Some results of night-time scintillations at low latitude

Ionospheric scintillation observations of VHF radio signals from FLEETSAT satellite (73°E longitude) at Bhopal from January 1990 to December 1990 have been used to study the characteristic variations of scintillation activity. It is found that scintillation occurrence is essentially a night-time phenomenon and day-time scintillations are very rare. Annual average nocturnal variation of percentage occurrence of scintillations shows maximum at around 2100–2200 hours LT. Seasonally, scintillations are most prominent during equinoxes and least during summer. Geomagnetic disturbances tend to decrease the occurrence of scintillations in the pre-midnight period.     

Simulation of flow over pool-riffle topography: A consideration of the velocity reversal hypothesis

Computer flow simulations using the HEC-2 step-backwater routine are used to demonstrate the effect of systematically varying river channel width, riffle spacing and channel roughness on the shear velocity, section-mean velocity and energy slope in fixed-bed pool-riffle sequences. Initial scaling is obtained by utilizing published information on hydraulic parameters within reaches of the River Severn. Subsequently this restriction is relaxed and the effect of varying parameter combinations within realistic limits is explored. The purpose of this exercise is to isolate those scenarios which may preclude or promote the occurrence of a competence ‘reversal’, such that pools scour at high flow whilst deposition occurs on riffles. It is concluded that rivers in which pools are hydraulically rougher than riffles are likely to demonstrate a competence reversal. For prescribed conditions, the critical discharge at which a reversal occurs is a negative function of riffle spacing and riffle width relative to pool width. Downstream variation in hydraulic roughness also has implications for the phase relationship of shear velocity maxima and minima in relation to the extremes in pool-riffle topography.     

Observations of geomagnetic pulsations and variations with a new borehole magnetometer down to depths of 3000 m

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A triaxial magnetometer has been developed for investigating the in situ skin effect of horizontal geomagnetic pulsations and variations in deep boreholes. The observations were carried out in the pilot borehole of the Continental Deep Drilling Program of Germany (KTB) down to depths of 3000 m and up to temperature of 90 C. A weak skin effect, due to the known very low conductivity of the penetrated crystalline rocks, of 90 to 95 per cent in amplitude and -5 to -10 rotation in phase has been observed at periods of 10 s and magnetometer depth of 2400 m.
An essential prerequisite for all calculations is the accurate determination of the orientation of the downhole magnetometer. It is demonstrated how oriented record samples of temporal variations at depth correlate precisely with those from the surface.
Results from surface magnetotelluric (MT) investigations show strong local distortions of the telluric field. The distortion of the MT tensor response has been determined by means of newly introduced skin-effect transfer functions, which are assumed to be undistorted.     

大震前地磁场时空间线性度变化的初步研究

把用来分析地震波波形的时间线性度和空间线性度两种方法，应用到地磁资料分析当中，具体分析处理了１９７６年７月２８日唐山Ｍｓ７．８地震和１９８９年１０月１９日大同Ｍｓ６．１地震前后地磁场资料，并对这两次地震前后地磁时空线性度变化情况进行了研究。所得结果表明：①较大地震前地磁场的时空线性度均可能呈现出较明显的下降异常变化，有些在震前回升，②各分量的时空线性度呈现异常的时间基本上同步，并与波速异常发展趋势基本相符。     

用第六代国际地磁参考场确定的东亚地磁非偶极场时空变化规律

利用近期公布的第六代国际地磁参考场（ＩＧＲＦ）计算，分析了１９４５年以来东亚地磁非偶极场的时空变化特征，并用中国地磁场模型对结果进行了检验，得到的主要结果是：１９４５－１９９０年，东亚地磁非偶极场Ｘ、Ｙ分量缓慢向北和向西方向移动，东亚磁异常中心位置基本稳定，中心附近Ｚ分量的强度变化具有明显的大约１５年左右的增强和减弱期。中心附近Ｘ、Ｙ的零值点的移动方向与地磁北极的移动方向一致。     

华北地台南缘燕山期板内花岗斑岩类地球化学特征及成分空间变化规律

华北地台南缘燕山期花岗斑岩类小岩体形成于大陆板内环境,它具有类似岛弧—活动大陆边缘钙碱系列岩石地球化学特征,其成分在空间上呈现极性特征。本文探讨了这种成分极性与中、新生代俯冲带花岗岩类的可比性,并根据锶、钕同位素资料揭示成岩物质的可能来源及造成成分空间变化的可能原因。     

第四纪时期地壳块体相对运动的古地磁记录的初步研究─-以陇西和鄂尔多斯块体相对运动为例

为了探讨用古地磁方法确定第四纪时期地壳块体相对运动状况，选择了分别处于陇西块体和鄂尔多斯块体内的兰州九州台和陕西洛川两个黄土剖面作为实验对象。在这两个黄土剖面的４个相同年代的层位采集定向大样，作黄土沉积剩余磁化矢量测量，并用虚磁极法拟合，初步结果表明，约１１０万ａ来陇西块体相对于鄂尔多斯块体作顺时针旋转，其转动量达９．０±４．７°     

关于地震台站极性校正的问题

国内外的台网中总是一些台站，其极性读取似乎是由大量台站Ｐ波初动的整体分布确定的震源机制相矛盾，这些矛盾通常被作为坏读（ｂａｄ ｒｅａｄｉｎｇ）处理，造成台站的极性问题的复杂原因究竟是什么，利用ＮＥＩＣ的核爆资料，文中给出两种可能推测：台站仪器本身的不可和地震本身的复杂性。