Quiescent Reconnection Rate Between Emerging Active Regions and Preexisting Field,with Associated Heating: NOAA AR 11112

When magnetic flux emerges from beneath the photosphere, it displaces the preexisting field in the corona, and a current sheet generally forms at the boundary between the old and new magnetic domains. Reconnection in the current sheet relaxes this highly stressed configuration to a lower energy state. This scenario is most familiar and most often studied in flares, where the flux transfer is rapid. We present here a study of steady, quiescent flux transfer occurring at a rate three orders of magnitude lower than that in a large flare. In particular, we quantify the reconnection rate and the related energy release that occurred as the new polarity emerged to form NOAA Active Region 11112 (SOL16 October 2010T00:00:00L205C117) within a region of preexisting flux. A bright, low-lying kernel of coronal loops above the emerging polarity, observed with the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory and the X-ray Telescope onboard Hinode, originally showed magnetic connectivity only between regions of newly emerged flux when overlaid on magnetograms from the Helioseismic and Magnetic Imager. Over the course of several days, this bright kernel advanced into the preexisting flux. The advancement of an easily visible boundary into the old flux regions allows measuring the rate of reconnection between old and new magnetic domains. We compare the reconnection rate with the inferred heating of the coronal plasma. To our knowledge, this is the first measurement of steady, quiescent heating related to reconnection. We determined that the newly emerged flux reconnects at a fairly steady rate of 0.38×10¹⁶ Mx?s^?1 over two days, while the radiated power varies between (2?–?8)×10²⁵ erg?s^?1 over the same time. We found that as much as 40 % of the total emerged flux at any given time may have reconnected. The total amounts of transferred flux (～?1×10²¹ Mx) and radiated energy (～?7.2×10³⁰ ergs) are comparable to that of a large M- or small X-class flare, but are stretched out over 45 hours.     

Coda wave attenuation in the Parecis Basin,Amazon Craton,Brazil: sensitivity to basement depth

Small local earthquakes from two aftershock sequences in Porto dos Gaúchos, Amazon craton—Brazil, were used to estimate the coda wave attenuation in the frequency band of 1 to 24 Hz. The time-domain coda-decay method of a single backscattering model is employed to estimate frequency dependence of the quality factor (Q _c) of coda waves modeled using Q_c = Q₀ f^hQ_{\rm c} =Q_{\rm 0} f^\eta , where Q ₀ is the coda quality factor at frequency of 1 Hz and η is the frequency parameter. We also used the independent frequency model approach (Morozov, Geophys J Int, 175:239–252, 2008), based in the temporal attenuation coefficient, χ(f) instead of Q(f), given by the equation c(f)=g+\fracpfQ_e \chi (f)\!=\!\gamma \!+\!\frac{\pi f}{Q_{\rm e} }, for the calculation of the geometrical attenuation (γ) and effective attenuation (Q_e^-1 )(Q_{\rm e}^{-1} ). Q _c values have been computed at central frequencies (and band) of 1.5 (1–2), 3.0 (2–4), 6.0 (4–8), 9.0 (6–12), 12 (8–16), and 18 (12–24) Hz for five different datasets selected according to the geotectonic environment as well as the ability to sample shallow or deeper structures, particularly the sediments of the Parecis basin and the crystalline basement of the Amazon craton. For the Parecis basin Q_c = (98±12)f^(1.14±0.08)Q_{\rm c} =(98\pm 12)f^{(1.14\pm 0.08)}, for the surrounding shield Q_c = (167±46)f^(1.03±0.04)Q_{\rm c} =(167\pm 46)f^{(1.03\pm 0.04)}, and for the whole region of Porto dos Gaúchos Q_c = (99±19)f^(1.17±0.02)Q_{\rm c} =(99\pm 19)f^{(1.17\pm 0.02)}. Using the independent frequency model, we found: for the cratonic zone, γ = 0.014 s^− 1, Q_e^-1 = 0.0001Q_{\rm e}^{-1} =0.0001, ν ≈ 1.12; for the basin zone with sediments of ~500 m, γ = 0.031 s^− 1, Q_e^-1 = 0.0003Q_{\rm e}^{-1} =0.0003, ν ≈ 1.27; and for the Parecis basin with sediments of ~1,000 m, γ = 0.047 s^− 1, Q_e^-1 = 0.0005Q_{\rm e}^{-1} =0.0005, ν ≈ 1.42. Analysis of the attenuation factor (Q _c) for different values of the geometrical spreading parameter (ν) indicated that an increase of ν generally causes an increase in Q _c, both in the basin as well as in the craton. But the differences in the attenuation between different geological environments are maintained for different models of geometrical spreading. It was shown that the energy of coda waves is attenuated more strongly in the sediments, Q_c = (78±23)f^(1.17±0.14)Q_{\rm c} =(78\pm 23)f^{(1.17\pm 0.14)} (in the deepest part of the basin), than in the basement, Q_c = (167±46)f^(1.03±0.04)Q_{\rm c} =(167\pm 46)f^{(1.03\pm 0.04)} (in the craton). Thus, the coda wave analysis can contribute to studies of geological structures in the upper crust, as the average coda quality factor is dependent on the thickness of sedimentary layer.     

Preserved‐amplitude angle domain migration by shot‐receiver wavefield continuation

We present preserved‐amplitude downward continuation migration formulas in the aperture angle domain. Our approach is based on shot‐receiver wavefield continuation. Since source and receiver points are close to the image point, a local homogeneous reference velocity can be approximated after redatuming. We analyse this approach in the framework of linearized inversion of Kirchhoff and Born approximations. From our analysis, preserved‐amplitude Kirchhoff and Born inverse formulas can be derived for the 2D case. They involve slant stacks of filtered subsurface offset domain common image gathers followed by the application of the appropriate weighting factors. For the numerical implementation of these formulas, we develop an algorithm based on the true amplitude version of the one‐way paraxial approximation. Finally, we demonstrate the relevance of our approach with a set of applications on synthetic datasets and compare our results with those obtained on the Marmousi model by multi‐arrival ray‐based preserved‐amplitude migration. While results are similar, we observe that our results are less affected by artefacts.     

REMOTE SENSING IN THE SOLUTION OF SCIENTIFIC AND ECONOMIC PROBLEMS IN CUBA

Remote sensing inventories of the land and marine resources of Cuba, both from satellite and aerial platforms, are assessed in terms of their contributions to research on the country's physical and economic geography. Under the auspices of an international cooperative program “Interkosmos,” maps of many types have been upgraded, the costs of surveys have been reduced dramatically, and the potential for monitoring natural and human-induced change is being realized more fully. In addition, a study of weather and other conditions affecting image quality led to a determination of optimal times for conducting remote sensing surveys. Translated from: Vestnik Moskovskogo Universiteta, geografiya, 1988, No. 3, pp. 36-41, by Edward Torrey, Alexandria, VA 22308.     

Multi-criteria modelling and clustering of spatial information

To improve the formal integration of verbally given spatial information in a geographical information system, a methodology for converting such information to a geographical representation was developed. This was applied to examples of a spatial-related analysis of natural language text messages in the domain of disaster management. This article presents an approach for such a conversion by using a suitable knowledge representation as well as formal modelling structures. The structures are provided by an ontology-supported knowledge base. With respect to spatial uncertainty, a formal representation based on possibility theory was defined. Moreover, a cluster algorithm was developed for handling information of different sources and building a spatial context.     

Recharge estimates for various land uses in the Guarani Aquifer System outcrop area

ABSTRACT

The Guarani Aquifer System (GAS) is a subsurface reservoir that contains the largest volume of fresh groundwater in South America. Despite the relevance of the GAS, a lack of attention has been paid to land use effects on its recharge. We present the most detailed long-term (2004–2011) results of land-use effects on recharge in an outcrop area of the GAS. Water table fluctuations (WTFs) were measured at 11 monitoring wells, which are distributed between different land uses (i.e. eucalyptus, sugarcane, citrus and grassland). Recharge was estimated using a point-scale method (WTF) for each monitored well. The annual recharge estimates for different land uses are eucalyptus forest (135 mm year^-1), sugarcane (248 mm year^-1), citrus areas (296 mm year^-1) and grassland (401 mm year^-1). The results indicate that the evapotranspiration seems to be a key parameter in the assessment of recharge in the study area.     

Scenarios in Global Environmental Assessments: Key characteristics and lessons for future use

Over the last 10 years a large set of global environmental assessment studies has been published that include scenario projections. Comparison of these studies shows that there is actually a limited set of scenario families that form the basis of many scenarios used in different environmental assessments. Mapping these scenario families allow a simpler comparison across the different assessments. The fact that many assessments can be positioned within these families gives some confidence of their relevance. It is also noticeable that several recent assessments have been focusing on more focussed policy-scenarios as variant to a single baseline. This is partly a response to a different stage in the policy-making process. While there are clear advantages of both categories of scenarios (explorative scenarios and baseline/policy variants), it might be important to test the robustness of scenario outcomes of the policy-scenario approach against the different storyline scenario-families identified in this paper.