【作者】 路屹雄；

【导师】 王元； 汤剑平；

【作者基本信息】 南京大学 ， 大气科学， 2011， 博士

【摘要】 全球模式能够较好地表征大尺度环流状况,但由于分辨率较低,难以捕捉到与非均匀下垫面局地强迫有关的中小尺度系统过程。动力降尺度指利用高分辨率有限区域模式来实现全球模式结果和局地强迫之间的非线性相互作用,以获取区域或局地的大气变化信息。目前动力降尺度在地面气温和降水区域气候模拟和气候变化预估方面得到了广泛研究,然而对近地层风的研究还不够深入和完整。本文首先分别从城市群和沿海复杂地形近地层风模拟的角度出发,重点讨论了下垫面动力和热力性质不均一分布对近地层风日变化特征的影响,然后对中国区域地面风速气候变化进行预估。主要研究内容和结论如下：1.利用较新的MODIS陆面类型资料以及WRF/Noah/UCM耦合模拟系统对珠江三角洲地区2008年近地层风场进行1-km分辨率的模拟,并将模拟结果与风廓线雷达和地面站观测数据进行了比较分析,研究发现：地面风速具有明显的日变化特征,白天大、夜间小；上层风速则表现为白天小、夜间大。模拟风速日变化与观测基本一致,较准确地再现上、下层风速反相变化特征。模拟风速值在1000m以内存在正偏差；在1000m以上存在负偏差。另外,通过将珠三角地区城市改为农田并进行敏感性试验,发现城市化使该地区地表能量收支结构发生了明显的改变,城市化使白天潜热通量减少,地面热通量增加,更多的热量存储于地面中并于夜间释放出来,夜间感热通量变大。相应地,城市化使地面风速白天减小、夜间则增大(冬季除外),夏季夜间地面风速增大尤为显著,约为1m/s。上述结果表明,WRF/Noah/UCM系统对于城市下垫面近地层风速变化具有较好的模拟性能,利用该系统研究城市气候效应对局地环流的影响具有一定的可靠性。2.海陵岛位于中国南部沿海地区,受东亚季风和海陆风环流的共同影响,岛上分布有多座小山,局地风况较为复杂。首先利用中尺度模式WRF对该地区环流系统进行了模拟,并与测风塔观测数据进行了对比,分析表明经向风模拟值相关系数为0.75-0.85,纬向风模拟值相关系数为0.5-0.75,WRF模式能够较好地再现该地区环流系统的时间变化特征。对于季节平均风场和海陆风的变化与观测基本一致。然而在地形起伏的小范围内(东西约25km,南北约18km),1-km分辨率WRF模拟风场分布趋于均匀。为此,引入边界层诊断模式CALMET对WRF结果进一步进行调整得到100-m分辨率风场精细结构,较为合理的反映出起伏地形对风场分布的影响。上述结果说明WRF/CALMET系统可以较好地刻画沿海复杂地形下小范围内风场精细结构。3.利用全球模式ECHAM5的结果驱动区域气候模式MM5,分别对中国地区当代(1981-2000年)和未来(2041-2060年)气候进行模拟,并利用地面气象站逐日风速观测资料,检验评估了MM5模拟的当代中国陆域地面(10 m AGL)风速分布及其变化特征；在此基础上,分析了IPCC　A1B’情景下中国陆域地面风速未来可能的变化特征。结果表明,MM5能够较好地模拟出平均风速和90th百分位风速的分布状况。A1B情景下,中国陆域大部分地区地面风速减小约0.1m/s；风速增大区主要位于东北地区、环渤海地区及西南地区。未来风速变化表现出明显的季节差异,夏、秋季中国东部地区风速增大,西部风速减小,呈“东增西减”型；冬、春季北部地区风速增大,南部地区风速减小,呈“北增南减”型。另外,分析表明未来极端强风事件发生频数也将减少。以上结果表明,区域气候模式MM5对于中国陆域地面风速具有一定的模拟能力,利用该模式预估中国陆域地面风速气候变化具有一定的可靠性。更多还原

【Abstract】 The general circulation models could represent the large-scale atmospheric conditions, but the mesoscale and smaller scale processes could not be captured due to coarse resolution. Dynamical downscaling introduces new scales through the non-linear interaction between the large-scale atmospheric circulation and the local forcing in limited-area models. Dynamical downscaling has been extensively used in regional climate modeling and climate change projection of precipitation and temperature, but is not sufficiently disscued in respect of low-levels winds which are essential for wind resource assessment and air quanlity studies. Therefore, this work is focus on the mesoscale low-levels winds obtained by dynamical downscaling. Firstly, discussions are presented based on the downscaled local winds over the urban agglomeration and coastal complex topography, respectively. Then, validation and projection of wind climate in China is studies under IPCC A1B scenario. The main results and conclusions are summarized as follows.Two 1-year experiments with different land use conditions were performed by WRF/Noah/UCM modeling system over the Pearl River Delta region in Chapter 2. With new MODIS land use data, the urban distribution was well represented in the control experiment (hereafter CTRL). The diurnal variation of wind speed observed by the wind-profiling radar was reproduced in CTRL. The simulated wind speed was overestimated below about 1 km, and underestimated above about 1 km. In addition, a sensitive experiment (hereafter NO-URBAN) with urban land use changed to cropland was performed in order to determine the impact of urbanization on the local circulation. Compared to NO-URBAN, CTRL produced smaller latent heat and larger ground heat fluxes during daytime, later more heat was released from the ground during nighttime, and then transferred to the atmosphere through positive sensible heat fluxes. Correspondingly, the surface wind speed decreased during daytime and increased during nighttime (excluding in winter). The wind speed increased about 1 m/s during nighttime in summer.In Chapter 3, the results from a hybrid approach that combines a mesoscale meteorological model with a diagnostic model to produce high-resolution wind fields in complex coastal topography are evaluated. The diagnostic wind model (California Meteorological Model, hereafter CALMET) with 100-m horizontal spacing was driven with outputs from the Weather Research and Forecasting (WRF) model to obtain near-surface winds for the 1-year period from 12 September 2003 to 11 September 2004. Results were compared with wind observations at 7 sites. Correlation coefficients indicate that the WRF-simulated winds were produced reasonably well. The correlation coefficients were ranging from 0.5 to 0.7 for the zonal wind component and from 0.75 to 0.85 for the meridional wind component. The variation of seasonally-averaged wind field and sea-breezes were reproduced. Moreover, combining the CALMET model with WRF significantly improves the spatial variability of the simulated wind fields. It can be concluded that the WRF/CALMET modeling system is capable of providing a detailed near-surface wind field, but the physics in the diagnostic CALMET model need to be further improved.In Chapter 4, surface wind climate in China in the late 20th century (1981-2000) and in the middle 21st century (2041-2060) was simulated by the regional climate model MM5, based on the multi-model datasets of 20C3M and the IPCC A1B scenario projection provided by ECHAM5, respectively. The simulated present wind climate was evaluated against the daily wind speed observations obtained from surface meteorological stations, and then future change of wind climate features was investigated in respect of climatological distributions and strong wind events. Results show that MM5 can reproduce the climatological patterns of both mean wind speed and 90th percentile wind speed. However, MM5 did not present the stilling trend which is obvious in the observations. Under the A1B scenario, Annual mean wind speed for 2041-2060 will be less than those for 1981-2000 by about 0.1 m/s in most area of China. Greater wind speed appears in northeast China, areas surrounding Bo Sea, and southwest China. Seasonal mean wind speed will increase over the eastern part of China, and decrease over the western part of China in warm seasons (summer and autumn). On the other hand, it will increase over the northern part of China, and decrease over the southern part of China in cold seasons (winter and spring). Moreover, it was found that the strong wind events will decrease under A1B scenario. It can be concluded that MM5 has certain capabilities of simulating surface wind climate in China, and the wind climate change projected based on this model is reliable to some extent.更多还原