Review of measurements of the RF spectrum of radiation from lightning   总被引：2，自引：0，他引：2  

Dr D. M. Le Vine 《Meteorology and Atmospheric Physics》1987,37(3):195-204

Summary A review is presented of the measurements reported in the literature of the spectrum of electromagnetic radiation from lightning in the frequency range from 1 kHz to 1 GHz. Measurements have been made either by monitoring the power received at inidividual frequencies using a narrow bandwidth recording device or by recording the transient (time dependent) radiation with a wide bandwidth device and then Fourier transforming the waveform to obtain a spectrum. Measurements of the first type were made extensively in the 1950's and 1960's and several composite spectra have been deduced by normalizing the data of different investigators to common units of bandwidth and distance. The composite spectra tend to peak near 5 kHz and then decrease roughly as 1/(frequency) up to nearly 100 MHz where scatter in the data make the behaviour uncertain. The spectrum obtained with measurements of the second type is similar. Recent experiments have extended the frequency range covered to several 10's of MHz and include spectra for return strokes, the stepped leader and for some intracloud processes. The spectrum of first return strokes obtained in this manner is very similar to the spectrum of the composite flash obtained from the narrowband measurements.With 9 Figures  相似文献   

Surface heat fluxes from a numerical weather prediction system     

J Y Simonot  H Le Treut 《Climate Dynamics》1987,2(1):11-28

Twenty-two months (July 1983-April 1985) of surface heat fluxes predicted at day 1 from a numerical weather prediction system have been processed. Monthly means and monthly standard deviations of available surface short-wave, long-wave, latent and sensible heat fluxes as well as annual means have been computed. The global mean of the annual net sea-surface heat flux is about 40 Wm^–2 and is therefore far from equilibrium. When used to force an oceanic model, these fluxes would tend to warm the ocean and would produce an unrealistic transport of heat by the oceanic general circulation. They therefore need to be corrected. This correction appears feasible because the main difference between these fluxes and long-term climatologies appears largely independent of the month and the latitude. This suggests that the errors have a systematic origin. The corrected fluxes allow both the reproduction of a realistic seasonal migration of the zero net heat-flux line and the reproduction of the annual meridional heat transport in the different oceans, within the range of previous estimates.  相似文献   

Wind-driven ocean circulation transition to barotropic instability     

Christian Le Provost  Jacques Verron 《Dynamics of Atmospheres and Oceans》1987,11(2)

This article deals with the ocean circulation driven by steady zonal winds, and damped by bottom and biharmonic friction, when represented by the simple barotropic vorticity equation. A double gyre antisymmetrical wind stress pattern in a square basin is considered. Wind forcing and dissipation parameters are chosen within the ranges of what has been used in previous studies. The flow characteristics for both steady and unsteady situations are tentatively described as functions of model external parameters through the analysis of a large set of numerical experiments. Functional relations are derived for the mid-latitude jet parameters (length, width and transport) on the basis of scaling arguments. With the diagrams established for these quantities in forcing and dissipation parameter relations allow quantitative predictions of model response to a wide range of parameter choices to be made. The transition to barotropic instability is interpreted by analysing and comparing the spin-up phase of different numerical experiments leading either to stable or unstable solutions. Two major types of destabilization are identified, namely through meandering of the mid-latitude eastward jet and Rossby wave radiation from the westward return flow. The characteristics of the flows are shown to be highly sensitive to the external parameter changes. Competition between eddy kinetic energy level and eastward jet extension appears to consttitute the key point of this class of solutions, controlling in particular the intensity of transport in the inner gyres, driven by the eddy field on the two sides of the mid-basin jet, in a very similar manner to that of the more complex multilayered EGCMs.  相似文献   

Kinematic evolution of the Tethys belt from the Atlantic ocean to the pamirs since the Triassic     

Lonid A. Savostin  Jean-Claude Sibuet  Lev P. Zonenshain  Xavier Le Pichon  Marie-Jos Roulet 《Tectonophysics》1986,123(1-4)

We present an updated series of kinematic reconstructions of the major plates around the Tethys from the Atlantic Ocean to the Pamirs between the Early Jurassic and the Present. This set is used elsewhere as a basis for paleogeographic maps of the entire region. The problems related to the positions of the continents in the Lower Triassic are also discussed. No direct analyses of magnetic anomalies and fracture zones in the Atlantic have been made. Rather, all available poles and rotations have been tested in order to eliminate or minimize possible kinematic errors. The reconstructions are shown for nine key geological periods which correspond to well recognized magnetic anomalies, except for the Jurassic-Cretaceous boundary and the Cretaceous-Tertiary boundary which correspond to interpolated positions. Paleolatitudes have been drawn using the study of Westphal et al. (1986). An attempt has been made to take into account the displacements caused by formation of the continental margins and basins by stretching. The resulting relative vector of motions along the northern boundary of the Tethys shows a significant change 80 m.y. ago. Left-lateral motion with compression dominates before whereas right-lateral motion with compression dominates after. To the east, rates of motion vary by a factor of three with time and four maxima can be clearly related to tectonic events in the Late Jurassic, Late Cretaceous, Eocene and post Middle Miocene. To the west, north of Apulia, on the contrary, the motion rate has not changed significantly since the Early Cretaceous and is close to 1 cm/yr as an average. These rather complex adjustments in rates and directions of relative motion are produced in great part through a complex migration of the Africa-Eurasia pole of rotation and seem to be mostly governed by the tectonics of the Tethys plate boundary.  相似文献   

Geological evolution of the tethys belt from the atlantic to the pamirs since the LIAS   总被引：3，自引：0，他引：3  

J. Dercourt  L.P. Zonenshain  L.-E. Ricou  V.G. Kazmin  X. Le Pichon  A.L. Knipper  C. Grandjacquet  I.M. Sbortshikov  J. Geyssant  C. Lepvrier  D.H. Pechersky  J. Boulin  J.-C. Sibuet  L.A. Savostin  O. Sorokhtin  M. Westphal  M.L. Bazhenov  J.P. Lauer  B. Biju-Duval 《Tectonophysics》1986,123(1-4)

We discuss nine palinspastic geological maps (Plates 1–9), at scale, which depict the evolution of the Tethys belt from the Pliensbachian (190 Ma) to the Tortonian (10 Ma). A Present structural map (Plate 10) is shown for comparison at the same scale with the same conventions. Our reconstructions are based on a kinematic synthesis (Savostin et al., 1986), a paleomagnetic synthesis (Westphal et al., 1986) and geological compilations and analyses concerning in particular the western domain (Ricou et al., 1986), the eastern passive margins (Kazmin et al., 1986a), the eastern active margins (Kazmin et al., 1986b), the Black Sea-Caspian Sea basins (Zonenshain and Le Pichon, 1986) and the ophiolites (Knipper et al., 1986).  相似文献   

Motions at core surface in the geostrophic approximation     

J.L. Le Mouël  C. Gire  T. Madden 《Physics of the Earth and Planetary Interiors》1985,39(4):270-287

Motions at the top of the core which generate the observed Secular Variation (S.V.) field are computed. To reduce the well known ambiguity of the solution, two constraints are added: the flow is a large scale one and is geostrophic. The computed flow then has a very simple geometry; its poloïdal part is roughly axisymmetrical with respect to an equatorial diameter. This geometry is almost unchanged from 1970 to 1980 while the intensity of the velocity is nearly doubled.  相似文献   

A mesoscale study of the elemental composition of aerosols emitted from Mt. Etna Volcano     

G. Bergametti  D. Martin  J. Carbonnelle  R. Faivre-Pierret  R. Vie Le Sage 《Bulletin of Volcanology》1984,47(4):1107-1114

An aircraft survey was carried out for the study of the gaseous and particulate emissions over Mt Etna Volcano in September 1983. Samples were collected in the range from 10 to 300 km; a satisfying conservation of the elemental composition of the aerosol has been observed. Some activity fluctuation, 150 km from the emitter, was attributed to an ash fall episode. Sampling assumed that some crustal elements in the volcanic aerosol can be used to measure the plume dilution factor. New estimations of volcanic particulate fluxes are given.  相似文献   

Elsevier''s mineral and rock table     

R.W. Le Maitre 《Engineering Geology》1983,19(4):287-288

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The 1975–1977 crisis of la Soufriere de Guadeloupe (F.W.I): A still-born magmatic eruption     

M. Feuillard  C.J. Allegre  G. Brandeis  R. Gaulon  J.L. Le Mouel  J.C. Mercier  J.P. Pozzi  M.P. Semet 《Journal of Volcanology and Geothermal Research》1983,16(3-4)

On July 8, 1976, eruptive activity broke out at la Soufrière de Guadeloupe (F.W.I) after about one year of increasing seismic activity. Seismic activity continued to increase until August 1976, reaching more than 1500 events (a 200-fold increase over the preceding quiet period of a few years) and an energy output of about 10¹⁷ ergs in a day. A total of 26 major phreatic eruptions similar to the July 8 outburst took place during an eight-months period. The steam blasts that characterized the eruptions gave rise to particle- and sometimes block-charged plumes that deposited an estimated 10⁶ m³ of solids. The H₂O-rich gases emitted during the blasts presumably contained other gases (H₂S, SO₂, CO₂...) that were partly adsorbed on solid particles. All material was erupted at temperatures of the order of 100° to 200°C.The observation of vertical migration of earthquake foci in less than a few hours and over about 6 km depth, and of abnormal variations of the geomagnetic field, indicate a deep energy source for the phreatic eruptions. A small proportion of the gases adsorbed on solid particles had a magmatic origin. However, most of the steam and the tephra seemed to originate from superficial levels of a hydrothermal system. Similar phreatic eruptions have occurred several times in recorded history. In the case of la Soufrière, the origin of the phreatic eruptions is best described by an abnormal energy input (versus steady-state) from a crustal magma chamber. The occurrence of truly magmatic eruptions is presumably inhibited by an extensive hydrothermal system. The abrupt release of more power from the magma chamber could have resulted in an explosive pyroclastic eruption.Substantial improvement of the Guadeloupe volcano observatory has followed the 1975–1977 crisis. Permanent telemetered geophysical networks and regular geochemical observations have provided a five year data base of the volcano behavior in its noneruptive state which can be compared to crisis situations.  相似文献   

基于Web技术的西北指导预报系统的设计与实现   总被引：1，自引：0，他引：1  

张鸿  缪雒  张铁军  王勇  阎晗 《干旱气象》2006,24(1):75-78

详细介绍西北指导预报系统的内容、体系结构、功能、特点,以及实现的关键技术。实际应用表明,利用动态服务器网页技术开发的基于浏览器/服务器3层网络体系结构的西北指导预报系统是一个功能较完善的气象预报信息管理系统,实现了各类气象信息的集成和共享。  相似文献