排序方式： 共有35条查询结果，搜索用时 15 毫秒
1.
B. Andersen V. Domingo A. Jiménez A. Jones S. Korzennik P. L. Pallé F. Pérez Hernández C. Régulo T. Roca Cortés L. L. Tomás 《Solar physics》1988,116(2):391-399
Monochromatic extinction coefficients at four wavelengths have been obtained over a period of more than two years at the Observatorio del Teide (Izaña Tenerife) using a full disc, direct sunlight, quadruple photometer devoted to the detection of integral luminosity oscillations of the Sun. The mean extinction coefficients (0.13 at 500 nm) show a seasonal variation of about 15%, the best atmospheric conditions being in winter and autumn. Moreover, in anyone day the extinction coefficient in the afternoon is always lower than the one in the morning by 7%. A one-year period fluctuation, with an amplitude of 0.035 mag, has been identified in the instrumental magnitudes outside the atmosphere, and is interpreted as the variation produced by the different Sun-Earth distance from winter to summer. Finally, the study made to detect periodic time fluctuations in both, Sun's magnitude and extinction coefficients, has given null results at levels of 0.04 and 1.8%, respectively. 相似文献
2.
Pall Bergthorsson 《Climatic change》1985,7(1):111-127
Haymaking and grazing in summer and winter are fundamental to Icelandic agriculture. This paper shows that the growth of grass depends very much on the climate, particularly the temperature, and that winter temperatures are especially important. The climate of Iceland is highly variable, and the long-term variations are great in comparison with most other European weather regions. This may be attributed partly to the role of the sea ice, which lags behind the variations in atmospheric temperature. From observations in this century it is possible to compute the potential livestock in the country as a function of temperature, and this computation is tested with historical data. A possible response to climatic variations, by varying the use of fertilizer to counteract the impact of cold preceding winters, is discussed. The paper also discusses the growth of barley and forests, which is barely possible in the cold climate and reacts strongly to climatic variations and changes. 相似文献
3.
The solar p-mode spectrum of very low I is measured with high accuracy for a long enough period of time so as to allow the search for solar cycle variations. In this paper solar cycle variations of the frequency and energy of the modes are confirmed. Moreover, a slight variation,within errors, of its rotational splitting with the solar cycle, is suggested. 相似文献
4.
Elevation gradients of European climate change in the regional climate model COSMO-CLM 总被引：1，自引：0，他引：1
A transient climate scenario experiment of the regional climate model COSMO-CLM is analyzed to assess the elevation dependency
of 21st century European climate change. A focus is put on near-surface conditions. Model evaluation reveals that COSMO-CLM
is able to approximately reproduce the observed altitudinal variation of 2 m temperature and precipitation in most regions
and most seasons. The analysis of climate change signals suggests that 21st century climate change might considerably depend
on elevation. Over most parts of Europe and in most seasons, near-surface warming significantly increases with elevation.
This is consistent with the simulated changes of the free-tropospheric air temperature, but can only be fully explained by
taking into account regional-scale processes involving the land surface. In winter and spring, the anomalous high-elevation
warming is typically connected to a decrease in the number of snow days and the snow-albedo feedback. Further factors are
changes in cloud cover and soil moisture and the proximity of low-elevation regions to the sea. The amplified warming at high
elevations becomes apparent during the first half of the 21st century and results in a general decrease of near-surface lapse
rates. It does not imply an early detection potential of large-scale temperature changes. For precipitation, only few consistent
signals arise. In many regions precipitation changes show a pronounced elevation dependency but the details strongly depend
on the season and the region under consideration. There is a tendency towards a larger relative decrease of summer precipitation
at low elevations, but there are exceptions to this as well. 相似文献
5.
Benedikt Halldorsson Apostolos S. Papageorgiou 《Bulletin of Earthquake Engineering》2012,10(4):1321-1337
The specific barrier model (SBM) is a particular case of a composite earthquake source model where the seismic moment is distributed in a deterministic manner on a rectangular fault plane on the basis of moment and area constraints. It is assumed that the fault surface is composed of an aggregate of subevents of equal diameter, the ‘barrier interval’. Furthermore, the subevents are assumed to rupture randomly and statistically independent of one another as the rupture front sweeps the fault plane. In the formulation of the far-field source spectrum of the SBM the ‘arrival time’ of the seismic radiation emitted by each subevent is specified via a probability density function (PDF). In the SBM the subevents are assumed to be of equal sizes (an assumption relaxed in a companion paper, referred to as Part I) and the PDF of ‘arrival times’ is assumed to be uniform. In this study we investigate the effects of different PDFs of ‘arrival times’ on the far-field source spectrum of the SBM. Different PDFs of ‘arrival times’ affect the source spectra primarily at the intermediate frequency range (between the first and second corner frequencies). Such effects become more pronounced as the earthquake magnitude increases. The far-field spectrum of seismic energy observed/recorded at a site depends on the location of the site relative to the causative fault plane, the location of rupture initiation (hypocenter) and the onset times of the rupturing subevents. All the above factors are effectively taken into account by the ‘isochrons’, which vary with source-site geometry. We investigate the selection of the appropriate PDF of seismic energy arrival times at a given site by computing isochrons for a grid of stations surrounding the earthquake fault, represented by the SBM. We show that only for stations located in a direction normal to the fault plane is the assumption of uniform PDF of ‘arrival times’ valid. At other sites non-uniform PDFs of ‘arrival times’ are observed. We identify and categorize the prevalent types of PDFs by directivity (forward vs. backward vs. neutral) and source-site distance (near-fault vs. far-field), show examples in which we group the stations accordingly. We investigate the effects of the different PDF-groups on the SBM source spectrum. Selection of the appropriate PDF for a given source-site configuration when simulating strong ground motions using the SBM in the context of the stochastic method is expected to yield more self-consistent, and physically realistic simulations. 相似文献
6.
Estimating coseismic deformations from near source strong motion records: methods and case studies 总被引：6，自引：5，他引：1
Digital strong-motion accelerographs have opened up the possibility of extracting ground motion characteristics at much lower frequencies than was offered by analogue instruments. High-quality digital data obtained close to the faults have tempted several efforts to retrieve permanent ground displacements after an earthquake. Such attempts have been partly successful, and somewhat subjective, the main reason being the presence of baseline offsets in the accelerometric data. We review existing methods for such applications, discuss their limitations and propose a more objective and improved scheme to make baseline adjustments and obtain permanent displacements. The proposed technique is applied to 26 digital recordings from the 29 May 2008 Ölfus Earthquake in South Iceland and 9 recordings from the 1999 Chi-Chi, Taiwan, Earthquake, and the permanent displacements obtained are compared with published results and GPS measurements from nearby stations. Our case studies show that the proposed technique, in addition to being simple and objective, is effective in making adjustments for baseline errors in accelerometric data. 相似文献
7.
Benedikt Halldorsson Ragnar Sigbjornsson Johannes Schweitzer 《Journal of Seismology》2009,13(1):173-178
A small-aperture, strong-motion array, the ICEARRAY, has been deployed in South Iceland, a region with a history of destructive
earthquakes, some exceeding magnitude 7. The array’s purpose is: (1) monitoring future significant events in the region, (2)
quantifying spatial variability of strong-motion over short distances and (3) shedding light on earthquake source processes.
The number of array stations and their arrangement were based on an optimisation of the shape of the corresponding array transfer
function (ATF). The optimal ICEARRAY configuration comprises 14 stations, has an aperture of ~1.9 km and a minimum interelement
distance of ~50 m and possesses a near-azimuthally independent ATF with a sharp main lobe, negligible sidelobes and a wavenumber
range of 1.5–24 rad/km. Accordingly, the ICEARRAY has the intended capabilities of capturing seismic waves in the frequency
range of 1–20 Hz, which is of main interest to earthquake engineering and engineering seismology applications. 相似文献
8.
Tjörnes fracture zone. New and old seismic evidences for the link between the North Iceland rift zone and the Mid-Atlantic ridge 总被引：1，自引：1，他引：0
The Tjörnes facture zone (TFZ) connects the EW extension of the Mid-Atlantic ridge north of Iceland to the extension of the North volcanic zone (NVZ) of Iceland. Earthquakes up to magnitude 7 (Ms) can occur in TFZ, volcanic eruptions have been observed and large crustal deformations are expected in similar way as have been observed in the NVZ. Most of the zone is below ocean, which limits the historical information and geological observations. For studying the dynamics of the zone we must rely on interpretation and modelling based on seismic observations, especially on microearthquake observations for the last 10 years. In this paper we demonstrate how microearthquakes can be applied to map the details of the plate boundary, and how this information can be applied to find epicenters and fault planes of large historical earthquakes, also how seismic information can be applied in dynamic modelling and to infer spatial and temporal interplay in activity, and to enhance hazard assessment. 相似文献
9.
G. R. Foulger G. Beutler Roger Bilham Pall Einarsson S. Fankhauser W. Gurtner U. Hugentobler W. Jason Morgan M. Rothacher Gunnar Thorbergsson U. Wild 《Journal of Geodesy》1993,67(3):148-172
Summary The 1986 GPS survey of Iceland aimed to: (1) establish geodetic control in the South Iceland Seismic Zone (SISZ), to study destructive earthquakes there, (2) measure a country-wide network to form the basis of a new first order national network. 51 points were surveyed, with 20–30 km spacings within the SISZ and 100 km spacings elsewhere. The data were processed using the Bernese GPS software Version 3. Analysis was difficult due to poor satellite geometry and short-period ionospheric variations. However, an ambiguity-fixed, ionosphere-free solution gave accuracies of 1–2 cm in the horizontal and 2–3 cm in the vertical for the SISZ network and an ambiguity-free, ionosphere-free solution yielded accuracies of about 5 cm for the country-wide network. An ionosphere-free solution for the total survey with ambiguities fixed for the SISZ network only gave marginal additional improvements over the two separate solutions. GPS surveying has continued annually in Iceland with measurements in South Iceland in 1989 and 1992 (Hackman 1991; Sigmundsson 1992) and in North Iceland in 1987, 1990 and 1992 (Jahn et al. 1992; Foulger et al. 1992). 相似文献
10.
A. Eff-Darwich S.G. Korzennik T. Roca Cortés F. Pérez Hernández P. Pallé 《Astrophysics and Space Science》1998,263(1-4):347-350
In recent years, the capability to detect and analyse solar oscillation acoustic modes has greatly improved. The development
of ground based networks like GONG or BiSON and the use of space platforms like SOHO has allowed us to study the structure
and dynamics of the Sun with unprecedented precision.
In this work we explore the distribution of the rotation in the solar interior, specially in the core. This kind of information
is essential in order to study the physical processes involved in the evolution of the Sun and many other stars.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献