On 2-3 October 2020, a heavy precipitation event severely affected northern Italy and in particular the western Alps, with rainfall amount exceeding 600 mm over 24 hours. This event was associated with a large-scale environment characteristic of heavy precipitation phenomena on the southern side of the Alps, i.e. an upper-level trough over the western Mediterranean basin. At the mesoscale, this configuration often induces a northward transport of large amount of moisture, organized in the form of a pre-frontal low-level jet that impinges on the orography and determines the distribution and the intensity of the rainfall. The present study shows that a relevant amount of moisture moved towards the Mediterranean basin within a long and narrow filament-shaped structure crossing the whole Atlantic Ocean. The presence of an atmospheric river (AR) represented a distinguishing aspect of the event, superimposed on the well-known dynamics-thermodynamics of heavy precipitation over the Alps. High-resolution numerical simulations are undertaken to investigate how the transport of water vapour associated with the AR has influenced the severity and dynamics of the heavy precipitation processes. The results add further details to the theoretical framework of heavy precipitation mechanisms in the area and improve our understanding of the complex interaction between large-scale flows and mesoscale dynamics during extreme precipitation episodes. The presence of ARs across the Mediterranean has been recently associated with heavy precipitation over southern Europe and Italy in particular. Together with previous findings, this study shows that, in addition to the local contribution from the Mediterranean Sea, a relevant amount of moisture may move from the tropics towards the Mediterranean, feeding precipitation systems. The assessment of AR characteristics and frequency, as well as their role on rainfall and on Mediterranean cyclone development, represents the framework of this ongoing research activity.
The role of Atmospheric Rivers in the Mediterranean in heavy precipitation events over the Alps
Davolio S;Laviola S;Levizzani V
2022
Abstract
On 2-3 October 2020, a heavy precipitation event severely affected northern Italy and in particular the western Alps, with rainfall amount exceeding 600 mm over 24 hours. This event was associated with a large-scale environment characteristic of heavy precipitation phenomena on the southern side of the Alps, i.e. an upper-level trough over the western Mediterranean basin. At the mesoscale, this configuration often induces a northward transport of large amount of moisture, organized in the form of a pre-frontal low-level jet that impinges on the orography and determines the distribution and the intensity of the rainfall. The present study shows that a relevant amount of moisture moved towards the Mediterranean basin within a long and narrow filament-shaped structure crossing the whole Atlantic Ocean. The presence of an atmospheric river (AR) represented a distinguishing aspect of the event, superimposed on the well-known dynamics-thermodynamics of heavy precipitation over the Alps. High-resolution numerical simulations are undertaken to investigate how the transport of water vapour associated with the AR has influenced the severity and dynamics of the heavy precipitation processes. The results add further details to the theoretical framework of heavy precipitation mechanisms in the area and improve our understanding of the complex interaction between large-scale flows and mesoscale dynamics during extreme precipitation episodes. The presence of ARs across the Mediterranean has been recently associated with heavy precipitation over southern Europe and Italy in particular. Together with previous findings, this study shows that, in addition to the local contribution from the Mediterranean Sea, a relevant amount of moisture may move from the tropics towards the Mediterranean, feeding precipitation systems. The assessment of AR characteristics and frequency, as well as their role on rainfall and on Mediterranean cyclone development, represents the framework of this ongoing research activity.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
