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Abstract The envelopes of dust clouds from the May 18, 1980 eruption of Mount St Helens in Washington State, U.S.A. were plotted as they traversed the northern United States and southern Canada. Visibility observations at many meteorological stations indicated the presence of volcanic ash and smoke and verified trajectory calculations. In addition, sulphur dioxide released by the volcano was detected as it passed over Toronto, Ontario, while satellite photographs showed dust clouds in the upper atmosphere. 相似文献
3.
Nonlinear dynamics of meteorological variables: multifractality and chaotic invariants in daily records from Pastaza, Ecuador 总被引：1，自引：0，他引：1
Humberto Millán Aleksandar Kalauzi Milena Cukic Riccardo Biondi 《Theoretical and Applied Climatology》2010,102(1-2):75-85
Weather represents the daily state of the atmosphere. It is usually considered as a chaotic nonlinear dynamical system. The objectives of the present study were (1) to investigate multifractal meteorological trends and rhythms at the Amazonian area of Ecuador and (2) to estimate some nonlinear invariants for describing the meteorological dynamics. Six meteorological variables were considered in the study. Datasets were collected on a daily basis from January 1st 2001 to January 1st 2005 (1,460 observations). Based on a new multifractal method, we found interesting fractal rhythms and trends of antipersistence patterns (Fractal Dimension >1.5). Nonlinear time series analyses rendered Lyapunov exponent spectra containing more than one positive Lyapunov exponent in some cases. This sort of hyperchaotic structures could explain, to some extent, larger fractal dimension values as the Kaplan–Yorke dimension was also in most cases larger than two. The maximum prediction time ranged from ξ?=?1.69 days (approximately 41 h) for E/P ratio to ξ?=?14.71 days for evaporation. Nonlinear dynamics analyses could be combined with multifractal studies for describing the time evolution of meteorological variables. 相似文献
4.
Quaternary Climate and Environment in the Lop Nur, Xinjiang 总被引：4，自引：0，他引：4
WANG Mill PU Qingyu Geological Society of Chin Baiwanzhuang Rd. Beijing LIU Chenglin CHEN YongzhiInstitute of Mineral Deposits Chinese Academy of Geological Sciences Baiwanzhuang Rd. Beijing 《《地质学报》英文版》2000,74(2):273-278
Since the middle Early Pleistocene (1.20 Ma B.P.), the desert steppe climate and environment have predominated in the Lop Nur area, Xinjiang, characterized by warm humid epochs interrupted by dry cold intervals. The grain-size and magnetic susceptibility curves record 30 climatic oscillations, each with a ca. 40 ka cycle, in the area since 1.2 Ma B.P., which reflects the controlling effects exerted by the astronomic factor on the environment. The Quaternary sedimentary environment in the Lop Nur gradually changed from a fresh lake through a brackish lake to a saline lake, showing a spiral evolution, and finally it evolved into a playa. 相似文献
5.
Óscar A. Barocio-León Roberto Millán-Núñez Eduardo Santamaría-del-Ángel Adriana González-Silvera Charles C. Trees 《Journal of Oceanography》2006,62(6):873-885
We have estimated the spatial variability of phytoplankton specific absorption coefficients (a*
ph
) in the water column of the California Current System during November 2002, taking into account the variability in pigment
composition and phytoplankton community structure and size. Oligotrophic conditions (surface Chl < 0.2 mg m−3) dominated offshore, while mesotrophic conditions (surface Chl 0.2 to 2.0 mg m−3) where found inshore. The specific absorption coefficient at 440 [a*
ph
(440)] ranged from 0.025–0.281 m2mg−1 while at 675 nm [a*
ph
(675)] it varied between 0.014 and 0.087 m2mg−1. The implementation of a size index based on HPLC data showed the community structure was dominated by picoplankton. This
would reduce the package effect in the variability of a*
ph
(675). Normalized a
ph
curves were classified in two groups according to their shape, separating all spectra with peaks between 440 and 550 nm as
the second group. Most samples in the first group were from surface layers, while the second group were from the deep chlorophyll
maximum or deeper. Accessory photoprotective pigments (APP) tended to decrease with depth and accessory photosynthetic pigments
(APS) to increase, indicating the importance of photoprotective mechanisms in surface layers and adaptation to low light at
depth. Samples with higher ratios of APP:APS (>0.4) were considered as phytoplankton adapted to high irradiances, and lower
ratios (<0.26) as adapted to low irradiances. We found a good relationship between APP:APS and a*
ph
(440) for the deeper layer (DCM and below), but no clear evidence of the factors causing the variability of a*
ph
(440) in the upper layer. 相似文献
6.
Nuria Castell Ariel F. Stein Enrique Mantilla Rosa Salvador Millán Millán 《Journal of Atmospheric Chemistry》2009,63(1):73-91
Understanding the chemical links between ozone (O3) and its two main precursors, nitrogen oxides (NOx) and volatile organic compounds (VOC), is important for designing effective
photochemical smog reduction strategies. This chemical relationship will determine which precursor (NOx or VOC) emission reduction
will be more effective for decreasing the ozone formation. Under certain conditions, ozone levels decrease as a result of
a reduction in NOx emissions but do not respond significantly to changes in VOC emissions (NOx-sensitive condition), while
under other conditions ozone concentrations decrease in response to reductions in VOCs and may even increase when NOx emissions
are reduced (VOC-sensitive conditions). Indicator species can be used to assess the sensitivity of ozone to changes in the
emissions of its precursors. These indicators are species or species ratios involved in ozone photochemistry which reflect
the primary chemical process through which the ozone was formed. In this work we use the MM5-CAMx model system to explore
the behaviour of various indicator species during two meteorological situations featuring different atmospheric conditions
in a complex terrain area. The results show that indicators based on nitrogen compounds (i.e,. NOy and NOz) are suitable for
defining the transition range from VOC- to NOx-sensitive chemistry, and that despite the uncertainties associated with the
use of chemical indicators, the ratios O3/NOy and O3/NOz may provide a simple and useful way to summarize the response of ozone to changes in NOx and VOC emissions in Southwestern
Spain. 相似文献
7.
Quaternary reactivation of flexural-slip folds by diapiric activity: example from the western Ebro Basin (Spain) 总被引：1，自引：0，他引：1
A. M. Casas I. Gil B. Leránoz H. Millán L. Simón 《International Journal of Earth Sciences》1994,83(4):853-867
In the western sector of the Ebro Basin two types of structures deform the Quaternary terraces and pediments developed by the Ebro River and its tributaries: (1) folds up to 10 km long in the lower levels of fluvial terraces and (2) normal listric faults that produce tilting and rollover anticlines of the Quaternary deposits. Both types of structures are linked to the geometrical and lithological features of the Tertiary beds that underlie the Quaternary deposits. Quaternary folds, whose axes are parallel to the strike of the Tertiary beds, are the result of reactivation of Tertiary large-scale (60 km long) folds due to diapirism of their gypsum cores, where the gypsum units reach a maximum thickness of 3 000 m. This reactivation produced flexural-slip in some beds on the limbs of the folds, bringing about the folding of the overlying Quaternary terraces. The mechanism of Quaternary folding involves layer-parallel shear in alternating Tertiary units and folding linked to detachments and reverse layer-parallel faults. Normal listric faults are widespread throughout the studied area. They are partly parallel to low dipping Tertiary beds and are the result of a NNE-SSW tectonic extension, compatible with minor structures and focal mechanisms of recent earthquakes. The relationship between the two kinds of Quaternary structures indicates that diapirism of the gypsum cores of the anticlines was activated by extensional tectonics. 相似文献
8.
Ramón Luna Carlos Millán Manuel Domingo Miguel Ángel Satorre 《Astrophysics and Space Science》2008,314(1-3):113-119
CO2 ices are known to exist in different astrophysical environments. In spite of this, its physical properties (structure, density,
refractive index) have not been as widely studied as those of water ice. It would be of great value to study the adsorption
properties of this ice in conditions related to astrophysical environments. In this paper, we explore the possibility that
CO2 traps relevant molecules in astrophysical environments at temperatures higher than expected from their characteristic sublimation
point. To fulfil this aim we have carried out desorption experiments under High Vacuum conditions based on a Quartz Crystal
Microbalance and additionally monitored with a Quadrupole Mass Spectrometer. From our results, the presence of CH4 in the solid phase above the sublimation temperature in some astrophysical scenarios could be explained by the presence of
several retaining mechanisms related to the structure of CO2 ice. 相似文献
9.
A two-part study conducted in Elimbah Creek, a shallow estuarine waterway in south-east Queensland, Australia, examined the variations in physico-chemical parameters of water quality, chlorophyll a, and faecal indicator bacteria abundances of total coliform, Escherichia coli and enterococci, spatially at high and low tide and also over a 12h tidal cycle. Gradients of increasing faecal indicator bacteria from the mouth to the upper, tidal freshwater reaches were observed, despite isolated peaks during either tidal phase. Phytoplankton biomass (measured as chlorophyll a) did not noticeably increase during the study. Variations in the abundances of all three faecal indicator bacteria and their correlations with physico-chemical parameters indicated that although the creek was likely subject to some level of faecal contamination, tidal movement serves to limit faecal indicator and phytoplankton levels in the creek through physico-chemical stress and dilution. However, each faecal indicator bacteria investigated provided different estimations of faecal contamination, which challenges the effectiveness of employing a single type of faecal indicator bacteria when investigating the level of faecal contamination in waterways. 相似文献
10.
A new jadeitite jade locality (Sierra del Convento, Cuba): first report and some petrological and archeological implications 总被引：1，自引：1，他引：0
Antonio García-Casco A. Rodríguez Vega J. Cárdenas Párraga M. A. Iturralde-Vinent C. Lázaro I. Blanco Quintero Y. Rojas Agramonte A. Kröner K. Núñez Cambra G. Millán R. L. Torres-Roldán S. Carrasquilla 《Contributions to Mineralogy and Petrology》2009,158(1):1-16
A new jadeitite jade locality has been discovered in the serpentinite-matrix subduction mélange of the Sierra del Convento
(eastern Cuba) in a context associated with tectonic blocks of garnet-epidote amphibolite, tonalitic–trondhjemitic epidote
gneiss, and blueschist. The mineral assemblages of jadeitite jade and jadeite rocks are varied and include combinations of
jadeite, omphacite, albite, paragonite, analcime, clinozoisite-epidote, apatite, phlogopite, phengite, chlorite, glaucophane,
titanite, rutile, zircon, and quartz formed during various stages in their P–T evolution. Field relationships are obscure,
but some samples made almost exclusively of jadeite show evidence of crystallization from fluid in veins. In one of these
samples studied in detail jadeite shows complex textural and chemical characteristics (including oscillatory zoning) that
denote growth in a changing chemical medium. It is proposed that interaction of an Al–Na rich fluid with ultramafic rocks
produced Al–Na–Mg–Ca fluids of varying composition. Episodic infiltration of these fluids, as a result of episodic opening
of the veins, developed oscillatory zoning by direct precipitation from fluid and after reaction of fluid with pre-existing
jadeite. The latest infiltrating fluids were richer in Mg–Ca, favouring the formation of omphacite and Mg–Ca rich jadeite
in open voids and the replacement of earlier jadeite by fine-grained omphacite + jadeite at 550–560°C. This new occurrence
of jadeite in Cuba opens important perspectives for archeological studies of pre-Columbian jade artifacts in the Caribbean
region. 相似文献