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21.
Extrapolation codes for modelling the magnetic field in the corona in Cartesian geometry do not take the curvature of the
Sun’s surface into account and can only be applied to relatively small areas, e.g., a single active region. We apply a method for nonlinear force-free coronal magnetic field modelling of photospheric vector
magnetograms in spherical geometry which allows us to study the connectivity between multi-active regions. We use Vector Spectromagnetograph
(VSM) data from the Synoptic Optical Long-term Investigations of the Sun (SOLIS) survey to model the coronal magnetic field,
where we study three neighbouring magnetically connected active regions (ARs 10987, 10988, 10989) observed on 28, 29, and
30 March 2008, respectively. We compare the magnetic field topologies and the magnetic energy densities and study the connectivities
between the active regions. We have studied the time evolution of the magnetic field over the period of three days and found
no major changes in topologies, as there was no major eruption event. From this study we have concluded that active regions
are much more connected magnetically than the electric current. 相似文献
22.
Tilaye Tadesse T. Wiegelmann P. J. MacNeice K. Olson 《Astrophysics and Space Science》2013,347(1):21-27
The magnetic fields in the solar atmosphere structure the plasma, store free magnetic energy and produce a wide variety of active solar phenomena, like flare and coronal mass ejections (CMEs). The distribution and strength of magnetic fields are routinely measured in the solar surface (photosphere). Therefore, there is considerable interest in accurately modeling the 3D structure of the coronal magnetic field using photospheric vector magnetograms. Knowledge of the 3D structure of magnetic field lines also help us to interpret other coronal observations, e.g., EUV images of the radiating coronal plasma. Nonlinear force-free field (NLFFF) models are thought to be viable tools for those task. Usually those models use Cartesian geometry. However, the spherical nature of the solar surface cannot be neglected when the field of view is large. In this work, we model the coronal magnetic field above multiple active regions using NLFFF extrapolation code using vector magnetograph data from the Synoptic Optical Long-term Investigations of the Sun survey (SOLIS)/Vector Spectromagnetograph (VSM) as a boundary conditions. We compare projections of the resulting magnetic field lines solutions with their respective coronal EUV-images from the Atmospheric Imaging Assembly (SDO/AIA) observed on October 15, 2011 and November 13, 2012. This study has found that the NLFFF model in spherical geometry reconstructs the magnetic configurations for several active regions which agrees to some extent with observations. During October 15, 2011 observation, there are substantial number of trans-equatorial loops carrying electric current. 相似文献
23.
ABSTRACT Reliable seasonal forecasting of water resources variability may be of great value for agriculture and energy management in Ethiopia. This work aims to develop statistical forecasting of seasonal total water storage (TWS) anomalies in Ethiopia using sea-surface temperature and sea-level pressure indices. Because of the spatial and temporal variability of TWS over the country, Ethiopia is divided into four regions each having similar TWS dynamics. Periods of long-term water deficit observed in GRACE TWS products for the region are found to coincide with periods of meteorological drought. Multiple linear regression is employed to generate seasonal forecasting models for each region. We find that the skill of the resulting models varies from region to region, with R 2 from 0.33 to 0.73 and correlation from 0.27 to 0.77 between predicted and observed values (using leave-one-out cross-validation). The skill of the models is better than the climatology in all regions. 相似文献
24.
Yared A. Bayissa Tsegaye Tadesse Mark Svoboda Brian Wardlow Calvin Poulsen John Swigart 《地理信息系统科学与遥感》2019,56(5):718-748
Developing a robust drought monitoring tool is vital to mitigate the adverse impacts of drought. A drought monitoring system that integrates multiple agrometeorological variables into a single drought indicator is lacking in areas such as Ethiopia, which is extremely susceptible to this natural hazard. The overarching goal of this study is to develop a combined drought indicator (CDI-E) to monitor the spatial and temporal extents of historic agricultural drought events in Ethiopia. The CDI-E was developed by combining four satellite-based agrometeorological input parameters – the Standardized Precipitation Index (SPI), Land Surface Temperature (LST) anomaly, Standardized Normalized Difference Vegetation Index (stdNDVI) and Soil Moisture (SM) anomaly – for the period from 2001 to 2015. The method used to combine these indices is based on a quantitative approach that assigns a weight to each input parameter using Principal Component Analysis (PCA). The CDI-E results were evaluated using satellite-based gridded rainfall (3-month SPI) and crop yield data for 36 intra-country crop growing zones for a 15-year period (2001 to 2015). The evaluation was carried out for the main rainfall season, Kiremt (June-September), and the short rainfall season, Belg (February-May). The results showed that moderate to severe droughts were detected by the CDI-E across the food insecure regions reported by FEWS NET during Kiremt and Belg rainfall seasons. Relatively higher correlation coefficient values (r > 0.65) were obtained when CDI-E was compared with the 3-month SPI across the majority of Ethiopia. The spatial correlation analyses of CDI-E and cereal crop yields showed relatively good correlations (r > 0.5) in some of the crop growing zones in the northern, eastern and southwestern parts of the country. The CDI-E generally mapped the spatial and temporal patterns of historic drought and non-drought years and hence the CDI-E could potentially be used to develop an agricultural drought monitoring and early warning system in Ethiopia. Moreover, decision makers and donors may potentially use CDI-E to more accurately monitor crop yields across the food-insecure regions in Ethiopia. 相似文献
25.
Jae H. Ryu Mark D. Svoboda John D. Lenters Tsegaye Tadesse Cody L. Knutson 《Climatic change》2010,101(3-4):575-597
The relationship between the El Niño-Southern Oscillation (ENSO) and hydrologic variability in the United States is investigated using Empirical Orthogonal Function (EOF)/Principal Component Analysis (PCA). The multivariate ENSO index (MEI) is utilized to identify strong coherences associated with multiple months (1-, 2-, 4-, 6-, 12-, 24-, 48-month) of the Log-Standardized Hydrologic Drought Index (LSHDI) in the conterminous states for the period 1950–2005. Based on 56 years of monthly streamflow data for 102 forecast climate divisions, this research explores the spatial and temporal variation of hydrologic responses corresponding to ENSO events. Preliminary results show that a potential predictor of the dominant streamflow modes in the northern Great Plains is identified from streamflows in western Arizona. Also, positive relationships between hydrologic drought and El Niño were found in the Pacific Northwest (Washington, Oregon, and northern California), whereas negative relationships were detected in southern California and the northern Great Plains. These findings will provide useful insights to help improve streamflow forecast potential and capabilities, and minimize the impacts of hydrologic events (e.g. floods and droughts) associated with ENSO events. 相似文献
26.
Constraints to smallholders production of frankincense in Metema district, North-western Ethiopia 总被引：1，自引：0，他引：1
Frankincense, an aromatic exudate obtained from several Boswellia species, is an important commodity with the potential to invigorate economic development of the drylands of Ethiopia. Local people have been producing and trading frankincense for centuries to diversify their income sources. However, local people's involvement in the production of frankincense varies considerably among the producing dryland regions of the country. The objectives of this study were to investigate: (i) the potential of frankincense production, (ii) socio-cultural, economic and policy factors affecting the involvement of local people in the production of frankincense, and (iii) the current status of Boswellia woodlands in Metema district, which is one of the major frankincense producing areas in Ethiopia. The results showed that Boswellia papyrifera comprised 51% of the species composition of the vegetation of the district with 253.5 kg/ha/year production potential. The total annual frankincense production potential of the district was estimated to be 79,168 tons. However, almost all inhabitants do not benefit economically from the species due to: (i) cultural influence (67%), (ii) unattractiveness of income from frankincense compared to other economic activities in the area (38%), property tenure (27%), government policy on incense production (20%), poor knowledge on frankincense production (19%) and unawareness of the potential of frankincense as a source of income (5%). The absence of direct economic benefits for the local people from the woodlands is triggering their widespread degradation mostly from human induced fire, improper forest use and agricultural land expansion. 相似文献
27.
Geology and mineral potential of Ethiopia: a note on geology and mineral map of Ethiopia 总被引：1，自引：0，他引：1
Solomon Tadesse Jean-Pierre Milesi Yves Deschamps 《Journal of African Earth Sciences》2003,36(4):273-313
This work presents a geoscientific map and database for geology, mineral and energy resources of Ethiopia in a digital form at a scale of 1:2,000,000, compiled from several sources. The final result of the work has been recorded on CD-ROM in GIS format so that the map and the database could be available to users on a personal computer.Metallic resources (precious, rare, base and ferrous–ferroalloy metals) are widely related to the metamorphic meta-volcano-sedimentary belts and associated intrusives belonging to various terranes of the Arabian–Nubian Shield, accreted during the East and West Gondwana collision (Neoproterozoic, 900–500 Ma).Industrial minerals and rock resources occur in more diversified geological environments, including the Proterozoic basement rocks, the Late Paleozoic to Mesozoic sediments and recent (Cenozoic) volcanics and associated sediments.Energy resources (oil, coal, geothermal resources) are restricted to Phanerozoic basin sediments and Cenozoic volcanism and rifting areas. 相似文献
28.
Tsegaye Tadesse Donald A. Wilhite Sherri K. Harms Michael J. Hayes Steve Goddard 《Natural Hazards》2004,33(1):137-159
Drought has an impact on many aspects of society. To help decision makers reduce the impacts of drought, it is important to
improve our understanding of the characteristics and relationships of atmospheric and oceanic parameters that cause drought.
In this study, the use of data mining techniques is introduced to find associations between drought and several oceanic and
climatic indices that could help users in making knowledgeable decisions about drought responses before the drought actually
occurs. Data mining techniques enable users to search for hidden patterns and find association rules for target data sets
such as drought episodes. These techniques have been used for commercial applications, medical research, and telecommunications,
but not for drought. In this study, two time-series data mining algorithms are used in Nebraska to illustrate the identification
of the relationships between oceanic parameters and drought indices. The algorithms provide flexibility in time-series analyses
and identify drought episodes separate from normal and wet conditions, and find relationships between drought and oceanic
indices in a manner different from the traditional statistical associations. The drought episodes were determined based on
the Standardized Precipitation Index (SPI) and Palmer Drought Severity Index (PDSI). Associations were observed between drought
episodes and oceanic and atmospheric indices that include the Southern Oscillation Index (SOI), the Multivariate ENSO Index
(MEI), the Pacific/North American (PNA) index, the North Atlantic Oscillation (NAO) Index, and the Pacific Decadal Oscillation
(PDO) Index. The experimental results showed that among these indices, the SOI, MEI, and PDO have relatively stronger relationships
with drought episodes over selected stations in Nebraska. Moreover, the study suggests that data mining techniques can help
us to monitor drought using oceanic indices as a precursor of drought. 相似文献