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941.
地形对涡旋自组织影响的初步研究 总被引:1,自引:3,他引:1
用一个带有地形项的f平面准地转正压涡度方程,实施5组积分时间长度为72h的试验,研究了中尺度地形对涡旋自组织的影响。结果指出:无地形时,准终态涡是一个带有螺旋带的类似台风的涡旋;有地形时,准终态涡是一个无螺旋带但有两个低涡量区的准圆形涡旋。有无地形两个准终态涡中心的位置可以相距100km以上。 相似文献
942.
943.
Most tropical cyclones have very few observations in their vicinity. Hence either they go undetected in standard analyses
or are analyzed very poorly, with ill defined centres and locations. Such initial errors obviously have major impact on the
forecast of cyclone tracks using numerical models. One way of overcoming the above difficulty is to remove the weak initial
vortex and replace it with a synthetic vortex (with the correct size, intensity and location) in the initial analysis. The
objective of this study is to investigate the impact of introducing NCAR–AFWA synthetic vortex scheme in the regional model
MM5 on the simulation of a tropical cyclone formed over the Arabian Sea during November 2003. Two sets of numerical experiments
are conducted in this study. While the first set utilizes the NCEP reanalysis as the initial and lateral boundary conditions,
the second set utilizes the NCAR–AFWA synthetic vortex scheme. The results of the two sets of MM5 simulations are compared
with one another as well as with the observations and the NCEP reanalysis. It is found that inclusion of the synthetic vortex
has resulted in improvements in the simulation of wind asymmetries, warm temperature anomalies, stronger vertical velocity
fields and consequently in the overall structure of the tropical cyclone. The time series of the minimum sea level pressure
and maximum wind speed reveal that the model simulations are closer to observations when synthetic vortex was introduced in
the model. The central minimum pressure reduces by 17 hPa while the maximum wind speed associated with the tropical cyclone
enhances by 17 m s −1 with the introduction of the synthetic vortex. While the lowest central pressure estimated from the satellite image is 988 hPa,
the corresponding value in the synthetic vortex simulated cyclone is 993 hPa. Improvements in the overall structure and initial
location of the center of the system have contributed to considerable reduction in the vector track prediction errors ie.
642 km in 24 h, 788 km in 48 h and 1145 km in 72 h. Further, simulation with the synthetic vortex shows realistic spatial
distribution of the precipitation associated with the tropical cyclone. 相似文献
944.
A semi-implicit semi-Lagrangian global nonhydrostatic model and the polar discretization scheme 总被引:2,自引:0,他引:2
YANG XueSheng CHEN JiaBin HU JiangLin CHEN DeHui SHEN XueShun ZHANG HongLiang State Key Laboratory of Severe Weather Chinese Academy of Meteorological Sciences Beijing China State Key Laboratory of Numerical Modeling for Atmospheric Sciences Geophysical Fluid Dynamics Institute of Atmospheric Physics Beijing China 《中国科学D辑(英文版)》2007,50(12):1885-1891
The Global/Regional Assimilation and PrEdiction System(GRAPES) is a newly developed global non-hydrostatic numerical prediction model,which will become the next generation medium-range opera-tional model at China Meteorological Administration(CMA).The dynamic framework of GRAPES is featuring with fully compressible equations,nonhydrostatic or hydrostatic optionally,two-level time semi-Lagrangian and semi-implicit time integration,Charney-Phillips vertical staggering,and complex three-dimensional pre-conditioned Helmholtz solver,etc.Concerning the singularity of horizontal momentum equations at the poles,the polar discretization schemes are described,which include adoption of Arakawa C horizontal grid with ν at poles,incorporation of polar filtering to maintain the computational stability,the correction to Helmholtz equation near the poles,as well as the treatment of semi-Lagrangian interpolation to improve the departure point accuracy,etc.The balanced flow tests validate the rationality of the treatment of semi-Lagrangian departure point calculation and the polar discretization during long time integration.Held and Suarez tests show that the conservation proper-ties of GRAPES model are quite good. 相似文献
945.
The tropical cyclones form over the oceanic regions where conventional meteorological observations are not available. This
contributes to a poor initial analysis of the cyclonic vortex and hence inadequate forecast. One way of overcoming the above
problem is to modify the initial analysis by replacing the weak and ill-defined vortex in the initial analysis with a synthetic
vortex having the correct size and intensity at the correct location. In this study we are investigating the effect of inclusion
of a synthetic vortex based on Rankine as well as on Holland wind profiles, using NCAR-AFWA bogussing scheme for the prediction
of four tropical cyclones, which formed over the Bay of Bengal during November 2002 and 2005, December 2005 and over the Arabian
Sea during May 2004, using the MM5 model. Two numerical experiments are designed in this study for each of the above four
cyclones. In the first experiment the model is integrated with a synthetic vortex based on Rankine wind profile while in the
second experiment we utilize the Holland wind profile. For the November 2002 cyclone, in both the experiments the model is
integrated from 10 November 2002 18 UTC to 12 November, 2002 12 UTC with the synthetic vortex inserted at the initial time.
The results of the study for the November 2002 cyclone show that the model simulation with the Holland vortex has produced
a stronger cyclone in terms of minimum sea-level pressure and maximum wind speed. Also, the results for the November 2002
cyclone with the Holland vortex showed a better longitudinal height section of the horizontal wind speed across the center
of the cyclone. The track error of the cyclone for the November 2002 cyclone is less in the model simulation with the Holland
vortex at the initial time and at 24 hours of forecast. The results for the November 2002 cyclone with the Rankine vortex
showed greater vertical wind speed as compared to the Holland vortex. However, for the November 2002 cyclone there were no
significant differences in the spatial distribution of precipitation for both the experiments. In order to provide an adequate
number of case studies for a good statistical sample, the present study is extended for three additional cyclones over the
Indian region. All four cyclones studied here show that the Holland vortex has produced a stronger cyclone in terms of the
minimum sea-level pressure and maximum wind speed. The Holland vortex showed a better vertical structure of wind speed in
the longitudinal height section at 24 hours of forecast for the November 2005 cyclone while the structure was better for the
Rankine vortex for the remaining two cyclones. There were no significant differences in the spatial distribution of precipitation
for the two experiments corresponding to all four cyclones. Some statistical results pertaining to all four cyclones are provided
such as the average track error as well as the average difference between the observed and the model minimum sea-level pressure
and the maximum wind speed. The statistical results corresponding to the average of all the four cyclones are at only a slight
variance with the results corresponding to the November 2002 cyclone. 相似文献
946.
The present article displays the results of theoretical investigation of the planetary ultra-low-frequency (ULF) electromagnetic wave structure, generation and propagation dynamics in the dissipative ionosphere. These waves are stipulated by a spatial inhomogeneous geomagnetic field. The waves propagate in different ionospheric layers along the parallels to the east as well as to the west and their frequencies vary in the range of (10–10−6) s−1 with a wavelength of order 103 km. The fast disturbances are associated with oscillations of the ionospheric electrons frozen in the geomagnetic field. The large-scale waves are weakly damped. They generate the geomagnetic field adding up to several tens of nanotesla (nT) near the Earth's surface. It is prescribed that the planetary ULF electromagnetic waves preceding their nonlinear interaction with the local shear winds can self-localize in the form of nonlinear long-living solitary vortices, moving along the latitude circles westward as well as eastward with a velocity different from the phase velocity of the corresponding linear waves. The vortex structures transfer the trapped particles of medium, as well as energy and heat. That is why such nonlinear vortex structures can be the structural elements of the ionospheric strong macro-turbulences. 相似文献
947.
948.
949.
950.
利用常规探空和地面资料以及NCEP再分析资料,对2006年1月漯河暴雪过程进行了诊断分析,结果表明:高空阶梯槽的形成和维持,为这次强降雪过程提供了有利的环流背景,中低空低涡切变线是主要影响系统;冷平流的持续使近地面层气温降至0℃以下,有利于雪的形态维持;高层辐散与低层辐合的耦合,使上升运动加强;低空急流输送了充沛的水汽,大气中水汽处于饱和状态有利于提高降水的转化率。 相似文献