Statistical Analysis of Nocturnal Downvalley Flows Over the Annual Cycle: Insights from a Pyrenean Valley (France)

Nocturnal downvalley flows were examined in a valley located in southern France, near the Pyrenees. Three meteorological stations were strategically placed at different locations within the valley, collecting a year-long dataset of near-surface observations. This dataset enables an investigation of how these flows are organized and evolve throughout the annual cycle.

To identify the downvalley flow events, we applied a breeze detection algorithm (Arrillaga et al., 2018; Román-Cascón et al., 2019). Once detected, the events were characterized in terms of onset, peak intensity, and duration, with particular attention paid to the synoptic conditions conducive to their development. A clustering approach was also employed to classify and compare subtypes of breeze days, providing insights into their controlling factors and distinctive features.

Furthermore, a statistical analysis differentiating various turbulence regimes (incorporating HOckey STick (HOST)  analysis) offers a deeper understanding of how turbulence interacts with flow dynamics. Overall, this work seeks to advance our knowledge of the mechanisms driving thermally-driven flows in complex terrain over a full annual cycle.