Secular variations in the spectrum of solar p-modes     

A. Jiménez  P. L. Pallé  C. Régulo  T. Roca Cortés 《Solar physics》1994,152(1):253-260

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   

LEGRI instrument health. A historical review     

Julia Suso  Pere Blay  Almudena Robert  Victor Reglero  Chris J. Eyles 《Astrophysics and Space Science》2001,276(1):299-309

LEGRI has been operating successfully on MINISAT-01 since its switch-on the 22nd of May 1997. HouseKeeping (HK) data have been continuously receivedfor nearly two years by LEGRI SOC in Valencia, and subsequently checked on adaily basis and then stored for long term monitoring analysis.LEGRI HouseKeeping data include three critical operating parameters:temperature, power and polarisation voltages. Six temperature sensors arespread over the different LEGRI units: Detector Unit, Data Processing Unit,High Voltage Unit and Star Sensor. Voltages are measured at eight differentpoints. Detector Unit temperature and polarisation voltage are thecritical parameters for LEGRI operation. Solid state detectors aresensitive to changes not only in polarisation but also in temperature.Around one and a half million of measurements for each of the HK fourteen parameters have been recorded and analysed. The data show a very remarkablestability, within the expected margins, and the averages are very close to theoptimal design values. Special attention has been paid to the detectorpolarisation voltages analysis with a mean value of 286 ± 2 V when the detectors are operating. Thermal control over all the LEGRI units shows a remarkable stability in their temperatures.On the detector plane a mean value of T _det = 13 ± 2 ^°C has been found.We can therefore conclude that LEGRI as a system has been operating withinits optimal design conditions. We also want to point out the excellentperformance of the MINISAT-01 thermal control system.  相似文献   

Structure of the 5-minute solar oscillations 1976–1980     

A. Claverie  G. R. Isaak  C. P. McLeod  H. B. Van Der Raay  T. Roca Cortès 《Solar physics》1981,74(1):51-57

The discrete structure in the 5 min velocity oscillations of the solar surface has been confirmed by a re-analysis of data obtained between 1976 and 1979, and in addition a preliminary analysis of 1980 data show excellent consistency of the determined frequencies over the five year period. It is further shown that atmospheric transparency, as measured by the power in the solar intensity fluctuations, shows no correlation with the measured amplitude of the velocity fluctuations, over 2 orders of magnitude.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.  相似文献   

The role of the Indian monsoon onset in the West African monsoon onset: observations and AGCM nudged simulations     

Emmanouil Flaounas  Serge Janicot  Sophie Bastin  Rémy Roca  Elsa Mohino 《Climate Dynamics》2012,38(5-6):965-983

In spring the inland penetration of the West African Monsoon (WAM) is weak and the associated rainband is located over the Guinean coast. Then within a few days deep convection weakens considerably and the rainband reappears about 20?days after over the Sahel, where it remains until late September signalling the summer rainy season. Over the period 1989–2008 a teleconnection induced by the Indian monsoon onset is shown to have a significant impact on the WAM onset, by performing composite analyses on both observational data sets and atmospheric general circulation model simulations ensembles where the model is nudged to observations over the Indian monsoon sector. The initiation of convective activity over the Indian subcontinent north of 15°N at the time of the Indian monsoon onset results in a westward propagating Rossby wave establishing over North Africa 7–15?days after. A back-trajectory analysis shows that during this period, dry air originating from the westerly subtropical jet entrance is driven to subside and move southward over West Africa inhibiting convection there. At the same time the low-level pressure field over West Africa reinforces the moisture transport inland. After the passage of the wave, the dry air intrusions weaken drastically. Hence 20?days after the Indian monsoon onset, convection is released over the Sahel where thermodynamic conditions are more favourable. This scenario is very similar in the observations and in the nudged simulations, meaning that the Indian monsoon onset is instrumental in the WAM onset and its predictability at intraseasonal scale.  相似文献   

Detection and temporal coherence of p‐modes below 1.4 mHz     

A. Eff‐Darwich  C. Rgulo  S.G. Korzennik  F. Prez Hernndez  T. Roca Corts 《Astronomische Nachrichten》2008,329(5):470-475

Data collected recently by the helioseismic experiments aboard the SOHO spacecraft have allowed the detection of low degree p‐modes with increasingly lower order n. In particular, the GOLF experiment is currently able to unambiguously identify low degree modes with frequencies as low as 1.3 mHz. The detection of p‐modes with very low frequency (i.e., low n), is difficult due to the low signal‐to‐noise ratio in this spectral region and its contamination by solar signals that are not of acoustic origin. To address this problem without using any theoretical a priory, we propose a methodology that relies only on the inversion of observed values to define a spectral window for the expected locations of these low frequency modes. The application of this method to 2920‐day‐long GOLF observations is presented and its results discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Heavy metals in particulate matter and sediments in the southern Barcelona sedimentation system (North-western Mediterranean)     

Pere Puig  Albert Palanques  Joan A. Sanchez-Cabeza  Pere Masqu 《Marine Chemistry》1999,63(3-4)

Concentrations of selected heavy metals (Cr, Cu, Ni, Pb and Zn) from surface sediments, suspended particulate matter and settling particles in the southern Barcelona continental margin were studied in order to evaluate the environmental impact of the anthropogenic metals discharged by the Llobregat River in this Mediterranean area. The temporal variation of heavy metals discharged by this river onto the continental shelf is clearly related to the river water flow. Part of the fine sediment and associated heavy metals transported by the Llobregat River during periods of low river flow accumulate on the river bed, and they are totally removed and discharged onto the Barcelona continental shelf during sporadic river water flow increases. Metals produce significant anomalies of chromium (×2.5), copper (×3.4) and zinc (×3.7) in the surface sediments of the Llobregat prodelta and tend to be transported along the continental shelf following the mean flow. Metals associated with the finest suspended flocs transferred to the slope are controlled by the shelf-slope density front and are transported along slope by the general geostrophic current, instead of accumulating and becoming concentrated in the slope bottom sediments. Settling particulate matter collected in sediment traps on the Barcelona continental slope offshore of the shelf-slope front shows low heavy metal concentrations except in a few sediment trap samples that are significantly metal-enriched in chromium (×4.5) and zinc (×6.8). This enrichment is associated with very short and sporadic river flow increases and is only recorded inside the Foix submarine canyon, which acts as a preferential conduit for the shelf-slope sediment transfer.  相似文献   

Ecological status of seagrass ecosystems: An uncertainty analysis of the meadow classification based on the Posidonia oceanica multivariate index (POMI)     

Bennett S  Roca G  Romero J  Alcoverro T 《Marine pollution bulletin》2011,62(8):1616-1621

Quantifying the uncertainty associated with monitoring protocols is essential to prevent the misclassification of ecological status and to improve sampling design. We assessed the Posidonia oceanica multivariate index (POMI) bio-monitoring program for its robustness in classifying the ecological status of coastal waters within the Water Framework Directive. We used a 7-year data set covering 30 sites along 500 km of the Catalonian coastline to examine which version of POMI (14 or 9 metrics) maximises precision in classifying the ecological status of meadows. Five factors (zones within a site, sites within a water body, depth, years and surveyors) that potentially generate classification uncertainty were examined in detail. Of these, depth was a major source of uncertainty, while all the remaining spatial and temporal factors displayed low variability. POMI 9 matched POMI 14 in all factors, and could effectively replace it in future monitoring programs.  相似文献   

A review of undulated sediment features on Mediterranean prodeltas: distinguishing sediment transport structures from sediment deformation   总被引：2，自引：0，他引：2  

Roger Urgeles  Antonio Cattaneo  Pere Puig  Camino Liquete  Ben De Mol  David Ambl��s  Nabil Sultan  Fabio Trincardi 《Marine Geophysical Researches》2011,32(1-2):49-69

Most Mediterranean prodeltas show undulated sediment features on the foresets of their Holocene wedges. These features have been described all along the Mediterranean for the last 30 years and interpreted as either soft sediment deformation and incipient landsliding, and more recently, as sediment transport structures. We perform a review and detailed analysis of these undulated sediment features using ultrahigh-resolution seismic and bathymetric data as well as geotechnical information and hydrodynamic time series and hydrographic transects. In this study we show that the characteristics of the sediment undulations (configuration of the reflections down section and between adjacent undulations and overall morphologic characteristics) are incompatible with a genesis by sediment deformation alone and do not show evidence of sediment deformation in most cases. Various processes in the benthic boundary layer can be invoked to explain the variety of features observed in the numerous areas displaying sediment undulations.  相似文献   

The influence of basement structure on the evolution of the Bicorb-Quesa Diapir (eastern Betics, Iberian Peninsula): contractive thin-skinned deformation above a pre-existing extensional basement fault     

M. Rubinat  E. Roca  M. Escalas  P. Queralt  O. Ferrer  J. J. Ledo 《International Journal of Earth Sciences》2013,102(1):25-41

On the basis of an analysis of structural surface data in addition to previously available and new magnetotelluric data, it was possible to reconstruct the evolution of Bicorb-Quesa Diapir. This was initiated as a reactive diapir in relation to a basement fault. The reactive diapir was rejuvenated by a thin-skinned compression during the Paleogene and rose during an extensional early-middle Miocene phase. Later, in the middle Miocene, the diapir was squeezed and then, in the late Miocene, was extensionally reactivated. The current reconstruction allows us to analyse a diapir affected by a thin-skinned contractional deformation located on top of a pre-existing basement fault. Our study highlights the role played by the geometric relationship between the propagation direction of the cover deformation and the basement fault.  相似文献   

Modelling a torrential event in a river confluence     

M. Roca  J.P. Martín-Vide  P.J.M. Moreta 《Journal of Hydrology》2009,364(3-4):207-215

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