Limiting the soil degradational impacts of wildfire in pine and eucalyptus forests in Portugal: A comparison of alternative post-fire management practices     

Richard A Shakesby  David J Boakes  Celeste de OA Coelho  AJ Bento Gonçalves  Rory PD Walsh 《Applied geography (Sevenoaks, England)》1996,16(4):337-355

In newly burnt and unburnt pine and eucalyptus forest in Portugal, overland flow and soil losses were monitored to assess the impacts of the following post-fire treatments: application of different quantities of logging litter; rip-ploughing compared with minimum tillage prior to planting eucalyptus seedlings; and clearance of pine needles and vegetation. Eucalyptus logging litter reduced soil losses by up to 95 per cent. The impact of pine logging litter was equivocal, but removal of pine needles increased soil losses elevenfold. Implications for soil longevity, soil quality and land management strategy are discussed.  相似文献   

Bathymetry,substrate and fishing areas of Southeast Atlantic high-seas seamounts   总被引：1，自引：0，他引：1  

OA Bergstad  ÅS Høines  R Sarralde  G Campanis  M Gil  F Ramil 《African Journal of Marine Science》2019,41(1):11-28

Most of the Southeast Atlantic Ocean is abyssal, and global bathymetries suggest that only ～3.2% of the areas beyond national jurisdiction (ABNJ; also known as the high seas, as defined in the United Nations Convention on the Law of the Sea [UNCLOS]) are shallower than 2 500 m. This study mapped bathymetry and characterised substrates in selected seamount summit areas, including several that have been or may become fishing areas. The southernmost location, the Schmitt-Ott Seamount, has exposed volcanic bedrock with surrounding flats covered by thin biogenic sediments and/or coral rubble that appears ancient. At Wüst, Vema, Valdivia and Ewing seamounts the basaltic base appears to be overlain by coral caps and other coral substrates (sheets, rubble). Adjacent summit plains have biogenic sediments of varying thickness. Vema has a flat, roughly circular summit, <100 m deep, with the shallowest point being a 22-m-deep summit knoll; the upper slopes have ancient coral framework, but the summit has a mixture of coralline and volcanic rock and coarse sediments, including extensive areas with coralline algae and kelp forests. Valdivia Bank is a 230-m-deep, flat, rocky area (～11 × 5 km), protruding steeply from the extensive multi-summit Valdivia subarea of the Walvis Ridge. The distribution of past fisheries in the Convention Area of the South East Atlantic Fisheries Organisation (SEAFO) was considered in relation to the new information on bathymetry and substrate.  相似文献   

Generation of zonal structures by internal gravity waves in the Earth’s atmosphere     

O. G. Onishchenko  O. A. Pokhotelov 《Doklady Earth Sciences》2012,445(1):845-848

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Nonstationary pearl pulsations as a signature of magnetospheric disturbances     

F. Z. Feygin  N. G. Kleimenova  O. A. Pokhotelov  M. Parrot  K. Prikner  K. Mursula  J. Kangas  T. Pikkarainen 《Annales Geophysicae》2000,18(5):517-522

We analyse long-lasting (several hours) Pc1 pearl pulsations with decreasing, increasing or constant central frequencies. We show that nonstationary pearl events (those with either decreasing or increasing central frequency) are observed simultaneously with increasing auroral magnetic activity at the nightside magnetosphere while the stationary events (constant central frequency) correspond to quiet magnetic conditions. Events with decreasing central frequency are observed mostly in the late morning and daytime whereas events with increasing central frequency appear either early in the morning or in the afternoon. We explain the diurnal distribution of the nonstationary pearl pulsations in terms of proton drifts depending on magnetic activity, and evaluate the magnetospheric electric field based on the variation of the central frequency of pearl pulsations.  相似文献   

Mode identification of terrestrial ULF waves observed by Cluster: A case study   总被引：1，自引：0，他引：1  

Y. Hobara  S.N. Walker  M. Dunlop  M. Balikhin  O.A. Pokhotelov  H. Nilsson  H. Rme 《Planetary and Space Science》2007,55(15):2257-2260

Using multipoint measurements from the Cluster mission wave identification techniques are applied to observations of ULF waves made in the terrestrial foreshock with the aim of identifying the modes and properties of the waves taking into account the effects of a high beta plasma. The wave properties in the spacecraft and plasma rest frames are experimentally derived using minimum variance analysis. Two waves with periods of 30 and 3 s dominate the dynamic frequency spectrum. The results indicate that these waves propagate in the fast magnetosonic and Alfvén/Ion Cyclotron modes, respectively. Both waves propagate in the upstream direction in the plasma rest frame but are convected downstream in the spacecraft frame. The measured wave properties in the plasma rest frame are in good agreement with those obtained from the theoretical kinetic dispersion relation taking into account the effects of different plasma beta. The dispersion results show a rather significant deviation from fluid model, especially when high beta plasma conditions occur. These experimentally derived foreshock ULF wave properties are in good agreement with previous results but when the effects of a high beta plasma are considered it is not as straight forward to choose the correct wave mode branch.  相似文献   

The role of proton injection processes in the nonlinear evolution of “pearls”     

Yu.G. Khabazin  O.A. Pokhotelov  A.V. Porotov 《Planetary and Space Science》1979,27(2):165-168

Given a constant number of resonant protons in a field tube the unstable wave amplitude reaches a steady value rapidly due to nonlinear effects. Observations show that the pearl amplitudes grow gradually for a long time. Consistency with observations is obtained by taking into account the processes of proton injection.  相似文献   

Pancake cyclones and anti-cyclones in the ionosphere     

V. I. Petviashvili  O. A. Pokhotelov  P. K. Shukla  L. Stenflo 《Astrophysics and Space Science》1993,202(2):363-372

The formation of pancake cyclones and anticyclones in the E-region of the Earth's ionosphere is considered. It is shown that the vortices can be maintained by the neutral winds or by chemical reactions including the energy release caused by the triple collisions of atomic oxygen with neutrals. It is found that the variations of the magnetic fields induced by the vortices are not localized and decrease slowly far from the vortex core. They can be easily detected by ground based magnetometers or by facilities on board the low-orbiting satellites.  相似文献   

Model of Jet Generation in Space Plasma     

Onishchenko  O. G.  Pokhotelov  O. A.  Belyaev  V. S.  Zagreev  B. V.  Matafonov  A. P. 《Geomagnetism and Aeronomy》2021,61(1):25-28

Geomagnetism and Aeronomy - A new analytical model for the generation of axially symmetric jets (directed jets) in a nondissipative, nonequilibrium stratified plasma has been created in the...  相似文献   

Kinetic theory of the magnetic Rayleigh-Taylor instability     

O. G. Onishchenko  O. A. Pokhotelov 《Geomagnetism and Aeronomy》2013,53(5):626-628

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GPS tomography in the polar cap: comparison with ionosondes and in situ spacecraft data   总被引：2，自引：1，他引：1  

Dimitry Pokhotelov  P. T. Jayachandran  Cathryn N. Mitchell  John W. MacDougall  Michael H. Denton 《GPS Solutions》2011,15(1):79-87

Tomographic 4D reconstructions of ionospheric anomalies appearing in the high-latitude polar cap region are compared with plasma density measurements by digital ionosonde located near the north magnetic pole at Eureka station and with in situ plasma measurements on-board DMSP spacecraft. The moderate magnetic storm of 14–17 October 2002 is taken as an example of a geomagnetic disturbance which generates large-scale ionospheric plasma anomalies at mid-latitudes and in the polar cap region. Comparison of the GPS tomographic reconstructions over Eureka station with the ionosonde measurements of the F layer peak densities indicates that the GPS tomography correctly predicts the time of arrival and passage of the ionospheric tongue of ionization over the magnetic pole area, although the tomographic technique appears to under-estimate the value of F peak plasma density. Comparison with the in situ plasma measurements by the DMSP SSIES instruments shows that the GPS tomography correctly reproduces the large-scale spatial structure of ionospheric anomalies over a wide range of latitudes from mid-latitudes to the high-latitude polar cap region, though the tomographic reconstructions tend to over-estimate the density of the topside ionosphere at 840 km DMSP orbit. This study is essential for understanding the quality and limitations of the tomographic reconstruction techniques, particularly in high-latitude regions where GPS TEC measurements and other ionospheric data sources are limited.  相似文献