The persistence of high values of relative humidity for several hours to a few days has wide‐ranging implications for natural and human systems. Among its many impacts, persistent high relative humidity contributes to reduced atmospheric visibility, fog frequency and duration, road and powerline icing, the occurrence of foliar plant disease and the temperature at which heat‐related morbidity and mortality can occur. Despite this, the characteristics of humidity spells—including shifts with climate change—are rarely investigated and consequently poorly understood. Hourly relative humidity, precipitation and temperature for 35 locations in the Lower Peninsula (LP) of Michigan during 2003–2017, and for seven locations during 1973–2017, were used to assess, by biweekly periods, spatial, intra‐annual and inter‐annual variations in the characteristics of relative humidity spells. Two humidity thresholds that accommodate a wide range of applications were used: (1) high relative humidity (HRH), defined as hourly values ≥60%, and extremely high relative humidity (EHRH), defined as hourly values ≥85%. Extended HRH and EHRH spells are frequent across the LP, with HRH spells often spanning 36 hr or longer and EHRH spells commonly persisting more than 12 hr. The probability of HRH and EHRH spells generally decreased with time during 1973–2017, particularly later in the period. Although most spells initiate in the late afternoon and early evening hours, this diurnal preference is less evident as spell length increases, especially for EHRH spells. Furthermore, precipitation is more likely to occur with EHRH spells compared to HRH spells. The orientation and strength of spatial gradients in average annual spell frequency are highly dependent on the choice of humidity and duration thresholds and the temperatures accompanying the spells. This study represents the first comprehensive analysis of the persistence of humidity spells and illustrates the potential usefulness of temporally‐flexible climatological summaries relevant for a wide range of applications.

中文翻译：

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持续高相对湿度的气候学：以美国密歇根州下半岛为例

持续数小时至数天的高相对湿度值对自然和人类系统具有广泛的影响。在其诸多影响中，持续的较高相对湿度会降低大气能见度，雾频率和持续时间，道路和电力线结冰，叶面植物病的发生以及与热相关的发病率和死亡率的温度。尽管如此，很少研究湿度法的特征（包括随着气候变化的变化），因此人们对其了解甚少。在2003–2017年期间，密歇根州下半岛（LP）的35个地点以及1973–2017年的七个地点的每小时相对湿度，降水和温度被用来每两周评估一次空间，相对湿度变化特征的年内和年际变化。使用了两个适用于广泛应用的湿度阈值：（1）高相对湿度（HRH）（定义为每小时值≥60％）和极高相对湿度（EHRH），定义为每小时值≥85％。在整个LP中，扩展的HRH和EHRH咒语很常见，HRH咒语通常持续36个小时或更长时间，而EHRH咒语通常持续超过12 hr。在1973-2017年期间，特别是在此期间的后期，HRH和EHRH咒语的概率通常随时间降低。尽管大多数咒语在下午和傍晚开始，但是随着咒语长度的增加，这种昼夜偏好就不那么明显了，特别是对于EHRH咒语。此外，与HRH咒语相比，EHRH咒语更容易发生降水。年平均咒语频率中空间梯度的方向和强度高度依赖于湿度和持续时间阈值以及伴随咒语的温度的选择。这项研究代表了对湿气持续性的首次全面分析，并说明了在时间上灵活的气候学摘要对于广泛应用的潜在用途。