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．     

Present-Day Sea Level Change: Observations and Causes

We investigate climate-related processes causing variations of the global mean sea level on interannual to decadal time scale. We focus on thermal expansion of the oceans and continental water mass balance. We show that during the 1990s where global mean sea level change has been measured by Topex/Poseidon satellite altimetry, thermal expansion is the dominant contribution to the observed 2.5 mm/yr sea level rise. For the past decades, exchange of water between continental reservoirs and oceans had a small, but not totally negligible contribution (about 0.2 mm/yr) to sea level rise. For the last four decades, thermal contribution is estimated to about 0.5 mm/yr, with a possible accelerated rate of thermosteric rise during the 1990s. Topex/Poseidon shows an increase in mean sea level of 2.5 mm/yr over the last decade, a value about two times larger than reported by historical tide gauges. This would suggest that there has been significant acceleration of sea level rise in the recent past, possibly related to ocean warming. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

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.      

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.     

太阳活动与全球气候变化

太阳不断向地球辐射电磁波和粒子, 太阳辐射是地球气候系统最主要的能量来源. 地球气候系统对太阳活动的响应是一个复杂的过程, 包括辐射过程、动力学过程以及微观物理过程等. 根据太阳辐射的卫星观测结果和重建结果, 例举了古气候、温度、大气环流和云量等方面太阳影响气候的观测证据, 论述了太阳影响气候的三种可能机制, 即太阳总辐射变化可以影响地表温度, 并通过海-气耦合改变大气环流; 太阳紫外辐射通过调制平流层的温度和风场影响下面的对流层; 太阳通过行星际磁场调制银河宇宙线, 而银河宇宙线通过电离大气影响云量, 进而改变地球的能量收支.      

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.     

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...     

An inter-comparison of zenith tropospheric delays derived from DORIS and GPS data

Doppler Orbitography Radiopositioning Integrated by Satellite (DORIS) and Global Positioning System (GPS) techniques are similarly affected by propagation delays in the neutral atmosphere (troposphere) and hence make use of similar data processing strategies for reducing this effect. We compare Zenith Tropospheric Delays (ZTDs) estimated from 52 DORIS and GPS station pairs co-located at 35 sites over the 2005–2008 period. We find an overall systematic negative mean bias of −4 mm and a median bias of −2 mm, with a large site-to-site scatter and especially stronger biases over South America, potentially linked to remaining problems related to the South Atlantic Anomaly (SAA) in the current DORIS data processing. The standard deviation of ZTD differences is in the range 4–12 mm over the globe (8 mm on average), with larger values located in the southern hemisphere. The spatial variability of differences is consistent with previous work but remains largely unexplained. DORIS is shown to be much less sensitive to instrumental changes than GPS (only the switch from Alcatel to Starec antenna at Toulouse is detected as an offset of −4 mm in the ZTD time series). On the opposite, discontinuities and spurious annual signals are found in the GPS ZTD solutions. A discontinuity of +5 mm is found on 5 November 2006, linked to the switch from relative to absolute GPS antenna models used in the data processing. The use of modified GPS antennas (e.g. at GODE) or improved antenna models is shown to reduce the spurious annual signal (e.g. from 5 mm to 2 mm at METS). Overall, the agreement between both techniques is good, though DORIS shows a significantly larger random scatter. The high stability and good spatial and temporal coverage make DORIS a potential candidate technique for meteorology and climate studies as long as reasonable time averaging can be applied (e.g. differences are reduced from 8.6 to 2.4 mm with 5-day averages) and no real-time application is considered. This technique could be considered as a potential contributor to Global Geodetic Observing System (GGOS) for climatology.