Characteristics of the changes in tropical cyclones influencing the South Korean region over the recent 10 years (2001–2010)     

Yumi Cha  Ki-Seon Choi  Ki-Ho Chang  Ji-Yeon Lee  Do-Shick Shin 《Natural Hazards》2014,74(3):1729-1741

Through the investigation of tropical cyclone (TC) characteristics related to climate change, this study found that the frequency of TCs occurring over the Western North Pacific has recently decreased slightly, while their average intensity has increased. The number of overall TCs that passed within the vicinity of South Korea has also been reduced, but the number of strong typhoons in the area, those with maximum wind speeds of more than 44 m/s, has significantly increased. These changes are closely related to the following phenomena. (1) The average genesis region of TCs that influence South Korea has moved eastward. Accordingly, the TCs tend to strengthen as they move westward for long distances along the Intertropical Convergence Zone (ITCZ) trade easterlies and the southern boundary of the North Pacific Subtropical High (NPSH). (2) The NPSH and Asia Monsoon trough, which are known to affect TC tracks, have extended to the northwest and southeast. This has caused TCs that travel to higher latitudes and curve back toward the Korean Peninsula to become more frequent. (3) TCs have approached the Korean Peninsula without hitting land. In addition, the sea surface temperature became higher than it was before. These factors have caused TCs to maintain their strength or become stronger than before.  相似文献   

A Periodicity Analysis of the Light Curve of 3C 454.3   总被引：2，自引：0，他引：2  

Huai-Zhen Li  Guang-Zhong Xie  Shu-Bai Zhou  Hong-Tao Liu  Guang-Wei Cha  Li Ma  Li-Sheng Mao National Astronomical Observatories / Yunnan Observatory  Chinese Academy of Sciences  Kunming  Graduate School of Chinese Academy of Sciences  Beijing Yunnan Astronomical Center  Yunnan University  Kunming Physics Department  Yunnan University  Kunming Physics Department  Yunnan Normal College  Kunming 《中国天文和天体物理学报》2006,6(4):421-429

We analyzed the radio light curves of 3C 454.3 at frequencies 22 and 37 GHz taken from the database of Metsahovi Radio Observatory, and found evidence of quasi-periodic activity. The light curves show great activity with very complicated non-sinusoidal variations. Two possible periods, a very weak one of 1.57±0.12 yr and a very strong one of 6.15±0.50 yr were consistently identified by two methods, the Jurkevich method and power spectrum estimation. The period of 6.15±0.50 yr is consistent with results previously reported by Ciaramella et al. and Webb et al. Applying the binary black hole model to the central structure we found black hole masses of 1.53×109M⊙and 1.86×108M⊙, and predicted that the next radio outburst is to take place in 2006 March and April.  相似文献   

The formation and fragmentation of the ring appearing in the collapse of a rotating cloud     

S.-H. Cha †  A. P. Whitworth 《Monthly notices of the Royal Astronomical Society》2003,340(1):91-104

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唐山地震高烈度区场地条件对震害的影响   总被引：1，自引：0，他引：1       下载免费PDF全文

刘朔宽  查小刚 《地震工程学报》1982,4(2):67-74

本文在详细调查了唐山地震高烈度区后认为,在10度以上的高烈度区内,不同地段的震害有明显的差异,其中场地条件(地基土、局部地形等)起着很重要的作用。文中还对煤田采空沉陷区边缘地带的震害进行了初步分析。  相似文献   

Brightness fluctuations in the K-line wings     

Milton Y. Cha  Frank Q. Orrall 《Solar physics》1973,28(2):333-341

A power-spectrum and cross-spectrum analysis has been made of measurements of temporal fluctuations of intensity observed in the K-line wing (2.07 Å from line center) and of simultaneous measurements of temporal fluctuations of Doppler displacement of the cores of 3931.122 Fe i and 3933 Ca ii (K₃). The measurements were made in a quiet region near the center of the Sun's disk. We find that the average power spectra of the intensity fluctuations have two significant peaks of about equal strength: one at 0.0033 Hz (300-s period); and one at about 0.001 Hz (1000-s period). The average rms value of these intensity fluctuations is 0.0435±0.0082. Maximum brightness comes before maximum violet displacement of the Fe i line. The mean of the best determined phases is 137° and of all the data 108°. At those places on the Sun where the 300-s oscillations can be identified in the k₃ core, the Doppler displacement of the Fe i line leads that of the K₃ core by a mean phase angle of 27°.  相似文献   

仙王座β型变星ν Eri的测光,分光观测及脉动模式的分析     

卢方军  刘学富 《天文学报》1994,35(3):305-317

本文给出了１９９１年１１月在北京天文台兴隆观测站对仙王座β型变星ν Ｅｒｉ进行的ｂ，ｙ波段光电测光结果，及１９９１年１２月在云南天文台观测获得的高分辨、大色散的ＳｉＩＩＩ线附近区的ＣＣＤ光谱，根据光变的多重周期分析结果，计算和分析了ν Ｅｒｉ的理论脉动模式，并以高分辨的ＳｉＩＩＩ线轮廓为例，分析了该星的谱线轮廓变化并计算了谱线的半宽，等值宽度以及视向速度。  相似文献   

Use of Tunisian raw clay to remove dye from aqueous solution     

Chaâri Islem  Jridi Kamel  Fakhfakh Emna  Jamoussi Fakher  Mnif Adel 《Arabian Journal of Geosciences》2016,9(10):564

This paper presents the first attempt to investigate the potential of Tunisian palygorskite-rich clay (Pal-clay) on the effectiveness of a textile dye “Direct orange 34” (DO34) removal. Important parameters which affect adsorption, such as initial solution pH, contact time, adsorbent mass, initial dye concentration, and temperature, were investigated. The raw Pal-clay was characterized using X-ray diffractometer (XRD), X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), cation exchange capacity (CEC), specific surface area (SSA) analysis, and point of zero charge (PZC) determination. The results showed that the Pal-clay has a high selectivity for DO34 and had maximum removal efficiency reaching up to about 91 %. The highest adsorption capacity was obtained at 25 °C and pH of 2. The dye uptake process fitted well to the pseudo-second-order kinetic expression and was best described by the Langmuir and Freundlich isotherms. Intra-particle diffusion studies showed that the adsorption mechanism was not exclusively controlled by the diffusion step and was more likely to be governed by external mass transfer. Thermodynamic parameters such as change in free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) were also calculated. The parameters revealed that the adsorption of dye by the raw clay is spontaneous and exothermic. The results indicate that the Pal-clay has a moderate adsorption capacity towards anionic dye.  相似文献   

Future changes in drought characteristics over South Korea using multi regional climate models with the standardized precipitation index     

Yeon-Woo Choi  Joong-Bae Ahn  Myoung-Seok Suh  Dong-Hyun Cha  Dong-Kyou Lee  Song-You Hong  Seung-Ki Min  Seong-Chan Park  Hyun-Suk Kang 《Asia-Pacific Journal of Atmospheric Sciences》2016,52(2):209-222

In this study, the projection of future drought conditions is estimated over South Korea based on the latest and most advanced sets of regional climate model simulations under the Representative Concentration Pathway (RCP4.5 and RCP8.5) scenarios, within the context of the national downscaling project of the Republic of Korea. The five Regional Climate Models (RCMs) are used to produce climate-change simulations around the Korean Peninsula and to estimate the uncertainty associated with these simulations. The horizontal resolution of each RCM is 12.5 km and model simulations are available for historical (1981-2010) and future (2021-2100) periods under forcing from the RCP4.5 and RCP8.5 scenarios. To assess the characteristics of drought on multiple time scales in the future, we use Standardized Precipitation Indices for 1-month (SPI- 1), 6-month (SPI-6) and 12-month (SPI-12). The number of drought months in the future is shown to be characterized by strong variability, with both increasing and decreasing trends among the scenarios. In particular, the number of drought months over South Korea is projected to increase (decrease) for the period 2041-2070 in the RCP8.5 (RCP4.5) scenario and increase (decrease) for the period 2071-2100 in the RCP4.5 (RCP8.5) scenario. In addition, the percentage area under any drought condition is overall projected to gradually decrease over South Korea during the entire future period, with the exception of SPI-1 in the RCP4.5 scenario. Particularly, the drought areas for SPI-1 in the RCP4.5 scenario show weakly positive long-term trend. Otherwise, future changes in drought areas for SPI-6 and SPI-12 have a marked downward trend under the two RCP scenarios.  相似文献   

Projections of high resolution climate changes for South Korea using multiple-regional climate models based on four RCP scenarios. Part 2: precipitation     

Seok-Geun Oh  Myoung-Seok Suh  Young-Suk Lee  Joong-Bae Ahn  Dong-Hyun Cha  Dong-Kyou Lee  Song-You Hong  Seung-Ki Min  Seong-Chan Park  Hyun-Suk Kang 《Asia-Pacific Journal of Atmospheric Sciences》2016,52(2):171-189

Precipitation changes over South Korea were projected using five regional climate models (RCMs) with a horizontal resolution of 12.5 km for the mid and late 21st century (2026-2050, 2076- 2100) under four Representative Concentration Pathways (RCP) scenarios against present precipitation (1981-2005). The simulation data of the Hadley Centre Global Environmental Model version 2 coupled with the Atmosphere-Ocean (HadGEM2-AO) was used as boundary data of RCMs. In general, the RCMs well simulated the spatial and seasonal variations of present precipitation compared with observation and HadGEM2-AO. Equal Weighted Averaging without Bias Correction (EWA_NBC) significantly reduced the model biases to some extent, but systematic biases in results still remained. However, the Weighted Averaging based on Taylor’s skill score (WEA_Tay) showed a good statistical correction in terms of the spatial and seasonal variations, the magnitude of precipitation amount, and the probability density. In the mid-21st century, the spatial and interannual variabilities of precipitation over South Korea are projected to increase regardless of the RCP scenarios and seasons. However, the changes in area-averaged seasonal precipitation are not significant due to mixed changing patterns depending on locations. Whereas, in the late 21st century, the precipitation is projected to increase proportionally to the changes of net radiative forcing. Under RCP8.5, WEA_Tay projects the precipitation to be increased by about +19.1, +20.5, +33.3% for annual, summer and winter precipitation at 1-5% significance levels, respectively. In addition, the probability of strong precipitation (≥ 15 mm d^-1) is also projected to increase significantly, particularly in WEA_Tay under RCP8.5.  相似文献   

Spatial distribution of stream sediment pollution by toxic trace elements at Tourtit and Ichoumellal abandoned mining areas (central Morocco)     

Chaïma Ahmedat  Sanaa Dabi  Mohamed Zahraoui  Iz-Eddine El Amrani El Hassani 《Arabian Journal of Geosciences》2018,11(3):55

This study presents a diagnostic of the current state of 114 stream sediment samples by their elemental concentrations (Sb, Cd, Pb, As, Cu, Zn, Ni, Cr, and Hg), collected from Ighardayane upstream on an area of 15 km² located at the SE part of central Morocco where Tourtit and Ichoumellal, two abandoned mining sites of Stibnite, are located. Several approaches were used to model the analysis (i) enrichment factor (EF), (ii) sediment pollution index (IPS), (iii) probable effect concentration-quotients (PEC-Qs), and (iv) potential ecological risk index (PERI). Results show highly contaminated areas around the old mining sites by Sb As, Pb, and Cd. Cadmium and lead show 86.9 and 12.29% (respectively) of trace element pollution according to sediment pollution index. Twenty-eight percent of the sampled area is potentially highly toxic because of the presence of Hg, Pb, and Cd. The very similar distribution of pollution and toxicity of most analyzed trace elements may originate from the same source, which corresponds to mining wastes where we recorded the highest pollution and toxicity degrees. This environmental issue represents the combination of Tourtit and Ichoumellal anthropic sources responsible of Sb, As, Pb, and Cd release and a probable natural source of Hg “that needs a further study,” which contribute in the degradation of an aquatic ecosystem of the same area. Therefore, both ecotoxicological analysis and stream sediment quality management should be carried out to control this aquatic ecosystem toxication.  相似文献