Global climatology of nocturnal low-level jets and associated moisture sources and sinks

Low-level jets (LLJs) are defined as regions of anomalously high wind speeds occurring within the first kilometre of the troposphere. They are filamentous structures that are usually strongly related to moisture transport. This study analysed the moisture transport associated with LLJs, and the role of LLJs in precipitation events that occasionally lead to extreme precipitation and major floods. A daily climatology dataset of nocturnal LLJs was developed and moisture transport was studied by analysing the source and sink regions. A nocturnal LLJ index based on the vertical structure of temporal wind variations was applied, and a total of 33 nocturnal LLJs were identified and characterised. The FLEXPART Lagrangian model was then used to simulate jet behaviour and to identify major source and sink regions during the period from 1980 to 2016. Differences between days with LLJs and days with no LLJs were subsequently calculated for each LLJ on a global scale with respect to moisture transport for the sources and sinks of moisture. Finally, each LLJ was analysed in terms of its associated socioeconomic impact and relationship with water scarcity.