低纬电离层f0F2夜间增强的模拟研究

以太阳活动低年冬季为代表,利用二维中低纬电离层理论模式模拟低纬电离层ｆ０Ｆ２夜间增强现象,探索在赤道异常驼峰纬度附近形成该现象的可能因素或物理机制,模式在给定磁子午面内解等离子体输运方程,给出电子及各离子的浓度,速度的时空分布。在所考察条件下,低纬驼峰纬度附近ｆ０Ｆ２模式值夜间出现了明显的增强特征。     

模式化分析F区电离层赤道异常槽

利用二维低纬电离层理论时变模式模拟低纬电离层演化，考察影响赤道异常槽位置的物理因素．计算结果显示赤道槽有明显的季节、地方时和经度变化．以１１０°Ｅ为例，北半球夏季期间赤道槽一般在磁倾赤道北侧，最北达３°-３．５°Ｎ，而在北半球冬季期间一般位于磁倾赤道南侧，最南可达４°－５°Ｓ．进一步分析发现，赤道槽季节变化中光化电离率季节改变的影响很小，主要由水平中性风季节变化贡献．计算以８３天为例，白天赤道槽在地理经度１００°Ｅ附近最南，２８５°Ｅ附近最北，与观测特征基本一致．主要是背景大气水平风场的经度差异导致赤道槽位置的经度变化，而非前人认为直接由磁偏角控制的．     

低高度内辐射带高能质子空间分布位形的研究

利用国际地磁参考场模式(IGRF模式)分析了1970-2000年低高度南大西洋负磁异常区位形的漂移与变化，给出了几个高度异常区中心位置磁场强度的变化和位置的变化。利用带电粒子的运动学方程，简要分析了低高度辐射带高能粒子的运动，得出在低高度，磁场是决定辐射带高能粒子空间强度与分布的决定性因素．低高度辐射带空间分布位形的变化特征应该与低高度南大西洋负磁异常区的变化特征基本一致．低高度南大西洋负磁异常区的特征可以作为低高度辐射带空间分布位形的一个初步判据。     

磁层－电离层电动耦合与中纬地磁指数的变化

本文探讨磁层一电离层耦合过程内中纬地磁指数的变化特点，并与极光电集流和赤道电集流（指数）变化相比较．相关分析和时序叠加分析均表明，高、中、低纬地磁指数变化可归结为磁层一电离层电动耦合的统一物理图象．有Ｒ事件的磁暴主相初期和无Ｒ事件的磁扰期内，赤道电集流和中纬地磁指数的变化各不相同．这再次证明，耦合分析中将磁层源扰动的直接穿透作用与经电离层内动力过程的效应二者加以区分和综合研究是很重要的．     

中性风对夜间低纬电离层参量的影响

利用一个改进的二维低纬电离层理论模式研究夜间中性风对低纬电离层多量的作用．模式计算结果表明：夜间中性风对低纬F层的影响与纬度、地方时有关．夜间低纬F层峰值电子浓度和峰高及其随时间的变化受中性风的影响与传统观点有所差异．低纬F层参量不只依赖于中性风的方向、强度,还与中性风场空间分布及时间变化率有关．中性风对低纬F层的影响值得重新认识．     

中性风和垂直漂移对低纬F区电离层影响初析

利用二维低纬电离层－等离子体层时变理论模式,模拟太阳活动高年春分条件下垂直漂移和中性风强度改变对低纬F区电离层参量的影响.模式在所考察的磁子午面内求解等离子体输运方程,给出离子浓度和速度随纬度、高度、地方时的变化.模式计算结果显示,调整垂直漂移和中性风强度对低纬F区电离层电子浓度的影响与电离层所处磁纬、垂直漂移和中性风作用时段等有关,呈现出一些新特点.结果对分析不同条件下垂直漂移和中性风对低纬F区电离层影响具有一定的指导意义.      

夜间f0F2存在季节异常现象

本文用1975.12—1986.12我国9个电离层站的资料分析得出,在一定的纬度和太阳活动条件下,夜间f_0F_2存在季节异常现象.夜间季节异常现象具有两个明显的特点:只有低纬才具有夜间季节异常特征;太阳活动高年夜间季节异常的程度增加.夜间季节异常是白天f_0F_2季节异常现象的延续,夏半球至冬半球的大气流动造成的中性气体浓度比(O/O_2和O/N_2)的季节变化,是形成f_0F_2季节异常的根本原因.并初步分析了夜间季节异常的低纬局限性及随太阳活动变化的成因.     

低纬地磁Z分量的半年变化

利用武汉、广州、泉州和琼中等4个低纬地磁站连续多年的地磁资料，计算了各月5个磁静日Z分量日均值与中午1100---1300时段平均值之差(Dz)，对每年12个Dz采用多元回归分析方法，得到各年的半年变化幅度和相位．结果表明：4个站的Dz每年都有半年变化现象；半年变化幅度与太阳活动有关，一般来说，太阳活动高年Dz半年变化幅度明显大于太阳活动低年；太阳活动本身的半年变化，对Dz半年变化幅度有显著的调制作用；Dz半年变化的相位在3—4月(或9—10月)，即极大值出现在分季；低纬地区地磁Z分量存在显著的半年变化，能够反映赤道电急流也有明显的半年变化，这再一次证明，赤道电急流幅度的半年变化，通过“喷泉效应”使得电离层，f0F2产生半年变化，其是产生，f0F2半年变化的一个主要因素．     

基于海南VHF雷达观测的低纬E区场向不规则体研究

利用海南VHF雷达（19.5°N,109.1°E;磁纬8.1°N）在2011年7月15—22日期间的连续观测数据,对东亚低纬3m尺度电离层场向不规则体（FAI）特性进行了分析. 主要结果表明,在整个观测期间,E区场向不规则体几乎每天发生,既可发生于夜间,也可发生于白天,且存在各种不同结构. 根据E区场向不规则体发生的时间及形态,可将其分为三种结构类型:低部连续型结构、上部下降型结构以及白天连续型结构. 这些低纬E区场向不规则体的回波谱特性与赤道电集流（EEJ）和中纬区E区场向不规则体中的2型回波相类似,但其随时间的变化与后两者存在明显差异,且与其他低纬区E区场向不规则体回波存在不同程度的差异.      

利用COSMIC数据研究顶部电离层O+扩散流的统计特征

从等离子体运动方程出发, 利用COSMIC星座的掩星数据, 借助相关经验模式, 计算了太阳活动低年顶部电离层O+场向扩散速度和扩散通量, 并分析了其全球分布和日变化特征. 结果表明, 白天等离子体扩散速度的方向随高度增加由向下(极向)逐步变为向上(赤道向), 方向转变的高度一般在hmF2+80 km以下. 在白天较高高度, 南北磁纬10o ~20 o存在着向上方向的最大扩散速度和扩散通量; 而在夜间, 南北磁纬30o~40 o存在向下方向的最大扩散速度和扩散通量. 在分点, 南北半球的扩散通量和扩散速度大致对称; 而在至点, 扩散通量存在着明显的南北半球不对称现象. 另外, 不同纬度的扩散速度有着不同的日变化特征.      

A regional model for the prediction of M(3000)F2 over East Asia

Research on empirical or physical models of ionospheric parameters is one of the important topics in the field of space weather and communication support services. To improve the accuracy of predicting the monthly median ionospheric propagating factor at 3000 km of the F2 layer (identified as M(3000)F2) for high frequency radio wave propagation, a model based on modified orthogonal temporal–spatial functions is proposed. The proposed model has three new characteristics: (1) The solar activity parameters of sunspot number and the 10.7-cm solar radio flux are together introduced into temporal reconstruction. (2) Both the geomagnetic dip and its modified value are chosen as features of the geographical spatial variation for spatial reconstruction. (3) A series of harmonic functions are used to represent the M(3000)F2, which reflects seasonal and solar cycle variations. The proposed model is established by combining nonlinear regression for three characteristics with harmonic analysis by using vertical sounding data over East Asia. Statistical results reveal that M(3000)F2 calculated by the proposed model is consistent with the trend of the monthly median observations. The proposed model is better than the International Reference Ionosphere (IRI) model by comparison between predictions and observations of six station, which illustrates that the proposed model outperforms the IRI model over East Asia. The proposed method can be further expanded for potentially providing more accurate predictions for other ionospheric parameters on the global scale.     

The relationship between ionospheric total electron content (TEC) over East Asia and the tropospheric circulation around the Qinghai-Tibet Plateau obtained with a partial correlation method

This paper reports a study on the relationship between ionospheric total electron content (TEC) over East Asia and the tropospheric circulation around the Qinghai-Tibet Plateau. Ionospheric TEC over East Asia are obtained from 25 observatories during 1996–2004. By applying a partial correlation method which can eliminate the influences of solar and geomagnetic activities, we find no significant correlation between TEC and the Asian zonal circulation index (Iz), but find a positive correlation between the day-to-day variability of TEC and Iz. We suggest that the positive correlation is closely related with the topography of the Qinghai-Tibet Plateau. The dynamical effect on airflow of the plateau can generate vortexes, and the vortexes may continuously excite internal gravity waves (IGWs) which transmit up to the ionosphere and cause regional wave disturbances. This study gives evidence for the dynamical mechanism of ionosphere–troposphere coupling and shows the importance of the Qinghai-Tibet Plateau in the ionosphere–troposphere coupling over East Asia.     

东亚地区Es特性研究

Es是发生在电离层E层高度上的偶发不规则结构,其电子密度最高可达E层背景电子密度的100倍以上. 远东地区是全球Es的高发区,其相关研究具有独特性和典型性,该地区Es形态学特性的深入研究对于探索Es成因及揭示其本质具有重要意义. 本文利用中国电离层垂测网50余年的垂测数据,结合日本垂测网数据对东亚地区Es的强度特性、空间分布特性、日变化、季节变化以及长期变化趋势进行了深入分析,得到一些有意义的结论.      

东亚地区电离层Es出现率峰值的时空演变

通过对东亚地区20多个台的电离层垂测资料,进行逐年、逐月与逐台的比较研究,发现Es出现率峰(Es出现率最大处)具有时空演变.冬季的白天,峰位于低纬;夏季的白天,峰的位置随太阳活动的不同而变动;春秋两季的峰不明显,隐约可见其振荡在类似于海口与国分寺的纬度之间;夜晚,兰州、新乡与国分寺,几乎既是夜晚各季节的主峰所在,又是白天冬夏季节的亚峰地点.可见Es出现率峰,有着十分规则的变化,这一点与以往结论有别.      

夏季强对流活动对东亚低纬电离层不规则体影响的事件分析

利用海南台站和东南亚地区的多种地基和天基观测手段,对2014年7月28日夜间观测到的东亚低纬F区不规则体事件的时空变化及其物理过程进行分析。结果表明,海南台站观测到了罕见的长时间持续的F区电离层不规则体,不同手段观测到的电离层不规则体存在明显的形态差异。不同台站观测到的电离层不规则体活动存在明显的差异。海南台站经度区南北异常峰附近的TEC起伏活动在日落后至午夜附近明显增强,在午夜后明显减弱。C/NOFS卫星轨迹午夜后逐渐接近于磁赤道,且处于较低高度上,几乎总会观测到弱等离子体扰动/泡的发生,与该区域地基观测的弱电离层不规则体活动存在明显的联系。SWARM卫星在黎明海南台站附近经度区仍观测到较强的赤道异常双峰结构,且西侧异常峰区附近仍存在明显的等离子体密度耗空/泡结构。海南台站西侧磁赤道区附近（中南半岛）强对流活动（MCC）激发的重力波种子扰动对东亚低纬区等离子体泡及准周期结构的产生发挥了重要作用。      

Time delay of ionospheric TEC storms to geomagnetic storms and pre-storm disturbance events in East Asia

Using the TEC data at Beijing (39.61°N, 115.89°E)/Yakutsk (62.03°N, 129.68°E) stations of East Asia regions and relevant geomagnetic data from 2010 to 2017, we have studied the time delay of ionospheric storms to geomagnetic storms and compare it with our previous results of Taoyuan (25.02°N, 121.21°E) station (Zhang et al., 2020). The data shows a well-known local time dependence of the time delay, and seasonal dependences are different at these stations. In addition, there is no correlation between the time delay and the magnetic storm intensity /solar activity, except the time delay of negative storms has weakly negative dependence on the solar activity. Comparing with the results of Taoyuan station which is located at EIA region in East Asia, we find that the time delay increases nonlinearly as the latitude decreases due to different ionospheric backgrounds at these places. Moreover, the pre-storm disturbance events are found to have similar statistical characteristics as the pre-storm enhancement in Europe middle latitudes (Bure?ová and La?tovi?ka, 2007). By subtracting the common features of the pre-storm disturbance events, we preliminarily infer that auroral activity might be main driver of the pre-storm disturbance events.     

Peculiarities of the nighttime winter foF2 increase over Irkutsk

An analysis of properties and peculiarities of the nighttime winter foF2 increases (NWI) in the East Siberia is made on data of ionospheric station Irkutsk in the periods 1958–1992 and 2002–2009 and the empirical model of the F2 layer critical frequency under the geomagnetic quiet conditions deduced from these data (model Q-F2). It is revealed, that the NWI is the stable regularity of the quiet ionosphere over Irkutsk. The amplitude of the NWI (the difference between maximum and minimum foF2 values at night hours) is the greatest in December–January and nearly the same at low and middle solar activity. It is a peculiarity of the quiet ionosphere in the East Siberia. Maximum in night foF2 under quiet geomagnetic conditions is observed mainly after midnight (02-04 LT) and is shifted to predawn hours as solar activity increases. At low solar activity the quiet ionosphere at ∼02–04 LT shows the following properties: (a) the fluctuations of foF2 and hmF2 are in the reverse correlation but this dependence is weak; (b) very strong fluctuations of foF2 (|δfoF2| > 30%) occur seldom (∼4% of events) and almost all of them are positive; an example of very strong fluctuations of foF2 up to 60% can be an extreme increase in the foF2 on 19.12.2008; (c) the very strong enhancements of foF2 in the NWI maximum can be observed at the low geomagnetic activity, they occur more often during substorms but very seldom during geomagnetic storms. Possible reasons of these properties of NWI are discussed.     

利用HRDI/UARS资料分析东亚区域中层大气纬向风气候特征

利用美国高层大气研究卫星(UARS)搭载的高分辨率多普勒测风仪(HRDI)获得的中层大气风场观测资料,对东亚区域中层大气纬向风的垂直分布与变化特征进行了分析研究.多年平均结果显示东亚区域中层大气纬向风具有显著的区域特征,与当前普遍使用的参考大气CIRA-86相比存在显著的不同.在冬季,东亚区域中间层西风急流中心位于25°-35°N之间的75 km高度,与CIRA-86相比,该中心纬度偏南5°,高度偏高10 km;在秋季,东亚区域低热层高度存在一个显著的从赤道到高纬度的东风带,而CIRA-86不存在.分析结果还表明,除了夏季中纬度地区,在东亚区域上空中高层大气各高度上均存在相当显著的区域尺度扰动结构.在热带,低热层高度纬向风无论冬夏,沿纬圈方向都表现出相当显著的不均匀性,夏季这种不均匀性进一步向下扩展到55 km高度.与上述热带扰动特征相比,中纬度地区夏季的纬向风在各个高度沿纬圈相当均匀,但是在冬季,中间层和低热层高度都存在沿纬圈方向显著的纬向风扰动结构.      

Controlling denitrification in closed artificial ecosystems.

Denitrification, the dissimilatory reduction of NO3- to N2O and N2, is found in a wide variety of organisms. In closed artificial systems, especially closed plant growth chambers, a significant loss of fixed-N occurs through denitrification, thereby decreasing the efficiency of the system and fouling the atmosphere with N2O. Denitrification is a form of anaerobic respiration. Whenever available, however, denitrifiers preferentially use O2 as their terminal electron acceptor. As a result, rates of denitrification and growth are a function of O2. Typically, in closed systems O2 consumption is greater than the diffusion of O2 through the medium to the cell, decreasing the O2 level near the cell and denitrification occurs. Using Pseudomonas fluorescens (ATCC # 17400) as a model organism grown in a two L bioreactor under varying levels of O2 we studied its effects on population growth and its ability to mitigate denitrification in closed systems. The results indicate that denitrification occurs in a closed system even when it is considered aerobic, that is well mixed and sparged with either air, or sufficient pure O2 to cause a complete turnover in the gaseous atmosphere in the bioreactor vessel every five minutes.     

离解反应速率常数中的方位因素

以碰撞理论为基础探讨了结构方位因素对离解反应速率常数的影响,建立了计及方位特征的离解反应模型,计算对比了热平衡假设下空气中几个典型的离解反应的Arrhenius图.结果表明,在所选实例中,除了反应N₂+N和O₂+O外,考虑方位因素后确实能够更好地理论估算出反应速率常数.对上述例外文中做了一定的讨论.