Diurnal photometric conditions at Teide observatory and long-term solar irradiance variations     

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   

Habitat, occurrence and conservation of Saharo-Arabian-Turanian element Forsskaolea tenacissima L. in the Iberian Peninsula   总被引：1，自引：0，他引：1  

Javier Cabello  Domingo Alcaraz  Francisco Gmez-Mercado  Juan F. Mota  Javier Navarro  Julio Peas  Esther Gimnez 《Journal of Arid Environments》2003,53(4):491-500

The aim of this study is to assess the Iberian populations of Forsskaolea tenacissima L. according to its biogeographical interest, habitat, geographical range and conservation status. Results point out that they are restricted to gravel wadis of Tabernas Desert (SE Spain), are scarcely included in protected areas and represent historically isolated populations with relict behaviour. We also describe a new association, Senecioni-Forsskaoleetum tenacissimae. Conservation status of species is cause for concern and two conservation actions must be carried out. Firstly, protected areas should house Forsskaolea populations and secondly, phytosociological characterization of a community allows inventorying its habitat and directing conservation efforts to community level.  相似文献   

Distribution of benthic flora in the lower course of the Valdivia River,Chile     

Carlos Ramírez  Heriberto Figueroa  Enrique Hauenstein  Domingo Contreras 《Estuaries and Coasts》1989,12(2):111-118

The Valdivia River (Lake Region, Chile) originates in Riñihue Lake and flows into the sea at Corral Bay (39°52′S latitude), changing names several times along its course. The aquatic benthic flora (algae and aquatic plants) of the Valdivia River was characterized, based on 22 sites sampled and 124 plant species collected. Four benthic vegetation zones were established using presence-absence data: a freshwater zone and a marine zone were found at the extremes of the transect; an estuarine zone and a discontinuity zone were detected in the middle of this transect. The freshwater zone was characterized by a relatively diverse assemblage of vascular plants, the marine zone was dominated by algae and was rich in species. By contrast the estuarine zone was inhabited by only a few species but in great abundance, while the discontinuity zone was poor, in species and low in cover vegetation.  相似文献   

Explicit solution of a free boundary problem for a nonlinear absorption model of mixed saturated-unsaturated flow     

Adriana C. Briozzo  Domingo A. Tarzia 《Advances in water resources》1998,21(8):1989

In wet soils, zones of saturation naturally develop in the vicinity of impermeable strata, surface ponds and subterranean cavities. Hydrology must be then concerned with transient flow through coexisting unsaturated and saturated zones. The models of advancing saturated zones necessarily involve a nonlinear free boundary problem.A closed-form analytic solution is presented for a nonlinear diffusion model under conditions of ponding at the surface. The soil water diffusivity is restricted to the special functional form D(θ) = a/(b − θ)², where θ is the water content field to be determined and a, b are positive constants. The explicit solution depends on a parameter C (determined by the data of the problem), according to two cases: 1 < C < C₁ or C ≥ C₁, where C₁ is a constant which is obtained as the unique solution of an equation. This result complements the study given in P. Broadbridge, Water Resources Research, 1990, 26, 2435–2443, in order to established when the explicit solution is available. The behavior of the bifurcation parameter C₁ as a function of the driving potential is studied with the corresponding limits for small and large values. Moreover, the sorptivity is proven to be continuously differentiable function of the variable C.  相似文献   

Results of the solar constant experiment onboard Spacelab 1     

D. A. Crommelynck  R. W. Brusa  V. Domingo 《Solar physics》1986,107(1):1-9

A cavity type absolute radiometer was flown on Spacelab 1 in December 1983. We obtain a value of the solar constant of 1361.5 W m^–2 with an estimated accuracy of ±2.3 W m^–2 or 0.17%. When comparing this with other recent determinations, we find discrepancies which we consider indicative of metrological problems in present day absolute radiometry.  相似文献   

Nonextensive Statistical Mechanics: Some Links with Astronomical Phenomena     

Constantino Tsallis  Constantino Tsallis  Domingo Prato  Angel R. Plastino  Angel R. Plastino 《Astrophysics and Space Science》2004,290(3-4):259-274

A variety of astronomical phenomena appear to not satisfy the ergodic hypothesis in the relevant stationary state, if any. As such, there is no reason for expecting the applicability of Boltzmann–Gibbs (BG) statistical mechanics. Some of these phenomena appear to follow, instead, nonextensive statistical mechanics. In the same manner that the BG formalism is based on the entropy S _BG=?k∑ _i p _i ln p _i, the nonextensive one is based on the form S _q=k(1 ?∑ _i p _i ^q)/(q? 1) (with S ₁=S _BG). The stationary states of the former are characterized by an exponential dependence on the energy, whereas those of the latter are characterized by an (asymptotic) power law. A brief review of this theory is given here, as well as of some of its applications, such as the solar neutrino problem, polytropic self-gravitating systems, galactic peculiar velocities, cosmic rays and some cosmological aspects. In addition to these, an analogy with the Keplerian elliptic orbits versus the Ptolemaic epicycles is developed, where we show that optimizing S _q with a few constraints is equivalent to optimizing S _BG with an infinite number of constraints.  相似文献   

The impact of ecosystem functional type changes on the La Plata Basin climate     

Seung-Jae LEE  E. Hugo BERBERY  Domingo ALCARAZ-SEGURA 《大气科学进展》2013,30(5):1387-1405

In this paper, the effects of land cover changes on the climate of the La Plata Basin in southern South America are investigated using the Weather and Research Forecasting (WRF) Model configured on a 30/10km two-way interactive nested grid. To assess the regional climate changes resulting from land surface changes, the standard land cover types are replaced by time-varying Ecosystem Functional Types (EFTs), which is a newly devised land-cover classification that characterizes the spatial and interannual variability of surface vegetation dynamics. These variations indicate that natural and anthropogenic activities have caused changes in the surface physical parameters of the basin, such as albedo and roughness length, that contributed to regional climate changes. EFTs are obtained from functional attributes of vegetation computed from properties of the Normalized Difference Vegetation Index (NDVI) to represent patches of the land surface with homogeneous energy and gas exchanges with the atmosphere. Four simulations are conducted, each experimental period ranging from September to November in two contrasting years, 1988 and 1998. The influence of an identical EFT change on the surface heat fluxes, 2-m temperature and humidity, 10-m winds, convective instabilities and large-scale moisture fluxes and precipitation are explored for 1988 (a dry year) and 1998 (a wet year). Results show that the surface and atmospheric climate has a larger response to the same EFT changes in a dry year for 2-m temperature and 10-m wind; the response is larger in a wet year for 2-m water vapor mixing ratio, convective available potential energy, vertically integrated moisture fluxes and surface precipitation. For EFTs with high productivity and a weak seasonal cycle, the nearsurface temperature during the spring of 1988 and 1998 increased by as much as 1℃ in the central and western portions of La Plata Basin. Additionally, for higher productivity EFTs, precipitation differences were generally positive in both dry and wet years, although the patterns are not uniform and exhibit certain patchiness with drier conditions.  相似文献   

Preface     

B. Fleck  V. Domingo  A. Poland 《Solar physics》1995,162(1-2):ix

  相似文献   

Limits on the 2.2-μm contrast ratio of the close-orbiting planet HD 189733b     

J. R. Barnes  Travis S. Barman  L. Prato  D. Segransan  H. R. A. Jones  C. J. Leigh  A. Collier Cameron  D. J. Pinfield 《Monthly notices of the Royal Astronomical Society》2007,382(1):473-480

We obtained 238 spectra of the close-orbiting extrasolar giant planet HD 189733b with resolution   R ∼ 15 000  during one night of observations with the Near-Infrared High-Resolution Spectrograph (NIRSPEC), at the Keck II Telescope. We have searched for planetary absorption signatures in the  2.0–2.4 μm  region where H₂O and CO are expected to be the dominant atmospheric opacities. We employ a phase-dependent orbital model and tomographic techniques to search for the planetary absorption signatures in the combined stellar and planetary spectra. Because potential absorption signatures are hidden in the noise of each single exposure, we use a model list of lines to apply a spectral deconvolution. The resulting mean profile possesses a signal-to-noise ratio (S/N) that is 20 times greater than that found in individual lines. Our spectral time series thus yields spectral signatures with a mean S/N = 2720. We are unable to detect a planetary signature at a contrast ratio of  log₁₀( F _p/ F _*) =−3.40  , with 63.8 per cent confidence. Our findings are not consistent with model predictions which nevertheless give a good fit to mid-infrared observations of HD 189733b. The 1σ result is a factor of 1.7 times less than the predicted 2.185-μm planet/star flux ratio of  log₁₀( F _p/ F _*) ∼−3.16  .  相似文献   

SOHO, Yohkoh, Ulysses and Trace: The four solar missions in perspective, and available resources     

V. Domingo 《Astrophysics and Space Science》2002,282(1):171-188

Four solar observing spacecraft, now in operation, have obtained and continue to obtain data during the late phase of solar cycle 22 and hopefully most of cycle 23. The data are available for scientific analysis, practically in an unrestricted manner. A large pool of software suited for the processing and to help programming any data analysis is freely available. An almost random list of results that are being obtained with this data is presented as an example of what can be done by analysing the data from these spacecraft, either alone or combining results among them, with ground observatories, or with other spacecraft, such as those that measure particles and fields in interplanetary space or in geospace, to study solar physics or solar-terrestrial relations. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献