Geoeffectiveness of solar wind interplanetary magnetic structures     

M.V. Alves  E. Echer  W.D. Gonzalez 《Journal of Atmospheric and Solar》2011,73(11-12):1380-1384

We address the geoeffectiveness of three interplanetary structures in the interplanetary space: magnetic clouds (MCs), interplanetary shocks (IPSs), and corotating interaction regions (CIRs). The geoeffectiveness is evaluated using the geomagnetic indices Kp, AE, and Dst. We find that MCs are more geoeffective than IPSs, or CIRs. The average values of magnetic indices are significantly enhanced during disturbed periods associated with MCs, IPSs and CIRs, compared to the whole interval. The highest effect is noted for MC disturbed periods.Results obtained for the three data sets are used to derive a theoretical (continuous) probability distribution function (PDF) by fitting the histograms representing the percentage of events against the intervals of magnetic index. PDFs allow estimation of the probability of a given level of geomagnetic activity to be reached after the detection, by in situ solar wind observations, of a given interplanetary structure approaching the Earth.  相似文献   

The California Current System in relation to the Northeast Pacific Ocean circulation     

Guillermo Auad  Dean Roemmich  John Gilson 《Progress in Oceanography》2011,91(4):576-592

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Water relations and hydraulic architecture of two Patagonian steppe shrubs: Effect of slope orientation and microclimate     

Patricia A. Iogna  Sandra J. Bucci  Fabián G. Scholz  Guillermo Goldstein 《Journal of Arid Environments》2011,75(9):763-772

On a local scale, topography influences microclimate, vegetation structure and the morpho-physiological attributes of plants. We studied the effects of microclimatic differences between NE- and SW-facing slopes on the water relations and hydraulic properties of two dominant shrubs of the Patagonian steppe in Argentina (Retanilla patagonica and Colliguaja integerrima). The NE-facing slope had higher irradiance and air saturation deficits and lower soil water availability and wind speed than the SW-facing slope. Predawn and midday Ψ_L and osmotic potentials were significantly lower in shrubs on the NE-facing slope. Osmotic adjustment and more elastic cell walls helped the plants to cope with a more xeric environment on NE-facing slope. Higher water deficits on NE-facing slope were partially compensated by a higher leaf and stem water storage. While stem hydraulic efficiency did not vary between slopes, leaf hydraulic conductance was between 40% and 300% higher on the NE-facing slope. Changes observed in leaf size and in SLA were consistent with responses to mechanical forces of wind (smaller and scleromorphic leaves on SW-facing slope). Morpho-physiological adjustments observed at a short spatial scale allow maintenance of midday Ψ_L above the turgor loss point and demonstrate that leaves are more responsive to microclimatic selective pressures than stems.  相似文献   

Colluvial sedimentation in a hyperarid setting (Atacama Desert,northern Chile): Geomorphic controls and stratigraphic facies variability     

Dario Ventra  Guillermo Chong Dìaz  Poppe l. De boer 《Sedimentology》2013,60(5):1257-1290

Research on colluvial depositional systems has recently emphasized periglacial and high‐altitude settings, and the relations between Quaternary slope stratigraphy and climate change. This article examines the role of variable slope morphology, surface hydrology and microclimate in controlling colluvial sedimentation along a coastal tract of the hyperarid Atacama Desert in northern Chile. Direct accessibility of active surfaces is accompanied by uninterrupted stratigraphic exposures along the base of slopes, allowing direct comparisons between surface processes and the resulting sedimentary record. Four slope sectors are identified, based on differences in morphology and processes over active surfaces. Colluvial sedimentation is controlled by complex interactions of slope gradients and profiles, exposure to dominant winds, and potential runoff pathways, which vary considerably between different sectors. Major differences are evident between these hyperarid deposits and slope sedimentation in periglacial and temperate settings, including the complete absence of pedogenic activity and clay minerals; the volume of aeolian deposits and their role in controlling processes which redistribute sediment downslope, extending colluvial aprons; and the occurrence of runoff processes only where favoured by particular topographic configurations. Depositional surfaces range from steep talus cones, to debris‐flow‐dominated and aeolian‐dominated colluvial aprons, to an aeolian ramp subject to reworking by mass flows and flash floods. Consequently, facies associations and architectures at outcrop are highly variable and highlight the importance of spatial variations in slope morphology and processes in producing distinct, coeval colluvial stratigraphies within a single environmental context. Discrepancies between active processes and the corresponding stratigraphic signatures are also evident in some sectors; for example, preservation of alluvial and aeolian facies in stratigraphic sections does not always reflect the dominant processes over active slopes. Together with the spatial variability in processes and deposits along these slopes, this suggests that caution is required when extracting palaeoenvironmental information from analyses of colluvial successions.  相似文献   

Analysis of anisotropy of magnetic susceptibility in iron-oolitic beds: a potential tool for paleocurrent identification     

Óscar Pueyo Anchuela  Javier Ramajo Cordero  Andrés Gil Imaz  Guillermo Meléndez Hevia 《International Journal of Earth Sciences》2013,102(4):1131-1149

A combined sedimentological, shape-preferred orientation and anisotropy of magnetic susceptibility (AMS) analysis has been performed at the Arroyofrío Bed (Callovian–Oxfordian boundary level) in the locality of Moneva (Iberian Range, NE Spain). The Arroyofrío bed is a widespread iron-ooid limestone interval forming a condensed sequence. The present study has focused on the analysis of the potential presence of a preferred ooid orientation at the Arroyofrío bed. The obtained data show that ooids were originally ellipsoidal and had an imbricate disposition with respect to the bedding/lamination surface. The main ooid orientation within the bedding plane shows a NNE–SSW trend. Results of AMS analyses show a magnetic foliation parallel or slightly imbricated with respect to bedding and magnetic lineation parallel to the main ooid orientation. Magnetic mineralogy of studied samples shows that AMS is mainly controlled by magnetite with minor contributions of hematite and paramagnetic minerals (that can reach contributions of 35 %). The analyzed ooids show axial ratios between 1.4 and 2.8 (intrinsic anisotropy), while the anisotropy of their distribution shows lower anisotropies (e.g., Rs = 1.15) or very low values of the anisotropic magnetic parameters (e.g., P′ < 1.01). Sedimentary texture, matrix features, bioturbation and fossil content influenced both ooid main orientation and the magnetic fabric. Magnetic lineation and main orientation of long ooid axes are transverse to the inferred coastline in the studied area and parallel to the expected paleocurrent direction with respect to the Ejulve-Maestrazgo paleogeographic high. The direct correlation between AMS magnetic lineation and the ooid analysis permits to demonstrate that the paleocurrent imprint can be recorded by means of AMS despite the highly ferromagnetic context fabric and at coarse deposits. Obtained results support the interest and reliability of AMS to unravel paleocurrent imprints for paleogeographic reconstructions.  相似文献   

Anthropogenic debris on beaches in the SE Pacific (Chile): Results from a national survey supported by volunteers     

Macarena Bravo  Mª de los ngeles Gallardo  Guillermo Luna-Jorquera  Paloma Núez  Nelson Vsquez  Martin Thiel 《Marine pollution bulletin》2009,58(11):1718-1726

Anthropogenic marine debris (AMD) is an ubiquitous problem, which has motivated public participation in activities such as beach surveys and clean-up campaigns. While it is known that beaches in the SE Pacific are also affected by this problem, the quantities and types of AMD remain largely unknown. In the context of an outreach project, volunteers (1500 high-school students) participated in a nation-wide survey of AMD on 43 beaches distributed randomly along the entire Chilean coast (18°S to 53°S). The mean density of AMD was 1.8 items m⁻² and the major types were plastics, cigarette butts and glass. Densities in central Chile were lower than in northern and southern Chile, which could be due to different attitudes of beach users or to intense beach cleaning in central regions. We suggest that public participation in surveys and cleaning activities will raise awareness and thereby contribute to an improvement of the situation.  相似文献   

Volcanoes in the pre-Columbian life,legend, and archaeology of Costa Rica (Central America)     

Guillermo E. Alvarado  Gerardo J. Soto 《Journal of Volcanology and Geothermal Research》2008

Costa Rica is located geographically in the southern part of the Central American Volcanic Front, a zone where interaction between the Mesoamerican and South American cultures occurred in pre-Columbian times. Several volcanoes violently erupted during the Holocene, when the first nomadic human hunters and later settlers were present. Volcanic rocks were the most important geo-resource in making artifacts and as construction materials for pre-Columbian inhabitants. Some pottery products are believed to resemble smoking volcanoes, and the settlements around volcanoes would seem to indicate their influence on daily life. Undoubtedly, volcanic eruptions disrupted the life of early settlers, particularly in the vicinity of Arenal and Irazú volcanoes, where archaeological remains show transient effects and displacement caused by periodical eruptions, but later resilient occupations around the volcanoes. Most native languages are extinct, with the exception of those presently spoken in areas far away from active volcanoes, where no words are related to volcanic phenomena or structures. The preserved legends are ambiguous, suggesting that they were either produced during the early Spanish conquest or were altered following the pre-Columbian period.  相似文献   

Quantum Instability of Magnetized Stellar Objects     

R. González Felipe  H. J. Mosquera Cuesta  A. Pérez Martínez  H. Pérez Rojas 《中国天文和天体物理学报》2005,5(4):399-411

The equations of state for degenerate electron and neutron gases are studied in the presence of magnetic fields. After including quantum effects in the investigation of the structural properties of these systems, it is found that some hypermagnetized stars can be unstable according to the criterion of stability of pressures. Highly magnetized white dwarfs should collapse producing a supernova type Ia, while superstrong magnetized neutron stars cannot stand their own magnetic field and must implode, too. A comparison of our results with a set of the available observational data of some compact stars is also presented, and the agreement between this theory and observations is verified.  相似文献   

An observational approach to stellar evolution     

Guillermo Haro 《Astrophysics》1988,29(1):414-417

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Using geomagnetic indices to forecast the next sunspot maximum     

Guillermo Gonzalez  Kenneth H. Schatten 《Solar physics》1988,114(1):189-192

The Babcock solar dynamo model and known interactions of the interplanetary magnetic field with the earth's magnetosphere are used to explain the relations found between geomagnetic indices at solar minimum and the sunspot number at the following solar maximum. We augment the work of Kane (1987) by updating his method of analysis, including recent smoothed aa and A_P indices. We predict a smoothed maximum sunspot number of 163±40 to peak in October 1990±9 months for solar cycle 22. This value is close to the Schatten and Sofia (1987) predicted value of 170±25, using more direct solar indicators.Now at Dept. of Astronomy, Univ. of Washington  相似文献