冬半年青藏高原低涡发生发展的天气学分析

本文针对冬半年高原低涡几个不同源地的低涡生成背景,着重分析500hpa环流场,指出:地形对低涡生成是非常重要的条件,但一定范围内有利的环境流场也是低涡生成不可缺少的外部条件。并给出了不同涡源区有利于低涡发生,发展的500hpa环流形势。     

利用自回归模型检测地球极移重力效应

同时采用4个台站的国际超导重力仪长期连续重力观测资料和国际地球自转服务中心提供的同步地球自转参数，研究了极移引起的地球重力场变化特征。利用自回归模型估计了各序列的功率谱密度和积谱密度，结果表明极移导致的重力效应的主要能量集中在Chandler摆动和周年项附近，叠积后实际重力观测与极移重力信号理论值之间的差异分别为0．4％和3．9％，说明超导重力仪可有效监测极移导致的重力变化。     

NORTHERN AND SOUTHERN HEMISPHERIC POLAR LOWS——A COMPARATIVE STUDY

Northern Hemispheric“polar lows”,i.e.maritime,small,but fairly intense cyclonic systems have been studied formore than two decades.Recently researchers have turned their attention towards the occurrence of polar lows and othersmall-scale cyclonic disturbances on the Southern Hemisphere.In this paper a short account of our present knowledgeof Northern Hemispheric polar lows will be given,followed by some preliminary results of an investigation of the natureand occurrence of polar lows on the Southern Hemisphere.     

Gravitational collapse and equilibrium conditions of a toroidal vortex with thermal pressure

We found the equilibrium conditions for a self-gravitating toroidal vortex by taking thermal pressure into account. These conditions are shown to significantly differ from those for a disk or a sphere. The evolution of a thin vortex turns it into a compact vortex that loses mechanical stability for low masses at a polytropic index γ<4/3 but retains stability for sufficiently high masses and densities determined by the velocity circulation in the vortex.     

Diffuse radiation,twilight, and photochemistry — I

A photochemical scheme which includes a detailed treatment of multiple scattering up to solar zenith angles of 96° (developed for use in a GCM) has been used to study partitioning within chemical families. Attention is drawn to the different zenith angle dependence of diffuse radiation for the two spectral regions <310 nm and >310 nm. The effect that this has on the so-called 40 km ozone problem is discussed. The importance of correctly including multiple scattering for polar ozone studies is emphasised.     

抑制栉孔扇贝第一极体对受精卵染色体行为及胚胎倍性组成的影响

采用细胞松弛素B（CB）处理，栉孔扇贝（Chlamys ferreri）抑制其受精卵的第一极体（PB1），研究抑制PB1对受精卵减数分裂过程及胚胎倍性组成的影响。结果发现，抑制第一极体显著改变了受精卵的染色体行为，在第二次减数分裂过程中共发现4种典型染色体分离类型，分别是三极分离（41．7％）、二极分离（11．7％）、双二极分离（24．9％）和非同步分离（2．8％），其余的受精卵（19．0％）染色体分离行为紊乱。对4-8细胞期胚胎的倍性组成进行分析，发现处理组中含有二倍体（10．9％）、三倍体（12．5％）、四倍体（19.5％）、五倍体（12．6％）以及非整倍体（46．6％）胚胎。研究结果表明，二极分离和双二极分离分别是形成三倍体和四倍体的主要机制，而其他的染色体分离行为将主要形成非整倍体。     

不等电极距情况下高密度电阻率法的反演结果分析

通过高密度电阻率法的模型实验,得出不等电极距情况对直立高阻薄板和低阻球体反演结果的影响:缺失电极对它正下方的ρ_s影响最大,而异常形态主要在水平方向有明显的变化,异常体随电极缺失的位置有趋势变化,电极缺失的数目越多,异常形态变化越大,但是从整体来看反演剖面图基本相似。     

Absolute velocity of North America during the Mesozoic from paleomagnetic data

We use paleomagnetic data to map Mesozoic absolute motion of North America, using paleomagnetic Euler poles (PEP). First, we address two important questions: (1) How much clockwise rotation has been experienced by crustal blocks within and adjacent to the Colorado Plateau? (2) Why is there disagreement between the apparent polar wander (APW) path constructed using poles from southwestern North America and the alternative path based on poles from eastern North America? Regarding (1), a 10.5° clockwise rotation of the Colorado Plateau about a pole located near 35°N, 102°W seems to fit the evidence best. Regarding (2), it appears that some rock units from the Appalachian region retain a hard overprint acquired during the mid-Cretaceous, when the geomagnetic field had constant normal polarity and APW was negligible.We found three well-defined small-circle APW tracks: 245–200 Ma (PEP at 39.2°N, 245.2°E, R=81.1°, root mean square error (RMS)=1.82°), 200–160 Ma (38.5°N, 270.1°E, R=80.4°, RMS=1.06°), 160 to 125 Ma (45.1°N, 48.5°E, R=60.7°, RMS=1.84°). Intersections of these tracks (the “cusps” of Gordon et al. [Tectonics 3 (1984) 499]) are located at 59.6°N, 69.5°E (the 200 Ma or “J1” cusp) and 48.9°N, 144.0°E (the 160 Ma or “J2” cusp). At these times, the absolute velocity of North America appears to have changed abruptly.North America absolute motion also changed abruptly at the beginning and end of the Cretaceous APW stillstand, currently dated at about 125 and 88 Ma (J. Geophys. Res. 97 (1992b) 19651). During this interval, the APW path degenerates into a single point, implying rotation about an Euler pole coincident with the spin axis.Using our PEP and cusp locations, we calculate the absolute motion of seven points on the North American continent. Our intention is to provide a chronological framework for the analysis of Mesozoic tectonics. Clearly, if APW is caused by plate motion, abrupt changes in absolute motion should correlate with major tectonic events. This follows because large accelerations reflect important changes in the balance of forces acting on the plate, the most important of which are edge effects (subduction, terrane accretion, etc.). Some tectonic interpretations: (1) The J1 cusp may be associated with the inception of rifting of North America away from land masses to the east; the J2 cusp seems to mark the beginning of rapid spreading in the North Atlantic. (2) The J2 cusp signals the beginning of a period of rapid northwestward absolute motion of western North America; motion of tectonostratigraphic terranes in the westernmost Cordillera seems likely to have been directed toward the south during this interval. (3) The interval 88 to 80 Ma saw a rapid decrease in the paleolatitude of North America; unless this represents a period of true polar wander, terrane motion during this time should have been relatively northward.