The current study aims to portray the specific weather patterns associated with hail falls in north-eastern Romania. This was done using multiple hail records data covering a long period of time (1981–2020). COST733 software enabled us to assess objectively the atmospheric circulation classification types for the middle troposphere (500 hPa) and also for the ground level (sea level pressure) over the study region. Based on these, we have identified 5 major weather patterns (MPs) which explain up to 85% of the recorded hail events over the region. In terms of wind vector direction and speed, driving the hailstorm cells, these MPs are represented by two main groups of synoptic patterns. The first one is characterized by weak advective patterns (cut-off lows, north-easterly anticyclonic flow), while the second one is characterized by strong advective patterns (westerly, south-westerly, and north-westerly atmospheric flows). Further, these major patterns are split into 16 combined circulation types (CCTs), as indicated by the atmospheric circulation at the ground level. Our analysis showed that in May and June hailstorms are determined especially by weak advective patterns over north-eastern Romania, while from June to August the strong advective patterns are more common for these extreme weather events. The atmospheric environment associated with these synoptic conditions, as indicated by instability parameters, is also described using a series of atmospheric parameters: sea pressure level, 500 hPa geopotential field, 700 hPa wind vector, and precipitation amount at the continental scale. This analysis indicates that hail occurs in a regional atmospheric environment characterized by a MUCAPE >500 J/kg and high wind shear in the lower troposphere. The results obtained are meant to become a useful tool in regional hail forecast.

中文翻译：

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罗马尼亚东北部有利于冰雹发生的大陆和区域天气背景

目前的研究旨在描绘罗马尼亚东北部与冰雹有关的特定天气模式。这是使用涵盖很长一段时间（1981-2020）的多个冰雹记录数据完成的。COST733 软件使我们能够客观地评估对流层中层（500 hPa）以及研究区域地面（海平面压力）的大气环流分类类型。基于这些，我们确定了 5 种主要天气模式 (MP)，它们解释了该地区多达 85% 的记录冰雹事件。在驱动冰雹单元的风矢量方向和速度方面，这些 MP 由两组主要的天气模式表示。第一个特点是平流模式较弱（截止低点，东北反气旋流），而第二种则以强烈的平流模式为特征（西风、西南风和西北风气流）。此外，这些主要模式分为 16 种组合环流类型 (CCT)，如地面大气环流所示。我们的分析表明，5 月和 6 月的冰雹尤其是由罗马尼亚东北部的弱平流模式决定的，而从 6 月到 8 月，这些极端天气事件更常见于强平流模式。与这些天气条件相关的大气环境，如不稳定性参数所示，也使用一系列大气参数来描述：海压水平、500 hPa 位势场、700 hPa 风矢量和大陆尺度的降水量。该分析表明，冰雹发生在以 MUCAPE >500 J/kg 和对流层低层的高风切变为特征的区域大气环境中。所得结果旨在成为区域冰雹预报的有用工具。