Atmospheric loss of energetic electrons in the Jovian synchrotron zone     

K. Wang  S.J. BoltonS.M. Gulkis  S.M. Levin 《Planetary and Space Science》2002,50(3):277-285

For decades, ground-based radio observations of Jovian synchrotron radiation have shown emission originating predominantly from the equatorial region and from high-latitude regions (lobes) near L∼2.5. The observations show a longitudinally asymmetric gap between the emission peaks of the lobes and the atmosphere of Jupiter. One possible explanation for these gaps is the loss of electrons through collisions with atmospheric neutrals as the electrons bounce along magnetic field lines and drift longitudinally in the presence of asymmetric magnetic fields. To assess this hypothesis, we applied the recently developed O6 and VIP4 magnetic field models to calculate the trajectories of electrons as they drift longitudinally in Jupiter's magnetic field, and derive the sizes of their equatorial drift loss cones. We then identified the shells on which electrons would be lost due to collisions with the atmosphere. The calculated drift loss cone sizes could be applied in future to the modeling of electron distribution functions in this region and could also be applied to the study of Jovian auroral zone. This method also allowed us to compute the shell-splitting effects for these drifting electrons and we find the shell-splitting to be small (?0.05R_J). This justifies a recent modeling assumption that particles drift on the same shells in a three-dimensional distribution model of electrons. We also compared the computed gaps with the observed gaps, and found that the atmospheric loss mechanism alone is not able to sufficiently explain the observed gap asymmetry.  相似文献   

Lightning generation in planetary atmospheres     

Zev Levin  William J. Borucki  Owen B. Toon 《Icarus》1983,56(1):80-115

The possibilities of lightning generation on other planets are considered, and the basic conditions that exist in terrestrial clouds during lightning discharges and the various theories of charge separation are reviewed. Recent measurements of cloud structure and whistlers, as well as optical observation of lightning on Jupiter, suggest that charge separation and lightning discharges occur on other planets in ways similar to those in which they occur on Earth. Using these terrestrial ideas, it is concluded that lightning on Venus will probably be found in clouds that are located in regions of convection such as those observed downwind of the subsolar point. It is also possible that if volcanoes on Venus are erupting, they too can produce lightning discharges in their plumes although it seems unlikely that this process can account for the observed rate of discharge. Jovian lightning is most probably generated in the lower water-ice clouds. These clouds are of moderate temperatures and have strong convection and large mass loading, all important ingredients for electrical buildup. Lightning is all but ruled out for Mars, even though some electrification is possible owing to the large dust storms on that planet.  相似文献   

Unusual eruption of the Main Pugachevo Gas-Water-Lithoclastic volcano of Sakhalin in winter 2005     

O. A. Mel&#;nikov  B. V. Levin  V. V. Ershov 《Doklady Earth Sciences》2006,411(8):1209-1211

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Decrease in Danish semi-natural grassland – a social construct or a real-world change?     

Stig Roar Svenningsen  Gregor Levin  Martin Rudbeck Jepsen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2015,115(2):157-166

During the past century, the western hemisphere has seen a general trend of agricultural expansion on the behalf of semi-natural habitat types, such as heathlands and meadows. This has been documented in numerous studies of land use change. This trend is reflected in today’s European rural landscapes, which are dominated by intensive agriculture. However, many of these studies are based on cartographical sources, such as topographical and thematic maps, and thus prone to uncertainties regarding classification systems over time, variations in definitions of land use categories and lacking documentations of land use definitions. For this study, we conducted two change detection studies, covering the same four study areas in Denmark. The first study was based on topographic maps, and indicates a strong decline in the amount of semi-natural grassland (SNG). This was contrasted by the second study, which was based on an interpretation of aerial photos, and which indicated a much less pronounced reduction of SNGs. Year to year comparisons of these two analyses also revealed large discrepancies in the coverage of SNGs. Our results indicate that change detection studies must account for uncertainties in classifications and results should be interpreted with caution.  相似文献   

A DEPARTMENTAL RESERVE OF GEODETIC ALGORITHMS AND PROGRAMS     

A. A. Levin  L. N. Medvedev 《地理信息系统科学与遥感》2013,50(2):141-144

The authors describe the organization and operation of a reserve or information bank of computer programs (OFAP) of the Main Administration of Geodesy and Cartography (GUGK). Available software includes programs for adjusting horizontal and vertical survey control nets and triangulation grids, calculating datum points, and processing astronomical determinations. The programs are designed and documented within individual GUGK departments, debugged and cataloged by reserve personnel, and copies delivered to user organizations and to a State Reserve of Algorithms and Programs (GosFAP). Translated from: Geodeziya i kartografiya, 1985, No. 4, pp. 47-50.  相似文献   

Effective ecosystem-based management must encourage regulatory compliance: A Gulf of California case study     

C.H. Ainsworth  H. Morzaria-Luna  I.C. Kaplan  P.S. Levin  E.A. Fulton  R. Cudney-Bueno  P. Turk-Boyer  J. Torre  G.D. Danemann  T. Pfister 《Marine Policy》2012

The Northern Gulf of California is an area important for small-scale fisheries in terms of economic activity and food security, but widespread non-compliance with fisheries regulations impedes effective management of resources and conservation efforts. Where a previous study evaluated quantitatively a theoretical situation in which all regulations are perfectly followed, this article compares a suite of recently proposed ecosystem-based management (EBM) policies against the expected benefits of full enforcement of current regulations. Policies evaluated include no-take marine protected areas (MPAs), breeding period closures, changes in hook size and fishing effort, and gear-specific spatial closures. No-take MPAs yield ecological benefits over a wide range of MPA sizes and characteristics, but do not increase overall catch. Seasonal closures are effective at reducing overfishing for the depleted leopard grouper (Mycteroperca rosacea); changing the hook size of artisanal longlines does not increase catch of either the target species or the assemblage, and gear-specific fishery closures for crab traps near Puerto Peñasco are effective at reducing overfishing of blue crab (Callinectes bellicosus and C. arcuatus). In general, full enforcement of existing regulations outperforms these EBM policies in terms of conservation benefits, but it may be less palatable to stakeholders as it requires major reductions in catch.  相似文献   

The effect of climate change on the mobility and stability of coastal sand dunes in Ceará State (NE Brazil)     

Haim Tsoar  Noam Levin  Luis P. Maia  Sonia H. Tatumi 《Quaternary Research》2009,71(2):217-397

The coast of Ceará State in NE Brazil is covered by vast fields of active and stabilized coastal sand dunes. Its tropical climate is characterized by two seasons, wet and dry, with wind intensity determined by the meridional shift of the Intertropical Convergence Zone. The wind power is negatively correlated with precipitation, and precipitation is negatively correlated with the difference between sea surface temperatures of the tropical Atlantic north and south of the equator. We present a model suggesting that during the Late Pleistocene wind power determined the mobility and stability of the dunes. Sand dunes accumulated during periods of high wind power (as it is today) and stabilized when wind power was low. Once the dunes were stabilized by vegetation they could not be activated even by increased wind power. Samples that were taken for luminescence dating from 25 stabilized dunes along the coasts of Ceará gave ages ranging from135 ka to < 100 yr. We postulate that these luminescence ages fall at the beginning of wet periods in NE Brazil characterized by low wind power. These paleoclimatic wet periods correlate well with the cold periods of stades in Greenland ice-core records.  相似文献   

Fire Weather in Israel — Synoptic Climatological Analysis     

Noam Levin  Hadas Saaroni 《GeoJournal》1999,47(4):523-538

The study examines the synoptic situations and weather conditions under which occurred Israel's largest forest fires between the years 1987–1995. Annual rainfall and maximum temperature were found to have a positive correlation with both the size of the burnt area and the frequency of fires. A negative correlation was found for the relative humidity at 12 UTC for the same parameters. The fire season in Israel starts in May and ends in November, the peak months being May, June and July. No large fires were observed during the rainy season, December–February, despite the relatively low precipitation characterizing the region. Atmospheric disturbances as well as quasi-stationary systems were found to be favorable for the development of forest fires in Israel: the North African (‘Sharav’) cyclone and the Red Sea trough, which are common during spring and autumn. These systems carry hot, dry air from the deserts and are responsible for 55% of the burnt area from major forest fires in Israel and up to 33% of the major forest fires. Sixty-five percent of the forest fires occurred during the summer all of them under the quasi-stationary system of the Persian Gulf trough. These fires did not spread as widely as those that occurred under the North African cyclone and the Red Sea trough systems. The role of weather in the propagation of fire is exemplified in the case study of the ‘Sha'ar ha Gai’ fire of July 1995 — the biggest forest fire in the history of Israel (1300 ha). This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Cyclic variations in the Earth’s flattening and questions of seismotectonics     

B. W. Levin  E. V. Sasorova  G. M. Steblov  A. V. Domanskii  A. S. Prytkov  E. N. Tsyba 《Izvestiya Physics of the Solid Earth》2017,53(4):540-544

For more than a decade, the global network of GPS stations whose measurements are part of the International GPS Service (IGS) have been recording cyclic variations in the radius vector of the geodetic ellipsoid with a period of one year and amplitude of ~10 mm. The analysis of the figure of the Earth carried out by us shows that the observed variations in the vertical component of the Earth’s surface displacements can induce small changes in the flattening of the Earth’s figure which are, in turn, caused by the instability of the Earth’s rotation. The variations in the angular velocity and flattening of the Earth change the kinetic energy of the Earth’s rotation. The additional energy is ~10²¹ J. The emerging variations in the flattening of the Earth’s ellipsoid lead to changes in the surface area of the Earth’s figure, cause the development of deformations in rocks, accumulation of damage, activation of seismotectonic processes, and preparation of earthquakes. It is shown that earthquakes can be caused by the instability of the Earth’s rotation which induces pulsations in the shape of the Earth and leads to the development of alternating-sign deformations in the Earth’s solid shell.  相似文献   

Occurrence and distribution of polycyclic aromatic hydrocarbons in surface sediments of San Diego Bay marinas     

Carlos Neira  Jennifer Cossaboon  Guillermo Mendoza  Eunha Hoh  Lisa A. Levin 《Marine pollution bulletin》2017,114(1):466-479

Polycyclic aromatic hydrocarbons (PAHs) have garnered much attention due to their bioaccumulation, carcinogenic properties, and persistence in the environment. Investigation of the spatial distribution, composition, and sources of PAHs in sediments of three recreational marinas in San Diego Bay, California revealed significant differences among marinas, with concentrations in one site exceeding 16,000 ng g^? 1. ‘Hotspots’ of PAH concentration suggest an association with stormwater outfalls draining into the basins. High-molecular weight PAHs (4–6 rings) were dominant (> 86%); the average percentage of potentially carcinogenic PAHs was high in all sites (61.4–70%) but ecotoxicological risks varied among marinas. Highly toxic benzo(a)pyrene (BaP) was the main contributor (> 90%) to the total toxic equivalent quantity (TEQ) in marinas. PAHs in San Diego Bay marina sediments appear to be derived largely from pyrogenic sources, potentially from combustion products that reach the basins by aerial deposition and stormwater drainage from nearby streets and parking lots.  相似文献