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沙尘暴作为地球上的极端环境事件,是一种具有突发性和持续时间较短特点的概率小危害大的灾害性天气现象[1]。沙尘可以通过直接效应改变辐射收支[2],也可以通过间接效应改变云的特性[3],从而影响着地-气系统的辐射平衡及降水。此外,沙尘也直接影响着空气质量和人体健康[4]。东亚是全球沙尘的主要排放源之一,我国北部的戈壁沙漠和西北部的塔克拉玛干沙漠是亚洲最大的沙尘来源[5]。因此,对我国西北地区进行沙尘模拟具有重要的现实意义。
WRF-Chem模式(Weather Research and Forecasting model coupled to Chemistry)是由美国国家海洋和大气管理局(NOAA)、美国能源部/太平洋西北国家实验室(DOE/PNNL)和美国国家大气研究中心(NCAR)联合开发的一种气象模块(WRF)和化学模块(Chem)在线完全耦合的新一代区域空气质量模式。该模式在区域沙尘的模拟方面具有较大优势[6]。松弛逼近方法(Nudging)是一种通过在控制方程中附加强迫项,逐渐把模式状态向观测状态逼近的同化方法。由于其计算成本较低、易于实现,因此具有很高的实用价值。研究表明,Nudging方法对气候以及天气尺度的数值模拟效果均有不同程度的改进[7-8]。
近年来,已有不少研究利用WRF-Chem模式在我国西北地区进行沙尘模拟且模拟结果均在不同程度上反映出起沙及沙尘分布[6,9-12],但是适用于我国西北地区沙尘模拟的模式参数设置仍存在着不确定性。对于Nudging方法,先前大多数研究多集中于该方法对模式模拟的各气象要素的影响[7-8,13]。目前对于利用WRF-Chem模式中不同起沙参数化方案结合Nudging方法对沙尘的模拟结果与卫星及地面观测资料的对比的研究仍然较少,因此利用不同的起沙参数化方案结合Nudging方法对我国西北地区的典型沙尘过程进行模式模拟,进而对模拟结果进行对比分析,找出更适合我国西北地区沙尘天气模拟的起沙方案及其结合Nudging方法后对模拟结果的影响,对我国西北地区沙尘天气的准确预报和进一步利用模式研究沙尘天气的气候效应具有重要的意义。
利用WRF-Chem模式4.1.3版本耦合GOCARTAFWA(简称AFWA)[14]及Shao04[15]起沙参数化方案结合Nudging方法对2020年4月9~11日我国西北地区的一次典型沙尘天气过程进行数值模拟,结合卫星及地面观测数据对模式模拟结果进行验证,并初步分析2种起沙方案及Nudging方法对我国西北地区沙尘天气过程模拟的影响。
起沙方案及Nudging对中国西北沙尘模拟的影响
Impacts of dust emission schemes and Nudgingon on dust simulation in northwest China
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摘要: 利用耦合了AFWA和Shao04起沙参数化方案的WRF-Chem模式结合Nudging方法,对2020年4月9~11日发生在我国西北地区的一次沙尘天气过程进行模拟,结合地面及卫星观测数据,对模式模拟沙尘的能力进行了初步验证,分析了不同起沙方案及其结合Nudging方法后对模式模拟结果的影响。结果表明,2种起沙方案均有能力再现此次沙尘天气过程,开启Nudging后2种方案模拟出的沙尘分布结果都有所改进。对于地面沙尘模拟,在沙尘源区不开Nudging的模式模拟结果更接近观测,在沙尘影响区开启Nudging后的模拟结果更优。整体而言,结合了Nudging方法的Shao04起沙方案对我国西北地区的沙尘过程具有更好的模拟能力。Nudging方法对模式模拟风场的能力改进较为明显,从而提高了模式对沙尘的模拟能力。Abstract: Combination of WRF-Chem Model coupled with the AFWA and Shao04 dust-emission schemes and Nudging method are employed to simulate a dust process in northwest China during April 9 to 11, 2020. The model to simulate the dust process has been preliminarily evaluated, and impacts of different dust-emission schemes and the improved mode with Nudging method on its simulation results have been analyzed by using the ground and satellite observation data. The results show the two dust-emission schemes are capable of reproducing the observed dust plume. The simulated dust plume of the two schemes has been improved with Nudging method. For the ground dust simulation, the results of the model without Nudging in the dust source area are most closely agreement with the observation, and the model simulation results in the impact area of dust performed a better simultaion with Nudging. Generally, the Shao04 dust-emission scheme combined with the Nudging can well simulate the dust process in the northwest of China. The Nudging method significantly improves the ability to simulate wind fields, thus enhancing the simulation ability.
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Key words:
- dust-emission parameterization scheme /
- Nudging method /
- WRF-Chem /
- dust weather /
- numerical simulation
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表 1 模式采用的物理化学参数化方案及设置
物理化学过程 参数化方案 Namelist配置项 选项 微物理过程 LIN [21] mp_physics 2 长波辐射 RRTMG [22] ra_lw_physics 4 短波辐射 RRTMG ra_sw_physics 4 积云对流 Grell-Freitas [23] cu_physics 3 陆面过程 unified Noah[24] sf_surface_physics 2 边界层 YSU[25] bl_pbl_physics 1 近地面层 MM5 Monin-Obukhov[26] sf_sfclay_physics 1 化学模块 GOCART RACM-KPP[27] chem_opt 301 光解过程 Fast-J[28] phot_opt 2 气溶胶光学特性 Maxwell[29] aer_op_opt 2 表 2 PM10观测站点信息
站点名 纬度/°N 经度/°E 海拔高度/m 武威站 37.931 1 102.621 9 1 527 张掖站 38.946 7 80.282 8 1 473 阿克苏站 41.163 6 79.948 5 1 163 和田站 37.115 2 79.948 5 1 732 -
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