GGM02 – An improved Earth gravity field model from GRACE

A new generation of Earth gravity field models called GGM02 are derived using approximately 14 months of data spanning from April 2002 to December 2003 from the Gravity Recovery And Climate Experiment (GRACE). Relative to the preceding generation, GGM01, there have been improvements to the data products, the gravity estimation methods and the background models. Based on the calibrated covariances, GGM02 (both the GRACE-only model GGM02S and the combination model GGM02C) represents an improvement greater than a factor of two over the previous GGM01 models. Error estimates indicate a cumulative error less than 1 cm geoid height to spherical harmonic degree 70, which can be said to have met the GRACE minimum mission goals. Electronic Supplementary Material Supplementary material is available in the online version of this article at     

冻土器的快速修复及改进

冻土器观测是地面气象观测项目之一.虽经多年使用,但至今仍没有改进.各站在冬季的观测使用中,最普遍出现的故障是内管中的铁链中断,中断后的链子堆积在冰柱上端而无法确定冻土刻度.冰柱稍短时,由于铁链堆积重量大造成冰柱整体下滑,出现记录失真.因此,发现铁链中断时,要及时修复.下面介绍快速修复冻土器的方法及改进措施.     

施放氢气球时存在的安全隐患及防范措施

针对采用球服务中的安全隐患，提出有效的防范措施，对开展此项工作的同志有很好的借鉴意义。     

一类广义Hamilton系统的辛格式

通过引人泊松括号，分析了无限维Hamilton的性质，并将其推广到广义Hamilton系统，且从理论和实用角度讨论了这类广义Hamilton系统的辛格式构造问题，从而为辛几何算法在一般的时间发展方程的数值求解提供新的具体途径。     

A mechanism for decadal changes of ENSO behavior: roles of background wind changes

This study explains why a number of El Nino properties (period, amplitude, structure, and propagation) have changed in a coherent manner since the late 1970s and why these changes had almost concurred with the Pacific decadal climate shift. Evidence is presented to show that from the pre-shift (1961-1975) to the post-shift (1981-1995) epoch, significant changes in the tropical Pacific are found in the surface winds and temperature, whereas changes in the thermocline are uncertain. Numerical experiments with the Cane and Zebiak model demonstrate that the decadal changes in the surface winds qualitatively reproduce the observed coherent changes in El Nino properties. The fundamental factor that altered the model's El Nino is the decadal changes of the background equatorial winds and associated upwelling. The annual cycle is also necessary for the mean state to modulate El Nino. From the pre- to post-shift epoch, the changes in the background winds and upwelling modify the structure of the coupled mode (eastward displacement of the equatorial westerly anomalies) by reallocating anomalous atmospheric heating and SST gradient along the equator. This structural change amplifies the ENSO cycle and prolongs the oscillation period by enhancing the coupled instability and delaying transitions from a warm to a cold state or vice versa. The changes in the mean currents and upwelling reduce the effect of the zonal temperature advection while enhance that of the vertical advection; thus, the prevailing westward propagation is replaced by eastward propagation or standing oscillation. Our results suggest a critical role of the atmospheric bridge that rapidly conveys the influences of extratropical decadal variations to the tropics, and the possibility that the Pacific climate shift might have affected El Nino properties in the late 1970s by changing the background tropical winds and the associated equatorial upwelling.     

北京北部城区 SO2和NO2浓度垂直分布特点初探

2001年1～3月在中国科学院大气物理研究所320 m铁塔10个不同高度(320、240、200、140、100、80、47、15、8 m和地面)使用无动力扩散采样器对SO2和NO2日平均总量及夜间平均浓度进行了观测.结果表明,200m以下高度SO2和NO2浓度较大.北京城区不同高度大气中SO2的浓度1月份最高.NO2浓度1月份和2月份呈现高值.不同高度SO2和NO2浓度与逆温强度有明显的正相关.     

岷江上游干扰岸坡主要表生地质灾害分布特征及成因浅析

岷江上游地处我国著名的南北向地震带的中段，因其特定的地质环境导致区内表生地质灾害极为严重。通过对岷江上游（汶川以上）河段的崩塌、滑坡、泥石流等表生地质灾害的调查研究，其分布沿岷江两岸具有明显的分段特征与河谷地貌分段基本一致，它们形成发展与特定地形地貌、易崩滑或软弱地层、特殊的构造部位、降雨等密切相关。     

Probabilistic analysis of peak response of MDOF systems with uncertain PSD function

The use of uniform hazard spectra which have the same probability of exceedance at different frequencies has been proposed for the future version of the National Building Code of Canada. Commonly used combination rules to estimate the peak responses of multi‐degree‐of‐freedom (MDOF) systems are the square root of sum of squares rule and the complete quadratic combination rule. However, the probability that the peak response of a MDOF system exceeds the one estimated by using these rules with the peak modal responses from the uniform hazard spectra cannot be inferred directly. The assessment of the probability of exceedance of the peak response of MDOF systems is presented by considering that the uncertainty in seismic excitation due to all potential earthquakes can be lumped in the power spectral density function of the ground acceleration with uncertain model parameters. This probability is evaluated based on the random vibration of linear systems and the first‐order reliability method. It is found that the under‐ or over‐estimations are less than about 5 or 10% if the modal contributions are not within 10–90% of, or not within 20–80% of, the absolute sum of the effective modal peak responses, respectively. Otherwise, severe under‐ or over‐estimation could result. Copyright © 2002 John Wiley & Sons, Ltd.     

东昆仑东段中更新世以来的成山作用及其动力转换

对东昆仑造山带东段第四纪构造及与地貌关系的分析表明，现代山盆相间的地貌格局成型于中更新世，且在中更新世以来发生了多次构造变形体制的转换。根据布青山北部查干额热格地区第四系剖面的构造、地层时代及地层与构造关系的分析表明，中更新世时期为伸展构造体制，昆仑山内部开始发生了差异隆升，布青山开始崛起。中更新世末应力体制发生急剧变化，由伸展体制转为收缩事件，又急速转为伸展构造体系，短暂的收缩事件造成了中更新世冲洪积层的褶皱，随后的伸展则导致了影响深刻的向北依次断落的阶地状正断层系统。晚更新世应力体系再度发生重大转换，伸展正断层体系被左旋走滑运动体系所代替，并一直延续至今。中更新世以来多次隆升构造变形体制的转换说明东昆仑地区的成山过程受控于多种动力背景，而非单一的挤压抬升。隆升构造变形体系的确定及其时代约束为深入刻划青藏高原东北缘隆升作用的动力过程提供了重要信息。     

离散裂隙渗流方法与裂隙化渗透介质建模

流体渗流模拟的连续介质方法通常适用于多孔地质体，并不一定适用于裂隙岩体，由于裂隙分布及其特征与孔隙差异较大。若流体渗流主要受裂隙的控制，对于一定尺寸的裂隙岩体，多孔介质假设则较难刻划裂隙岩体的渗流特征。离散裂隙渗流方法不但可直接用于模拟裂隙岩体非均质性和各向异性等渗流特征，而且可用其确定所研究的裂隙岩体典型单元体及其水力传导（渗透）张量大小。主要讨论了以下问题：（1）饱和裂隙介质中一般的离散流体渗流模拟；（2）裂隙岩体中的REV（典型单元体）及其水力传导（渗透）张量的确定；（3）利用离散裂隙网络流体渗流模型研究裂隙方向几何参数对水力传导系数和REV的影响；（4）在二维和三维离散裂隙流体渗流模型中对区域大裂隙和局部小裂隙的处理方法。调查结果显示离散裂隙流体渗流数学模型可用来评价不同尺度上的裂隙岩体的水力特征，以及裂隙方向对裂隙化岩体的水力特征有着不可忽视的影响。同时，局部小裂隙、区域大裂隙应当区别对待，以便据其所起的作用及水力特征，建立裂隙化岩体相应的流体渗流模型。