Atmospheric rivers : regional weather patterns and impacts

Abstract

Atmospheric rivers (ARs) are large, narrow concentrations of moisture that play a crucial role in transporting moisture from the equator to the poles. They strongly influence regional weather, particularly in midlatitude regions where they often contribute to extreme precipitation and subsequent flooding. This can be amplified further when ARs pass through mountain ranges. My study aimed to assess the impact of ARs on regional weather patterns. I focus on the interaction between synoptic-scale dynamics, mid-level moisture transport, and orographic effects. Combining 500 hPa geopotential height and 700 hPa relative humidity data, I examined AR events in Italy, Spain, and California. I identified key mechanisms that drive intense rainfall. My findings confirm that ARs are strongly influenced by upper-level troughs and mid-level moisture plumes, which, when aligned, drive intense regional precipitation. Orography further amplifies this effect by enhancing rainfall on windward slopes and stalling moisture plumes over steep terrain, as seen, for example, in the Apennines and Sierra Nevada. Regional variability also emerged. In the Mediterranean, for example, cutoff lows trap moisture, while an California event demonstrated the influence of steep pressure gradients and El Niño conditions. My results support the broader consensus that ARs are critical drivers of hydrological extremes that have noteworthy societal implications, such as flood risk management and climate adaptation. My research highlights the interconnected nature of ARs within the atmosphere and reinforces their importance in both present-day weather and future climate projections.