The Landfall and Inland Penetration of a Flood-Producing Atmospheric River in Arizona. Part II: Sensitivity of Modeled Precipitation to Terrain Height and Atmospheric River Orientation
The Landfall and Inland Penetration of a Flood-Producing Atmospheric River in Arizona. Part II: Sensitivity of Modeled Precipitation to Terrain Height and Atmospheric River Orientation
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DOI：
10.1175/jhm-d-13-0176.1
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发表时间：
2014-10-01
影响因子：
3.8
通讯作者：
Ralph, F. Martin
中科院分区：
文献类型：
--
作者：
Hughes, Mimi;Mahoney, Kelly M.;Ralph, F. Martin
这份手稿记录了基于2010年1月一次大气河（AR）事件的数值模拟实验，该事件在亚利桑那州造成了极端降水。使用网格间距为3千米的天气研究与预报（WRF）模式的控制实验（CNTL）与观测结果吻合良好。敏感性实验包括：1）模型网格间距从81千米依次减小到3千米；2）抬高上游地形，用于评估内陆降水量和水平水汽通量对模型网格分辨率以及下加利福尼亚地形高度的敏感性。干燥比（衡量气团越过地形后干燥程度的指标）随下加利福尼亚地形高度的增加而增大，随网格间距变粗而减小。随后，亚利桑那州的降水量随下加利福尼亚地形高度的增加而减少，尽管它随网格间距变粗变化不大。下加利福尼亚北部的干燥比远大于南部。因此，呈南风方向的大气河，其水汽输送能够经过下加利福尼亚北部较高山脉的南侧，然后穿过加利福尼亚湾，能够在亚利桑那州产生大量降水。针对以亚利桑那州中部为重点的子区域，使用地形降水线性模型（LM）进行了进一步的实验。大气河的实际入射角（211度）接近区域平均降水量较大的最佳角度。由于大气河角度的变化，区域平均降水量的变化较小（约6%）；然而，在测试的物理合理的大气河角度范围内，流域平均降水量的变化要大得多，可达33%。在下加利福尼亚地形改变实验中看到的线性模型降水敏感性比大气河角度改变实验中的更大。
This manuscript documents numerical modeling experiments based on a January 2010 atmospheric river (AR) event that caused extreme precipitation in Arizona. The control experiment (CNTL), using the Weather Research and Forecasting (WRF) Model with 3-km grid spacing, agrees well with observations. Sensitivity experiments in which 1) model grid spacing decreases sequentially from 81 to 3 km and 2) upstream terrain is elevated are used to assess the sensitivity of interior precipitation amounts and horizontal water vapor fluxes to model grid resolution and height of Baja California terrain. The drying ratio, a measure of airmass drying after passage across terrain, increases with Baja's terrain height and decreases with coarsened grid spacing. Subsequently, precipitation across Arizona decreases as the Baja terrain height increases, although it changes little with coarsened grid spacing. Northern Baja's drying ratio is much larger than that of southern Baja. Thus, ARs with a southerly orientation, with water vapor transports that can pass south of the higher mountains of northern Baja and then cross the Gulf of California, can produce large precipitation amounts in Arizona. Further experiments are performed using a linear model (LM) of orographic precipitation for a central-Arizona-focused subdomain. The actual incidence angle of the AR (211 degrees) is close to the optimum angle for large region-mean precipitation. Changes in region-mean precipitation amounts are small (similar to 6%) owing to AR angle changes; however, much larger changes in basin-mean precipitation of up to 33% occur within the range of physically plausible AR angles tested. Larger LM precipitation sensitivity is seen with the Baja-terrain-modification experiments than with AR-angle modification.