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TRAMS_RUC_1km模式初边值方案的改进研究
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中国气象局广州热带海洋气象研究所

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Revised initial field and lateral boundary condition for TRAMS_RUC_1km model
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    摘要:

    本文从垂直分辨率、时间更新频率和要素完整性三个方面,对水平网格距为1km的华南区域短临预报模式(TRAMS_RUC_1km: Tropical Region Assimilation Model for South China Sea _ The Rapid Update Cycle _ 1km)中的初始场和侧边界方案进行改进研究。首先选择一次华南飑线个例进行敏感性试验,研究结果表明:(1)提高初始场和侧边界的垂直分辨率以后,模式对飑线内部中小尺度对流系统引起的强降水中心的模拟结果明显更加接近实况,而增加中低层的垂直分辨率对预报的改进起到了主要作用。(2)将模式侧边界时间更新频率从6小时一次提高到1小时一次以后,模式侧边界要素场的逐小时剧烈变化信息可以比较完整的保留下来。在使用高时间分辨率的侧边界条件进行模拟时,粤西沿海地区的水汽辐合明显加强,这对原来模式预报飑线移速偏慢现象会有改善作用。(3)当模式侧边界条件具有较高的时空分辨率时,进一步补充垂直速度和云微物理变量的侧边界条件对于飑线模拟结果的影响并不明显。总的来说,提高初始场和侧边界的垂直分辨率以及增加侧边界更新的时间分辨率,对于区域高分辨率模式对这次华南飑线预报效果的改进具有重要意义,而忽略垂直速度和云微物理量的侧边界条件则是一种可以接受的简化。在个例研究的基础上,利用改进后的初边界条件进行为期一个月(2019年4月份)的批量试验,评估结果表明新方案对于逐小时降水空间分布和日变化特征的模拟均有明显改善。

    Abstract:

    In the TRAMS_RUC_1km (Tropical Region Assimilation Model for South China Sea _ The Rapid Update Cycle _ 1km) model, the initial field and lateral boundary condition scheme was revised (including its vertical resolution, time update frequency and completeness) and tested with a typical squall line case. Preliminary analysis revealed: (1)The meso-scale character of precipitation in squall line was better simulated after increasing vertical resolution of initial field and lateral boundary, while increasing vertical resolution of middle and low layers played the most critical role in it. (2)The diurnal change of lateral boundary forcing got more accurate after increasing its time update frequency. The squall line moved south after using high frequency updated boundary condition, because of the convergence of moist flux alone coastline was strengthened. (3)With high vertical resolution and high update frequency of lateral boundary condition, lateral forcing of vertical speed and cloud particle had no obvious impact on forecast of squall line. In general, it was important to increasing the vertical resolution of initial field and lateral boundary field, the time update frequency was also needed to be increased, while the lateral forcing of vertical speed and cloud particle could be omitted. The impact of new scheme was verified against observation in April of 2019 (last for a month). The distribution pattern and diurnal cycle of mean hourly precipitation were improved significantly with the revised initial and lateral condition.

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  • 收稿日期:2019-07-05
  • 最后修改日期:2019-09-27
  • 录用日期:2019-12-03
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