Seasonal length-of-day changes and atmospheric angular momentum oscillations in their temporal variability

Recently, effective atmospheric-angular-momentum (AAM) functions as calculated from National Centers for Environmental Prediction (NCEP) (formerly National Meteorological Center, NMC) and National Center for Atmospheric Research (NCAR) Reanalyses have become available for the years 1958 to 1998. Concerning the wind terms, the top level in the atmosphere used here is 10 hPa. Compared with earlier NMC model versions, which incorporate wind fields up to 100 hPa since 1976 and up to 50 hPa since 1981, the reanalyses have produced improved data series over a longer period than before. The axial AAM component χ₃ is associated with changes in length of day (LOD). Motivated by better quality and continuity of the series AAM (NCEP) Reanalysis, the problem of the seasonal imbalances in the solid Earth–atmosphere axial angular momentum budget is re-examined. To assess better the estimates of the annual and semiannual oscillations in LOD and AAM and of the residual oscillations derived as difference series between LOD and AAM, the series of LOD data from three analysis centers [International Earth Rotation Service (IERS), GeoForschungZentrum Potsdam (GFZ) and Jet Propulsion Laboratory Pasadena (JPL)] and of AAM data in terms of χ₃(W), χ₃(P) and χ₃(P+IB) from four meteorological centers [NCEP, Japan Meteorological Agency (JMA), European Centre for Medium-Range Weather Forecasts (ECMWF) and the UK Meteorological Office (UKMO)] are used in this study. The main analysis steps were removing gaps, filtering out the seasonal oscillations, calculating optimal estimates of the parameters of the oscillations and calculating the difference series between the LOD and AAM systems as well as the residuals in the axial angular momentum budget in the LOD–AAM systems. The results derived as difference series between the different LOD, AAM and LOD–AAM systems show to what extent the variations reflect systematic differences and significant signals, respectively, which is important for future activities in this field. Received: 2 February 1999 / Accepted: 30 November 1999     

Secular changes of LOD associated with a growth of the inner core

From recent estimates of the age of the inner core based on the theory of thermal evolution of the core, we estimate that nowadays the growth of the inner core may perhaps contribute to the observed overall secular increase of LOD caused mainly by tidal friction (i.e., 1.72 ms per century) by a relative decrease of 2 to 7 µs per century. Another, albeit much less plausible, hypothesis is that crystallization of the inner core does not produce any change of LOD, but makes the inner core rotate differentially with respect to the outer core and mantle. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

GPS连续观测资料不同方案计算结果对比分析

本文利用GPS连续观测资料,从单天误差、重复率统计两方面对比分析了Gamit/Globk中6种不同计算方案的结果,重点分析了参考框架的选取与约束,并总结了利于形变研究和形变信息提取的数据处理方案:对小的区域网形变分析而言,定框架时不宜使用过多的测站,应该选区域网周边较稳定的点做为框架点进行GLORG计算,通过IGS轨道...     

广州市低温日的气候特点及其变化

统计了1951～2008年广州市最低气温≤5℃的低温日数,发现近58年来呈现年低温日数减少、低温终日提前、低温期缩短的趋势,年低温日数主要有2～3年和7～8年的变化周期.对低温日数异常年景冬季500 hPa环流进行合成分析发现,广州年低温日数显著偏多和偏少年份的亚欧地区冬季500 hPa高度距平场基本呈反位相分布.另外...     

1971—2008年青岛地区雷电时空分布特征

选取1971—2008年青岛地区7个地面观测站雷暴日资料和2006—2009年闪电定位系统监测资料,统计分析青岛雷暴的时空分布规律,并以某大型石化项目为例,分析了该区域地闪的分布特征。结果表明：近38 a青岛地区雷暴日空间分布自东南向西北逐渐增多,季节性分布特征明显,主要集中在7月和8月。根据闪电定位资料,借助分析软件...     

On the 60-year signal from the core

The decadal variation in the length of day and in the Earth's magnetic field is analyzed by empirical mode decomposition (EMD). The existence of a periodicity of about 60-years in the Earth's angular velocity has often been inferred and is confirmed here, with a new estimate of approximately 62 years. The existence of a similar periodicity in the geomagnetic field has been controversial. From the time series analyses presented here of the magnetic declination at 10 observatories, it is concluded that a geomagnetic periodicity of about 62?±?3 years does exist. A similar analysis of the magnetic inclination at five observatories gives a period of 58?±?5 years. The declination data from four observatories is found to correlate with the length of day signal, with a correlation coefficient of approximately 0.6.     

格尔木地磁Z分量静日变化特征与前兆异常分析

研究了格尔木地震台1996-2006年地磁模拟资料和2008-2011年的数字化资料,通过对台站磁静日低点时间、日变幅度、日变形态的分析,确认地磁z分量磁静日低点时间在地方时12时左右;日变幅月均值呈现明显的波浪式起伏变化,其年均值与太阳黑子数保持一致;地磁日变形态较为规则,有1个低点和2个高点;在前兆异常分析中,认为低点时间异常和日变形态双低点异常与周边强震具有一定的对应关系。     

预报能力评分R值的应用

许绍燮院士1973年提出的预报能力评分R值,除了用于地震预报效能评价外,还可用于判断物理量的聚集程度和关联信息评价。本文给出了3个应用实例:余震序列响应周期扫描,确定太阳风磁场优势聚集方向,余震序列与其震前太阳风磁场方位的关联性评价。     

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