Effects of Geometries and Substructures of ICMEs on Geomagnetic Storms     

Jae-Ok Lee  Kyung-Suk Cho  Rok-Soon Kim  Soojeong Jang  Katsuhide Marubashi 《Solar physics》2018,293(9):129

To better understand geomagnetic storm generations by ICMEs, we consider the effect of substructures (magnetic cloud, MC, and sheath) and geometries (impact location of flux-rope at the Earth) of the ICMEs. We apply the toroidal magnetic flux-rope model to 59 CDAW CME–ICME pairs to identify their substructures and geometries, and select 20 MC-associated and five sheath-associated storm events. We investigate the relationship between the storm strength indicated by minimum Dst index \((\mathrm{Dst}_{\mathrm{min}})\) and solar wind conditions related to a southward magnetic field. We find that all slopes of linear regression lines for sheath-storm events are steeper (\({\geq}\,1.4\)) than those of the MC-storm events in the relationship between \(\mathrm{Dst}_{\mathrm{min}}\) and solar wind conditions, implying that the efficiency of sheath for the process of geomagnetic storm generations is higher than that of MC. These results suggest that different general solar wind conditions (sheaths have a higher density, dynamic and thermal pressures with a higher fluctuation of the parameters and higher magnetic fields than MCs) have different impact on storm generation. Regarding the geometric encounter of ICMEs, 100% (2/2) of major storms (\(\mathrm{Dst}_{\mathrm{min}} \leq -100~\mbox{nT}\)) occur in the regions at negative \(P_{Y}\) (relative position of the Earth trajectory from the ICME axis in the \(Y\) component of the GSE coordinate) when the eastern flanks of ICMEs encounter the Earth. We find similar statistical trends in solar wind conditions, suggesting that the dependence of geomagnetic storms on 3D ICME–Earth impact geometries is caused by asymmetric distributions of the geoeffective solar wind conditions. For western flank events, 80% (4/5) of the major storms occur in positive \(P_{Y}\) regions, while intense geoeffective solar wind conditions are not located in the positive \(P_{Y}\). These results suggest that the strength of geomagnetic storms depends on ICME–Earth impact geometries as they determine the solar wind conditions at Earth.  相似文献   

Relation of CME Speed and Magnetic Helicity in CME Source Regions on the Sun during the Early Phase of Solar Cycles 23 and 24     

R.-S. Kim  S.-H. Park  S. Jang  K.-S. Cho  B. S. Lee 《Solar physics》2017,292(4):66

To investigate the relations between coronal mass ejection (CME) speed and magnetic field properties measured in the photospheric surface of CME source regions, we selected 22 disk CMEs in the rising and early maximum phases of the current Solar Cycle 24. For the CME speed, we used two-dimensional (2D) projected speed observed by the Large Angle and Spectroscopic Coronagraph onboard the Solar and Heliospheric Observatory (SOHO/LASCO), as well as a 3D speed calculated from the triangulation method using multi-point observations. Two magnetic parameters of CME source regions were considered: the average of magnetic helicity injection rate and the total unsigned magnetic flux. We then classified the selected CMEs into two groups, showing: i) a monotonically increasing pattern with one sign of helicity (group A: 16 CMEs) and ii) a pattern of significant helicity injection followed by its sign reversal (group B: 6 CMEs). We found that: 1) 3D speed generally shows better correlations with the magnetic parameters than the 2D speed for 22 CME events in Solar Cycle 24; 2) 2D speed and the magnetic parameters of 22 CME events in this solar cycle have lower values than those of 47 CME events in Solar Cycle 23; 3) all events of group B in Solar Cycle 24 occur only after the beginning of the maximum phase, a trend well consistent with that shown in Solar Cycle 23; 4) the 2D speed and the helicity parameter of group B events continue to increase in the declining phase of Solar Cycle 23, while those of group A events abruptly decrease in the same period. Our results indicate that the two CME groups have a different tendency in the solar cycle variations of CME speed and the helicity parameters. Active regions that show a complex helicity evolution pattern tend to appear in the maximum and declining phases, while active regions with a relatively simple helicity evolution pattern appear throughout the whole solar cycle.  相似文献   

人工植被和流动沙丘近地面层湍流通量的计算     

刘树华  辛国君  陈荷生  冯金朝  刘立超 《气象》1993,19(9):9-13

提出了由Ｂｕｓｉｎｇｅｒ建议的无量纲廓线通用函数形式的近地面层稳定度参数ζ的相似方程分析解。代替了以往采用数值迭代法求ζ，并应用于沙漠人工植被和裸露流动沙丘上的实例资料分析。采用目前广泛应用的空气动力学方法，分别计算了动量和热量交换系数，感热和潜热通量，并由波文比－能量平衡方法进行了验证。结果表明：采用Ｂｕｓｉｎｇｅｒ无量纲通量廓线关系形式的近地面层稳定度参数ζ的相似方程分析解，代替以往惯用的数值  相似文献   

Notes on late Cenomanian and Turonianammonites from Touraine,Western France     

W.J. Kennedy  F. Amédro  G. Badillet  J.M. Hancock  C.W. Wright 《Cretaceous Research》1984,5(1):29-45

Recent collecting in the type area of the Turonian stage and adjacent parts of Touraine in western France provides new geographic and stratigraphic records as well as additional systematic information on species of the ammonite genera Puzosia, Watinoceras, Metoicoceras, Mammites, Prohauericeras, Collignoniceras, Lecointriceras, Subprionocyclus and Sciponoceras.  相似文献   

Fracture strength of dry silicate rocks at high confining pressures and activity of acoustic emission   总被引：1，自引：0，他引：1  

Mitsuhiko Shimada  Akio Cho  Hideo Yukutake 《Tectonophysics》1983,96(1-2)

Three dry silicate rocks, gabbro, dunite and eclogite, were triaxially compressed up to a confining pressure of 3 GPa at room temperature. These rocks exhibited brittle fracture behavior up to the highest confining pressure. The change of the mechanism of fracture in the brittle region is suggested from the measurement of the compressive fracture strength and the activity of acoustic emission. The existence of the “high-pressure brittle-fracture” phase is proposed. The fracture strength increased with increase of confining pressure. The increasing rate of strength was lowered at a value of confining pressure: at about 0.8 GPa on gabbro; at about 1.0 GPa on dunite; and at about 1.5 GPa on eclogite. At lower confining pressures than the above value, the acoustic emission rate began to increase at the onset of dilatancy and increased rapidly followed by fracture as the axial stress was increased. At the higher confining pressures, however, the acoustic emission rate did not increase rapidly before final fracture, and stayed constant to the fracture. The similar behavior was shown on the granite studied previously. It is interesting that the frictional strength forms the boundary between “low- and high-pressure brittle-fracture” phases.  相似文献   

Improvement of spatial interpolation accuracy of daily maximum air temperature in urban areas using a stacking ensemble technique     

Dongjin Cho  Cheolhee Yoo  Yeonsu Lee  Jaese Lee 《地理信息系统科学与遥感》2020,57(5):633-649

ABSTRACT

The reliable and robust monitoring of air temperature distribution is essential for urban thermal environmental analysis. In this study, a stacking ensemble model consisting of multi-linear regression (MLR), support vector regression (SVR), and random forest (RF) optimized by the SVR is proposed to interpolate the daily maximum air temperature (T_max) during summertime in a mega urban area. A total of 10 geographic variables, including the clear-sky averaged land surface temperature and the normalized difference vegetation index, were used as input variables. The stacking model was compared to Cokriging, three individual data-driven methods, and a simple average ensemble model, all through leave-one-station-out cross validation. The stacking model showed the best performance by improving the generalizability of the individual models and mitigating the sensitivity to the extreme daily T_max. This study demonstrates that the stacking ensemble method can improve the accuracy of spatial interpolation of environmental variables in various research fields.  相似文献   

Evolution of the eastern margin of Korea: Constraints on the opening of the East Sea (Japan Sea)   总被引：2，自引：2，他引：2  

Han-Joon Kim  Gwang Hoon Lee  Hyeong-Tae Jou  Hyun-Moo Cho  Hai-Soo Yoo  Gun-Tae Park  Ji-Soo Kim 《Tectonophysics》2007,436(1-4):37-55

We interpreted marine seismic profiles in conjunction with swath bathymetric and magnetic data to investigate rifting to breakup processes at the eastern Korean margin that led to the separation of the southwestern Japan Arc. The eastern Korean margin is rimmed by fundamental elements of rift architecture comprising a seaward succession of a rift basin and an uplifted rift flank passing into the slope, typical of a passive continental margin. In the northern part, rifting occurred in the Korea Plateau that is a continental fragment extended and partially segmented from the Korean Peninsula. Two distinguished rift basins (Onnuri and Bandal Basins) in the Korea Plateau are bounded by major synthetic and smaller antithetic faults, creating wide and considerably symmetric profiles. The large-offset border fault zones of these basins have convex dip slopes and demonstrate a zig-zag arrangement along strike. In contrast, the southern margin is engraved along its length with a single narrow rift basin (Hupo Basin) that is an elongated asymmetric half-graben. Analysis of rift fault patterns suggests that rifting at the Korean margin was primarily controlled by normal faulting resulting from extension rather than strike-slip deformation. Two extension directions for rifting are recognized: the Onnuri and Hupo Basins were rifted in the east-west direction; the Bandal Basin in the east–west and northwest–southeast directions, suggesting two rift stages. We interpret that the east–west direction represents initial rifting at the inner margin; while the Japan Basin widened, rifting propagated southeastward repeatedly from the Japan Basin toward the Korean margin but could not penetrate the strong continental lithosphere of the Korean Shield and changed the direction to the south, resulting in east–west extension to create the rift basins at the Korean margin. The northwest–southeast direction probably represents the direction of rifting orthogonal to the inferred line of breakup along the base of the slope of the Korea Plateau; after breakup the southwestern Japan Arc separated in the southeast direction, indicating a response to tensional tectonics associated with the subduction of the Pacific Plate in the northwest direction. No significant volcanism was involved in initial rifting. In contrast, the inception of sea floor spreading documents a pronounced volcanic phase which appears to reflect asthenospheric upwelling as well as rift-induced convection particularly in the narrow southern margin. We suggest that structural and igneous evolution of the Korean margin, although it is in a back-arc setting, can be explained by the processes occurring at the passive continental margin with magmatism influenced by asthenospheric upwelling.  相似文献   

Effect of spatial variability of cross‐correlated soil properties on bearing capacity of strip footing     

Sung Eun Cho  Hyung Choon Park 《国际地质力学数值与分析法杂志》2010,34(1):1-26

Geotechnical engineering problems are characterized by many sources of uncertainty. Some of these sources are connected to the uncertainties of soil properties involved in the analysis. In this paper, a numerical procedure for a probabilistic analysis that considers the spatial variability of cross‐correlated soil properties is presented and applied to study the bearing capacity of spatially random soil with different autocorrelation distances in the vertical and horizontal directions. The approach integrates a commercial finite difference method and random field theory into the framework of a probabilistic analysis. Two‐dimensional cross‐correlated non‐Gaussian random fields are generated based on a Karhunen–Loève expansion in a manner consistent with a specified marginal distribution function, an autocorrelation function, and cross‐correlation coefficients. A Monte Carlo simulation is then used to determine the statistical response based on the random fields. A series of analyses was performed to study the effects of uncertainty due to the spatial heterogeneity on the bearing capacity of a rough strip footing. The simulations provide insight into the application of uncertainty treatment to geotechnical problems and show the importance of the spatial variability of soil properties with regard to the outcome of a probabilistic assessment. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Retrieval of outgoing longwave radiation from COMS narrowband infrared imagery     

Myung-Sook Park  Chang-Hoi Ho  Heeje Cho  Yong-Sang Choi 《大气科学进展》2015,32(3):375-388

Hourly outgoing longwave radiation(OLR) from the geostationary satellite Communication Oceanography Meteorological Satellite(COMS) has been retrieved since June 2010. The COMS OLR retrieval algorithms are based on regression analyses of radiative transfer simulations for spectral functions of COMS infrared channels. This study documents the accuracies of OLRs for future climate applications by making an intercomparison of four OLRs from one single-channel algorithm(OLR12.0using the 12.0 μm channel) and three multiple-channel algorithms(OLR10.8+12.0using the 10.8 and 12.0 μm channels; OLR6.7+10.8using the 6.7 and 10.8 μm channels; and OLR All using the 6.7, 10.8, and 12.0 μm channels). The COMS OLRs from these algorithms were validated with direct measurements of OLR from a broadband radiometer of the Clouds and Earth's Radiant Energy System(CERES) over the full COMS field of view [roughly(50°S–50°N, 70°–170°E)] during April 2011.Validation results show that the root-mean-square errors of COMS OLRs are 5–7 W m-2, which indicates good agreement with CERES OLR over the vast domain. OLR6.7+10.8and OLR All have much smaller errors(～ 6 W m-2) than OLR12.0and OLR10.8+12.0(～ 8 W m-2). Moreover, the small errors of OLR6.7+10.8and OLR All are systematic and can be readily reduced through additional mean bias correction and/or radiance calibration. These results indicate a noteworthy role of the6.7 μm water vapor absorption channel in improving the accuracy of the OLRs. The dependence of the accuracy of COMS OLRs on various surface, atmospheric, and observational conditions is also discussed.  相似文献   

Fracture roughness and thermal exchange: A case study at Soultz-sous-Forêts     

Amélie Neuville  Renaud Toussaint  Jean Schmittbuhl 《Comptes Rendus Geoscience》2010,342(7-8):616-625

Heat exchange during laminar flow in an open fracture is studied numerically on the basis of the Stokes equation in the limit of hydrothermal lubrication. We examine the influence of fracture roughness on hydraulic permeability and heat flux through the fracture sides when a cold fluid is injected into a homogeneous hot host rock. Spatial temperature fluctuations inside the fluid are studied assuming the temperature of the rock to be constant and the fracture aperture to be self-affine. An application to the case study at the deep geothermal reservoir of Soultz-sous-Forêts, France, is presented. Finally, a thermal model based on sparse spatial information of the geometrical aperture is successfully proposed to reproduce the response of the fracture.  相似文献