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鉴于热带气旋（TC）对我国沿海地区的影响,研究全球变暖背景下未来登陆我国TC活动的变化,对于我国沿海地区的防灾减灾具有重要意义。基于CMIP5中全球气候模式HadGEM2-ES数据,文中利用区域气候模式RegCM4开展了历史时期和3种情景（RCP2.6、RCP4.5和RCP8.5）下未来东亚区域气候的动力降尺度模拟,检验了模式对历史登陆我国TC活动及其相关大尺度环境场的模拟能力,并预估了3种情景下2030—2039年、2050—2059年和2089—2098年,登陆我国TC的路径、强度和频率的变化特征。结果表明：模式能合理地再现东亚区域历史时期（1986—2005年）大气环流场的空间结构以及登陆我国TC的特征;在3种情景下未来登陆我国TC的平均强度和数量均有不同程度的增加,尤其是台风及以上级别TC的总数明显增加,其中RCP8.5情景最突出,到21世纪末期（2089—2098年）登陆我国TC的平均强度、台风及以上级别TC总数的年平均值较历史时期将分别增加7.56%和1.05个;不同情景下未来登陆我国TC的路径均有不同程度的北移趋势,且全球升温的幅度越大,北移趋势越明显,这可能与未来中国近海显著变暖和垂直风切变减弱有关。未来我国沿海地区尤其是中高纬度很可能将面临日益严峻的TC灾害风险,亟需尽快开展防灾减灾及对策研究。 相似文献
16.
Four co-ignimbrite plumes were generated along the flow path of the pyroclastic flow of 7 August 1980 at Mount St. Helens.
Three of the plumes were generated in discrete pulses which can be linked to changes in slope along the channel. One plume
was generated at the mouth of the channel where the flow decelerated markedly as it moved onto the lower slopes of the pumice
plain. Plume generation here may be triggered by enhanced mixing due to a hydraulic jump associated with an abrupt slope change.
Measurements of plume ascent velocity and width show that the co-ignimbrite plumes increased in velocity with height. The
plumes have initial velocities of 1–2 m/s. Two of the plumes reached a velocity maximum (4.6 and 8.8 m/s, respectively, at
heights of 270 and 315 m above the flow) and thereafter decelerated. The other plumes reached velocities of 6.2 and 13 m/s.
The four plumes become systematically less energetic downstream as measured by their ascent rates, which can be interpreted
as a consequence of decreasing interaction of the pyroclastic flow front with the atmosphere. Theoretical models of both co-ignimbrite
plumes and discrete co-ignimbrite clouds assume that there is no initial momentum, and both are able to predict the observed
acceleration stage. The rising plumes mix with and heat air and sediment out particles causing their buoyancy to increase.
Theoretical models agree well with observations and suggest that the initial motion of the ascending material is best described
as a discrete thermal cloud which expands as it entrains air, whereas the subsequent motion of the head may become influenced
by material supplied from the following plume. The models agree well with observations for an initial temperature of the ash
and air mixture in the range of 500–600 K, which is in turn consistent with the measured initial ash temperature of around
920 K. Ash masses of 3.4×105 to 1.8×106 kg are estimated.
Received: 11 January 1996 / Accepted: 7 October 1996 相似文献
17.
Parameterization of Sheared Convective Entrainment in the First-Order Jump Model: Evaluation Through Large-Eddy Simulation 总被引：2，自引：0，他引：2
In this note, two different approaches are used to estimate the entrainment-flux to surface-flux ratio for a sheared convective
boundary layer (CBL); both are derived under the framework of the first-order jump model (FOM). That suggested by Sun and
Wang (SW approach) has the advantage that there is no empirical constant included, though the dynamics are described in an
implicit manner. The second, which was proposed by Kim et al. and Pino et al. (KP approach), explicitly characterizes the
dynamics of the sheared entrainment, but uncertainties are induced through the empirical constants. Their performances in
parameterizing the CBL growth rate are compared and discussed, and a new value of the parameter A
3 in the KP approach is suggested. Large-eddy simulation (LES) data are employed to test both approaches: simulations are conducted
for the CBL growing under varying conditions of surface roughness, free-atmospheric stratification, and wind shear, and data
used when the turbulence is in steady state. The predicted entrainment rates in each case are tested against the LES data.
The results show that the SW approach describes the evolution of the sheared CBL quite well, and the KP approach also reproduces
the growth of the CBL reasonably, so long as the value of A
3 is modified to 0.6. 相似文献
18.
GNSS精密单点定位中的实时质量控制 总被引：2，自引：1，他引：1
提出了一套适用于GNSS精密单点定位(PPP)的实时质量控制方法,重点研究了钟跳探测与修复、周跳探测与标记、抗差估计方法,并在现有质量控制方法的基础上进行了改进。对比分析了不同质量控制方案对PPP的影响,结果表明,钟跳不利于周跳探测,严重影响非差PPP的精度和效率,必须对其进行探测与修复;联合MW、GF组合可以探测出绝大多数周跳,且较使用单一方法更为准确、可靠;采用改进的抗差估计有效抑制了残余粗差对精密定位的影响,显著提高了PPP的精度和可靠性。 相似文献
19.
Smoothing and Change Point Detection for Gamma Ray Count Data 总被引：1，自引：0，他引：1
Gamma ray detectors are used to measure the natural radioactivity of rocks. For a number of boreholes drilled at a site the gamma ray detector is lowered into each borehole and counts of gamma ray emissions at different depths are recorded as the instrument is gradually raised to ground level. The profile of gamma counts can be informative about the geology at each location. The raw count data are highly variable, and in this paper we describe the use of adaptive smoothing techniques and change point models in order to identify changes in the geology based on the gamma logs. We formulate all our models for the data in the framework of the class of generalized linear models, and describe computational methods for Bayesian inference and model selection for generalized linear models that improve on existing techniques. Application is made to gamma ray data from the Castelreagh Waste Management Centre which served as a hazardous waste disposal facility for the Sydney region between March 1974 and August 1998. Understanding the geological structure of this site is important for further modelling the transport of pollutants beneath the waste disposal area. 相似文献
20.
A non-hydrostatic numerical model, the Regional Atmospheric Modeling System (RAMS), has been used to investigate the development of katabatic jumps in Coats Land, Antarctica. In the control run with a 5 m s-1downslope directed initial wind, a katabatic jump develops near the foot of the idealized slope. The jump is manifested as a rapid deceleration of the downslope flow and a change from supercritical to subcritical flow, in a hydraulic sense, i.e., the Froude number (Fr) of the flow changes from Fr > 1 to Fr> 1. Results from sensitivity experiments show that an increase in the upstream flow rate strengthens the jump, while an increase in the downstream inversion-layer depth results in a retreat of the jump. Hydraulic theory and Bernoulli's theorem have been used to explain the surface pressure change across the jump. It is found that hydraulic theory always underestimates the surface pressure change, while Bernoulli's theorem provides a satisfactory estimation. An analysis of the downs balance for the katabatic jump indicates that the important forces are those related to the pressure gradient, advection and, to a lesser extent, the turbulent momentum divergence. The development of katabatic jumps can be divided into two phases. In phase I, the t gradient force is nearly balanced by advection, while in phase II, the pressure gradient force is counterbalanced by turbulent momentum divergence. The upslope pressure gradient force associated with a pool of cold air over the ice shelf facilitates the formation of the katabatic jump. 相似文献