Variations in High-frequency Oscillations of Tropical Cyclones over the Western North Pacific     

Shumin CHEN  Weibiao LI  Zhiping WEN  Mingsen ZHOU  Youyu LU  Yu-Kun QIAN  Haoya LIU  Rong FANG 《大气科学进展》2018,35(4):423-434

Variations in the high-frequency oscillations of tropical cyclones(TCs) over the western North Pacific(WNP) are studied in numerical model simulations. Power spectrum analysis of maximum wind speeds at 10 m(MWS_(10)) from an ensemble of15 simulated TCs shows that oscillations are significant for all TCs. The magnitudes of oscillations in MWS_(10) are similar in the WNP and South China Sea(SCS); however, the mean of the averaged significant periods in the SCS(1.93 h) is shorter than that in the open water of the WNP(2.83 h). The shorter period in the SCS is examined through an ensemble of simulations,and a case simulation as well as a sensitivity experiment in which the continent is replaced by ocean for Typhoon Hagupit(2008). The analysis of the convergence efficiency within the boundary layer suggests that the shorter periods in the SCS are possibly due to the stronger terrain effect, which intensifies convergence through greater friction. The enhanced convergence strengthens the disturbance of the gradient and thermal wind balances, and then contributes to the shorter oscillation periods in the SCS.  相似文献   

Atmospheric Response to Mesoscale Ocean Eddies over the South China Sea     

Haoya LIU  Weibiao LI  Shumin CHEN  Rong FANG  Zhuo LI 《大气科学进展》2018,35(9):1189-1204

The South China Sea(SCS) is an eddy-active area. Composite analyses based on 438 mesoscale ocean eddies during 2000–2012 revealed the status of the atmospheric boundary layer is influenced remarkably by such eddies. The results showed cold-core cyclonic(warm-core anticyclonic) eddies tend to cool(warm) the overlying atmosphere and cause surface winds to decelerate(accelerate). More than 5% of the total variance of turbulent heat fluxes, surface wind speed and evaporation rate are induced by mesoscale eddies. Furthermore, mesoscale eddies locally affect the columnar water vapor, cloud liquid water, and rain rate. Dynamical analyses indicated that both variations of atmospheric boundary layer stability and sea level pressure are responsible for atmospheric anomalies over mesoscale eddies. To reveal further details about the mechanisms of atmospheric responses to mesoscale eddies, atmospheric manifestations over a pair of cold and warm eddies in the southwestern SCS were simulated. Eddy-induced heat flux anomalies lead to changes in atmospheric stability. Thus, anomalous turbulence kinetic energy and friction velocity arise over the eddy dipole, which reduce(enhance) the vertical momentum transport over the cold(warm) eddy, resulting in the decrease(increase) of sea surface wind. Diagnoses of the model's momentum balance suggested that wind speed anomalies directly over the eddy dipole are dominated by vertical mixing terms within the atmospheric boundary layer, while wind anomalies on the edges of eddies are produced by atmospheric pressure gradient forces and atmospheric horizontal advection terms.  相似文献   

EFFECTS OF SEDIMENT GRADATION ON THE GEOMETRY OF RIVER DELTAS     

Chjeng-Lun SHIEH  Chih-Ming TSENG  and Shaohua Marko HSUProfessor  Department of Hydraulics  Ocean Engineering  Director  Disaster Prevention Research Center  National Cheng-Kung University  Tainan  Taiwan    China. Ph.D. Candidate  Department of H 《国际泥沙研究》2001,16(1)

l INTRODUCTlONIn this study, formation of alluvial deltas was treated as a river-dominated type of topograPhy process,caused simply by sediment deposition from a channel into a wide basin. The influences of waves, tides,and density differences related to coastal effects were excluded. There have been numerous experimentalstUdies on river delta problems. For examPle, Shieh et al. (1988, 1997) used coarse sediment asexperimental material and revealed the development and the geometric simil…  相似文献   

MODELING UNSTEADY TURBIDITY CURRENTS IN A STEEP NARROW RESERVOIR     

Shaohua Marko HSU  Associate Professor  Dr. Department of Hydraulic Engineering  Feng Chia University  Taichung  Taiwan  China Wei-Sheng YU Environment Section  Agricultural Engineering Research Center  Chungli  Taiwan  China Tzu-Ming LIU Graduate stu 《国际泥沙研究》1997,(3)

1.IN~DUCTIONTurbiditycurrentisoneclassofflowsnameddensitycurrentorgravitycurrent(therHunterRouse(Yih(1980)),whichdePictstheintmsionofheaVyfluidintoalighterone.Usually,thedensitydifferencebetWeentWonuidisrelativelysmallandmixingacrosstheimerfaceoccurs.ThedrivingforceofdensitycurrentsisnotdensitydifferenceitselfbutthedifferenceinspeCmcweights.Turbiditycurrentisnamedwhenthedensitydifferenceisespeciallycausedbysuspendedfinesedimentparticles.Sincesediment-ladenflowcaninteraCtwiththelowerbou…  相似文献   

2015年西北太平洋台风季提早展开:2015/2016超级厄尔尼诺的影响   总被引：1，自引：0，他引：1       下载免费PDF全文

钱伊恬  徐邦琪 《大气科学学报》2016,39(6):788-800

2015年1-5月西北太平洋上异常出现了7个热带风暴（Tropical Storms,TS）,其中有5个发展成台风（Typhoons,TY）,分别为气候平均态（1979-2015年）的2.5和3.6倍,亦即2015年的台风季提前展开。利用ERA-Interim再分析资料、JTWC热带气旋最佳化路径数据等资料,通过计算台风生成指数（Genesis Potential Index,GPI）和比较天气尺度和季节内振荡分量,探讨2015年台风季提前的原因。结果表明：1）2015年初异常活跃的台风活动与2015/2016年超级El Niño事件于西北太平洋上引发的海气状态异常有关。2）通过对大尺度环境场和台风潜在生成指数（GPI）的诊断分析发现,动力因子（低层涡度、垂直速度）和热力因子（与海表面温度、大气温度有关的潜在强度、中低层大气相对湿度）均对2015年1-5月台风的发生有正贡献。其中,涡度项的贡献最大,相对湿度的贡献次之。3）3~10 d天气尺度扰动和10~90 d季节内振荡在2015年1-5月也异常活跃,有利于TS和TY的生成与发展。  相似文献   

The Structure of the Kuenlunkuan Granodiorite and its Relation to the Formation of the Ore-bearing Quartz Veins     

Y.C.HSU 《地质学报》1943,(Z1):77-85,87,88

正 The Kuenlunknan Granodiorite, whick occurs slightly to the west of the apex of the Kuangi are, is exposed at the southern end of the Tamingshan anticline. The mass is injeated into the Lower Devonian and Pre-Devonian rocks. This pluton is  相似文献   

Laboratory Observations on Internal Solitary Wave Evolution over A Submarine Ridge     

Chen-Yuan CHEN John Rong-Chung HSU Ching-Feng KUO Hsin-Hsun CHEN Min-Hung CHENG 《中国海洋工程》2006,20(1):61-72

Laboratory experiments were conducted in a wave flume on internal solitary wave （ISW） of depression and elevation types propagating over a submarine ridge in semicircular/triangular shape. Tests were arranged in series for combinations of submarine ridges of different heights and ISW of different amplitudes. The resuhant wave motions were found differing from thee of surface gravity waves. In deeper water, where an ISW of depression-type prevailed, the process of wave breaking displayed downward motion with continuous eddy on the front face of the ridge followed by upward motion towards the apex of the obstacle. Experimental results also suggested that blockage parameter ξ could be applied to classify various degrees of ISW-ridge interaction, i.e., ξ 〈 0.5 for weak interaction, 0.5 〈 ξ 〈 0.7 for moderate interaction, and 0.7 〈 ξ for wave breaking.  相似文献   

Factors Limiting the Forecast Skill of the Boreal Summer Intraseasonal Oscillation in a Subseasonal-to-Seasonal Model     

Zheng HE  Pangchi HSU  Xiangwen LIU  Tongwen WU  Yingxia GAO 《大气科学进展》2019,36(1):104-118

In this study,we evaluate the forecast skill of the subseasonal-to-seasonal(S2S)prediction model of the Beijing Climate Center(BCC)for the boreal summer intraseasonal oscillation(BSISO).We also discuss the key factors that inhibit the BSISO forecast skill in this model.Based on the bivariate anomaly correlation coefficient(ACC)of the BSISO index,defined by the first two EOF modes of outgoing longwave radiation and 850-hPa zonal wind anomalies over the Asian monsoon region,we found that the hindcast skill degraded as the lead time increased.The ACC dropped to below 0.5for lead times of 11 days and longer when the predicted BSISO showed weakened strength and insignificant northward propagation.To identify what causes the weakened forecast skill of BSISO at the forecast lead time of 11 days,we diagnosed the main mechanisms responsible for the BSISO northward propagation.The same analysis was also carried out using the observations and the outputs of the four-day forecast lead that successfully predicted the observed northward-propagating BSISO.We found that the lack of northward propagation at the 11-day forecast lead was due to insufficient increases in low-level cyclonic vorticity,moistening and warm temperature anomalies to the north of the convection,which were induced by the interaction between background mean flows and BSISO-related anomalous fields.The BCC S2S model can predict the background monsoon circulations,such as the low-level southerly and the northerly and easterly vertical shears,but has limited capability in forecasting the distributions of circulation and moisture anomalies.  相似文献   

北半球大气遥相关型冬夏差异及其与温度场关系的探讨   总被引：2，自引：2，他引：0  

陈芳丽  黎伟标 《大气科学》2009,33(3):513-523

利用55年的NCEP/NCAR再分析资料, 采用合成分析等方法探讨了冬、 夏季北半球大气遥相关型的差异及其与温度场的关系。主要结果有: 北半球冬、 夏季典型的大气遥相关型具有很大的差异, 且大气遥相关路径的偏折与温度场的变化有密切的关系。北半球冬季, 呈经向型分布特征的大气遥相关路径在温度纬向梯度正负号发生改变处发生偏折; 而在北半球夏季, 由于温度场分布呈现纬向特征, 遥相关路径不易产生南北向的偏折, 从而使得异常中心基本上沿纬圈分布, 呈明显的纬向特征。此外, 由于冬季等温线南北起伏明显的区域往往位于东西方向海陆交界处, 因此冬季大气遥相关路径往往在东西向海陆交界处发生偏折。  相似文献   

Validation of ECMWF and NCEP–NCAR Reanalysis Data in Antarctica   总被引：3，自引：0，他引：3  

YU Lejiang  ZHANG Zhanhai  ZHOU Mingyu  Shiyuan ZHONG  Donald LENSCHOW  Hsiaoming HSU  WU Huiding  SUN Bo 《大气科学进展》2010,27(5):1151-1168

The European Center for Medium-Range Weather Forecast (ECMWF) Re-Analysis (ERA-40) and the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) ECMWF (ERA-40) and NCEP-NCAR reanalysis data were compared with Antarctic station observations, including surface-layer and upper-layer atmospheric observations, on intraseasonal and interannual timescales. At the interannual timescale, atmospheric pressure at different height levels in the ERA-40 data are in better agre...  相似文献