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Dynamic and Thermodynamic Impacts of Climate Change on Organized Convection in Alaska Basile Poujol, Andreas Prein, Maria Molina, Caroline Muller

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Dynamic and Thermodynamic Impacts of Climate Change on Organized Convection in Alaska Basile Poujol, Andreas Prein, Maria Molina, Caroline Muller Dynamic and Thermodynamic Impacts of Climate Change on Organized Convection in Alaska Basile Poujol, Andreas Prein, Maria Molina, Caroline Muller To cite this version: Basile Poujol, Andreas Prein, Maria Molina, Caroline Muller. Dynamic and Thermodynamic Impacts of Climate Change on Organized Convection in Alaska. Climate Dynamics, Springer Verlag, In press. hal-03023340 HAL Id: hal-03023340 https://hal.archives-ouvertes.fr/hal-03023340 Submitted on 25 Nov 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Climate Dynamics Dynamic and Thermodynamic Impacts of Climate Change on Organized Convection in Alaska --Manuscript Draft-- Manuscript Number: Full Title: Dynamic and Thermodynamic Impacts of Climate Change on Organized Convection in Alaska Article Type: Original Article Keywords: Convective systems; Moisture; CAPE; CIN; Sea ice loss; Convection-permitting modeling Corresponding Author: Basile Poujol, B.Sc. Département de Géosciences, Ecole Normale Supérieure, PSL Res. Univ., Paris 75005 Paris, FRANCE Corresponding Author Secondary Information: Corresponding Author's Institution: Département de Géosciences, Ecole Normale Supérieure, PSL Res. Univ., Paris Corresponding Author's Secondary Institution: First Author: Basile Poujol, B.Sc. First Author Secondary Information: Order of Authors: Basile Poujol, B.Sc. Andreas F. Prein, Ph.D. Maria Molina, Ph.D. Caroline Muller, Ph.D. Order of Authors Secondary Information: Funding Information: National Science Foundation Not applicable (1852977) U.S. Army Corps of Engineers Not applicable (Climate Preparedness and Resilience Program) H2020 European Research Council Dr Caroline Muller (805041) Abstract: Convective storms can cause economic damage and harm to humans by producing flash floods, lightning and severe weather. While organized convection is well studied in the tropics and mid-latitudes, few studies have focused on the physics and climate change impacts of pan-Arctic convective systems. Using a convection-permitting model we showed in a predecessor study that organized convective storm frequency might triple by the end of the century in Alaska assuming a high emission scenario. The present study assesses the reasons for this rapid increase in organized convection by investigating dynamic and thermodynamic changes within future storms and their environments, in light of canonical existing theories for mid-latitude and tropical deep convection. In a future climate, more moisture originates from Arctic marine basins increasing relative humidity over Alaska due to the loss of sea ice, which is in sharp contrast to lower-latitude land regions that are expected to become drier. This increase in relative humidity favors the onset of organized convection through more unstable thermodynamic environments, increased low-level buoyancy, and weaker downdrafts. Our confidence in these results is increased by showing that these changes can be analytically derived from basic physical laws. This suggests that organized thunderstorms might become more frequent in other pan-Arctic continental regions Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation highlighting the uniqueness and vulnerability of these regions to climate change. Suggested Reviewers: David Romps University of California Berkeley [email protected] Paul O'Gorman Massachusetts Institute of Technology [email protected] Jan Haerter Kobenhavns Universitet Niels Bohr Instituttet [email protected] Christopher Moseley National Taipei University [email protected] Christopher Holloway University of Reading [email protected] Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation Manuscript Click here to access/download;Manuscript;template.tex Click here to view linked References Noname manuscript No. (will be inserted by the editor) 1 Dynamic and Thermodynamic Impacts of Climate 2 Change on Organized Convection in Alaska 3 Basile Poujol · Andreas F. Prein · 4 Maria J. Molina · Caroline Muller 5 6 Received: date / Accepted: date 7 Abstract Convective storms can cause economic damage and harm to humans by 8 producing flash floods, lightning and severe weather. While organized convection 9 is well studied in the tropics and mid-latitudes, few studies have focused on the 10 physics and climate change impacts of pan-Arctic convective systems. 11 Using a convection-permitting model we showed in a predecessor study that orga- 12 nized convective storm frequency might triple by the end of the century in Alaska 13 assuming a high emission scenario. The present study assesses the reasons for this 14 rapid increase in organized convection by investigating dynamic and thermody- 15 namic changes within future storms and their environments, in light of canonical 16 existing theories for mid-latitude and tropical deep convection. 17 In a future climate, more moisture originates from Arctic marine basins increas- 18 ing relative humidity over Alaska due to the loss of sea ice, which is in sharp 19 contrast to lower-latitude land regions that are expected to become drier. This in- B.Poujol D´epartement de G´eosciences, Ecole´ Normale Sup´erieure,PSL. Res. Univ., Paris, France E-mail: [email protected] A.F. Prein National Center for Atmospheric Research, Boulder, CO USA M.J.Molina National Center for Atmospheric Research, Boulder, CO USA C.Muller CNRS, Laboratoire de M´et´eorologieDynamique / Institut Pierre Simon Laplace, Ecole´ Nor- male Sup´erieure,Paris, France 2 Basile Poujol et al. 20 crease in relative humidity favors the onset of organized convection through more 21 unstable thermodynamic environments, increased low-level buoyancy, and weaker 22 downdrafts. Our confidence in these results is increased by showing that these 23 changes can be analytically derived from basic physical laws. This suggests that 24 organized thunderstorms might become more frequent in other pan-Arctic con- 25 tinental regions highlighting the uniqueness and vulnerability of these regions to 26 climate change. 27 Keywords Convective systems · Moisture · CAPE · CIN · Sea ice loss · 28 Convection-permitting modeling 29 1 Introduction 30 Organized convective storms are a common feature of the climate system in con- 31 tinental regions, where they typically occur in the summer [Houze Jr, 2004]. They 32 are of particular importance since they can produce large amounts of precipita- 33 tion as well as severe hazards (e.g., hail, flash floods), and play an important 34 role in the hydrological cycle. The characteristics of these storms has been shown 35 to largely depend on dynamical and thermodynamic environments (e.g., [Geerts 36 et al., 2017]), which can be supportive for deep convection and for convective 37 organization. 38 Key ingredients for intense, deep convection to occur in the mid-latitudes are 39 usually a buoyant low level air mass, measured by convective available potential 40 energy (CAPE) [Moncrieff and Miller, 1976], a large amount of moisture usually 41 provided by local evaporation or by advection driven by a low-level jet from mar- 42 itime regions [Stensrud, 1996], and a forcing mechanism such as solar heating, or 43 vertical lifting. Moreover, low-level and tropospheric wind shear [Weisman and Ro- 44 tunno, 2004], dry environments [McCaul Jr et al., 2005], and large-scale potential 45 vorticity or uplift [Antonescu et al., 2013] have been shown to be associated with 46 the organization of storms. Finally, convective inhibition (CIN) can be important Title Suppressed Due to Excessive Length 3 47 for the buildup of CAPE [Parker, 2002], although too much inhibition can prevent 48 convection initiation without sufficiently strong forcing. 49 All of the above processes have complex interactions in the atmosphere and 50 convective storms themselves have a strong influence on the state of the tropo- 51 sphere [Emanuel et al., 1994]. Deep convection can occur in a statistical equilib- 52 rium with its environment, which is called the radiative-convective equilibrium in 53 the tropics [Held et al., 1993]. The accumulation of large amounts of CAPE that, 54 when released, can produce very intense organized storms is rare and concentrated 55 in specific regions, such as the U.S. Great Plains, South American Pampas and 56 Gran Chaco, Sahel, and Northern India [Zipser et al., 2006], although one can also 57 find large CAPE occasionally elsewhere. However, convection can also organize 58 only due to radiative and thermodynamic feedbacks, without any other mechani- 59 cal triggering when radiative-convective equilibrium is satisfied (see [Wing et al., 60 2017] for a review). 61 Ingredients for deep, organized convection have been shown to change with 62 increasing surface temperature and moisture. In particular, atmospheric CAPE is 63 expected to increase significantly over continents and oceans in general circulation 64 models [Chen et al., 2020], high-resolution regional climate models [Rasmussen 65 et al., 2017], and idealized cloud-resolving models [Muller et al., 2011]. This in- 66 crease of CAPE is
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