Rocha Cesar B.

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Rocha
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Cesar B.
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Blocking statistics in a varying climate: Lessons from a "traffic jam" model with pseudostochastic forcing

2019-09-12 , Paradise, Adiv , Rocha, Cesar B. , Barpanda, Pragallva , Nakamura, Noboru

Recently Nakamura and Huang proposed a semiempirical, one-dimensional model of atmospheric blocking based on the observed budget of local wave activity in the boreal winter. The model dynamics is akin to that of traffic flow, wherein blocking manifests as traffic jams when the streamwise flux of local wave activity reaches capacity. Stationary waves modulate the jet stream’s capacity to transmit transient waves and thereby localize block formation. Since the model is inexpensive to run numerically, it is suited for computing blocking statistics as a function of climate variables from large-ensemble, parameter sweep experiments. We explore sensitivity of blocking statistics to (i) stationary wave amplitude, (ii) background jet speed, and (iii) transient eddy forcing, using frequency, persistence, and prevalence as metrics. For each combination of parameters we perform 240 runs of 180-day simulations with aperiodic transient eddy forcing, each time randomizing the phase relations in forcing. The model climate shifts rapidly from a block-free state to a block-dominant state as the stationary wave amplitude is increased and/or the jet speed is decreased. When eddy forcing is increased, prevalence increases similarly but frequency decreases as blocks merge and become more persistent. It is argued that the present-day climate lies close to the boundary of the two states and hence its blocking statistics are sensitive to climate perturbations. The result underscores the low confidence in GCM-based assessment of the future trend of blocking under a changing climate, while it also provides a theoretical basis for evaluating model biases and understanding trends in reanalysis data.

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On the steadiness and instability of the Intermediate Western Boundary Current between 24 degrees and 18 degrees S

2019-12-06 , Napolitano, Dante C. , da Silveira, Ilson C. A. , Rocha, Cesar B. , Flierl, Glenn R. , Calil, Paulo H. R. , Martins, Renato P.

The Intermediate Western Boundary Current (IWBC) transports Antarctic Intermediate Water across the Vitória–Trindade Ridge (VTR), a seamount chain at ~20°S off Brazil. Recent studies suggest that the IWBC develops a strong cyclonic recirculation in Tubarão Bight, upstream of the VTR, with weak time dependency. We herein use new quasi-synoptic observations, data from the Argo array, and a regional numerical model to describe the structure and variability of the IWBC and to investigate its dynamics. Both shipboard acoustic Doppler current profiler (ADCP) data and trajectories of Argo floats confirm the existence of the IWBC recirculation, which is also captured by our Regional Oceanic Modeling System (ROMS) simulation. An “intermediate-layer” quasigeostrophic (QG) model indicates that the ROMS time-mean flow is a good proxy for the IWBC steady state, as revealed by largely parallel isolines of streamfunction ψ⎯ and potential vorticity Q⎯; a ψ⎯−Q⎯ scatter diagram also shows that the IWBC is potentially unstable. Further analysis of the ROMS simulation reveals that remotely generated, westward-propagating nonlinear eddies are the main source of variability in the region. These eddies enter the domain through the Tubarão Bight eastern edge and strongly interact with the IWBC. As they are advected downstream and negotiate the local topography, the eddies grow explosively through horizontal shear production.

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Characterizing the transition from balanced to unbalanced motions in the Southern California Current

2019-02-21 , Chereskin, Teresa K. , Rocha, Cesar B. , Gille, Sarah T. , Menemenlis, Dimitris , Passaro, Marcello

As observations and models improve their resolution of oceanic motions at ever finer horizontal scales, interest has grown in characterizing the transition from the geostrophically balanced flows that dominate at large‐scale to submesoscale turbulence and waves that dominate at small scales. In this study we examine the mesoscale‐to‐submesoscale (100 to 10 km) transition in an eastern boundary current, the southern California Current System (CCS), using repeated acoustic Doppler current profiler transects, sea surface height from high‐resolution nadir altimetry and output from a (1/48)° global model simulation. In the CCS, the submesoscale is as energetic as in western boundary current regions, but the mesoscale is much weaker, and as a result the transition lacks the change in kinetic energy (KE) spectral slope observed for western boundary currents. Helmholtz and vortex‐wave decompositions of the KE spectra are used to identify balanced and unbalanced contributions. At horizontal scales greater than 70 km, we find that observed KE is dominated by balanced geostrophic motions. At scales from 40 to 10 km, unbalanced contributions such as inertia‐gravity waves contribute as much as balanced motions. The model KE transition occurs at longer scales, around 125 km. The altimeter spectra are consistent with acoustic Doppler current profiler/model spectra at scales longer than 70/125 km, respectively. Observed seasonality is weak. Taken together, our results suggest that geostrophic velocities can be diagnosed from sea surface height on scales larger than about 70 km in the southern CCS.

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EUREC4A

2021-08-25 , Stevens, Bjorn , Bony, Sandrine , Farrell, David , Ament, Felix , Blyth, Alan , Fairall, Christopher W. , Karstensen, Johannes , Quinn, Patricia K. , Speich, Sabrina , Acquistapace, Claudia , Aemisegger, Franziska , Albright, Anna Lea , Bellenger, Hugo , Bodenschatz, Eberhard , Caesar, Kathy-Ann , Chewitt-Lucas, Rebecca , de Boer, Gijs , Delanoë, Julien , Denby, Leif , Ewald, Florian , Fildier, Benjamin , Forde, Marvin , George, Geet , Gross, Silke , Hagen, Martin , Hausold, Andrea , Heywood, Karen J. , Hirsch, Lutz , Jacob, Marek , Jansen, Friedhelm , Kinne, Stefan , Klocke, Daniel , Kölling, Tobias , Konow, Heike , Lothon, Marie , Mohr, Wiebke , Naumann, Ann Kristin , Nuijens, Louise , Olivier, Léa , Pincus, Robert , Pöhlker, Mira L. , Reverdin, Gilles , Roberts, Gregory , Schnitt, Sabrina , Schulz, Hauke , Siebesma, Pier , Stephan, Claudia Christine , Sullivan, Peter P. , Touzé-Peiffer, Ludovic , Vial, Jessica , Vogel, Raphaela , Zuidema, Paquita , Alexander, Nicola , Alves, Lyndon , Arixi, Sophian , Asmath, Hamish , Bagheri, Gholamhossein , Baier, Katharina , Bailey, Adriana , Baranowski, Dariusz , Baron, Alexandre , Barrau, Sébastien , Barrett, Paul A. , Batier, Frédéric , Behrendt, Andreas , Bendinger, Arne , Beucher, Florent , Bigorre, Sebastien P. , Blades, Edmund , Blossey, Peter , Bock, Olivier , Böing, Steven , Bosser, Pierre , Bourras, Denis , Bouruet-Aubertot, Pascale , Bower, Keith , Branellec, Pierre , Branger, Hubert , Brennek, Michal , Brewer, Alan , Brilouet, Pierre-Etienne , Brügmann, Björn , Buehler, Stefan A. , Burke, Elmo , Burton, Ralph , Calmer, Radiance , Canonici, Jean-Christophe , Carton, Xavier , Cato, Gregory, Jr. , Charles, Jude Andre , Chazette, Patrick , Chen, Yanxu , Chilinski, Michal T. , Choularton, Thomas , Chuang, Patrick , Clarke, Shamal , Coe, Hugh , Cornet, Céline , Coutris, Pierre , Couvreux, Fleur , Crewell, Susanne , Cronin, Timothy W. , Cui, Zhiqiang , Cuypers, Yannis , Daley, Alton , Damerell, Gillian M. , Dauhut, Thibaut , Deneke, Hartwig , Desbios, Jean-Philippe , Dörner, Steffen , Donner, Sebastian , Douet, Vincent , Drushka, Kyla , Dütsch, Marina , Ehrlich, André , Emanuel, Kerry A. , Emmanouilidis, Alexandros , Etienne, Jean-Claude , Etienne-Leblanc, Sheryl , Faure, Ghislain , Feingold, Graham , Ferrero, Luca , Fix, Andreas , Flamant, Cyrille , Flatau, Piotr Jacek , Foltz, Gregory R. , Forster, Linda , Furtuna, Iulian , Gadian, Alan , Galewsky, Joseph , Gallagher, Martin , Gallimore, Peter , Gaston, Cassandra J. , Gentemann, Chelle L. , Geyskens, Nicolas , Giez, Andreas , Gollop, John , Gouirand, Isabelle , Gourbeyre, Christophe , de Graaf, Dörte , de Graaf, Geiske E. , Grosz, Robert , Güttler, Johannes , Gutleben, Manuel , Hall, Kashawn , Harris, George , Helfer, Kevin C. , Henze, Dean , Herbert, Calvert , Holanda, Bruna , Ibanez-Landeta, Antonio , Intrieri, Janet , Iyer, Suneil , Julien, Fabrice , Kalesse, Heike , Kazil, Jan , Kellman, Alexander , Kidane, Abiel T. , Kirchner, Ulrike , Klingebiel, Marcus , Körner, Mareike , Kremper, Leslie Ann , Kretzschmar, Jan , Krüger, Ovid O. , Kumala, Wojciech , Kurz, Armin , L'Hégareta, Pierre , Labaste, Matthieu , Lachlan-Cope, Thomas , Laing, Arlene , Landschützer, Peter , Lang, Theresa , Lange, Diego , Lange, Ingo , Laplace, Clément , Lavik, Gauke , Laxenaire, Rémi , Le Bihan, Caroline , Leandro, Mason , Lefevre, Nathalie , Lena, Marius , Lenschow, Donald , Li, Qiang , Lloyd, Gary , Los, Sebastian , Losi, Niccolò , Lovell, Oscar , Luneau, Christopher , Makuch, Przemyslaw , Malinowski, Szymon , Manta, Gaston , Marinou, Eleni , Marsden, Nicholas , Masson, Sebastien , Maury, Nicolas , Mayer, Bernhard , Mayers-Als, Margarette , Mazel, Christophe , McGeary, Wayne , McWilliams, James C. , Mech, Mario , Mehlmann, Melina , Meroni, Agostino Niyonkuru , Mieslinger, Theresa , Minikin, Andreas , Minnett, Peter J. , Möller, Gregor , Morfa Avalos, Yanmichel , Muller, Caroline , Musat, Ionela , Napoli, Anna , Neuberger, Almuth , Noisel, Christophe , Noone, David , Nordsiek, Freja , Nowak, Jakub L. , Oswald, Lothar , Parker, Douglas J. , Peck, Carolyn , Person, Renaud , Philippi, Miriam , Plueddemann, Albert J. , Pöhlker, Christopher , Pörtge, Veronika , Pöschl, Ulrich , Pologne, Lawrence , Posyniak, Michał , Prange, Marc , Quinones Melendez, Estefania , Radtke, Jule , Ramage, Karim , Reimann, Jens , Renault, Lionel , Reus, Klaus , Reyes, Ashford , Ribbe, Joachim , Ringel, Maximilian , Ritschel, Markus , Rocha, Cesar B. , Rochetin, Nicolas , Röttenbacher, Johannes , Rollo, Callum , Royer, Haley M. , Sadoulet, Pauline , Saffin, Leo , Sandiford, Sanola , Sandu, Irina , Schäfer, Michael , Schemann, Vera , Schirmacher, Imke , Schlenczek, Oliver , Schmidt, Jerome M. , Schröder, Marcel , Schwarzenboeck, Alfons , Sealy, Andrea , Senff, Christoph J. , Serikov, Ilya , Shohan, Samkeyat , Siddle, Elizabeth , Smirnov, Alexander , Späth, Florian , Spooner, Branden , Stolla, M. Katharina , Szkółka, Wojciech , de Szoeke, Simon P. , Tarot, Stéphane , Tetoni, Eleni , Thompson, Elizabeth , Thomson, Jim , Tomassini, Lorenzo , Totems, Julien , Ubele, Alma Anna , Villiger, Leonie , von Arx, Jan , Wagner, Thomas , Walther, Andi , Webber, Ben , Wendisch, Manfred , Whitehall, Shanice , Wiltshire, Anton , Wing, Allison A. , Wirth, Martin , Wiskandt, Jonathan , Wolf, Kevin , Worbes, Ludwig , Wright, Ethan , Young, Shanea , Zhang, Chidong , Zhang, Dongxiao , Ziemen, Florian , Zinner, Tobias , Zöger, Martin

The science guiding the EUREC4A campaign and its measurements is presented. EUREC4A comprised roughly 5 weeks of measurements in the downstream winter trades of the North Atlantic – eastward and southeastward of Barbados. Through its ability to characterize processes operating across a wide range of scales, EUREC4A marked a turning point in our ability to observationally study factors influencing clouds in the trades, how they will respond to warming, and their link to other components of the earth system, such as upper-ocean processes or the life cycle of particulate matter. This characterization was made possible by thousands (2500) of sondes distributed to measure circulations on meso- (200 km) and larger (500 km) scales, roughly 400 h of flight time by four heavily instrumented research aircraft; four global-class research vessels; an advanced ground-based cloud observatory; scores of autonomous observing platforms operating in the upper ocean (nearly 10 000 profiles), lower atmosphere (continuous profiling), and along the air–sea interface; a network of water stable isotopologue measurements; targeted tasking of satellite remote sensing; and modeling with a new generation of weather and climate models. In addition to providing an outline of the novel measurements and their composition into a unified and coordinated campaign, the six distinct scientific facets that EUREC4A explored – from North Brazil Current rings to turbulence-induced clustering of cloud droplets and its influence on warm-rain formation – are presented along with an overview of EUREC4A's outreach activities, environmental impact, and guidelines for scientific practice. Track data for all platforms are standardized and accessible at https://doi.org/10.25326/165 (Stevens, 2021), and a film documenting the campaign is provided as a video supplement.

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