Nowcasting convective activity for the Sahel: A simple probabilistic approach using real-time and historical satellite data on cloud-top temperature
Nowcasting convective activity for the Sahel: A simple probabilistic approach using real-time and historical satellite data on cloud-top temperature
复制标题
萨赫勒地区对流活动的临近预报：利用云顶温度的实时和历史卫星数据的简单概率方法
DOI：
10.1002/qj.4607
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发表时间：
2024
影响因子：
8.9
通讯作者：
Anderson S
中科院分区：
文献类型：
--
作者：
Anderson S
强降雨引发的山洪经常在非洲各地造成重大破坏和生命损失。在萨赫勒地区，由中尺度对流系统驱动的这些事件的自动预测和警报系统有限，数值天气预报仍然缺乏技巧。地面观测网络也很稀疏，用于便利传统临近预报方法的实用气象雷达也很少。专注于西萨赫勒地区，我们提出了一种新的方法，生产概率临近预报的对流活动提前六个小时，使用目前的位置观测到的对流。MCS的对流部分，与极端和强降水相关，从16年的气象卫星第二代热红外云顶温度数据中识别出来，并计算出位置条件概率的离线数据库。通过该数据库，可以以最少的计算快速生成真实的即时临近预报。临近预报给出了在每个网格点周围的正方形邻域内发生对流的概率，说明了小尺度对流的固有不可预测性。与气候参考相比，正式的验证方法表明，临近预报在预测研究区域的对流活动方面是熟练的，适用于一天中的所有时间，并考虑到6小时的提前时间。临近预报也很擅长捕捉塞内加尔达喀尔上空极端的24小时雨量计累积。临近预报技能在下午达到高峰，在晚上达到最低。我们发现，最佳邻域大小随提前时间而变化，从临近预报原点的10公里到6小时提前时间的100公里左右。这种简单而熟练的临近预报方法对于西非和其他具有长期雷暴的地区的业务预警非常有价值，并有助于减少暴雨和洪水的影响。
Flash flooding from intense rainfall frequently results in major damage and loss of life across Africa. In the Sahel, automatic prediction and warning systems for these events, driven by Mesoscale Convective Systems (MCSs), are limited, and Numerical Weather Prediction (NWP) forecasts continue to have little skill. The ground observation network is also sparse, and very few operational meteorological radars exist to facilitate conventional nowcasting approaches. Focusing on the western Sahel, we present a novel approach for producing probabilistic nowcasts of convective activity out to six hours ahead, using the current location of observed convection. Convective parts of the MCS, associated with extreme and heavy precipitation, are identified from 16 years of Meteosat Second Generation thermal–infrared cloud‐top temperature data, and an offline database of location‐conditioned probabilities calculated. From this database, real‐time nowcasts can be quickly produced with minimal calculation. The nowcasts give the probability of convection occurring within a square neighbourhood surrounding each grid point, accounting for the inherent unpredictability of convection at small scales. Compared to a climatological reference, formal verification approaches show the nowcasts to be skilful at predicting convective activity over the study region, for all times of day and out to the six‐hour lead time considered. The nowcasts are also skilful at capturing extreme 24‐hour rain gauge accumulations over Dakar, Senegal. The nowcast skill peaks in the afternoon, with a minimum in the evening. We find that the optimum neighbourhood size varies with lead time, from 10 km at the nowcast origin to around 100 km at a six‐hour lead time. This simple and skilful nowcasting method could be highly valuable for operational warnings across West Africa and other regions with long‐lived thunderstorms, and help to reduce the impacts from heavy rainfall and flooding.