The initial stage of development of type IV radio bursts and the relation to expanding magnetic bottles     

Kunitomo Sakurai 《Solar physics》1973,31(2):483-492

Using the observed data for wide-band type IV solar radio bursts, the onset time differences between the microwave and metric frequencies and the peak flux intensities of the metric component are analyzed as a function of the longitudinal position of the associated flares on the solar disk. It is shown that this time difference is dependent on the position of the associated flare and that the peak flux intensity reaches maximum when a flare occurs in the region 10 to 40 ° west of the central meridian of the solar disk. These results are explained by taking into account the eastward expansion of magnetic bottles which trap mildly relativistic electrons responsible for type IV bursts. Discussion is given on the relation between these magnetic bottles and shock waves which excite type II radio bursts.NASA Associate with University of Maryland, Astronomy Program.  相似文献   

Energetic electrons associated with solar flares and their relation to type I noise activity     

Kunitomo Sakurai 《Solar physics》1971,16(1):198-207

The generation of energetic electrons is always associated with the solar flares which occur within the sunspot groups that are highly active in emitting type I noise storms. The number of the solar flares which are associated with the distinct electron events observed at the earth tends to increase in association with the westward movement of these active groups. This tendency is not contradictory to the close association between electron producing solar flares and type I active regions if we take into account the limited directivity of type I noise storms associated with these sunspot groups.The acceleration of the energetic electrons associated with solar flares seems to be closely related to the type I active regions where the enormous numbers of suprathermal electrons exist and play a role in generating these radio noise storms.NAS-NRC Associate with NASA.  相似文献   

An emission pathway for stabilization at 6?Wm?2 radiative forcing   总被引：1，自引：0，他引：1  

Toshihiko Masui  Kenichi Matsumoto  Yasuaki Hijioka  Tsuguki Kinoshita  Toru Nozawa  Sawako Ishiwatari  Etsushi Kato  P. R. Shukla  Yoshiki Yamagata  Mikiko Kainuma 《Climatic change》2011,109(1-2):59-76

Representative Concentration Pathway 6.0 (RCP6) is a pathway that describes trends in long-term, global emissions of greenhouse gases (GHGs), short-lived species, and land-use/land-cover change leading to a stabilisation of radiative forcing at 6.0 Watts per square meter (Wm^?2) in the year 2100 without exceeding that value in prior years. Simulated with the Asia-Pacific Integrated Model (AIM), GHG emissions of RCP6 peak around 2060 and then decline through the rest of the century. The energy intensity improvement rates changes from 0.9% per year to 1.5% per year around 2060. Emissions are assumed to be reduced cost-effectively in any period through a global market for emissions permits. The exchange of CO₂ between the atmosphere and terrestrial ecosystem through photosynthesis and respiration are estimated with the ecosystem model. The regional emissions, except CO₂ and N₂O, are downscaled to facilitate transfer to climate models.  相似文献   

Burial of organic carbon in Holocene sediments of the Zhujiang (Pearl River) and Changjiang (Yangtze River) estuaries   总被引：1，自引：0，他引：1  

Shouye Yang  Min Tang  Wyss W.-S. Yim  Yongqiang Zong  Guangqing Huang  Adam D. Switzer  Yoshiki Saito 《Marine Chemistry》2011,123(1-4):1-10

The East Asian marginal seas are important sinks of terrigenous materials transported by large rivers. In this study two cores from the Changjiang (Yangtze River) and Zhujiang (Pearl River) estuaries and one core from the inner shelf off of Hong Kong were investigated to examine the burial of organic matter during the postglacial period and its possible links with paleoenvironmental changes. Based on a simple two end-member mixing model, the terrestrial organic matter supplied primarily from the Zhujiang and Changjiang dominates the estuarine areas while marine organic matter contributes more to the inner-mid shelf. The competing contributions of terrestrial and marine organic matter are responsible for the downcore variations of organic elemental compositions. The overall decreasing shifts of total organic carbon concentrations and total organic carbon to total nitrogen ratios in the Zhujiang estuarine sediments since 6.5 kaBP seems to support the notion that depth profiles of organic matter compositions deposited in the Zhujiang Estuary can aid in the reconstruction of monsoon history in the Holocene. Nevertheless, organic matter compositions in the Changjiang Estuary and inner shelf off of southeastern Hong Kong respond in a different and more complex way to freshwater discharges or precipitation changes (monsoon variability) in the catchments, owing to complex controls of deposition and preservation of organic matter in these estuarine and shelf environments. Caution is therefore needed in using organic elemental and isotopic compositions to decipher paleoenvironmental changes in East Asian continental shelves where intense river–sea interactions occur and sedimentary environments change drastically.  相似文献   

Modeling of 500-year tsunamis for probabilistic design of coastal infrastructure in the Pacific Northwest     

Kwok Fai Cheung  Yong Wei  Yoshiki Yamazaki  Solomon C.S. Yim 《Coastal Engineering》2011

This paper describes the development of tsunami scenarios from the National Seismic Hazard Maps for design of coastal infrastructure in the Pacific Northwest. The logic tree of Cascadia earthquakes provides four 500-year rupture configurations at moment magnitude 8.8, 9.0, and 9.2 for development of probabilistic design criteria. A planar fault model describes the rupture configurations and determines the earth surface deformation for tsunami modeling. A case study of four bridge sites at Siletz Bay, Oregon illustrates the challenges in modeling of tsunamis on the Pacific Northwest coast. A nonlinear shallow-water model with a shock-capturing scheme describes tsunami propagation across the northeastern Pacific as well as barrier beach overtopping, bore formation, and detailed flow conditions at Siletz Bay. The results show strong correlation with geological evidence from the six paleotsunamis during the last 2800 years. The proposed approach allows determination of tsunami loads that are consistent with the seismic loads currently in use for design of buildings and structures.  相似文献   

Stoichiometry among bioactive trace metals in seawater on the Bering Sea shelf   总被引：2，自引：1，他引：1  

Abigail Parcasio Cid  Syouhei Urushihara  Tomoharu Minami  Kazuhiro Norisuye  Yoshiki Sohrin 《Journal of Oceanography》2011,67(6):747-764

The distribution of Al, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb in seawater was investigated on the Bering Sea shelf (56–64°N, 165–169°W) in September 2000. The unfiltered and filtered seawater samples were used for determination of total dissolvable (TD) and dissolved (D) metals (M), respectively. The TD-M concentrations were generally higher than in the Pacific Ocean. TD-Cd was highest in deep water of the outer shelf domain and dominated by dissolved species. The other TD-M were highest at stations close to the Yukon River delta and had higher fractions of labile particulate (LP) species that were obtained as the difference between TD-M and D-M. Dissolved Al, Ni, and Cu were characterized by input from the Yukon River. Dissolved Mn and Co showed maximums on the bottom of the coastal domain, suggesting influence of sedimentary Mn reduction. The correlations of D-Zn, D-Cd, and macronutrients indicated their distributions were largely controlled through uptake by microorganisms and remineralization from settling particles. All these three processes (river input, sedimentary reduction, and biogeochemical cycle) had an influence on the distribution of D-Fe. D-Pb was fairly uniformly distributed in the study area. The stoichiometry of D-M in the Bering Sea shelf showed enrichment of Co and Pb and depletion of Ni, Cu, Zn, and Cd compared with that in the North Pacific. The LP-M/LP-Al ratio revealed significant enrichment of the other eight metals relative to their crustal abundance, suggesting importance of formation of Fe–Mn oxides and adsorption of trace metals on the oxides.  相似文献   

Structure and characteristics of submonthly-scale waves along the Indian Ocean ITCZ     

Yoshiki Fukutomi  Tetsuzo Yasunari 《Climate Dynamics》2013,40(7-8):1819-1839

This study examines wave disturbances on submonthly (6–30-day) timescales over the tropical Indian Ocean during Southern Hemisphere summer using Japanese Reanalysis (JRA25-JCDAS) products and National Oceanic and Atmospheric Administration outgoing longwave radiation data. The analysis period is December–February for the 29 years from 1979/1980 through 2007/2008. An extended empirical orthogonal function (EEOF) analysis of daily 850-hPa meridional wind anomalies reveals a well-organized wave-train pattern as a dominant mode of variability over the tropical Indian Ocean. Daily lagged composite analyses for various atmospheric variables based on the EEOF result show the structure and evolution of a wave train consisting of meridionally elongated troughs and ridges along the Indian Ocean Intertropical Convergence Zone (ITCZ). The wave train is oriented in a northeast–southwest direction from Sumatra toward Madagascar. The waves have zonal wavelengths of about 3,000–5,000 km and exhibit westward and southwestward phase propagation. Individual troughs and ridges as part of the wave train sequentially travel westward and southwestward from the west of Sumatra into Madagascar. Meanwhile, eastward and northeastward amplification of the wave train occurs associated with the successive growth of new troughs and ridges over the equatorial eastern Indian Ocean. This could be induced by eastward and northeastward wave energy dispersion from the southwestern to eastern Indian Ocean along the mean monsoon westerly flow. In addition, the waves modulate the ITCZ convection. Correlation statistics show the average behavior of the wave disturbances over the tropical Indian Ocean. These statistics and other diagnostic measures are used to characterize the waves obtained from the composite analysis. The waves appear to be connected to the monsoon westerly flow. The waves tend to propagate through a band of the large meridional gradient of absolute vorticity produced by the mean monsoon westerly flow. This suggests that the monsoon westerly flow provides favorable background conditions for the propagation and maintenance of the waves and acts as a waveguide over the tropical Indian Ocean. The horizontal structure of the wave train may be interpreted as that of a mixture of equatorial Rossby waves and mixed Rossby-gravity wavelike gyres.  相似文献   

Sediment distribution and depositional processes along the fluvial to marine transition zone of the Mekong River delta,Vietnam     

Marcello Gugliotta  Yoshiki Saito  Van Lap Nguyen  Thi Kim Oanh Ta  Toru Tamura 《Sedimentology》2019,66(1):146-164

The area of coastal rivers with a combination of fluvial, tidal and wave processes is defined as the fluvial to marine transition zone and can extend up to several hundreds of kilometres upstream of the river mouth. The aim of this study is to improve the understanding of sediment distribution and depositional processes along the fluvial to marine transition zone using a comprehensive dataset of channel bed sediment samples collected from the Mekong River delta. Six sediment types were identified and were interpreted to reflect the combined action of fluvial and marine processes. Based on sediment‐type associations, the Mekong fluvial to marine transition zone could be subdivided into an upstream tract and a downstream tract; the boundary between these two tracts is identified 80 to 100 km upstream of the river mouth. The upstream tract is characterized by gravelly sand and sand and occasional heterolithic rhythmites, suggesting bed‐load supply and deposition mainly controlled by fluvial processes with subordinate tidal influence. The downstream tract is characterized by heterolithic rhythmites with subordinate sand and mud, suggesting suspended‐load supply and deposition mainly controlled by tidal processes with subordinate fluvial influence. Sediment distributions during wet and dry seasons suggest significant seasonal changes in sediment dynamic and depositional processes along the fluvial to marine transition zone. The upstream tract shows strong fluvial depositional processes with subordinate tidal influence during the wet season and no deposition with weak fluvial and tidal processes during the dry season. The downstream tract shows strong coexisting fluvial and tidal depositional processes during the wet season and strong tidal depositional processes with negligible fluvial influence during the dry season. Turbidity maxima are present along the downstream tract of the fluvial to marine transition zone during both wet and dry seasons and are driven by a combination of fluvial, tidal and wave processes.  相似文献   

Erosion and accretion processes in a muddy dissipative coast,the Chao Phraya River delta,Thailand     

Katsuto Uehara  Pramot Sojisuporn  Yoshiki Saito  Thanawat Jarupongsakul 《地球表面变化过程与地形》2010,35(14):1701-1711

Seasonal variation in seabed elevation in the muddy intertidal zone of the Chao Phraya River delta, an area of serious coastal erosion for 40 years, was assessed using information on waves and tides predicted by numerical simulations. The study area is under the influence of the Southeast Asian monsoon climate and lies in the innermost part of a sheltered gulf, across which a low‐gradient slope has developed. Observations, aimed at evaluating the effectiveness of a prototype breakwater on mitigating coastal erosion, indicated that the seasonal variation in the seabed elevation, typically about 30 cm, was caused primarily by seasonal changes in wave direction and height. The breakwater seems to have contributed to a net rise in the seabed level at sites behind the structure. Seabed erosion was most apparent during the northeast monsoon, when waves are weak. Erosion under this low wave energy state was attributed to the combined effect of wave breaking and the low tidal level. A difference in the observed seabed accretion rate between the transitional intermonsoon period and the succeeding southwest monsoon period was attributed to the direction of the wave energy flux; offshore sediments seem to have been supplied efficiently to the study area by waves during the transitional period. Another potential cause of seabed erosion and accretion during the wet southwest monsoon season was the discharge of water and sediments from local canals associated with intense tropical rainfall; this discharge seems to be linked to land use in the coastal area. The results of this study show the importance of monitoring across‐shore sediment transport for better understanding of coastal erosion processes. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Stratigraphic development during the Late Pleistocene and Holocene offshore of the Yellow River delta, Bohai Sea   总被引：10，自引：0，他引：10  

Jian Liu  Yoshiki Saito  Hong Wang  Liangyong Zhou  Zigeng Yang 《Journal of Asian Earth Sciences》2009,36(4-5):318-331

A 61-m-long sediment core (HB-1) and 690 km of high-resolution seismic profiles from offshore of the Yellow River delta, Bohai Sea, were analyzed to document the stratigraphy and sea-level changes during the Late Pleistocene and Holocene. Accelerator mass spectrometry ¹⁴C dating and analyses of benthic foraminifera, ostracods, the mineral composition, and sedimentary characteristics were performed for core HB-1, and seven depositional units (DU 1–DU 7 in descending order) were identified. The seismic reflection data were interpreted in light of the sedimentological data of the core and correlated with other well-studied cores obtained previously in the Bohai Sea area. Seven seismic units (SU 1 to SU 7 in descending order) were distinguished and interpreted as follows: SU 7 corresponds to marine facies in Marine Isotopic Stage (MIS) 5; SU 6, to terrestrial facies in MIS 4; SU 5 and SU 4, to alternating terrestrial and marine facies (DU 7–DU 5) in MIS 3; SU 3, to terrestrial facies (DU 4) in MIS 2; SU 2, to Holocene marine facies (DU 3 and DU 2); and SU 1, to modern Yellow River delta sediments deposited since 1855 (DU 1).The sedimentary facies from DU 7 to DU 5 reflect sea-level fluctuations during MIS 3, and the boundary between DU 5 and DU 6, which coincides with that between SU 4 and SU 5, is a distinctive, laterally continuous, undulating erosion surface, with up to 20 m of relief. This surface reflects subaerial exposure between transgressions during MIS 3. Estimated sea levels during MIS 3 ranged from −35 ± 5 to −60 ± 5 m or lower, with short-term fluctuations of 20 m. Sedimentary environments in the Bohai Sea area were governed mainly by eustatic sea-level changes and the Bohai Strait topography, which controls the entry of sea water into the Bohai Sea area.The mineral composition of the sediment core suggests that the Yellow River did not discharge into the Bohai Sea, or at least did not influence the study area significantly, during parts of MIS 3 and MIS 2 to the early Holocene (11–8.5 cal kyr BP).  相似文献