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11.
Tilaye Tadesse Alexei A. Pevtsov T. Wiegelmann P. J. MacNeice S. Gosain 《Solar physics》2014,289(11):4031-4045
Solar eruptive phenomena, like flares and coronal mass ejections (CMEs), are governed by magnetic fields. To describe the structure of these phenomena one needs information on the magnetic flux density and the electric current density vector components in three dimensions throughout the atmosphere. However, current spectro-polarimetric measurements typically limit the determination of the vector magnetic field to only the photosphere. Therefore, there is considerable interest in accurate modeling of the solar coronal magnetic field using photospheric vector magnetograms as boundary data. In this work, we model the coronal magnetic field for global solar atmosphere using nonlinear force-free field (NLFFF) extrapolation codes implemented to a synoptic maps of photospheric vector magnetic field synthesized from the Vector Spectromagnetograph (VSM) on Synoptic Optical Long-term Investigations of the Sun (SOLIS) as boundary condition. Using the resulting three-dimensional magnetic field, we calculate the three-dimensional electric current density and magnetic energy throughout the solar atmosphere for Carrington rotation 2124 using our global extrapolation code. We found that spatially, the low-lying, current-carrying core field demonstrates a strong concentration of free energy in the active-region core, from the photosphere to the lower corona (about 70 Mm). The free energy density appears largely co-spatial with the electric current distribution. 相似文献
12.
T. Wiegelmann J. K. Thalmann B. Inhester T. Tadesse X. Sun J. T. Hoeksema 《Solar physics》2012,281(1):37-51
The Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) provides photospheric vector magnetograms with a high spatial and temporal resolution. Our intention is to model the coronal magnetic field above active regions with the help of a nonlinear force-free extrapolation code. Our code is based on an optimization principle and has been tested extensively with semianalytic and numeric equilibria and applied to vector magnetograms from Hinode and ground-based observations. Recently we implemented a new version which takes into account measurement errors in photospheric vector magnetograms. Photospheric field measurements are often affected by measurement errors and finite nonmagnetic forces inconsistent for use as a boundary for a force-free field in the corona. To deal with these uncertainties, we developed two improvements: i) preprocessing of the surface measurements to make them compatible with a force-free field, and ii) new code which keeps a balance between the force-free constraint and deviation from the photospheric field measurements. Both methods contain free parameters, which must be optimized for use with data from SDO/HMI. In this work we describe the corresponding analysis method and evaluate the force-free equilibria by how well force-freeness and solenoidal conditions are fulfilled, by the angle between magnetic field and electric current, and by comparing projections of magnetic field lines with coronal images from the Atmospheric Imaging Assembly (SDO/AIA). We also compute the available free magnetic energy and discuss the potential influence of control parameters. 相似文献
13.
Tadesse Yihunie 《International Journal of Earth Sciences》2002,91(5):922-933
Polydeformed and metamorphosed Neoproterozoic rocks of the East African Orogen in the Negele area constituted three lithostructurally distinct and thrust-bounded terranes. These are, from west to east, the Kenticha, Alghe and Bulbul terranes. The Kenticha and Bulbul terranes are metavolcano-sedimentary and ultramafic sequences, representing parts of the Arabian-Nubian Shield (ANS), which are welded to the central Alghe gneissic terrane of the Mozambique Belt affinity along N-S-trending sheared thrust contacts. Structural data suggest that the Negele basement had evolved through three phases of deformation. During D1 (folding) deformation, north-south upright and inclined folds with north-trending axes were developed. East and west-verging thrusts, right-lateral shearing along the north-oriented Kenticha and Bulbul thrust contacts and related structural elements were developed during D2 (thrusting) deformation. The pervasive D1 event is interpreted to have occurred at 620-610 Ma and the D2 event ended prior to 554 Ma. Right-lateral strike-slips along thrust contacts are interpreted to have been initiated during late D2. During D3, left-lateral strike-slip along the Wadera Shear Zone and respective strike-slip movements along conjugate set of shear zones were developed in the Alghe terrane, and are interpreted to have occurred later than 557 Ma. The structural data suggest that eastward thrusting of the Kenticha and westward tectonic transport of the Bulbul sequences over the Alghe gneissic terrane of the Mozambique Belt, during D2, were accompanied by right-lateral strike-slip displacements along thrust contacts. Right-lateral strike-slip movements along the Kenticha thrust contact, further suggest northward movement of the Kenticha sequence during the Pan-African orogeny in the Neoproterozoic. Left-lateral strike-slip along the orogen-parallel NNE-SSW Wadera Shear Zone and strike-slip movements along a conjugate set of shear zones completed final terrane amalgamation between the Arabian-Nubian Shield and the Mozambique Belt in Neoproterozoic southern Ethiopia. 相似文献
14.
A. E. C. Duker T. M. Tadesse T. Soentoro C. de Fraiture J. S. Kemerink-Seyoum 《Climate Policy》2019,19(6):S36-S46
ABSTRACTChanges in agricultural practices can play a pivotal role in climate change mitigation by reducing the need for land use change as one of the biggest sources of GHG emissions, and by enabling carbon sequestration in farmers’ fields. Expansion of smallholder and commercial agriculture is often one of the main driving forces behind deforestation and forest degradation. However, mitigation programmes such as REDD+ are geared towards conservation efforts in the forestry sector without prominently taking into account smallholder agricultural interests in project design and implementation. REDD+ projects often build on existing re- and afforestation projects without major changes in their principles, interests and assumptions. Informed by case study research and interviews with national and international experts, we illustrate with examples from Ethiopia and Indonesia how REDD+ projects are implemented, how they fail to adequately incorporate the demands of smallholder farmers and how this leads to a loss of livelihoods and diminishing interest in participating in REDD+ by local farming communities. The study shows how the conservation-based benefits and insecure funding base in REDD+ projects do not compensate for the contraction in livelihoods from agriculture. Combined with exclusive benefit-sharing mechanisms, this results in an increased pressure on forest resources, diverging from the principal objective of REDD+. We note a gap between the REDD+ narratives at international level (i.e. coupling development with a climate agenda) and the livelihood interests of farming communities on the ground. We argue that without incorporating agricultural interests and a review of financial incentives in the design of future climate finance mechanisms, objectives of both livelihood improvements and GHG emission reductions will be missed.Key policy insights
REDD+ is positioned as a promising tool to meet climate, conservation and development targets. However, these expectations are not being met in practice as the interests of smallholder farmers are poorly addressed.
REDD+ policy developers and implementers need more focus on understanding the interests and dynamics of smallholder agriculturalists to enable inclusive, realistic and long-lasting projects.
For REDD+ to succeed, funders need to consider how to better ensure long-term livelihood security for farming communities.
15.
Traditional approaches to risk communication ignore the emotional, cognitive and social factors that interact to influence the meaning people attribute to hazards and protective actions. The aim of this study was to investigate the emotional and cognitive factors predicting preparedness intention and community’s preparedness for flood hazards. A cross-sectional study was conducted between June and July 2015, in Dire Dawa town, Ethiopia. Using stratified systematic random sampling, a structured questionnaire was administered to individuals aged 18 and over in 660 households. Data were analyzed using structural equation modeling (SEM) (STATA version 13.0). The study participants’ mean age was 34 years, ranging from 18 to 80 (SD?=?12) with equal gender balance. SEM analysis revealed that the total effects of preparedness intention (path coefficient (β)?=?0.202, 95% CI: [0.036, 0.369]), past flood disaster experience (β?=?0.034, 95% CI: [0.008, 0.061]), trust (β?=?0.100, 95% CI: [0.059, 0.142]), anxiety (β?=?0.026, 95% CI: [0.018, 0.034), positive outcome expectancy (β?=???0.139, 95% CI: [??0.253, ??0.026]), negative outcome expectancy (β?=?0.105, 95% CI: [0.062, 0.149]), perceived flood likelihood (β?=?0.049, 95% CI: [0.012, 0.086]) and consequence (β?=???0.040, 95% CI: [??0.077, ??0.003]) on community preparedness for flood hazards were statistically significant. The main implication of these findings is that people affected by hazard events in the past experience more anxiety and are more likely to participate in community preparedness activities than those who were not affected. 相似文献
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Estimation of sedimentation in reservoirs helps in the management and design of the reservoir's useful capacity. This research was done on the Awash River basin at the Koka Dam Reservoir in Ethiopia. The method applied was the loose integration of the Soil and Water Assessment Tool(SWAT) model and Hydrologic Engineering Center-River Analysis System(HEC-RAS) model for the estimation of the sediment load reaching the reservoir. The SWAT model was used for the estimation of erosion at the catchment level,and the HEC-RAS model was applied to estimate the sediment transport in the river channel. The implemented method allows sedimentation in the floodplains and bed shear stress to be considered in the sediment modeling, which cannot be considered in the SWAT model. In addition, the river cross sectional properties and the hydrodynamic processes in the rivers were considered in the modeling process. The data used in this study are a combination of i) observed data collected by government agencies, ii) data available online in data repositories, and iii) data extracted from remote sensing in the Shuttle Radar Topographic Mission(SRTM) Digital Elevation Model(DEM). The calibration and validation of the SWAT model was done by using Sequential Uncertainty Fitting(SUIF-2) calibration and validation tools. The HEC-RAS model was calibrated by adjusting the roughness factor. The output from the integrated approaches gives better estimates of flow and sediment near the inlet to the reservoir, with coefficients of determination of 0.85 and 0.67, respectively, and Nash Sutcliffe coefficients of model fit efficiency of 0.90 and 0.62, respectively, for daily simulations. 相似文献
18.
Determinants of farmers’ choice of adaptation methods to climate change in the Nile Basin of Ethiopia 总被引：6，自引：0，他引：6
Temesgen Tadesse Deressa Rashid M. Hassan Claudia Ringler Tekie Alemu Mahmud Yesuf 《Global Environmental Change》2009,19(2):248-255
This study identifies the major methods used by farmers to adapt to climate change in the Nile Basin of Ethiopia, the factors that affect their choice of method, and the barriers to adaptation. The methods identified include use of different crop varieties, tree planting, soil conservation, early and late planting, and irrigation. Results from the discrete choice model employed indicate that the level of education, gender, age, and wealth of the head of household; access to extension and credit; information on climate, social capital, agroecological settings, and temperature all influence farmers’ choices. The main barriers include lack of information on adaptation methods and financial constraints. 相似文献
19.
Tilaye Tadesse T. Wiegelmann P. J. MacNeice B. Inhester K. Olson A. Pevtsov 《Solar physics》2014,289(3):831-845
Measurements of magnetic fields and electric currents in the pre-eruptive corona are crucial to the study of solar eruptive phenomena, like flares and coronal mass ejections (CMEs). However, spectro-polarimetric measurements of certain photospheric lines permit a determination of the vector magnetic field only at the photosphere. Therefore, there is considerable interest in accurate modeling of the solar coronal magnetic field using photospheric vector magnetograms as boundary data. In this work, we model the coronal magnetic field above multiple active regions with the help of a potential field and a nonlinear force-free field (NLFFF) extrapolation code over the full solar disk using Helioseismic and Magnetic Imager (SDO/HMI) data as boundary conditions. We compare projections of the resulting magnetic field lines with full-disk coronal images from the Atmospheric Imaging Assembly (SDO/AIA) for both models. This study has found that the NLFFF model reconstructs the magnetic configuration closer to observation than the potential field model for full-disk magnetic field extrapolation. We conclude that many of the trans-equatorial loops connecting the two solar hemispheres are current-free. 相似文献
20.
Abstract The feasibility of using a geographic information system (GIS) to evaluate the subsurface transport of volatile organic compounds (VOCs) is evaluated. A GIS analysis based on selected soil properties and a flow path model were used to demonstrate the visualization of a probable path taken by diffusing VOC vapors in the vadose zone. The model uses soil properties such as texture, organic matter content, water content, bulk density, and permeability as path finding indices. The values of the soil properties used in the validation of this model were obtained from the respective County Soil Survey Reports. The various combinations of these soil properties resulted in deviations from the anticipated path taken by the diffusing organic vapors as they migrated through the subsurface. The model was evaluated using two soil systems and estimated diffusion coefficients. A proportionality constant (k) was calculated and used in conjunction with the assigned soil property values in the calculation of diffusion coefficients (Df) for trichloroethylene (TCE) vapors for each soil system. For each case, the model depicts the probable path taken by the VOC vapors as being the route through the soils having characteristics most favorable for chemical migration. Specifically, the soils along the predicted flow path have combinations of high moisture contents, low bulk densities, clay and organic matter contents as well as higher porosity and permeability than soils along any other possible flow path in the given soil systems. 相似文献