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Luca Cantarello, Onno Bokhove, and Steven Tobias

Abstract

An isentropic 1½-layer model based on modified shallow-water equations is presented, including terms mimicking convection and precipitation. This model is an updated version of the isopycnal single-layer modified rotating shallow water (modRSW) model. The clearer link between fluid temperature and model variables together with a double-layer structure make this revised, isentropic model a more suitable tool to achieve our future goal: to conduct idealized experiments for investigating satellite data assimilation. The numerical model implementation is verified against an analytical solution for stationary waves in a rotating fluid, based on Shrira’s methodology for the isopycnal case. Recovery of the equivalent isopycnal model is also verified, both analytically and numerically. With convection and precipitation added, we show how complex model dynamics can be achieved exploiting rotation and relaxation to a meridional jet in a periodic domain. This solution represents a useful reference simulation or “truth” in conducting future (satellite) data assimilation experiments, with additional atmospheric conditions and data. A formal analytical derivation of the isentropic 1½-layer model from an isentropic two-layer model without convection and precipitation is shown in a companion paper (Part II).

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Onno Bokhove, Luca Cantarello, and Steven Tobias

Abstract

In this Part II paper we present a fully consistent analytical derivation of the “dry” isentropic 1½-layer shallow-water model described and used in Part I of this study, with no convection and precipitation. The mathematical derivation presented here is based on a combined asymptotic and slaved Hamiltonian analysis, which is used to resolve an apparent inconsistency arising from the application of a rigid-lid approximation to an isentropic two-layer shallow-water model. Real observations based on radiosonde data are used to justify the scaling assumptions used throughout the paper, as well as in Part I. Eventually, a fully consistent isentropic 1½-layer model emerges from imposing fluid at rest (v1 = 0) and zero Montgomery potential (M1 = 0) in the upper layer of an isentropic two-layer model.

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Bjorn Stevens, Felix Ament, Sandrine Bony, Susanne Crewell, Florian Ewald, Silke Gross, Akio Hansen, Lutz Hirsch, Marek Jacob, Tobias Kölling, Heike Konow, Bernhard Mayer, Manfred Wendisch, Martin Wirth, Kevin Wolf, Stephan Bakan, Matthias Bauer-Pfundstein, Matthias Brueck, Julien Delanoë, André Ehrlich, David Farrell, Marvin Forde, Felix Gödde, Hans Grob, Martin Hagen, Evelyn Jäkel, Friedhelm Jansen, Christian Klepp, Marcus Klingebiel, Mario Mech, Gerhard Peters, Markus Rapp, Allison A. Wing, and Tobias Zinner

Abstract

A configuration of the High-Altitude Long-Range Research Aircraft (HALO) as a remote sensing cloud observatory is described, and its use is illustrated with results from the first and second Next-Generation Aircraft Remote Sensing for Validation (NARVAL) field studies. Measurements from the second NARVAL (NARVAL2) are used to highlight the ability of HALO, when configured in this fashion, to characterize not only the distribution of water condensate in the atmosphere, but also its impact on radiant energy transfer and the covarying large-scale meteorological conditions—including the large-scale velocity field and its vertical component. The NARVAL campaigns with HALO demonstrate the potential of airborne cloud observatories to address long-standing riddles in studies of the coupling between clouds and circulation and are helping to motivate a new generation of field studies.

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Stephanie Fiedler, Traute Crueger, Roberta D’Agostino, Karsten Peters, Tobias Becker, David Leutwyler, Laura Paccini, Jörg Burdanowitz, Stefan A. Buehler, Alejandro Uribe Cortes, Thibaut Dauhut, Dietmar Dommenget, Klaus Fraedrich, Leonore Jungandreas, Nicola Maher, Ann Kristin Naumann, Maria Rugenstein, Mirjana Sakradzija, Hauke Schmidt, Frank Sielmann, Claudia Stephan, Claudia Timmreck, Xiuhua Zhu, and Bjorn Stevens

Abstract

The representation of tropical precipitation is evaluated across three generations of models participating in phases 3, 5, and 6 of the Coupled Model Intercomparison Project (CMIP). Compared to state-of-the-art observations, improvements in tropical precipitation in the CMIP6 models are identified for some metrics, but we find no general improvement in tropical precipitation on different temporal and spatial scales. Our results indicate overall little changes across the CMIP phases for the summer monsoons, the double-ITCZ bias, and the diurnal cycle of tropical precipitation. We find a reduced amount of drizzle events in CMIP6, but tropical precipitation occurs still too frequently. Continuous improvements across the CMIP phases are identified for the number of consecutive dry days, for the representation of modes of variability, namely, the Madden–Julian oscillation and El Niño–Southern Oscillation, and for the trends in dry months in the twentieth century. The observed positive trend in extreme wet months is, however, not captured by any of the CMIP phases, which simulate negative trends for extremely wet months in the twentieth century. The regional biases are larger than a climate change signal one hopes to use the models to identify. Given the pace of climate change as compared to the pace of model improvements to simulate tropical precipitation, we question the past strategy of the development of the present class of global climate models as the mainstay of the scientific response to climate change. We suggest the exploration of alternative approaches such as high-resolution storm-resolving models that can offer better prospects to inform us about how tropical precipitation might change with anthropogenic warming.

Open access
Peter Bissolli, Catherine Ganter, Ademe Mekonnen, Ahira Sánchez-Lugo, Zhiwei Zhu, A. Abida, W. Agyakwah, Laura S. Aldeco, Eric J. Alfaro, Teddy Allen, Lincoln M. Alves, Jorge A. Amador, B. Andrade, P. Asgarzadeh, Grinia Avalos, Julian Baez, M. Yu. Bardin, E. Bekele, Renato Bertalanic, Oliver Bochníček, Brandon Bukunt, Blanca Calderón, Jayaka D. Campbell, Elise Chandler, Candice S Charlton, Vincent Y. S. Cheng, Leonardo A. Clarke, Kris Correa, Catalina R. Cortés Salazar, Felipe Costa, Lenka Crhová, Ana Paula Cunha, Mesut Demircan, K. R. Dhurmea, Diana A. Domínguez, Dashkhuu Dulamsuren, M. ElKharrim, Jhan-Carlo Espinoza, A. Fazl-Kezemi, Nava Fedaeff, Chris Fenimore, Steven Fuhrman, Karin Gleason, Charles “Chip” P. Guard, Samson Hagos, Mizuki Hanafusa, Richard R. Heim Jr., John Kennedy, Sverker Hellström, Hugo G. Hidalgo, I. A. Ijampy, Gyo Soon Im, G. Jumaux, K. Kabidi, Kenneth Kerr, Yelena Khalatyan, Valentina Khan, Mai Van Khiem, Tobias Koch, Gerbrand Koren, Natalia N. Korshunova, A. C. Kruger, Mónika Lakatos, Jostein Mamen, Hoang Phuc Lam, Mark A. Lander, Waldo Lavado-Casimiro, Tsz-Cheung Lee, Kinson H. Y. Leung, Xuefeng Liu, Rui Lu, José A. Marengo, Mohammadi Marjan, Ana E. Martínez, Charlotte McBride, Mirek Mietus, Noelia Misevicius, Aurel Moise, Jorge Molina-Carpio, Natali Mora, Awatif E. Mostafa, O. Ndiaye, Juan J. Nieto, Kristin Olafsdottir, Reynaldo Pascual Ramírez, David Phillips, Amos Porat, Esteban Rodriguez Guisado, Madhavan Rajeevan, Andrea M. Ramos, Cristina Recalde Coronel, Alejandra J. Reyes Kohler, M. Robjhon, Josyane Ronchail, Roberto Salinas, Hirotaka Sato, Hitoshi Sato, Amal Sayouri, Serhat Sensoy, Amsari Mudzakir Setiawan, F. Sima, Adam Smith, Matthieu Sorel, Sandra Spillane, Jacqueline M. Spence, O. P. Sreejith, A. K. Srivastava, Tannecia S. Stephenson, Kiyotoshi Takahashi, Michael A. Taylor, Wassila M. Thiaw, Skie Tobin, Lidia Trescilo, Adrian R. Trotman, Cedric J. Van Meerbeeck, A. Vazifeh, Shunya Wakamatsu, M. F. Zaheer, F. Zeng, and Peiqun Zhang
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