南海夏季风与登陆我国大陆初旋的关系

利用1948---2009年南海夏季风指数、NCEP/NCAR月平均再分析位势高度场、风场资料, 首次分析了南海夏季风与每年登陆中国大陆的首个热带气旋(初旋)的关系. 结果表明: 初旋的登陆日、登陆纬度、生成纬度与当年登陆中国大陆热带气旋的频数、活动期、强度等相关性较好; 强(弱)南海夏季风指数年份, 登陆大陆热带气旋数偏多(少)、初旋登陆日偏迟(早)、初旋登陆点偏南(北). 从流场上看, 强(弱)南海夏季风指数年份, 对应的季风槽偏强(弱), 其异常风场和初旋路径也截然不同. 从年际变化上看, 南海夏季风指数明显呈减弱趋势, 而初旋登陆点则有一定北移.     

中层大气静力稳定性减弱趋势——历史火箭探空数据分析

大气静力稳定性参数Brunt-Vaisala频率反映了以温度垂直梯度为代表的大气整体结构的特征. 全球增暖背景下, 学术界对中层大气静力稳定性的响应形式还相当缺乏了解. 利用历史火箭探空资料, 考察了1962–1991年期间从赤道到北半球中纬度地区中层大气静力稳定性(Brunt-Vaisala频率的平方, N²)的长期趋势. 结果表明, 对于选取的6个典型站点, 在平流 层上部到中间层中部区域(48–60 km), 所有站点大气静力稳定性一致呈现显著减弱的长期趋势. 48–60 km整层平均N²长期趋势统计结果表明, 在两个热带站点, N²长期趋势一致, 每十年减小0.11×10^-4 s^-2; 随着纬度增加, 在从22°N (Barking Sand 站)向38°N (Wallops Island 站)过渡的区间内, N²趋势从-0.16×10^-4 s^-2/decade增强到-0.22×10^-4 s^-2/decade.     

涡旋轴对称化的分形维数表征

涡旋轴对称化是影响热带气旋预报的重要动力学过程．截止目前的研究,均用等值线图形主观识别涡旋轴对称化．本文用一个准地转无幅散的正压涡度方程模式,数值积分48h,模拟了初始非轴对称涡旋演变为轴对称涡旋的轴对称化过程．根据模式输出数据,计算了逐时涡旋外缘线的分形维数DB,用分形维数DB的逐时变化客观表征涡旋轴对称化．在此基础上,计算了分形维数De与热带气旋尺度参数R。和热带气旋强度参数Vmax的相关系数．结果显示,DB与Rm的相关系数为-0．70,DB与Kmax的相关系数为-0．75,相关均显著．用此途径,客观表征了涡旋轴对称化与热带气旋参数的联系．结果在热带气旋预报中有应用前景．     

宽视场大相对孔径星敏感器光学系统设计

介绍了一种用于卫星姿态控制的星敏感器光学系统,该光学系统焦距为51 mm,相对孔径为1/1.1,视场角为21°×21°（圆视场2ω＝30°）,光谱范围为0.5～0.85 μm,采用了复杂化双高斯结构.与普通成像系统不同的是,该系统要求对不同光谱的恒星所采集到的点像能量中心是一致的,且星像点像的弥散圆须控制在一定的范围内.具有倍率色差小、轴上和轴外能量分布比较一致的特点.     

基于COSMIC掩星资料的全球第二对流层顶详细特征

使用2006年12月–2008年11月COSMIC (constellation observing system for meteorology, ionosphere and climate)掩星湿廓线资料对第二对流层顶的全球分布特征进行统计, 对比三个站点的无线电探空仪和COSMIC的对流层顶资料, 研究结果表明: 1) 第二对流层顶的出现频率在副热带急流区较高,冬季在北半球为50%–70%, 在南半球为20%–40%; 2) 赤道带的第二对流层顶出现频率约为20%–26%, 与越赤道急流和对流层顶上的毛卷云有关; 3) 在副热带急流区, 第一对流层顶的温度基本高于第二对流层顶; 4) 在热带, 对流层顶厚度和第二对流层顶出现频率随纬度减小; 热带以外, 对流层顶厚度随纬度增加, 在冬半球60^o有最大值7–8 km; 5) 单站点对流层顶的日变化剧烈程度与COSMIC和探空仪的对流层顶高度偏差正相关．     

基于飞秒激光微加工的介质膜损伤修复研究

针对波长1053 nm, 0°高反介质膜元件, 采用有限时域差分法, 模拟分析了损伤修复点边缘与法线的夹角对膜层内电场强度分布的影响, 该角度越小, 修复点的损伤阈值越高. 通过优化飞秒激光微加工过程中的焦斑尺寸、脉冲能量、扫描步长和扫描次数等参数, 获得了夹角为25°、深度为14 μm的修复点. 该修复点典型的损伤阈值为21 J/cm², 是修复前的2.3倍, 50个修复点的测试结果表明该修复参数具有非常好的可重复性. 修复点的测试结果还验证了修复点边缘与法线的夹角大小与其损伤阈值的关系, 45°的电场强度最大值约为25°的2.5倍, 而45°的损伤阈值约为25°的1/2, 模拟和实验结果一致性较好. 同时, 实验验证了微加工的激光脉宽对修复点损伤阈值的影响, 在只改变脉宽的情况下, 脉宽越长, 损伤阈值越低.     

导电突扩管中磁流体管流的数值模拟

采用基于OpenFOAM环境自主开发的低磁雷诺数磁流体求解器,对45°和90°突扩矩形管中液态金属流体在受到垂直流向的外加磁场作用时的速度、感应电流、压力的分布及突扩位置处的MHD三维现象进行数值模拟.结果表明：磁场沿突扩方向时,由于无回流涡,45°比90°突扩管在肩部位置速度分布更优.哈特曼数增大,强射流和突扩结构,在突扩肩部位置引发流动的不稳定性.伴随感应电流的不稳定,流动不稳定发展到突扩位置上游.磁场沿垂直突扩方向时感应电流的三维效应显著.哈特曼数增大,MHD压降显著增大.同方向磁场和相同哈特曼数,不同突扩角度的三维无量纲压力梯度无明显差异.     

X波段微带余割平方扩展波束天线阵赋形优化遗传算法研究

提出了一种改进型自适应遗传算法, 该算法用logistic函数拟合交叉概率和变异概率, 以赌轮盘选择和精英保留相结合的方式, 在全局寻找最优解. 与经典遗传算法相比, 改进型自适应遗传算法可以大大提高算法的求解质量. 本文基于改进的自适应遗传算法研究设计了-3 dB范围为0°-12°, -10 dB波束宽度为65°, 波束覆盖为65°, 天线频带范围为8.5-9.8 GHz, 中心频率为9.05 GHz的X波段微带余割平方扩展波束天线阵. 研究结果表明改进型自适应遗传算法对方向图的拟合程度具有较大提高, 适应度值可以从0.07以下提升到0.09以上.     

入口段协同式翅片强化单相对流换热数值模拟

对二维平行平板通道入口段内设置协同式折流翅片的层流换热和流动特性进行了数值模拟。研究了翅片倾角以及通道长高比L／H对换热和阻力特性的影响。研究的Re数范围为100-1000。在翅片倾角β=0°-21.8°范围内, 通道内平均Nu数随翅片倾角β的增大而单调增大,随通道长度增大而单调减小。如果从相同泵功下强化效果来评价, 则是小倾角翅片较优,并且随Re数增大强化效果减弱。另外,分析表明,场的协同确实与换热率密切相关。     

载能Ni原子斜入射Pt(111)表面的分子动力学模拟

采用嵌入原子方法的原子间相互作用势,利用分子动力学模拟,详细研究不同角度入射的载能Ni原子在Pt(111)基体表面的沉积过程.结果表明,随着入射角度θ从0°增加到80°,溅射产额、表面吸附原子产额、空位产额的变化情况均可按入射角度近似地分为θ≤20°,20° < θ < 60°和θ≥60°三个区域.当θ≤20°时,载能沉积对基体表面的影响与垂直入射时的情况类似,表面吸附原子的分布较为集中,入射原子容易达到基体表面第二层及以下,对基体内部晶格产生-定的影响;在20° < θ < 60°的范围内,入射原子的注入深度有所下降,对基体内部晶格的影响减小,表面吸附原子的分布较为均匀,有利于薄膜的均匀成核与层状生长;当θ≥60°时,所有入射原子均直接被基体表面反射,表面吸附原子产额、溅射产额、表面空位产额均接近0,载能沉积作用没有体现.     

Diurnal and seasonal variations in h’F and foF2 over low (Indian) and mid (Japanese) latitude stations — a comparative study

Using the simultaneous data of ionosonde from a low latitude station, Waltair, India (17.7°N,83.3°E) in the Indian sector and a mid latitude station, Kokubunji, Japan (35.7°N,139.5°E) in the Japanese sector during the high sunspot year of 2001, a comparative study of the variations in the diurnal, seasonal and day to day characteristics of the ionospheric F-region parameters, such as the virtual height of the F-layer (h’F) and the critical frequency of the F₂ layer (foF2), are studied. The effect of geomagnetic activity variations of the F-region parameters over the low and mid latitude stations is also presented.     

Comparison of the variations in the intensity of global electromagnetic resonance and ground surface temperature

We compare the dynamics of the intensity of the global electromagnetic (Schumann) resonance monitored in Japan with the global ground surface temperature (GST) over the period from November 1998 to May 2002. It is shown that the Schumann resonance (SR) intensity varies coherently with the ground surface temperature at mid-latitudes: the relevant cross-correlation coefficient exceeds 0.8. The linear correlation of data decreases with a decreasing latitude interval. We applied the principal component analysis (PCA) to distinguish inter-annual trends (anomalies) in the records from the periodic annual and semi-annual variations. The annual component of the SR intensity behaves similarly to the mid-latitude GST, while the inter-annual variations in the electromagnetic data are similar to those of the GST in the tropics. The regression analysis allowed us to obtain the analytical expressions relating the SR intensity with both the mid-latitude and low-latitude GST. Application of these equations allowed us to retrieve the observed SR pattern from the ground surface temperature and to “reconstruct” the variations in the tropical GST from recorded SR intensity. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 12, pp. 1035–1050, December 2008.     

热带海洋与中低纬大气相互作用的信息传输特征分析

基于传递熵概念和方法定义气象场的信息源特征度、信息汇特征度和信息传输平衡特征度.使用海表温度和高度场资料计算海气相互作用过程中的信息传递.侧重分析赤道中东太平洋(20?S-20?N,170?E-100?W)与热带地区、北半球和南半球中高纬度地区大气之间的信息传递,给出信息传递的区域和全球分布特征;并提取海表温度指数和高度场指数分析赤道中东太平洋与大气信息传递特征的季节变化和年代际变化.研究结果表明,海洋信息源主要分布在热带地区,大气信息汇主要分布在中纬度地区,从热带地区到中纬度地区,海洋对大气的强迫作用在减弱,而大气对海洋的强迫作用在增强;不同区域不同层次的高度场对赤道中东太平洋海表温度有着不同的响应,热带中东太平洋上空高度场最大延迟为4个月.欧亚大陆中部上空和北美大陆上空高度场均随时间延迟呈现波动性变化:欧亚大陆中部上空高度场随时间延迟呈现增强的趋势,而北美大陆上空高度场随时间延迟呈现减弱的趋势.海表温度指数对热带中东太平洋上空850 hPa和欧亚大陆中部上空500 hPa高度场指数的传递熵以2000 s最弱,而海表温度指数对北美大陆上空700 hPa高度场指数的传递熵以2000 s最强.表明不同年代际背景下不同区域大气对赤道中东太平洋海表温度异常的响应是不同的.然而不同季节的响应却十分相似:冬季最强,秋季次之,春季再次,夏季最弱.     

Characteristics of nighttime VLF/ELF emissions with frequency drift and estimation of the large-scale electric field from the frequency drift observed at a low latitude Indian ground station, Jammu

Characteristics of nighttime VLF/ELF emissions are examined on the basis of the data obtained at our low latitude ground station Jammu (geomagnetic latitude, 22°26′ N; L = 1.17), India during our VLF/ELF campaign. From the detailed analysis of a huge amount of acquired VLF/ELF data at Jammu we have found three remarkable events which clearly exhibit a rise in their frequency in pre and past midnight sectors during magnetically quiet and substorm periods. Our analysis shows that the frequency drift in VLF/ELF emissions seems to be a rare phenomenon at low latitudes during magnetically quiet and substorm periods in pre and post midnight sectors. This property of temporal frequency drift (regular frequency increases with time) in VLF/ELF emissions observed at our station Jammu are interpreted in terms of a quasi-linear electron cyclotron instability model for wave excitation. The initial frequency increase is believed to be due to a combind effect of L-shell drift of energetic electrons. Further, the frequency drifts in VLF/ELF emissions observed at Jammu have been used to estimate the large scale electric field during quiet and substorm periods in pre and post midnight sectors. This investigation would be most useful for the study of the wave-particle interaction processes, magnetospheric plasma structure and particle dynamics, especially during quiet periods in premidnight sector at low latitudes.     

Cloud Morphology Over Three Indian Tropical Stations for Earth Space Communication

Microwave and millimeter wave frequency bands are in demand for requirement of larger bandwidth for various applications of radio systems. In future in India too, microwave and millimeter wave frequencies will be in use very extensively for radio communication purposes and remote sensing applications. But, the attenuation due to cloud as well as thermal noise associated with could in millimeter wave and microwave frequency bands are of great concern to system engineers and radio researchers. Both cloud attenuation and cloud noise temperature lead to degradation in the performance of microwave communication and radar propagation. The effects of rain on radio wave are more than cloud but the occurrence of cloud is more than rain. In some parts of India cloud occurs for weeks together. The cloud morphology particularly in relation to radio wave propagation over different geographical region of India is therefore very essential and important. In view of this, systematic studies on cloud occurrence morphology over different geographical locations in India have been undertaken. In recent past some results on cloud occurrences over different stations in India have been reported. In this paper, cloud characteristics and cloud attenuation over three more stations are presented. Based on low level cloud coverage observations, cloud occurrences frequency over Mumbai (19.07°N, 72.50°E), Nagpur (21.06°N, 79.03°E) and Ahmadabad (23.04°N, 72.38°E) situated in Indian tropical west coast, central plain and semi arid region of western India in different months during daytime and nighttime has been deduced. The low-level cloud over Mumbai, Nagpur and Ahamedabad has been found to occur for many days and nights and particularly in the months of June, July, August and September. The attenuation of radio wave due to clouds at various frequencies ∼10, 18, 32, 44 and 70 GHz over the aforesaid three stations also been deduced.     

Some results of measurement of atmospheric temperature and density using artificial periodic inhomogeneities of the ionospheric plasma

We present the preliminary results of measurement of atmospheric temperature and density at the E-region heights near Nizhny Novgorod in the 1990–1991 period (λ=56.15°N, ϕ=44.3°E). The monthly mean temperature and density are given in the height interval 100–110 km for September and October 1990. The temporal variations of temperature and density, associated with the propagation of acoustic-gravity and internal waves, are presented. The influence of natural turbulence on the measurement accuracy has been analyzed. The method is based on the generation of artificial periodic inhomogeneities (APIs) by a powerful radio wave and registration of the amplitudes of pulse probe radio waves backscattered by APIs. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 3, pp. 348–357, March, 1998.     

Recent atomic clock comparisons at NIST

The record of atomic clock frequency comparisons at NIST over the past half-decade provides one of the tightest constraints of any present-day temporal variations of the fundamental constants. Notably, the 6-year record of increasingly precise measurements of the absolute frequency of the Hg⁺ single-ion optical clock (using the cesium primary frequency standard NIST-F1) constrains the temporal variation of the fine structure constant α to less than 2 · 10⁻⁶yr⁻¹ and offers a Local Position Invariance test in the framework of General Relativity. The most recent measurement of the frequency ratio of the Al⁺ and Hg⁺ optical clocks is reported with a fractional frequency uncertainty of ±5.2 · 10⁻¹⁷. The record of such measurements over the last year sensitively tests for a temporal variation of α and constrains , consistent with zero.     

Effect of cloud on atmospheric ozone formation over Kolkata (22°34′N, 88°24′E), India

The paper presents the nature of variations of clouds and total ozone over Kolkata (22°34′N, 88°24′E), India. The low-level cloud over Kolkata has been noticed to occur for many days and nights, particularly in the months from June to September. The low level cloud occurrences were minimum in winter months. The effect of cloud occurrence on ozone concentration has been critically analyzed and explained. It has been observed that the concentration of ozone increased with the increase of cloud occurrence. The related possible chemical explanation for ozone production processes has been offered.     

Trend of extreme precipitation events over China in last 40 years

Using the daily precipitation data of 740 stations in China from 1960 to 2000, the analysis on the variations and distributions of the frequency and the percentage of extreme precipitation to the annual rainfall have been performed in this paper. Results indicate that the percentage of heavy rains （above 25mm/day） in the annual rainfall has increased, while on average the day number of heavy rains has slightly reduced during the past 40 years. In the end of 1970s and the beginning of 1980s, both the number of days with extreme precipitation and the percentage of extreme precipitation abruptly changed over China, especially in the northern China. By moving t test, the abrupt change year of extreme precipitation for each station and its spatial distribution over the whole country are also obtained. The abrupt change years concentrated in 1978-1982 for most regions of northern China while occurred at various stations in southern China in greatly different/diverse years. Besides the abrupt change years of extreme precipitation at part stations of Northwest China happened about 5 years later in comparison with that of the country＇s average.