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951.
952.
The mesoscale orographic effects on typhoon Aere's precipitation are simulated using an Advanced Regional Eta-coordinate Model (AREM) version 3.0. In particular, the effects of the latent heat release are studied by two comparable experiments: with and without condensational heating. The results show that the typhoon rainfall is tripled by the southeastern China mesoscale terrain, and the condensational heating is responsible for at least half of the increase. One role of the latent heat release is to warm the atmosphere, leading to a depression of the surface pressure, which then causes a larger pressure difference in the zonal direction. This pressure gradient guides the water vapour to flow into the foothills, which in turn amplifies the water vapour flux divergence amplified, causing the typhoon rainfall to increase eventually. The other role of the latent heat release is to make the convection more organized, resulting in a relatively smaller rain area and stronger precipitation. 相似文献
953.
A numerical study of tropospheric ozone in the springtime in East Asia 总被引:11,自引:0,他引:11
The Models-3 Community Multi-scale Air Quality modeling system (CMAQ)coupled with the Regional Atmospheric Modeling System (RAMS)is applied to East Asia to study the transport and photochemical transformation of tropospheric ozone in March 1998.The calculated mixing ratios of ozone and carbon monoxide are compared with ground 1evel observations at three remote sites in Japan and it is found that the model reproduces the observed features very well.Examination of several high episodes of ozone and carbon monoxide indicates that these elevated levels are found in association with continental outflow,demonstrating the critical role of the rapid transport of carbon monoxide and other ozone precursors from the continental boundary layer.In comparison with available ozonesonde data,it is found that the model-calculated ozone concentrations are generally in good agreement with the measurements,and the stratospheric contribution to surface ozone mixing ratios is quite limited. 相似文献
954.
The accurate determination of surface-layer turbulent fluxes over urban areas is critical to understanding urban boundary layer (UBL) evolution. In this study, a remote-sensing technique using a large aperture scintillometer (LAS) was investigated to estimate surface-layer turbulent fluxes over a highly heterogeneous urban area. The LAS system, with an optical path length of 2.1 km, was deployed in an urban area characterized by a complicated land-use mix (residential houses, water body, bare ground, etc.). The turbulent sensible heat (Q H) and momentum fluxes (τ) were estimated from the scintillation measurements obtained from the LAS system during the cold season. Three-dimensional LAS footprint modeling was introduced to identify the source areas ("footprint") of the estimated turbulent fluxes. The analysis results showed that the LAS-derived turbulent fluxes for the highly heterogeneous urban area revealed reasonable temporal variation during daytime on clear days, in comparison to the land-surface process-resolving numerical modeling. A series of sensitivity tests indicated that the overall uncertainty in the LAS-derived daytime Q H was within 20%-30% in terms of the influence of input parameters and the non-dimensional similarity function for the temperature structure function parameter, while the estimation errors in τ were less sensitive to the factors of influence, except aerodynamic roughness length. The 3D LAS footprint modeling characterized the source areas of the LAS-derived turbulent fluxes in the heterogeneous urban area, revealing that the representative spatial scales of the LAS system deployed with the 2.1 km optical path distance ranged from 0.2 to 2 km2 (a "micro-α scale"), depending on local meteorological conditions. 相似文献
955.
A CLOUD-RESOLVING MODELING STUDY OF SURFACE RAINFALL PROCESSES ASSOCIATED WITH LANDFALLING TYPHOON KAEMI(2006) 总被引:5,自引:0,他引:5
The detailed surface rainfall processes associated with landfalling typhoon Kaemi(2006) are investigated based on hourly data from
a two-dimensional cloud-resolving model simulation. The model is integrated for 6 days with imposed large-scale vertical velocity, zonal
wind, horizontal temperature and vapor advection from National Center for Environmental Prediction (NCEP) / Global Data Assimilation System
(GDAS) data. The simulation data are validated with observations in terms of surface rain rate. The Root-Mean-Squared (RMS) difference in
surface rain rate between the simulation and the gauge observations is 0.660 mm h-1, which is smaller than the standard
deviations of both the simulated rain rate (0.753 mm h-1) and the observed rain rate (0.833 mm h-1). The simulation
data are then used to study the physical causes associated with the detailed surface rainfall processes during the landfall. The results
show that time averaged and model domain-mean Ps mainly comes from large-scale convergence (QWVF) and local vapor loss
(positive QWVT). Large underestimation (about 15%) of Ps will occur if QWVT and QCM (cloud
source/sink) are not considered as contributors to Ps. QWVF accounts for the variation of Ps during most
of the integration time, while it is not always a contributor to Ps. Sometimes surface rainfall could occur when divergence is
dominant with local vapor loss to be a contributor to Ps. Surface rainfall is a result of multi-timescale interactions.
QWVE possesses the longest time scale and the lowest frequency of variation with time and may exert impact on Ps in
longer time scales. QWVF possesses the second longest time scale and lowest frequency and can explain most of the variation of
Ps. QWVT and QCM possess shorter time scales and higher frequencies, which can explain more detailed
variations in Ps. Partitioning analysis shows that stratiform rainfall is dominant from the morning of 26 July till the late night of 27 July. After that, convective rainfall dominates till about 1000 LST 28 July. Before 28 July, the variations of in rainfall-free regions contribute less to that of the domain-mean QWVT while after that they contribute much, which is consistent to the corresponding variations in their fractional coverage. The variations of QWVF in rainfall regions are the main contributors to that of the domain-mean QWVF, then the main contributors to the surface rain rate before the afternoon of 28 July. 相似文献
956.
下击暴流的数值模拟研究 总被引:10,自引:3,他引:10
下击暴流是危害飞行安全的一种重要天气现象,特别是尺度为1—4km的微下击暴流。为了了解下击暴流的发展过程,以及大气环境条件和云-降水微物理结构对下击暴流发生演变的影响,利用我们设计发展的非静力全弹性中尺度-γ模式,以一次发生了下击暴流的大气的温、湿、风实测资料为算例进行了数值模拟研究。计算结果给出了下击暴流发生发展的过程,以及在发展过程中各种物理量的变化,得出一些大气环境条件及水凝物粒子微结构对下击暴流发展的影响机理,有助于台站预报员掌握这种天气现象的出现和演变。 相似文献
957.
An ocean general circulation model (OGCM) is used to demonstrate remote effects of tropical cyclone wind (TCW) forcing in the tropical Pacific. The signature of TCW forcing is explicitly extracted using a locally weighted quadratic least=squares regression (called as LOESS) method from six-hour satellite surface wind data; the extracted TCW component can then be additionally taken into account or not in ocean modeling, allowing isolation of its effects on the ocean in a clean and clear way. In this paper, seasonally varying TCW fields in year 2008 are extracted from satellite data which are prescribed as a repeated annual cycle over the western Pacific regions off the equator (poleward of 10°N/S); two long-term OGCM experiments are performed and compared, one with the TCW forcing part included additionally and the other not. Large, persistent thermal perturbations (cooling in the mixed layer (ML) and warming in the thermocline) are induced locally in the western tropical Pacific, which are seen to spread with the mean ocean circulation pathways around the tropical basin. In particular, a remote ocean response emerges in the eastern equatorial Pacific to the prescribed off-equatorial TCW forcing, characterized by a cooling in the mixed layer and a warming in the thermocline. Heat budget analyses indicate that the vertical mixing is a dominant process responsible for the SST cooling in the eastern equatorial Pacific. Further studies are clearly needed to demonstrate the significance of these results in a coupled ocean-atmosphere modeling context. 相似文献
958.
局地云量变化气候效应的数值模拟 总被引:3,自引:3,他引:3
本文用统计得到的东半球夏季平均云量资料,利用改进的云-辐射计算模式,在三维有限区域模式中模拟局地云量变化的气候效应。模拟结果表明,高原地区和热带辐合带云量变化造成的气候效应都主要表现在青藏高原地区。在低反照率时,高原地区云量减少使该地区地表加热,引起高低空气压系统加强;高反照率时结果相反。热带辐合带云量减少会引起青藏高原地区降温和气压系统减弱。 相似文献
959.
一次湖北暴雪天气的诊断与模拟 总被引:2,自引:1,他引:2
利用NCEP GFS资料分析了2007年1月15—16日鄂东南地区降雪过程,对造成暴雪过程的天气系统发生、发展背景场进行分析。并利用中尺度数值天气模式WRF模拟了这次暴雪过程,探讨了其发生发展的机制。天气系统的背景分析表明,这次暴雪过程主要是受700 hPa西南急流和地面冷空气的共同影响而产生的,降水过程与西南急流的变化密切联系。WRF模式较好地再现了此次暴雪的过程。模拟结果表明西南急流的减弱和移出,对应着降雪的开始和停止;在西南急流的左侧,由于低层涡度的增加,使低空辐合、高空辐散,在连续性原理和动力机制约束下导致上升运动的加强是该次暴雪的形成机制。模式结果说明,产生暴雪的上升运动要远小于产生暴雨的上升运动,且在暴雪过程中,中层为上升运动,近地层和高层伴随着下沉运动。 相似文献
960.