对流层特大暴雨天气对电离层变化的影响

研究气象活动对电离层变化的影响．利用时序叠加方法，通过对1958-1998年期间发生在武汉的5次特大暴雨天气事件对武汉上空电离层变化的影响进行分析，发现：(1)特大暴雨能够引起低电离层，fbEs和，f0Es参量较明显地减小；(2)特大暴雨对电离层F区寻常波描迹的最低虚高h′F和电离层等效峰高hpF的参量也有一定影响，且随着雨量的增大这种影响作用也会增加；(3)特大暴雨对电离层其他参量影响甚弱或没有影响．本文认为，特大暴雨天气事件对电离层的影响主要来自于动力过程，特别是特大暴雨激发的或相伴的大气重力波、潮汐波和行星波等长周期大尺度过程的作用．     

Dissipation of magnetic fields in active galactic nuclei

A model for the emission processes causing rapid variability (less than one day) in active galactic nuclei is developed. Relativistic electron beams escape from reconnection sheets in coronae of accretion disks and excite plasma turbulence with a typical frequency , which depends on the electron number densityn (see also the contribution by R. van Oss). The finite lengths of different beams emerging from different reconnection sheets allows that the waves arecoherently scattered to frequencies ²_pe. For Lorentz factors 10³ and densities typical for disk coronaen10⁶ cm ^–3 (derived from iron line observations) one easily reaches the optical, frequency range. The time scale of the variability is then caused by the relaxation of the electron beams. Likewise, this model explains the very rapid variability in the X-ray (less than 10 minutes) by changing the parameters slightly. According to this scenario the higher the variable frequency is, the closer to the central black hole it should originate.     

转子叶片加工误差对1.5级跨声速压气机气动性能的影响

压气机叶片加工误差不可避免,将在一定程度上影响压气机的气动性能.为研究叶片加工误差对跨声速压气机气动性能的影响,以燃气轮机进口1.5级跨声速压气机为对象,通过三坐标测量跨声速转子叶片叶型数据,获得了加工误差分布特征;针对实测转子叶片,采用三维CFD数值模拟方法,研究了轮廓度、位置度和扭转角综合误差对压气机转子和级特性线...     

Statistical characterisation of spread F over South Africa

The occurrence of mid-latitude spread F (SF) over South Africa has not been extensively studied since the installation of the DPS-4 digisondes in 1996 and 2000 at Grahamstown (33.32 °S, 26.50 °E) and Madimbo (22.38 °S, 30.88 °E) respectively. This study is intended to quantify the probability of occurrence of F region disturbances associated with SF over South Africa. A study was conducted using data for 8 years (2001–2008) over Madimbo (with a time resolution of 30 min) and Grahamstown (with a variable time resolution of 15 and 30 min). In this study, SF has been classified into frequency SF (FSF), range SF (RSF) and mixed SF (MSF). The SF events were identified by manually identifying ionograms showing SF and tabulating them according to type for further statistical analysis. The results show that the diurnal pattern of SF peaks strongly between 01:00 and 02:00 local time, LT (LT = UT + 2 h), where UT is the universal time. This pattern is true for all seasons and types of SF at Madimbo and Grahamstown in 2001 and 2005, except for RSF which had peaks during autumn and spring in 2001 at Madimbo. The probability of both MSF and FSF tends to increase with decreasing solar activity, with a peak in 2005 (a moderate solar activity period). The seasonal peaks of MSF and FSF are more frequent during winter months at both Madimbo and Grahamstown. In this study, SF was evident in ∼0.03% and ∼0.06% of the available ionograms at Madimbo and Grahamstown respectively during the 8 years.     

Solar Irradiance Variability Since 1978

Since November 1978 a set of total solar irradiance (TSI) measurements from space is available, yielding a time series of more than 25 years. Presently, there are three TSI composites available, called PMOD, ACRIM and IRMB, which are all constructed from the same original data, but use different procedures to correct for sensitivity changes. The PMOD composite is the only one which also corrects the early HF data for degradation. The results from the detailed analysis of the VIRGO radiometry allow a good understanding of the effects influencing the long-term behaviour of classical radiometers in space. Thus, a re-analysis of the behaviour of HF/NIMBUS-7 and ACRIM-I/SMM was indicated. For the former the situation is complicated by the fact that there are no in-flight means to determine changes due to exposure to solar radiation by comparison with a less exposed radiometer on the same spacecraft. The geometry and optical property of the cavity of HF is, however, very similar to the PMO6-type radiometers, so the behaviour of the PMO6V radiometers on VIRGO can be used as a model. ACRIM-I had to be revised mainly due to a henceforth undetected early increase and a more detailed analysis of its degradation. The results are not only important for solar radiometry from space, but they also provide a more reliable TSI during cycle 21. The differences between the revised PMOD composite and the ACRIM and IRMB are discussed by comparison with a TSI reconstruction from Kitt-Peak magnetograms. As the PMOD composite is the only one which has reliable data for cycle 21, the behaviour of the three solar cycles can now be compared and the similarities and differences discussed.     

组合压气机中导流叶片的尾迹抖动特性

为明确多排叶栅压气机中影响静叶尾迹抖动特性的因素及机理,探索调制静叶尾迹抖动周期和幅值的方法,采用数值方法对设计流量为1.12kg/s,转速为60000r/min的一级轴流和离心叶轮组成的组合压气机的非定常流场进行模拟.结果表明:静叶尾迹抖动除受几何因素影响外,还受上下游转子干涉影响,且上下游转子叶片通过频率的异同将影响静叶尾迹抖动的周期性.当上下游转子叶片同频通过时,改变动叶的时序位置可以调制静叶尾迹抖动幅值的大小.另外,静叶尾迹抖动幅值沿叶高方向并不相同,低叶高处静叶尾迹抖动幅值明显大于中、高叶高处静叶尾迹抖动幅值.      

2000年和2001年52°N地区OI5577气辉强度与原子氧浓度峰值的时间变化特征

分析了2000年和2001年期间52°N地区OI5577气辉强度的夜间变化特征和季节变化特征．利用由 OI5577气辉强度反演原子氧浓度峰值的方法反演出原子氧浓度的峰值,分析了峰值的夜间变化特征和季节变化特征．结果表明, OI5577气辉强度的夜间变化特征随季节变化, 2000年春季的夜间强度最大值出现在0000LT 之后,夏季和秋季的出现在0000LT之前,冬季的出现在0000LT,2001年春季和秋季的夜间强度最大值出现在0000LT之前,夏季和冬季的出现在0000LT;OI5577气辉强度在2000年2月份,8月份和10月份出现最大值,在2001年9月份有最大值．就主要特征而言,反演出的原子氧浓度峰值的夜间变化特征和季节变化特征分别与OI5577气辉强度的一致．     

Influence of the 27-day solar flux variations on the ionosphere parameters measured at Irkutsk in 2003–2005

We present an investigation of the influence of the 27-day solar flux variations, caused by solar rotation, on the ionosphere parameters such as the F2 layer critical frequency (foF2) and the total electron content (TEC). Our observational data were obtained with the Irkutsk Digisonde (DPS-4) located at 52.3 North and 104.3 East during the period from 2003 to 2005. In addition, we use TEC data from the Global Ionosphere Maps (GIM) based on Global Positioning System (GPS) satellites. The solar radiation flux at a wavelength of 10.7 cm (F10.7 index) is used as an index characterizing the solar activity level. A good correlation between observed ionosphere parameters and solar activity variations is found especially in autumn-to-winter season. We estimate the impact of the 27-day solar flux variations on the day-to-day variability and determine the time delay of the ionosphere response.     

Quantifying the role of solar radiative forcing over the 20th century

The 20th century temperature anomaly record is reproduced using an energy balance model, with a diffusive deep ocean. The model takes into account all the standard radiative forcings, and in addition the possibility of a non-thermal solar component. The model is parameterized and then optimized to produce the most likely values for the climate parameters and radiative forcings which reproduce the 20th century global warming. We find that the best fit is obtained with a negligible net feedback. We also show that a non-thermal solar component is necessarily present, indicating that the total solar contribution to the 20th century global warming, of ΔT_solar = 0.27 ± 0.07 °C, is much larger than can be expected from variation in the total solar irradiance alone. However, we also find that the largest contribution to the 20th century warming comes from anthropogenic sources, with ΔT_man = 0.42 ± 0.11 °C.