关于在地震预报中遇到的几个问题的探讨

地震台站工作人员 ,在进行观测资料分析、地震预报研究过程中 ,往往会遇到的几个问题 :1、手段单一 ,对于前兆现象无法全面表述。 2、如何识别异常与地震之间的关系。 3、如何兼顾点和面的关系。     

季节性冰封热融浅湖水温原位观测及其分层特征

为探究季节性冰封浅湖热力学特征,于2010年10月至2013年7月对高原腹地一典型热融湖塘冰层生消、水/冰温及气象条件开展原位观测,分析了水温分布时间变化、温跃层以及冰生消对水温结构的影响。结果发现:冰面升华显著,贯穿整个冰期;水温日变化、季节变化和垂直结构受气温、大气辐射、风速、冰生消和湖底沉积层热贡献影响显著;在"无冰期-结冰前-冰生长期-冰融化期-融化后-无冰期"年循环过程中水温垂直结构分别呈现出"分层-翻转-逆温分层-逆温与正温共存-翻转-分层"的循环过程。分层期水温结构仅由上部混合层和温跃层构成,且偶因强风搅动而全湖翻转混合。可见,相比大中型湖泊,季节性冰封浅湖热力学结构差异显著。     

Characterization of hard‐to‐differentiate dune stratification types in the Permian Coconino Sandstone (Arizona,USA)

Dune stratification types, which include grainfall, grainflow and ripple lamination, provide a record of the fine‐scale processes that deposited sediment on palaeo‐dune foresets. While these facies are relatively easy to distinguish in some cross‐bedded sandstones, for others – like the Permian Coconino Sandstone of northern and central Arizona – discrete stratification styles are hard to recognize at the bedding scale. Furthermore, few attempts have been made to classify fine‐scale processes in this sandstone, despite its renown as a classic aeolian dune deposit and Grand Canyon formation. To interpret depositional processes in the Coconino Sandstone, cross‐bed facies were characterized using a suite of sedimentary textures and structures. Bedding parameters were described at multiple scales via a combination of field and laboratory methods, including annotated outcrop photomosaics, strike and dip measurements, sandstone disaggregation and laser‐diffraction particle analysis, high‐resolution scans of thin sections, and scanning electron microscopy. Cross‐beds were observed to be laterally extensive along‐strike, with most dip angles ranging from the mid‐teens to mid‐twenties. While some cross‐bed sets are statistically coarser near their bases, others exhibit no significant vertical sorting trends. Both massive and laminated textures are visible in high‐resolution scans of thin sections, but laminae contacts are commonly indistinct, making normal and reverse grading difficult to define. Diagenetic features, such as stylolite seams and large pores, are also present in some samples and might indicate alteration of original textures like detrital clay laminae and carbonate minerals. Observed textures and sedimentary structures suggest that the cross‐beds may consist of grainflow and grainfall deposits, but these remain difficult to differentiate at outcrop and thin‐section scales. This characterization of fine‐scale processes will play a critical part in the development of depositional models for the Coconino Sandstone and elucidate interpretations for similar cross‐bedded formations.     

降水现象仪观测应用评估

利用2017年9月至2018年8月北京20个站降水现象仪采集数据与人工平行观测数据,对降水现象仪进行了对比评估。结果表明:降水现象仪的缺测率为0.01%,空报率为0.6%,捕获率为93.5%,漏报率为27.9%,错报率为10.0%。从统计结果可知,降水现象仪的缺测率、空报率较低,捕获率较高,体现出设备性能良好的一面,漏报率和错报率偏高,表明设备漏识别和错误识别的情况较多,漏报主要发生在弱降水过程中,错报主要出现在毛毛雨的识别上。设备测量和人工观测降水开始时间一致性较好,终止时间一致性偏差;降水现象仪现存问题:在大雨强时易出现雨滴叠加误识别,在小雨强时识别率会降低,在无降水错误输出降水现象方面缺少质控。     

地磁台站建设中磁测异常现象分析

地磁台建设磁性跟踪测试工作很重要,通过对跟踪磁测中发现的一个异常现象的分析,计算了不同重量、距离的铁磁性物质对磁房建筑场地磁场的影响,讨论了排除施工现场磁性干扰的一些办法,并得出各种重量铁磁性物质与磁房建筑物的安全距离,还讨论了地磁台部分建筑材料的选择问题。     

1617号鲇鱼台风登陆后引发不同性质暴雨的成因对比分析

2016年9月28日1617号台风"鲇鱼"登陆后由台风本体环流和外围环流引发了不同性质的暴雨,这是本次秋季登陆台风暴雨预报的难点。利用常规气象观测资料以及NCEP的1°×1°再分析资料等,对不同性质暴雨的成因进行了诊断对比分析。结果表明:浙江东南部对流性降水和江西南部稳定性降水的大气层结结构具有明显的差异。中高纬度低槽距离台风较远,冷空气主要从低层入侵台风西北侧,破坏台风低层的暖心结构。台风外围中层干冷空气随东南风向浙江东南部输送,并叠加在低层暖湿气流之上,形成上冷下暖的不稳定层结,同时在对流层上层有干冷空气下沉至台风环流中下层(干侵入),导致浙江文成附近出现了局地特大暴雨。江西南部由于低层被湿冷空气占据,层结较为稳定,降水发展平缓。低空东南急流为台风外围环流暴雨提供了充足的水汽,浙江东南部地形对降水起到了增幅作用。不稳定层结及中层冷空气的输送对对流性暴雨的激发作用可以为登陆台风降水性质和强度预报提供参考依据。     

南海中部海域障碍层特征及其形成机制

南海中部海域(10°~19°N,108°~122°E)存在显著的季节变化的障碍层.障碍层发生概率夏季最大(52.8%),秋季次之(41.0%),春季最小(10.5%).夏季(2000年8~9月)障碍层最显著,平均厚度约为14.2m;除114°E以东、吕宋岛以西海域为障碍层的多发区外,中南半岛东南海域(12°~14°N,110°~114°E)也存在显著的障碍层;春季(1998年4~6月)和秋季(1998年12月)障碍层平均厚度分别为6.8和11.2m,障碍层多位于114°E以东、吕宋岛以西海域.此外,吕宋岛以西海域(12°~16°N,116°~120°E)及中沙和西沙群岛附近(16°~18°N,110°~116°E)海域障碍层年发生几率超过20%,相对而言,其他海域障碍层年发生几率偏小.降水机制和层结机制分别是南海中部海域春、夏季和秋季障碍层形成的主要原因.其中,降水机制及东南向的Ekman平流较好的解释了春、夏季吕宋岛以西附近海域成为障碍层多发区的原因;此外,强降水是夏季中南半岛东南海域(12°~14°N,110°~114°E)障碍层产生的关键,反气旋涡(暖涡)有助于形成更强的障碍层,上升流对障碍层的影响有待进一步研究.     

The impact of northern Indian Ocean rivers on the Bay of Bengal using NEMO global ocean model

The effect of river runoff over the northern Indian Ocean(NIO) especially over the Bay of Bengal(Bo B) has been studied using global Nucleus for European Modelling of the Ocean(NEMO). Two sensitivity experiments, with and without river runoff are conducted and the influence of river runoff on the Indian Ocean hydrography,stratification and circulation features are studied. It is found that due to river runoff surface salinity over the northern Bo B decreases by more than 5 and the East India Coastal Current strengthens by 2 cm/s during post monsoon season. The fresh river water reaches up to 15°N in the Bo B and is the main cause for low salinity there.Sea surface temperature in the northwestern Bo B increases by more than 0.2℃ due to the river runoff in summer monsoon while surface cooling upto 0.2℃ is seen in north-west part of Bo B in winter season. The seasonal mixed layer depth in the region is found to be dependent on river runoff. The effect of vertical shear and Brunt Vaisala frequency on stratification is also examined. The ocean water becomes highly stratified up to 3 035 m due to the river runoff. It is found that the energy required for mixing is high in the northern and coastal Bo B.     

Trophic modeling of the Northern Humboldt Current Ecosystem, Part II: Elucidating ecosystem dynamics from 1995 to 2004 with a focus on the impact of ENSO

The Northern Humboldt Current Ecosystem is one of the most productive in the world in terms of fish production. Its location near to the equator permits strong upwelling under relatively low winds, thus creating optimal conditions for the development of plankton communities. These communities ultimately support abundant populations of grazing fish such as the Peruvian anchoveta, Engraulis ringens. The ecosystem is also subject to strong inter-annual environmental variability associated with the El Niño Southern Oscillation (ENSO), which has major effects on nutrient structure, primary production, and higher trophic levels. Here our objective is to model the contributions of several external drivers (i.e. reconstructed phytoplankton changes, fish immigration, and fishing rate) and internal control mechanisms (i.e. predator-prey) to ecosystem dynamics over an ENSO cycle. Steady-state models and time-series data from the Instituto del Mar del Perú (IMARPE) from 1995 to 2004 provide the base data for simulations conducted with the program Ecopath with Ecosim. In simulations all three external drivers contribute to ecosystem dynamics. Changes in phytoplankton quantity and composition (i.e. contribution of diatoms and dino- and silicoflagellates), as affected by upwelling intensity, were important in dynamics of the El Niño of 1997–98 and the subsequent 3 years. The expansion and immigration of mesopelagic fish populations during El Niño was important for dynamics in following years. Fishing rate changes were the most important of the three external drivers tested, helping to explain observed dynamics throughout the modeled period, and particularly during the post-El Niño period. Internal control settings show a mix of predator–prey control settings; however a “wasp-waist” control of the ecosystem by small pelagic fish is not supported.     

1997–1998 El Niño off Peru: A numerical study

An eddy-resolving numerical simulation for the Peru–Chile system between 1993 and 2000 is analyzed, mainly for the 1997–1998 El Niño. Atmospheric and lateral oceanic forcings are realistic and contain a wide range of scales from days to interannual. The solution is validated against altimetric observations and the few in situ observations available. The simulated 1997–1998 El Niño closely resembles the real 1997–1998 El Niño in its time sequence of events. The two well-marked, sea-level peaks in May–June and November–December 1997 are reproduced with amplitudes close to those observed. Other sub-periods of the El Niño seem to be captured adequately. Simple dynamical analyses are performed to explain the 1997–1998 evolution of the upwelling in the model. The intensity of the upwelling appears to be determined by an interplay between alongshore, poleward advection (related to coastal trapped waves) and wind intensity, but also by the cross-shore geostrophic flow and distribution of the water masses on a scale of 1000 km or more (involving Rossby waves westward propagation and advection from equatorial currents). In particular, the delay of upwelling recovery until fall 1998 (i.e., well after the second El Niño peak) is partly due to the persistent advection of offshore stratified water toward the coast of Peru. Altimetry data suggest that these interpretations of the numerical solution also apply to the real ocean.