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71.
Statistical studies of hard X-ray flares position on the solar disk have shown that the more energetic hard X-rays have a
tendency to be more concentrated near the limb rather than at disk center, whereas lower-energy hard X-ray emission seems
isotropic. Since the high-frequency radio emission is believed to be produced by the same energetic electron population responsible
for the high-energy hard X-rays, we searched the microwave/millimeter emitting bursts for center-to-limb variation in their
emission. A total of 499 bursts observed by the radio telescopes in Bern at the frequencies of 3.1, 5.2, 8.4, 11.8, 19.6,
35.0, and 50.0 GHz were analyzed. Simultaneous Hα flares were used for determination of the radio burst position on the solar
disk. For each of the 7 frequencies, the peak flux and duration were studied as a function of heliocentric position. For 312
bursts, spectral parameters such as spectral index, peak frequency, and flux at spectral maximum were analyzed. For a subset
of 43 bursts with emission at all frequencies, the emission and spectral parameters were analyzed. Center-to-limb variations
of the spectral parameters for all bursts were sought. In order to interpret the observational results, we have performed
a numerical simulation of gyrosynchrotron spectra. We find that high-frequency events, which are also the more energetic ones,
have larger center-to-limb variations in their parameters than do the overall flares. Moreover, this behavior agrees with
theoretical predictions. 相似文献
72.
We have resolved the stars in the halo and in the diffuse northeastern shell of the nearest giant elliptical galaxy NGC 5128
using VLT with FORS1 and ISAAC. Dominating feature in the optical-near IR color-magnitude diagrams is abroad red giant branch,
indicating a large spread in metallicity of the stars. We have detected a significant number of sources brighter than the
tip of the red giant branch. The variability monitoring of these bright red giants shows that they are long period variables
similar to Miras.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
73.
74.
Abrahan Mora Juan A. Alfonso Luzmila Sánchez Malvis Calzadilla Soraya Silva John J. LaBrecque José A. Azócar 《水文研究》2009,23(3):476-485
Monthly analyses of pH, conductance, alkalinity, total suspended solids, dissolved major cations (Na, K, Ca and Mg), and selected dissolved trace elements (Fe, Al, Mn, Cu, Zn and Cr) were conducted on waters of the lower Orinoco River from February 2004 to May 2006. The data show strong seasonal variability. Major cations had maximum concentrations at low water, and were correlated with pH, conductance and alkalinity because of the tributaries coming from the Andean zones, where the weathering of evaporites and carbonate shales controls water chemistry. K concentrations did not show any relation with evaporite weathering, probably because large amounts of K come from the Guayana Shield rivers as a consequence of feldspar weathering. The concentrations of dissolved Fe, Mn and Cu were highest during the high water stage. Concentrations of the elements K, Cr, Zn and Cu are correlated with each other but not with dissolved Fe and Al, which probably are complexed with humic and fulvic substances. Mn concentrations did not show relationships with other variables. Inter‐annual variability of dissolved elements is explained by temporal changes in precipitation. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
75.
da Silva Fabricio Polifke da Silva Alfredo Silveira da Silva Maria Gertrudes Alvarez Justi Pires Gisele Dornelles 《Natural Hazards》2022,110(1):695-718
Natural Hazards - The ability to forecast extreme precipitation events has become increasingly important over the last decades due to their significant impacts on society and properties. In this... 相似文献
76.
Xavier Bruna Catarino Egydio-Silva Marcos Sadowski Georg Robert de Assis Silva Bruno Takara Victor Junji 《Geotechnical and Geological Engineering》2022,40(3):1345-1361
Geotechnical and Geological Engineering - To optimize the prediction of structural geological conditions in the underground as of data collected at the surface, due to the usual great uncertainties... 相似文献
77.
Lago Larissa Neves Casagrande Michéle Dal Toé da Conceição Ribeiro Roberto Carlos de Albuquerque e Silva Ben-Hur 《Geotechnical and Geological Engineering》2022,40(3):1585-1595
Geotechnical and Geological Engineering - The aggregates consist approximately 85% of the total volume in asphalts pavements, and their properties influence directly their behavior. Therefore, it... 相似文献
78.
Chaulagain Hemchandra Rodrigues Hugo Silva Vitor Spacone Enrico Varum Humberto 《Natural Hazards》2015,78(1):583-602
Natural Hazards - Seismic risk in the form of impending disaster has been seen from past records that moderate-to-large earthquakes have caused the loss of life and property in all parts of Nepal.... 相似文献
79.
The South American Monsoon System (SAMS) is a major climatic feature of South America, and its domain extends from Amazon to La Plata basin. The SAMS region is vulnerable to variations of climate and precipitation patterns, which could impact economic activities and lead to potential societal consequences. In the face of a warming future scenario, the importance of the study of the past climate with numerical simulations is to evaluate the climate models and to assure the reliability of future projections. Here we investigate the Mid-Holocene SAMS, evaluating changes in strength, life cycle and associated dynamical mechanisms in ten Earth System Models simulations. Our results show that the SAMS was weaker in the Mid-Holocene than in the pre-industrial climate in December–January–February (DJF), but stronger in September–October–November (SON). This is probably a consequence of insolation variations in the Mid-Holocene, which contributed to changes in the moisture flux from the Atlantic Ocean to the continent, the strength of the upper-level atmospheric circulation, and the amount of precipitation over the SAMS region. Moreover, we suggest that the life cycle of the SAMS was altered during the Mid-Holocene, with an earlier onset and demise. Our results also indicate that Mid-Holocene SAMS changes are connected to precipitation variations near Northeast Brazil, in a dipole configuration of precipitation between western Amazon and Northeast Brazil, due to the influence of the Walker cell. Finally, this study highlights a need for improvement of the numerical models to better simulate the amount of precipitation over South America and the upper-level circulation over western Amazon in SON, which are crucial factors for a more realistic representation of the SAMS. 相似文献
80.
Jhan Carlo Espinoza Josyane Ronchail Matthieu Lengaigne Nelson Quispe Yamina Silva Maria Laura Bettolli Grinia Avalos Alan Llacza 《Climate Dynamics》2013,41(7-8):1983-2002
This study investigates the spatial and temporal characteristics of cold surges that propagates northward along the eastern flank of the Andes from subtropical to tropical South America analysing wintertime in situ daily minimum temperature observations from Argentina, Bolivia and Peru and ERA-40 reanalysis over the 1975–2001 period. Cold surges usually last 2 or 3 days but are generally less persistent in the southern La Plata basin compared to tropical regions. On average, three to four cold surges are reported each year. Our analysis reveals that 52 % of cold episodes registered in the south of La Plata basin propagate northward to the northern Peruvian Amazon at a speed of around 20 m s?1. In comparison to cold surges that do not reach the tropical region, we demonstrate that these cold surges are characterized, before they reach the tropical region, by a higher occurrence of a specific circulation pattern associated to southern low-level winds progression toward low latitudes combined with subsidence and dry condition in the middle and low troposphere that reinforce the cold episode through a radiative effect. Finally, the relationship between cold surges and atmosphere dynamics is illustrated for the two most severe cold intrusions that reached the Peruvian and Bolivian Amazon in the last 20 years. 相似文献