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Andrs Folguera Antonio Introcaso Mario Gimnez Francisco Ruiz Patricia Martinez Cynthia Tunstall Ezequiel García Morabito Víctor A. Ramos 《Tectonophysics》2007,439(1-4):129-147
The western retroarc of the Southern Andes between 38° and 40° S is formed by a NNW-elongated ridge not associated with stacked thrust sheets. On the contrary, during the last 4–3 Ma this ridge was affected by extensional deformation, regional uplift and related folding on a very broad scale. Receiver function analysis shows that the drainage divide area and adjacent retroarc lie over an attenuated crust. Expected crustal thickness at these latitudes is around 38 km, whereas in this part of the retroarc the thickness is less than 32 km. The causes for such attenuation have been linked to a moderate steepening of the subducted Nazca plate beneath the South American plate, which is suggested by a westward shift and narrowing of the magmatic arc during the last 4 to 5 Ma. Gravimetric studies show that the upper plate did not react homogeneously to slab steepening, but ancient sutures and lithospheric discontinuities deeply buried under Mesozoic to Cenozoic sequences in the retroarc were locally reactivated. These processes resulted in an asthenospheric anomaly that correlates at the surface with the area of Pliocene to Quaternary doming, widespread extension and three radial troughs. Two of the troughs have accommodated substantial amounts of extension, but the third was probably aborted at an early stage. Moreover, the presence of an anomalous concentration of calderas and large volcanic centers over the proposed asthenospheric anomaly, and their age distribution, may indicate minor migration of the asthenospheric anomaly between 4 and 2 Ma through the western South American plate. 相似文献
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Concurrent imaging of chlorophyll fluorescence,Chlorophyll a content and green fluorescent proteins‐like proteins of symbiotic cnidarians 
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下载免费PDF全文 Miguel Costa Leal Bruno Jesus João Ezequiel Ricardo Calado Rui Jorge Miranda Rocha Paulo Cartaxana João Serôdio 《Marine Ecology》2015,36(3):572-584
Research on photosynthetic cnidarians has been mainly focused on the symbiosis established between the cnidarian host and its dinoflagellates endosymbionts from genus Symbiodinium. Despite the potential of imaging techniques for assessing the spatial distribution of key parameters of cnidarian photobiology, such as photochemical activity, chlorophyll a content or green fluorescent proteins (GFPs), to our best knowledge, no study has ever attempted to simultaneous map these three features. In this study, we developed a modified imaging pulse amplitude fluorometer by applying excitation light of different wavelengths and selectively detecting short spectral bands through bandpass filters. The imaging system was used to sequentially excite and quantify chlorophyll variable fluorescence (maximum quantum yield of photosystem II, Fv/Fm), Chl a content (normalized difference vegetation index) and relative content of GFPs. The spatial distribution of these photophysiological parameters was mapped both horizontally, across the surface of the soft corals Sarcophyton cf. glaucum and Sinularia flexibilis and the zoanthid Protopalythoa sp., and vertically, throughout a vertical section of S. cf. glaucum. Results showed bleached areas within each individual coral colony and registered photophysiological changes with S. cf. glaucum tissue depth. Analysis of Protopalythoa sp. polyps’ expansion revealed differential surface patterns of NDVI and GFP concentration, and a negative relation between these latter parameters within each polyp. This novel non‐invasive approach allowed a high‐resolution characterization of the spatial relationship between these key parameters through the analysis of image information on a pixel‐by‐pixel basis, which has great potential for investigating the physiological state of symbiotic associations. 相似文献
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Plasma and magnetic field parameter variations across fast forward interplanetary shocks are analyzed during the last solar
cycle minimum (1995–1996, 15 shocks), and maximum year 2000 (50 shocks). It was observed that the solar wind velocity and
magnetic field strength variation across the shocks were the parameters better correlated with Dst. Superposed epoch analysis centered on the shock showed that, during solar minimum, B
z
profiles had a southward, long-duration variation superposed with fluctuations, whereas in solar maximum the B
z
profile presented 2 peaks. The first peak occurred 4 hr after the shock, and seems to be associated with the magnetic field
disturbed by the shock in the sheath region. The second peak occurred 19 hr after the shock, and seems to be associated with
the ejecta fields. The difference in shape and peak in solar maximum (Dst peak =−50 nT, moderate activity) and minimum (Dst peak =−30 nT, weak activity) in average Dst profiles after shocks are, probably, a consequence of the energy injection in the magnetosphere being driven by different
interplanetary southward magnetic structures. A statistical distribution of geomagnetic activity levels following interplanetary
shocks was also obtained. It was observed that during solar maximum, 36% of interplanetary shocks were followed by intense
(Dst≤−100 nT) and 28% by moderate (−50≤Dst <−100 nT) geomagnetic activity. During solar minimum, 13% and 33% of the shocks were followed by intense and moderate geomagnetic
activity, respectively. Thus, during solar maximum a higher relative number of interplanetary shocks might be followed by
intense geomagnetic activity than during solar minimum. One can extrapolate, for forecasting goals, that during a whole solar
cycle a shock has a probability of around 50–60% to be followed by intense/moderate geomagnetic activity. 相似文献
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We study the interplanetary features and concomitant geomagnetic activity of the two high-speed streams (HSSs) selected by the Whole Heliosphere Interval (WHI) campaign participants: 20 March to 16 April 2008 in Carrington rotation (CR) 2068. This interval was chosen to perform a comprehensive study of HSSs and their geoeffectiveness during this ??deep?? solar minimum. The two HSSs within the interval were characterized by fast solar-wind speeds (peak values >?600 km?s?1) containing large-amplitude Alfvénic fluctuations, as is typical of HSSs during normal solar minima. However, the interplanetary magnetic field (IMF) magnitude [B o] was exceptionally low (??3??C?5 nT) during these HSSs, leading to lower than usual IMF B z values. The first HSS (HSS1) had favorable IMF polarity for geomagnetic activity (negative during northern Spring). The average AE and Dst for the HSS1 proper (HSS1P) were +?258 nT and ??21 nT, respectively. The second HSS (HSS2) had a positive sector IMF polarity, one that is less favorable for geomagnetic activity. The AE and Dst index averages were +?188 nT and ??7 nT, both lower than corresponding numbers for the first event, as expected. The HSS1P geomagnetic activity is comparable to, and the HSS2P geomagnetic activity lower than, corresponding observations for the previous minimum (1996). Both events?? geomagnetic activities are lower than HSS events previously studied in the declining phase (in 2003). In general, V sw was faster for the HSSs in 2008 compared to 1996. The southward IMF B z was lower in the former. The product of these two parameters [V sw and IMF B z ] comprises the solar-wind electric field, which is most directly associated with the energy input into the magnetosphere during the HSS intervals. Thus the combined effects led to the solar wind energy input in 2008 being slightly less than that in 1996. A detailed analysis of magnetic-field variances and Alfvénicity is performed to explore the characteristics of Alfvén waves (a central element in the geoeffectiveness of HSSs) during the WHI. The B z variances in the proto-CIR (PCIR) were ???30 nT2 and <?10 nT2 in the high speed streams proper. 相似文献
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We address the geoeffectiveness of three interplanetary structures in the interplanetary space: magnetic clouds (MCs), interplanetary shocks (IPSs), and corotating interaction regions (CIRs). The geoeffectiveness is evaluated using the geomagnetic indices Kp, AE, and Dst. We find that MCs are more geoeffective than IPSs, or CIRs. The average values of magnetic indices are significantly enhanced during disturbed periods associated with MCs, IPSs and CIRs, compared to the whole interval. The highest effect is noted for MC disturbed periods.Results obtained for the three data sets are used to derive a theoretical (continuous) probability distribution function (PDF) by fitting the histograms representing the percentage of events against the intervals of magnetic index. PDFs allow estimation of the probability of a given level of geomagnetic activity to be reached after the detection, by in situ solar wind observations, of a given interplanetary structure approaching the Earth. 相似文献
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E. Echer B.T. Tsurutani F.L Guarnieri J.U. Kozyra 《Journal of Atmospheric and Solar》2011,73(11-12):1330-1338
The seven CAWSES interplanetary fast forward shocks and their geomagnetic effects during 2004–2005 have been analyzed. It is found that the arrival time of the shocks at Earth can be estimated within an accuracy of ～5 min. Furthermore, AL decreases are found to occur within 10 min of shock impingement on the magnetopause. It was also determined that there is a direct correlation between the interplanetary magnetic field southward directed (IMF Bs) prior to shock arrival and substorms triggered by the shocks. If the IMF is northward prior to shock arrival, the geomagnetic activity is present but is low. One interpretation of this result is that the preconditioning energy stored in the magnetotail leaks away rapidly. A correlation between substorm peak AL and shock strength (Mach number) has also been noted, which could imply that shock strength is important for the amount of energy released into the magnetosphere/ionosphere. 相似文献
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R.R.S. De Mendonça J.-P. Raulin F.C.P. Bertoni E. Echer V.S. Makhmutov G. Fernandez 《Journal of Atmospheric and Solar》2011,73(11-12):1410-1416
We present results obtained at El Leoncito (CASLEO, San Juan, Argentina) with the CARPET charged particles detector installed in April 2006. The observed modulation of the cosmic ray flux is discussed as a function of its time variability and it is related to longer solar activity variations and to shorter variations during solar and geomagnetic transient activity. Short period (few minutes, few hours) cosmic ray modulation events are observed during rain time (precipitation) and significant variations of the atmospheric electric field. Complementary observations of the atmospheric electric field indicate that its time variations play an important role in the detected cosmic ray event. 相似文献
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A. Prestes N.R. Rigozo D.J.R. Nordemann C.M. Wrasse M.P. Souza Echer E. Echer M.B. da Rosa P.H. Rampelotto 《Journal of Atmospheric and Solar》2011,73(11-12):1587-1593
This study of Sun–Earth relationships is based on tree growth rings analysis of araucarias (Araucaria angustifolia) collected at Severiano de Almeida (RS) Brazil. A chronology of 359 years was obtained, and the classical method of spectral analysis by iterative regression and wavelet method was applied to find periodicities and trends contained in the tree growth. The analysis of the dendrochronological series indicates representative periods of solar activity of 11 (Schwabe cycle), 22 (Hale cycle), and 80 (Gleissberg cycle) years. The result shows the possible influence of the solar activity on tree growth in the last 350 years. Periods of 2–7 years were also found and could represent a response of the trees to local climatic conditions. Good agreement between the time series of tree growth rings and the 11 year solar cycle was found during the maximum solar activity periods. 相似文献