Statistical Downscaling Using Localized Constructed Analogs (LOCA)
Statistical Downscaling Using Localized Constructed Analogs (LOCA)
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DOI：
10.1175/jhm-d-14-0082.1
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发表时间：
2014-12-01
影响因子：
3.8
通讯作者：
Thrasher, Bridget L.
中科院分区：
文献类型：
--
作者：
Pierce, David W.;Cayan, Daniel R.;Thrasher, Bridget L.
本文介绍了一种统计降尺度气候模式模拟日温度和降水的新技术，并在美国西部进行了演示。局部构造类似物（LOCA）方法使用多尺度空间匹配方案从观测中选择合适的模拟日，产生适合水文模拟的降尺度估计。首先，通过将待降尺度的模型场与与被降尺度点正相关的区域上的观测日数进行匹配，选择候选观测模拟日数池，从而使降尺度结果与被降尺度域的程度自然独立。然后，在被缩小的网格单元周围的局部区域中最匹配的一个候选模拟日是在那里使用的单个模拟日。大多数网格单元只使用单个本地选择的模拟日进行缩小，但是其相邻单元识别不同模拟日的位置使用中心和相邻模拟日的加权组合来减少边缘不连续。相比之下，现有的构造模拟方法通常使用整个域相同的30个模拟天的加权平均值。通过大大减少这种平均，LOCA可以更好地估计极端日数，构建更真实的缩小尺度场空间相干性描述，并减少产生过多轻降水日数的问题。LOCA方法的计算成本比现有的构造模拟技术要高，但在计算资源有限的情况下，它仍然可以缩小大量气候模式模拟的尺度。
A new technique for statistically downscaling climate model simulations of daily temperature and precipitation is introduced and demonstrated over the western United States. The localized constructed analogs (LOCA) method produces downscaled estimates suitable for hydrological simulations using a multiscale spatial matching scheme to pick appropriate analog days from observations. First, a pool of candidate observed analog days is chosen by matching the model field to be downscaled to observed days over the region that is positively correlated with the point being downscaled, which leads to a natural independence of the downscaling results to the extent of the domain being downscaled. Then, the one candidate analog day that best matches in the local area around the grid cell being downscaled is the single analog day used there. Most grid cells are downscaled using only the single locally selected analog day, but locations whose neighboring cells identify a different analog day use a weighted combination of the center and adjacent analog days to reduce edge discontinuities. By contrast, existing constructed analog methods typically use a weighted average of the same 30 analog days for the entire domain. By greatly reducing this averaging, LOCA produces better estimates of extreme days, constructs a more realistic depiction of the spatial coherence of the downscaled field, and reduces the problem of producing too many light-precipitation days. The LOCA method is more computationally expensive than existing constructed analog techniques, but it is still practical for downscaling numerous climate model simulations with limited computational resources.