Studying the spatiotemporal distribution and motion of water vapour (WV), the most variable greenhouse gas in the troposphere, is pivotal, not only for meteorology and climatology, but for geodesy, too. In fact, WV variability degrades, in an unpredictable way, almost all geodetic observation based on the propagation of electromagnetic signal through the atmosphere. We use data collected on a dense GPS network, designed for the purposes of monitoring the active Neapolitan (Italy) volcanoes, to retrieve the tropospheric delay parameters and precipitable water vapour (PWV). This study has two main targets: (a) the analysis of long datasets (11 years) to extract trends of climatological meaning for the region; (b) studying the main features of the time evolution of the PWV during heavy raining events to gain knowledge on the preparatory stages of highly impacting thunderstorms. For the latter target, both differential and precise point positioning (PPP) techniques are used, and the results are compared and critically discussed. An increasing trend, amounting to about 2 mm/decades, has been recognized in the PWV time series, which is in agreement with the results achieved in previous studies for the Mediterranean area. A clear topographic effect is detected for the Vesuvius volcano sector of the network and a linear relationship between PWV and altitude is quantitatively assessed. This signature must be taken into account in any modelling for the atmospheric correction of geodetic and remote-sensing data (e.g., InSAR). Characteristic temporal evolutions were recognized in the PWV in the targeted thunderstorms (which occurred in 2019 and 2020), i.e., a sharp increase a few hours before the main rain event, followed by a rapid decrease when the thunderstorm vanished. Accounting for such a peculiar trend in the PWV could be useful for setting up possible early warning systems for those areas prone to flash flooding, thus potentially providing a tool for disaster risk reduction.

中文翻译：

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密集 GPS 阵列导致那不勒斯和维苏威地区（意大利）的对流层延迟：对天气预报和气候监测的贡献

研究对流层中变化最大的温室气体水蒸气 (WV) 的时空分布和运动，不仅对于气象学和气候学，而且对于大地测量学也至关重要。事实上，几乎所有基于电磁信号在大气中传播的大地测量观测，WV 可变性都会以一种不可预测的方式降低。我们使用在密集 GPS 网络上收集的数据，该网络旨在监测那不勒斯（意大利）的活跃火山，以检索对流层延迟参数和可降水水汽 (PWV)。本研究有两个主要目标：(a) 分析长数据集（11 年）以提取该地区气候意义的趋势；(b) 研究大雨事件期间 PWV 时间演变的主要特征，以了解强影响雷暴的准备阶段。对于后一个目标，使用差分和精确点定位 (PPP) 技术，并对结果进行比较和批判性讨论。在 PWV 时间序列中已经认识到增加的趋势，达到大约 2 毫米/十年，这与之前地中海地区研究取得的结果一致。网络的维苏威火山部分检测到明显的地形效应，并定量评估 PWV 与高度之间的线性关系。在对大地测量和遥感数据（例如 InSAR）进行大气校正的任何建模中都必须考虑该特征。在目标雷暴（发生在 2019 年和 2020 年）中，PWV 具有特征性的时间演变，即在主要降雨事件发生前几个小时急剧增加，然后在雷暴消失后迅速减少。考虑 PWV 的这种特殊趋势可能有助于为易发生山洪暴发的地区建立可能的早期预警系统，从而有可能为减少灾害风险提供工具。