Ensemble initialization of the oceanic component of a coupled model through bred vectors at seasonal-to-interannual timescales
Ensemble initialization of the oceanic component of a coupled model through bred vectors at seasonal-to-interannual timescales
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DOI：
10.5194/gmd-7-453-2014
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发表时间：
2013-10
影响因子：
5.1
通讯作者：
J. Baehr;R. Piontek
中科院分区：
文献类型：
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作者：
J. Baehr;R. Piontek
抽象的。我们评估了在耦合模式的海洋分量中实施的两种扰动技术在季节到年际时间尺度上的集合传播：（1）通常用于十年预测的滞后初始条件;（2）通常用于天气和季节预报的繁殖向量。我们表明，相对于未初始化的参考模拟繁殖矢量的实现可以提高集成传播相比，滞后初始化的时间尺度从一个月到三年。由于繁殖的载体到目前为止大多是在短时间内使用，我们最初专注于在海洋组件繁殖的载体的实施。我们引入了一个深度相关的垂直重标度规范，占垂直依赖的变化，并扩展常用的上层海洋重标度规范的完整的水柱。我们进一步表明，（地下）海洋足以繁殖温度和盐度（即，标量），并且依赖于控制物理学来将温度和盐度扰动传递到流场。使用这些繁殖的向量与12个月的重新缩放间隔，我们初始化后报模拟，并将它们与滞后初始条件初始化后报模拟。我们通过分析Talagrand图和扩展错误率来量化集成扩展。对于温度和盐度，滞后的初始化合奏是特别分散的可预测的前置时间的头几个月。与繁殖向量初始化的合奏提高了传播的温度和盐度为0-700米和1000-3500米的手段，相比滞后合奏在几个月到一年的前置时间。随着前置时间增加到数年，两种集合初始化技术之间的差异变得更加难以辨别。虽然结果需要在一个初始化的框架中得到确认，但本分析代表了在从季节到年际时间尺度的过渡中，特别是在长达一年的前置时间内，朝着改进集合生成迈出的第一步。
Abstract. We evaluate the ensemble spread at seasonal-to-interannual timescales for two perturbation techniques implemented in the ocean component of a coupled model: (1) lagged initial conditions as commonly used for decadal predictions; (2) bred vectors as commonly used for weather and seasonal forecasting. We show that relative to an uninitialized reference simulation the implementation for bred vectors can improve the ensemble spread compared to lagged initialization at timescales from one month up to three years. As bred vectors have so far mostly been used at short timescales, we initially focus on the implementation of the bred vectors in the ocean component. We introduce a depth-dependent vertical rescaling norm, accounting for the vertical dependence of the variability, and extending the commonly used upper-ocean rescaling norm to the full water column. We further show that it is sufficient for the (sub-surface) ocean to breed temperature and salinity (i.e., scalar quantities), and rely on the governing physics to carry the temperature and salinity perturbations to the flow field. Using these bred vectors with a rescaling interval of 12 months, we initialize hindcast simulations and compare them to hindcast simulations initialized with lagged initial conditions. We quantify the ensemble spread by analyzing Talagrand diagrams and spread–error ratios. For both temperature and salinity, the lagged initialized ensemble is particularly under-dispersive for the first few months of predictable lead time. The ensemble initialized with bred vectors improves the spread for temperature and salinity for the 0–700 m and 1000–3500 m means, compared to the lagged ensemble at lead times of several months to one year. As the lead time increases to years, the differences between the two ensemble initialization techniques become more difficult to discern. While the results need to be confirmed in an initialized framework, the present analysis represents a first step towards improved ensemble generation at the transition from seasonal to interannual timescales, in particular at lead times up to one year.