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A cold pool perturbation scheme to improve convective initiation in convection-permitting models
Quarterly Journal of the Royal Meteorological Society ( IF 3.0 ) Pub Date : 2021-03-30 , DOI: 10.1002/qj.4032 Mirjam Hirt 1 , George C. Craig 1
Quarterly Journal of the Royal Meteorological Society ( IF 3.0 ) Pub Date : 2021-03-30 , DOI: 10.1002/qj.4032 Mirjam Hirt 1 , George C. Craig 1
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Cold pools originate from evaporation in precipitating downdraughts and spread as density currents at the surface. Vertical motion at the leading edge of the cold pool is an important trigger for new convective cells in organised convective storms. However, these motions are poorly resolved at the grid lengths of a kilometre or more used in convection-permitting models. Consequently, the simulated gust fronts do not trigger enough new convection, leading to precipitation deficits and a lack of convective organization. To address these deficits, we introduce a cold pool perturbation (CPP) scheme that strengthens vertical velocity at the simulated cold pool gust fronts. This is achieved by relaxing the vertical velocity in the gust front region towards a target value derived from similarity theory. Applying the CPP scheme for simulations of a highly convective 10-day period, we find increased precipitation amplitudes during the afternoon. There is also evidence for improvements in the location of precipitation and for stronger organization of convection, although substantial errors remain. The cold pools themselves become more frequent, larger and more intense. An additional potentially beneficial influence was found for convective initiation at sea breeze fronts.
中文翻译：
在对流允许模型中改善对流启动的冷池扰动方案
冷池起源于下沉气流中的蒸发，并在地表以密度流的形式传播。冷池前缘的垂直运动是有组织的对流风暴中新对流单元的重要触发因素。然而，在允许对流模型中使用的一公里或更长的网格长度时，这些运动的解析度很差。因此，模拟的阵风锋不会触发足够的新对流，导致降水不足和缺乏对流组织。为了解决这些缺陷，我们引入了冷池扰动 (CPP) 方案，该方案可增强模拟冷池阵风前沿的垂直速度。这是通过将阵风锋区的垂直速度向从相似理论推导出的目标值放宽来实现的。将 CPP 方案应用于模拟 10 天强对流期间，我们发现下午的降水幅度增加。也有证据表明降水位置的改善和对流组织的加强，尽管仍然存在大量错误。冷池本身变得更频繁、更大和更强烈。还发现了对海风前沿的对流产生的另一个潜在有益影响。
更新日期：2021-06-03
中文翻译：
在对流允许模型中改善对流启动的冷池扰动方案
冷池起源于下沉气流中的蒸发，并在地表以密度流的形式传播。冷池前缘的垂直运动是有组织的对流风暴中新对流单元的重要触发因素。然而，在允许对流模型中使用的一公里或更长的网格长度时，这些运动的解析度很差。因此，模拟的阵风锋不会触发足够的新对流，导致降水不足和缺乏对流组织。为了解决这些缺陷，我们引入了冷池扰动 (CPP) 方案，该方案可增强模拟冷池阵风前沿的垂直速度。这是通过将阵风锋区的垂直速度向从相似理论推导出的目标值放宽来实现的。将 CPP 方案应用于模拟 10 天强对流期间，我们发现下午的降水幅度增加。也有证据表明降水位置的改善和对流组织的加强，尽管仍然存在大量错误。冷池本身变得更频繁、更大和更强烈。还发现了对海风前沿的对流产生的另一个潜在有益影响。
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