Contrasting stable water isotope signals from convective and large-scale precipitation phases of a heavy precipitation event in southern Italy during HyMeX IOP 13: a modelling perspective

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Lee, Keun-Ok, Aemisegger, Franziska, Pfahl, Stephan, Flamant, Cyrille, Lacour, Jean-Lionel, Chaboureau, Jean-Pierre
• Other Authors: Laboratoire d'aérologie (LAERO), Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Observatoire Midi-Pyrénées (OMP), Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales Toulouse (CNES)-Centre National de la Recherche Scientifique (CNRS)-Météo-France-Centre National de la Recherche Scientifique (CNRS), Institute for Atmospheric and Climate Science Zürich (IAC), Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology Zürich (ETH Zürich), Institut für Meteorologie Berlin, Freie Universität Berlin, TROPO - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Institute of Earth Sciences Reykjavik, University of Iceland Reykjavik
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2019
• Subjects: [PHYS.PHYS.PHYS-AO-PH]Physics [physics]/Physics [physics]/Atmospheric and Oceanic Physics [physics.ao-ph]; North Atlantic
• Online Access: https://insu.hal.science/insu-02151544; https://insu.hal.science/insu-02151544/document; https://insu.hal.science/insu-02151544/file/acp-19-7487-2019.pdf; https://doi.org/10.5194/acp-19-7487-2019

International audience The dynamical context and moisture transport pathways embedded in large-scale flow and associated with a heavy precipitation event (HPE) in southern Italy (SI) are investigated with the help of stable water isotopes (SWIs) based on a purely numerical framework. The event occurred during the Intensive Observation Period (IOP) 13 of the field campaign of the Hydrological Cycle in the Mediterranean Experiment (HyMeX) on 15 and 16 October 2012, and SI experienced intense rainfall of 62.4 mm over 27 h with two precipitation phases during this event. The first one (P1) was induced by convective precipitation ahead of a cold front, while the second one (P2) was mainly associated with precipitation induced by large-scale uplift. The moisture transport and processes responsible for the HPE are analysed using a simulation with the isotope-enabled regional numerical model COSMO iso. The simulation at a horizontal grid spacing of about 7 km over a large domain (about 4300 km ×3500 km) allows the isotopes signal to be distinguished due to local processes or large-scale advection. Backward trajectory analyses based on this simulation show that the air parcels arriving in SI during P1 originate from the North Atlantic and descend within an upper-level trough over the northwestern Mediterranean. The descending air parcels reach elevations below 1 km over the sea and bring dry and isotopically depleted air (median δ 18 O ≤ −25 ‰, water vapour mixing ratio q ≤ 2 g kg −1) close to the surface, which induces strong surface evaporation. These air parcels are rapidly enriched in SWIs (δ 18 O ≥ −14 ‰) and moistened (q ≥ 8 g kg −1) over the Tyrrhenian Sea by taking up moisture from surface evaporation and potentially from evaporation of frontal precipitation. Thereafter, the SWI-enriched low-level air masses arriving upstream of SI are convectively pumped to higher altitudes, and the SWI-depleted moisture from higher levels is transported towards the surface within the downdrafts ahead of the cold front over ...