Spectral analysis of Pennocarboniferous geomagnetic variation data from glacial rhythmites     

M. Ernesto  I. G. Pacca 《Geophysical Journal International》1981,67(3):641-647

Summary. Palaeomagnetic results for a sequence of Permocarboniferous rhythmites presented in the previous paper have been submitted to maximum entropy spectral analysis to test whether these palaeomagnetic data could supply information on geomagnetic variations. There is a good correlation between the thickness of the rhythmites and sunspot spectra, suggesting that these sediments are really seasonal. The palaeomagnetic spectra are compared with those of observatory records. Periods of approximately 24.4, 12.4, 8.6, 6.7 and 5.5 found for palaeomagnetic data have corresponding values in the geomagnetic spectrum. Most of these periods, however, are the same as those found in the thickness data, implying that magnetization can be influenced by the sedimentation process as suggested by other investigators. On the other hand, both geomagnetic and climatic (thickness) variations seem to be related to solar activity. Therefore, at least indirectly, palaeomagnetic data may reflect geomagnetic variations.  相似文献   

A Gravimetric Geoid Computation and Comparison with GPS Results in Northern Andalusia (Spain)     

De Lacy  M.C.  Rodríguez-Caderot  G.  Marín  E.  Ruiz  A.  Borque  M.J.  Gil  A.J.  Biagi  L. 《Studia Geophysica et Geodaetica》2001,45(1):55-66

Two new GPS surveys have been carried out to check the accuracy of an existing gravimetric geoid in a test area located in northern Andalusia (Spain). The fast collocation method and the remove-restore procedure have been used for the computation of the quasigeoid model. The Spanish height system is based on orthometric heights, so the gravimetrically determined quasigeoid has been transformed to a geoid model and then compared to geoid undulations provided by GPS and levelling at benchmarks belonging to the Spanish first-order levelling network. The discrepancies between the gravimetric solution and GPS/levelling undulations amount to ±2 cm for one survey and ±5 cm for another after fitting a plane to the geoid model.  相似文献   

Maritime Europe and EU enlargement. A geopolitical perspective     

Juan Luis Suárez de Vivero  Juan Carlos Rodríguez Mateos 《Marine Policy》2006

The 2004 enlargement of the European Union (EU), as well as the further enlargements planned from 2007 onwards (Romania, Bulgaria, Croatia and Turkey), entail changes of a geo-political nature that not only imply an increase in size (a rise in the number of States, new boundaries), but, more especially, also involve a shift in the EU's maritime status, with its projection towards the Atlantic now being checked by a swing towards continental Europe and its inland seas. In view of the new political map being drawn up, two questions beg to be asked: to what extent is Europe's maritime condition being strengthened; and, does the new maritime Europe constitute an opportunity, or does it aggravate the already-existing problems and threats?  相似文献   

Geoid determination in central Spain from gravity and height data     

A. J. Gil  M. J. Sevilla  G. Rodríguez-Caderot 《Journal of Geodesy》1993,67(1):41-50

Summary The least-squares collocation method has been used for the computation of a geoid solution in central Spain, combining a geopotential model complete to degree and order 360, gravity anomalies and topographic information. The area has been divided in two 1°× 1° blocks and predictions have been done in each block with gravity data spacing about 5 × 5 within each block, extended 1/2°. Topographic effects have been calculated from 6 × 9 heights using an RTM reduction with a reference terrain model of 30 × 30 mean heights.  相似文献   

Tropospheric degradation products of CH2FCF3 (HFC-134a)     

Ernesto C. Tuazon  Roger Atkinson 《Journal of Atmospheric Chemistry》1993,16(4):301-312

Chlorine atom-initiated photooxidations of CH₂FCF₃ (HFC-134a) in O₂-N₂ diluent were carried out to identify the products formed from the \(CF_3 CHF\dot O\) radical reactions and to determine the product yields as a function of temperature, pressure and O₂ concentration. CF₃C(O)F and HC(O)F were the major ‘first-generation’ products observed, along with smaller yields of C(O)F₂ and, as yet, undetermined yields of CF₃OOOCF₃ and CF₃OOC(O)F. The relative importance of the two major \(CF_3 CHF\dot O\) reaction pathways, is expressed by the rate constant ratio $$k_{O_2 } /k_d = 3.2 \times 10^{ - 25} e^{(3510 \pm 470)/T} cm^3 molecule^{ - 1}$$ The decomposition reaction leading to HC(O)F and ?F₃ radical products is predicted to be the dominant pathway at the Earth's surface while mainly CF₃C(O)F formation will occur at the tropopause.  相似文献   

Stratification of the 5-min oscillation through the solar photosphere     

Rodríguez Hidalgo  I.  Ruiz Cobo  B.  Collados  M. 《Solar physics》1997,172(1-2):77-83

The inversion of the radiative transfer equation has been applied to a time series of low spatial resolution Ki 7699 Å line spectra, allowing us to obtain a sequence of instantaneous models which are compared to the mean one to derive the 5-min oscillation stratification. The resulting models are reliable from log 0 to log -3.5. The increase of the velocity oscillation amplitude towards higher photospheric layers has been confirmed and quantified. Significant oscillation is observed in temperature.  相似文献   

Photometry and spectroscopy of the solar granulation along the polar axis and equator     

I. Rodríguez Hidalgo  M. Collados  M. Vázquez 《Astrophysics and Space Science》1990,170(1-2):23-30

From high-resolution CCD images of granulation obtained at the Swedish Solar Tower of the Observatorio del Roque de los Muchachos at different positions on the solar disk, mean bi-dimensional spatial power spectra have been obtained at each position and restored following the method proposed by Rodríguez Hidalgoet al. (1990). The variation with latitude of the power spectrum, of the granular brightness contrast and of the mean wave number of the power spectrum are presented. The analysis is completed with spectroscopic observations obtained at the Gregory Coudé Telescope of the Observatorio del Teide. The centre-to-limb and latitudinal variation of the bisectors, residual intensities and equivalent widths are shown for several photometric lines.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.  相似文献   

Fried's parameter derived from observations of granulation outside the disk centre     

I. Rodríguez Hidalgo  M. Collados  M. Vázquez 《Astrophysics and Space Science》1990,170(1-2):155-159

A new method has recently been developed to obtain the Fried's parameter from observations of granulation outsude the disk centre, based on the different degradation suffered by the images on the directions parallel and perpendicular to the solar limb, due to the geometrical foreshortening. This procedure has been applied to CCD images obtained at the Swedish Solar Tower of the Observatorio del Roque de los Muchachos, with satisfactory results which are presented and discussed.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.  相似文献   

Frequency and duration of historical droughts from the 16th to the 19th centuries in the Mexican Maya lands, Yucatan Peninsula     

Blanca Mendoza  Virginia García-Acosta  Victor Velasco  Ernesto Jáuregui  Rosa Díaz-Sandoval 《Climatic change》2007,83(1-2):151-168

Using unprecedented catalogues of past severe drought data for the Yucatan Peninsula between 1502 and 1900 coming from historical written documentation, we identified five conspicuous time lapses with no droughts between 1577–1647, 1662–1724, 1728–1764, 1774–1799 and 1855–1880, as well as time epochs with most frequent droughts between 1800 and 1850. Moreover, the most prominent periodicity of the historical drought time series was that of ∼40 years. Using the Palmer Drought Severity Index for the Yucatan Peninsula for the period 1921–1987 we found prominent negative phases between ∼1942–1946 and 1949–1952, 1923–1924, 1928–1929, 1935–1936, 1962–1963, 1971–1972 and 1986–1987. Two prominent periodicities clearly appear at ∼5 and 10 years. Most modern and historical severe droughts lasted 1 year, and share a quasi-decadal frequency. Also, in the first 66 years of the twentieth century the frequency of occurrence of severe drought has been lower compared with the nineteenth century. Some of the major effects and impacts of the most severe droughts in the Yucatan region are examined. We also studied the relation between historical and modern droughts and several large scale climate phenomena represented by the Atlantic Multidecadal Oscillation (AMO) and the Southern Oscillation Index (SOI). Our results indicate that historical droughts and the cold phase of the AMO coincide, while the influence of the SOI is less clear. The strongest coherence between historical droughts and AMO occurred at periodicities of ∼40 years. For modern droughts the coherence of a drought indicator (the Palmer Drought Severity Index) is similar with AMO and SOI, although it seems more sustained with the AMO. They are strongest at ∼10 years and very clearly with the AMO cold phase. Concerning the solar activity proxies and historical droughts, the coherence with a record of beryllium isotope Be¹⁰, which is a good proxy of cosmic rays, is higher than with Total Solar Irradiance. We notice that the strongest coherence between historical droughts and Be¹⁰ occurs at periods ∼60–64 years. When studying modern droughts and solar activity, frequencies of ∼8 years appear, and the coherences are similar for both sunspots and cosmic rays. Comparing natural terrestrial and solar phenomena, we found that the most sustained and strongest modulation of historical drought occurrence is at ∼60–64 years and is between the historical drought series and the solar proxy Be¹⁰. For modern droughts we notice that the coherence is similar among AMO, SOI and the solar indices. We can conclude that the sea surface temperatures (AMO) and solar activity leave their signal in terms of severe droughts in the Maya lands, however in the long term, the influence of the SOI on this type of phenomenon is less clear.  相似文献   

The Southern Region of Peru Earthquake of June 23rd, 2001     

Hernando Tavera  Efraín Fernández  Isabel Bernal  Yanet Antayhua  Consuelo Agüero  Henry Salas Simeón Rodríguez  Luis Vilcapoma  Yolanda Zamudio  David Portugal  Adolfo Inza  Julia Carpio  Freddy Ccallo  Igor Valdivia 《Journal of Seismology》2006,10(2):171-195

The western border of South America is one of the most important seismogenic regions in the world. In this region the most damaging earthquake ever recorded occurred. In June 23rd, 2001, another very strong earthquake (Mw = 8.1–8.2) occurred and produced death and damages in the whole southern region of Peru. This earthquake was originated by a friction process between Nazca and South American plates and affected an area of about 300 km × 120 km defined by the distribution of more than 220 aftershocks recorded by a local seismic network that operated 20 days. The epicenter of the main shock was localized in the northwestern extremity of the aftershock area, which suggests that the rupture propagated towards the SE direction. The modeling of P-wave for teleseismic distances permitted to define a focal mechanism of reverse type with NW-SE oriented nodal planes and a possible fault plane moving beneath almost horizontally in NE direction. The source time function (STF) suggests a complex process of rupture during 85 sec with 2 successive sources. The second one of greater size, and located approximately 100–120 km toward the SE direction was estimated to have a rupture velocity of about 2 km/sec on a 28°-dipping plane to the SE (N135°). A second event happened 45 sec after the first one with an epicenter 130km farther to the SE and a complex STF. This event and the second source of the main shock caused a Tsunami with waves from 7 to 8 meters that propagated almost orthogonally to the coast line, by affecting mainly the Camaná area.Three of all the aftershocks presented magnitudes greater or equal to Mw = 6.6, two of them occurred in front of the cities of Ilo and Mollendo (June 26th and July 7th) with focal mechanisms similar to the main seismic event. The aftershock of July 5th shows a normal mechanism at a depth of 75 km, and is therefore most likely located within the subducting Nazca plate and not in the coupling. The aftershocks of June 26th (Mw = 6.6) and July 5th (Mw = 6.6) show simple short duration STF. The aftershock of July 7th (Mw = 7.5) with 27-second duration suggests a complex process of energy release with the possible occurrence of a secondary shock with lower focal depth and focal mechanism of inverse type with a great lateral component. Simple and composed focal mechanisms were elaborated for the aftershocks and all have similar characteristics to the main earthquake.The earthquake of June 23rd caused major damages in the whole southern Peru. The damage in towns of Arequipa, Moquegua allow to consider maximum intensities from 6 to 7 (MSK79). In Alto de la Alianza and Ciudad Nueva zones from Tacna, the maximum intensity was of 7⁻ (MSK79).  相似文献