissolved organic carbon (DOC) and CO₂) were investigated in the surface groundwater of a catchment in northern Germany, the Fuhrberger Feld Aquifer (FFA). We sampled 79 plots that were selected according to the three criteria of land use, historical land use conversion (1954–1995) and groundwater level. We sampled three sites within each plot. The sampling depth was 0.5 m below the groundwater surface.We found no indication for the occurrence of autotrophic denitrification in the surface groundwater. Heterotrophic denitrification was identified as the main process for N₂O accumulation. The variability of N₂O concentrations on the plot-scale was extremely high and was poorly explained by the three sampling criteria. Other denitrification-related variables such as NO₃, SO₄ and DOC were less variable. The selection criteria land use and groundwater level clearly influenced the order of magnitude of N₂O concentrations in the surface groundwater. Under arable land, high NO₃ concentrations resulted in high N₂O concentrations. The surface groundwater under forest and pasture was almost NO₃-free and had also very small N₂O concentrations. Plots where the distance from the soil surface to the groundwater surface was large (>1 m up to 3.4 m) showed higher N₂O concentrations in the surface groundwater than plots where the distance was small (<1 m). A larger distance from the soil surface to the groundwater leads to a longer residence time and more decomposition of DOC in the soil. Consequently the less bioavailable DOC could inhibit the efficiency of the heterotrophic denitrification in the groundwater, yielding more N₂O. Elevated organic carbon levels in plots with historic land use conversion (pasture to arable) were very stable and did not influence N₂O concentrations. The high within plot variability showed that an upscaling of N₂O from the plot-scale to the catchment-scale is possible as long as the groundwater level regime and the land use do not change.     

三峡水库澎溪河消落区土-气界面CO2和CH4通量初探

水库近岸湿地(消落区)温室气体(CO₂、CH₄)产汇是水库温室气体效应问题的重要组成部分.本文以三峡水库支流澎溪河的白家溪、养鹿两处大面积消落区为研究对象,于2010年6 9月水库低水位运行期间,对近岸消落区土-气界面CO₂、CH₄通量进行监测.白家溪消落区土-气界面CO₂通量均值为12.38±2.42 mmol/(m²·h);CH₄通量均值为0.0112±0.0064 mmol/(m²·h).养鹿消落区CO₂、CH₄通量均值分别为10.54±5.17、0.14±0.16 mmol/(m²·h).总体上,6 9月土-气界面CO₂通量呈增加趋势,而CH₄通量水平呈现显著的递减趋势.消落区土地出露后植被恢复,在一定程度上促进了土壤有机质含量的增加,使得6 9月CO₂释放通量的总体趋势有所增加.消落区退耕后,其甲烷氧化菌的活性得到恢复,加之在土地出露曝晒过程中土壤透气性增强,使得消落区土壤对大气中CH₄吸收氧化潜势增强.尽管如此,仍需进一步的研究以明晰消落区土-气界面CO₂、CH₄产汇的主要影响因素.     

降水过程对断层CO2气体异常排放响应的个例分析

为了从观测事实的角度揭示岩石圈的热异常对大气圈的影响,本文利用怀来后郝窑测点的断层气CO2排放观测数据和中国752站降水的逐日观测资料,分析了断层气CO2异常排放与降水事件的时空演变联系.个例分析结果表明,断层气CO2的异常排放会导致局地降水的增多.以1991年为例,伴随着断层气CO2排放的异常增加,在大范围降水负异常的背景下,CO2排放点周边区域出现显著的降水正异常（降水距平百分率大于零）区.同时,CO2异常幅度较大的时段,相应的降水正异常区的中心值也较大.此外,分析降水响应断层气CO2排放异常的时间还发现,断层气CO2异常排放对其后10天内的降水过程影响最为显著.