Analysis of the vortivity and divergence of the thermal wind in pure geostrophic flow

By applying the horizontal del operator to the thermal wind equation in vectorial form and considering only horizontal geostrophic motion, expressions are found for the vorticity and divergence of thermal wind. It is shown that vorticity, in the case of pure geostrophic flow at all levels, depends upon four factors, namely: latitude, horizontal distribution of temperature, temperature lapse rate and divergence of horizontal temperature gradient. The divergence of the thermal wind, on the other hand, depends only upon the orientation of the mean isotherms of an isobaric layer relative to the parallel circles. These terms are evaluated and it is shown that the latitude term and the lapse rate term are far greater than the remaining terms of the vorticity equation for geostrophic flow. A criterion is then given which enables to determine the conditions for irrotational horizontal motion with vertical geostrophic wind shear.

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Zusammenfassung Durch Anwendung des horizontalenNabla-Operators auf die thermische Windgleichung in vektorieller Form und bei ausschließlicher Berücksichtigung der geostrophischen Horizontalbewegung lassen sich Ausdrücke für die vorticity und die Divergenz des thermischen Windes herleiten. Es wird gezeigt, daß die vorticity im Falle einer rein geostrophischen Strömung in allen Niveaus von folgenden vier Faktoren bedingt ist: Breite, horizontale Temperaturverteilung, vertikaler Temperaturgradient und Divergenz des horizontalen Temperaturgradienten. Andrerseits hängt die Divergenz des thermischen Windes nur von der Orientierung der mittleren Isothermen einer in Bezug auf die Parallelkreise isobaren Schicht ab. Diese vier Terme werden ausgewertet und es wird gezeigt, daß das Breitenglied und der Term für den Vertikalgradienten viel größer sind als die übrigen Terme der vorticity-Gleichung für geostrophische Strömung. Schließlich wird ein Kriterium entwickelt, das gestattet, die Bedingungen für rotorfreie Horizontalbewegung mit vertikaler geostrophischer Windscherung zu bestimmen.

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Résumé On peut déduire des équations sur la rotationelle et la divergence du vent thermique en appliquant l'opérateur nabla horizontal à l'équation du vent thermique sous une forme vectorielle et en ne considérant que le mouvement géostrophique horizontal. On démontre que la rotationelle, dans le cas d'un courant géostrophique pur, dépend dans tous les niveaux des quatre facteurs suivants: latitude, répartition horizontale de la température, gradient vertical de la température et divergence du gradient horizontal de température. D'autre part, la divergence du vent thermique ne dépend que de l'orientation des isothermes moyennes d'une couche isobare par rapport aux parallèles. En évaluant ces quatre termes, on montre que les termes relatifs à la latitude et au gradient vertical sont beaucoup plus grands que les autres termes de l'équation de la rotationelle pour un courant géostrophique. Pour terminer, l'auteur développe un critère qui permet de déterminer les conditions pour un mouvement horizontal irrotationel mais avec un cisaillement vertical géostrophique du vent.

     

Analysing Lava Risk for the Etnean Area: Simulation by Cellular Automata Methods

The model SCIARA, based on the Cellular Automata paradigm, is a versatile instrument whose scope is to analyse volcanic risk from lava flows.The possible fields of intervention are:[(a)] Long term forecasting of the flow direction at various eruption rates and points of emission by locating potential risk areas and permitting the creation of detailed maps of risk;[(b)] The possibility to follow the progress of an event and predict its evolution;[(c)] The verification of the possible effects of human intervention on real or simulated flows in stream deviation.A risk scenario has been developed for the Etnean territories of the towns of Nicolosi, Pedara and S. Alfio, simulating possible episodes with different vent locations along the fracture opened in the 1989 eruption and successively activated in the 1991–1993 eruption.The main characteristics of lava flows, that might be dangerous to the inhabited areas, have been analysed on the basis of the carried out Cellular Automata.     

Short Term and Short Range Seismicity Patterns in Different Seismic Areas of the World

The aim of this work is to quantitatively set up a simple hypothesis for occurrence of earthquakes conditioned by prior events, on the basis of a previously existing model and the use of recent instrumental observations. A simple procedure is presented in order to determine the conditional probability of pairs of events (foreshock-mainshock, mainshock-aftershock) with short time and space separation. The first event of a pair should not be an aftershock, i.e., it must not be related to a stronger previous event. The Italian earthquake catalog of the Istituto Nazionale di Geofisica (ING) (1975–1995, M 3.4), the earthquake catalog of the Japan Meteorological Agency (JMA) (1983–1994, M 3.0) and that of the National Observatory of Athens (NOA) (1982–1994, M 3.8) were analyzed. The number of observed pairs depends on several parameters: the size of the space-time quiescence volume defining nonaftershocks, the inter event time, the minimum magnitude of the two events, and the spatial dimension of the alarm volume after the first event. The Akaike information criterion has been adopted to assess the optimum set of space-time parameters used in the definition of the pairs, assuming that the occurrence rate of subsequent events may be modeled by two Poisson processes with different rates: the higher rate refers to the space-time volume defined by the alarms and the lower one simulates earthquakes that occur in the nonalarm space-time volume. On the basis of the tests carried out on the seismic catalog of Italy, the occurrence rate of M 3.8 earthquakes followed by a M 3.8 mainshock within 10 km and 10 days (validity) is 0.459. We have observed, for all three catalogs, that the occurrence rate density for the second event of a couple (mainshock or aftershock) of magnitude M₂ subsequent to a nonaftershock of magnitude M₁ in the time range T can be modeled by the following relationship: (T, M₂) = 10^{a + b(M1 - M2)} with b varying from 0.74 (Japan) to 1.09 (Greece). The decrease of the occurrence rate in time for a mainshock after a foreshock or for large aftershocks after a mainshock, for all three databases, obeys the Omori's law with p changing from 0.94 (Italy) to 2.0 (Greece).     

Mantle source heterogeneity in the Campanian Region (South Italy) as inferred from geochemical and isotopic features of mafic volcanic rocks with shoshonitic affinity

Summary Major, trace element and Sr-Nd-isotopic data on mafic volcanic rocks with shoshonitic affinity from the islands of Procida and Ventotene (Campanian Region, South Italy) are reported. Within-suite chemical and isotopic variations are interpreted in terms of open system differentiation processes held responsible for enrichment in a number of trace elements and for radiogenic Sr observed in both Procida and Ventotene volcanic sequences. Conversely, trace element contents and Sr-Nd-isotopic compositions of the least-evolved among the investigated samples are thought to reflect source region characteristics with only negligible crustal contamination of the primary magmas.The data support an origin from distinct source regions for the primary magmas. In the case of Ventotene, the source would have been asthenospheric and/or lithospheric mantle with features similar to transitional mid-ocean ridge basalts (T-MORB), modified by enriching agents made up mainly of subducted slab-released components coming from marly sediments (about 7%) similar to cherts from Tuscan Apennines plus a limestone contribution. In the case of Procida, the source would have been asthenospheric and/or lithospheric mantle with a slightly more enriched T-MORB-like feature with respect to Ventotene, modified by slab-derived enriching agents, likely represented by a small amount of sediments (about 2.5%) of oceanic nature (mostly terrigenous/pelagic). These differences are constrained by lower Zr/Nb, Y/Nb, Sc/Nb, V/Nb, LILE/HFSE, LREE/HFSE and⁸⁷Sr/⁸⁶Sr, higher Ba/La and¹⁴³Nd/¹⁴⁴Nd ratios, as well as by the lack of a detectable negative Eu anomaly, in the least-evolved volcanic rocks of Procida, with respect to those of Ventotene, which show conversely a significant negative Eu anomaly. Thus, a sharp heterogeneity exists in the mantle beneath the Campanian Region. It is thought to be the consequence of two different slabs which are in contact along the Volturno River Plain tectonic line: a continental slab, seismically inactive, descending beneath the Latium Region, and an oceanic slab, seismically active, descending beneath the Calabria, up to the Campanian Region.

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Résumé De nouvelles analyses géochimiques d'éléments majeurs et en traces ainsi que des rapports isotopiques du Sr et du Nd sont été obtenues sur des roches volcaniques mafiques à affinité shoshonitiques provenant des îles de Procida et Ventotene (Région Campanienne, Italie du Sud). Les variations géochimiques et isotopiques observées au sein des séries volcaniques de ces deux îles sont interprétées en terme de processus de différenciation en système ouvert, tenu pour responsable d'un enrichissement d'un certain nombre d'éléments en traces et de leur composition en Sr radiogénique. Cependant, les teneurs en éléments traces et les compositions isotopiques en Sr et Nd des échantillons les moins évolués parmi ceux étudiés reflètent les caractéristiques de leur source, avec une contamination crustale très négligeable des magmas primitifs.Ces données démontrent que des sources distinctes sont à l'origine des magmas primitifs. Pour Ventotene, cette source doit être un manteau asthénosphérique et/ou lithosphérique dont la signature est similaire à celle de basaltes transitionnels de dorsale océanique (T MORB), légèrement enrichie en éléments dérivants d'une croûte plongeant dans une subduction comme des sédiments mameux (pour environ 7%) analogues aux cherts des Appenins de Toscane et comportant un apport en calcaire. Dans le cas de Procida, cette source doit être un manteau asthénosphérique et/ou lithosphérique montrant une signature de type T-MORB légèrement plus enrichie qu' à Ventotene, également modifiée par un apport venant d'une croûte en subduction, probablement une faible quantité (environ 2.5%) de sédiments de nature océanique (principalement terrigène/pélagique). Ces différences sont attestées par des rapports Zr/Nb, Y/Nb, Sc/Nb, V/Nb, LILE/HFSE, LREE/HSFE and⁸⁷Sr/⁸⁶Sr plus bas et des rapports Ba/La et¹⁴³Nd/¹⁴⁴Nd plus harts, ainsi que par l'absence d'une anomalie en Eu dans les compositions des roches volcaniques les moins évoluées de Procida par rapport à celles de Ventotene, qui elles, au contraire, montrent une anomalie en Eu significative.Ainsi, une importante hétérogénéité du manteau existe sous la Campanie. Cette hétérogénéité doit être la conséquence de la nature différente des croûtes en subduction et qui sont en contact le long de la ligne tectonique de la plaine de la rivière Volturno: an Nord-Ouest, une croûte continentale, sismiquement inactive, plonge sous le Latium alors qu'au Sud-Est, une croûte océanique, sismiquement active, plonge sous la Calabre et jusque sous la Campanie.

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With 9 Figures     

高美古与凤凰山水汽含量的统计分析

介绍了利用北京师范大学研制的ＩＲＡ－９３５型红外水汽测量仪对云南丽江高美古天文候选点及昆明凤凰山对比点上空垂直大气水汽积分含量Ｗ０的观测结果,给出了两地Ｗ０的日变化曲线及分布图,并对全年测量数据的统计结果作了分析和讨论     

一次致灾超级单体雹暴过程数值模拟和发展机制分析

利用高分辨率中尺度数值模式WRF,模拟了2019年3月21日发生在浙江省的一次大范围致灾超级单体雹暴过程,结合多普勒雷达探测产品,分析了风暴的雷达回波结构、流场结构、各类水成物等特征及其演变,并探究冰雹形成的物理机制。结果表明:此次雹暴过程是在高空急流轴右侧和低层切变线相重叠的区域发生和发展的,强垂直风切变有利于雹暴的维持和发展。实况超级单体雹暴在雷达回波上呈现出钩状回波、持久深厚的中气旋、典型的高悬强回波、有界弱回波区和三体散射现象。模拟试验成功地模拟出了雹暴云团的水平演变和垂直结构特征。合适的0℃和-20℃高度以及-20~0℃层厚度有利于雹粒的增长。雹粒子主要由云水、过冷雨水和雪粒子转化形成,再通过碰并过冷云水、冰晶、雪粒子而不断增长。     

辽宁省地震易发区地震危险性研究

盘锦、海城、营口地区是辽宁省内地震活动性最强、地震危险性最高的地区。该地区开展了大量重点工程地震安全性评价、区域性地震区划和地震小区划工作，但尚未开展基于场地条件的区域尺度地震危险性研究。独有的沉积特点使该地区场地条件较复杂，因此在地震危险性概率分析中考虑场地条件是必要的。本文基于新一代中国地震动参数区划图基本原理和技术原则，结合盘锦、海城、营口地区场地条件特征，采用基于地形坡度的方法对场地条件进行分类，确定场地地震动影响系数，给出该地区基于区域场地条件的地震危险性分布，相关研究结果可为地震风险评估和防震减灾规划提供参考。     

Reply to Discussion of “Perceptual models of uncertainty for socio-hydrological systems: a flood risk change example”*

ABSTRACT

Ertsen discusses the representation of reality and uncertainty in our paper, raising three critical points. In response to the first, we agree that discussion of different interpretations of the concept of uncertainty is important when developing perceptual models – making different uncertainty interpretations explicit was a key motivation behind our method. Secondly, we do not, as Ertsen suggests, deny anyone who is not a “certified” scientist to have relevant knowledge. The elicitation of diverse views by discussing perceptual models is a basis for open discussion and decision making. Thirdly, Ertsen suggests that it is not useful to treat socio-hydrological systems as if they exist. We argue that we act as “pragmatic realists” in most practical applications by treating socio-hydrological systems as an external reality that can be known. But the uncertainty that arises from our knowledge limitations needs to be recognized, as it may impact on practical decision making and associated costs.     

Exploring the role of risk perception in influencing flood losses over time

ABSTRACT

What implications do societies’ risk perceptions have for flood losses? This study uses a stylized, socio-hydrological model to simulate the mutual feedbacks between human societies and flood events. It integrates hydrological modelling with cultural theory and proposes four ideal types of society that reflect existing dominant risk perception and management: risk neglecting, risk monitoring, risk downplaying and risk controlling societies. We explore the consequent trajectories of flood risk generated by the interactions between floods and people for these ideal types of society over time. The results suggest that flood losses are substantially reduced when awareness-raising attitudes are promoted through inclusive, participatory approaches in the community. In contrast, societies that rely on top-down hierarchies and structural measures to protect settlements on floodplains may still suffer significant losses during extreme events. This study illustrates how predictions formed through social science theories can be applied and tested in hydrological modelling.