CHHC: Swiss Hail Climatology
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The data contain the monthly and yearly number of hail days, the monthly and yearly maximum hailstone sizes, the long-term average number of hail days per year and month of the summer half-year (April to September), per square kilometer, for Switzerland. Due to the infrequent occurrence of hail, averaging of hailstone sizes over many years is not meaningful. The long term average numbers of days with hailstone sizes of at least 2 cm and 4 cm are provided as climatology. Hail cannot be measured on the ground over a wide area. The size is therefore derived from radar measurements. A hail day is defined as a day on which a high probability of hail on the ground was derived from the radar parameter Probability Of Hail POH. The number of hail days of at least 2 cm and 4 cm, respectively is based on radar parameter Maximum Expected Severe Hailstone Sizes (MESHS). The 24 hours between 06 UTC and 06 UTC of the following day are considered. The return period data contain the return values of the radar-derived maximum expected hailstone sizes over a square kilometer (MESHS) and the application-focused largest expected hail stone size over a reference area of 100 square meters (LEHA), respectively, as a function of the return period T. They describe the hailstone size that is exceeded with a probability of 1/T per year under today's climate conditions, at a fixed location. The return values were determined using a stochastic resampling approach based on observed radar hail footprint data of the period 2002-2020. Hailstone sizes MESHS are given in classes from 2 cm to greater than 6 cm in 0.5 cm increments, with the lower end being inclusive and the upper end exclusive: the grid value 2 represents values from 2 cm (incl.) to 2.5 cm (excl.). Hailstone sizes LEHA are given in classes from 2 cm to greater than 5 cm in 1 cm increments, with the lower end being inclusive and the upper end exclusive: the grid value 2 represents values from 2 cm (incl.) to 3 cm (excl.). Created by MeteoSwiss within the scope of the project Hail Climate Switzerland.
本数据集涵盖瑞士范围内每平方千米的逐月、逐年冰雹日数，逐月、逐年最大冰雹粒径，以及夏半年（4月至9月）各月与全年的长期平均冰雹日数。由于冰雹发生频次较低，多年粒径平均并无实际意义，因此本数据集提供了冰雹粒径≥2厘米与≥4厘米的长期平均冰雹日数作为气候学统计值。 冰雹难以在大范围地面开展观测，因此其粒径通过雷达观测数据反演得到。本数据集将冰雹日定义为：通过雷达参数冰雹概率（Probability Of Hail, POH）反演得到地面冰雹发生概率较高的日期。≥2厘米与≥4厘米冰雹日数分别基于雷达参数最大预期强冰雹粒径（Maximum Expected Severe Hailstone Sizes, MESHS）计算，统计时段为世界协调时06时至次日06时的24小时周期。 重现期数据分别包含基于雷达反演的每平方千米最大预期冰雹粒径（MESHS），以及面向应用场景的100平方米参考区域内最大预期冰雹粒径（LEHA）随重现期T的变化关系。此类重现值表征在当前气候条件下，某固定位置处每年有1/T概率被超过的冰雹粒径。重现值基于2002年至2020年的雷达冰雹足迹观测数据，通过随机重采样方法计算得到。 MESHS冰雹粒径按0.5厘米为间隔划分为分级区间，区间范围为2厘米至大于6厘米，采用左闭右开规则：网格值2对应粒径范围为2厘米（含）至2.5厘米（不含）。 LEHA冰雹粒径按1厘米为间隔划分为分级区间，区间范围为2厘米至大于5厘米，同样采用左闭右开规则：网格值2对应粒径范围为2厘米（含）至3厘米（不含）。 本数据集由瑞士气象局（MeteoSwiss）在“瑞士冰雹气候”项目框架下制作完成。
