1981～2010年北京地区极端降水变化特征

采用北京地区20个常规气象站1981~2010年逐日降水数据,对北京地区极端降水的空间分布特征进行了分析。得到以下主要结论:1981~2010年,北京地区极端降水百分位数(第90、95和99个百分位数)阈值表现出较一致的空间分布特征,以第95个百分位数阈值计算的极端降水日数与降水阈值和降水量的分布有较大差异,极端降水量对总降水量的贡献可达30%~37%,极端降水强度分布与极端降水阈值分布相似。近30年,北京地区多数站点的极端降水量、降水日数和降水强度呈下降趋势,极端降水量以上甸子、怀柔、平谷和观象台下降较为明显,可达到40 mm(10 a)–1以上,极端降水强度以顺义、海淀、观象台、大兴和上甸子等站下降较为显著,每10 a降水强度减小趋势可达4 mm d–1,极端降水日数变化分布与极端降水量变化分布类似,极端降水强度变化与降水量和降水日数变化的分布有明显不同。     

STUDY ON DYNAMICS OF TROPICAL CISK-ROSSBY WAVES AND MECHANISM OF 30-50 DAY OSCILLATIONS

To add to the growing mature research on the tropical 30-50 day oscillations from a new prospective, the current work bases on dynamic analysis of baroclinic quasi-geostrophic models to discuss dynamic mechanisms for the generation and propagation of CISK-Rossby waves, and to understand restraints and effects of different wave structures and thermodynamic forcing on the 30-50 day oscillations in the tropical atmosphere. Some important properties of the oscillation propagation have been explained and, in detail, with respect to its meridional propagation and vertical “baroclinic” structure. The work has come up with some new opinions and viewpoints. New opinions about the propagation and energy dispersion are to be proved by more observations and study.     

Aspects Of Ring Lasers As Local Earth Rotation Sensors

Ring laser rotation sensors are best known from inertial navigation, wherethey have many advantages over mechanical gyroscopes. They have recentlybeen greatly improved, and show potential as fully independent length-of-daysensors. We discuss some important aspects of current limitations in theirperformance. In particular we demonstrate a novel scheme for thestabilisation of a large ring laser against frequency pulling effectsinduced by backscatter.     

磁暴对辽宁地区核旋总强度通化值的影响及提高通化精度的方法

通过不同K指数的磁暴对辽宁省磁测点总强度通化值的影响,发现在8个地磁测点,不但干扰幅度不一洋,而且以沈阳台为基准点做的通化值不能完全消除外空场的干扰。磁静日通化值一般不超过1.6nT,而磁暴日通化值可达4.0nT左右。不论磁静日或磁暴日,标准偏差随通化台距离增加而增加,通过加权和五天磁静日方法可提高通化值的精度。     

用单台Z／H法研究陕西地区深部电导率

利用陕西地磁台站的磁静日资料和单台Ｚ／Ｈ磁测深法研究了陕西地区深部电导率状况。多年和多台的平均结果为：陕西地区电磁感应比例尺度Ｃｒ１约９００ｋｍ，高于磁场梯度法测定的华北地区结果，但接近单台Ｚ／Ｈ法测定的兰州地区值；Ｃｒ２为５００ｋｍ，和华北地区的结果接近；Ｃｉ－Ｔ曲线高于华北地区值；内外场之比｜Ｑ１｜、｜Ｑ２｜、｜Ｑ３｜约为０．４，和全球平均结果一致；σ＊－ｈ１曲线显示在２５０ｋｍ附近有一高电导层。     

Comparison of length of day with oceanic and atmospheric angular momentum series

This is a companion paper to earlier comparisons and study of operational polar motion series, published recently in the same journal. In this contribution, four operational, publicly available, length-of-day (LOD) time series have been compared to the atmospheric angular momentum (AAM) augmented with recent oceanic angular momentum (OAM) data during September 1997–July 2000, using several intervals ranging from 3 days to almost 3 years. Additionally, the LOD of the International GNSS Service (IGS) historical series and a new LOD combination (CMB) were also analyzed. All the six LOD series showed an overall correlation exceeding 0.99 for the complete interval of almost 3 years. Even for the shortest interval of only 3 days, the correlation was still higher than 0.60. The combined AAM + OAM series with inverted barometer corrections always gave the best correlation. The Rapid Service LOD of the International Earth Rotation and Reference Systems Service (IERS) compared the best at all intervals but the shortest one, where the CMB LOD was the best with a correlation of 0.73, followed by both IGS series with a correlation of about 0.71. Prior to all the correlation analyses, in addition to the removal of all the known (conventional) LOD tidal variations with periods ranging from 5.6 days to 18.6 years and lunar fortnightly and monthly oceanic tides, small corrections of lunar fortnightly and monthly tides, semi-annual, annual periodical signals, drift and scale had to be estimated with respect to the combined AAM + OAM series.     

A model for solar quiet day variation at low latitude from past observations using singular spectrum analysis

Singular spectrum isolates significant principal components in a time series from the embedded noise. This tool-kit is used to reconstruct trend-free individual time series, formed by restricting the mean monthly hourly values of geomagnetic field to one hour at a time at a low latitude station Alibag (dipole latitude 9.5°N). Each reconstructed component is extrapolated over the next 12 values using an autoregressive model based on Burg’s maximum entropy algorithm. Details of a numerical approach to increase the reliability of extrapolation are highlighted. The extrapolated reconstructed components are then combined to generate predicted monthly values for each hour. The mean diurnal variation for any month obtained from the extrapolated individual hourly time series compares favorably with the observations. This approach to Sq(H) modelling incorporating both long and short term variations will be beneficial in the derivation of Dst index.     

南极中山站极夜、极昼期间S_q~p、S_D的变化规律及特征

本文利用１９９１年度南极中山站的地磁资料，分析研究极夜（５、６、７月）及极昼（１１、１２月）期间Ｓ、ＳＤ的变化特征。研究结果表明，Ｈ、Ｄ、Ｚ三个分量的Ｓ、ＳＤ在极夜期间的变化幅度都小于极昼期间的变化幅度，Ｓ在世界时ＵＴ６时左右出现极值。这是由于在５、６、７月的太阳直射点在北半球，太阳紫外辐射和Ｘ射线辐射减少，在１１、１２月太阳的直射点在南半球，太阳紫外线和Ｘ射线辐射增大，致使空间电高层等效电流发生变化所产生。