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Allen J. Riordan, J. Thomas Anderson, and S. Chiswell

Abstract

The analysis of the rainband structure and wind fields associated with a coastal front along the North Carolina shoreline is described. Dual-Doppler radar and the augmented GALE (Genesis of Atlantic Lows Experiment) ensemble of in situ stations depict shallow, convective rainbands that overtake the front from the warm-air sector and intensify at the surface front location. Clockwise band rotation is shown to be caused by the difference in alignment between the echo motion and the rainband axes and by new development ahead of the front.

Radar measurements depict the circulation systems associated with a portion of one rainband in the cold air ahead of the front. Here shallow precipitation cores are vertically tilted due to the frontal wind shear. Circulation cells and most precipitation cores are centered just above the frontal inversion, as inferred by the wind shift line aloft. This feature is nearly horizontal in the cross-frontal direction but slopes downward in a direction roughly parallel to the front.

Ahead of the front, main updrafts in and above the cold air are found near the upwind portion of precipitation cores and along two well-defined lines aligned roughly perpendicular to the front. These lines propagate northward and affect several nearby surface sites prior to frontal passage. The speed of northward propagation is consistent with gravity wave theory, while on the larger scale the front appears to behave as the leading edge of a density current. The major features found in this case are compared and contrasted with those of a synoptic-scale warm front.

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Céline Bonfils, Gemma Anderson, Benjamin D. Santer, Thomas J. Phillips, Karl E. Taylor, Matthias Cuntz, Mark D. Zelinka, Kate Marvel, Benjamin I. Cook, Ivana Cvijanovic, and Paul J. Durack

Abstract

The 2011–16 California drought illustrates that drought-prone areas do not always experience relief once a favorable phase of El Niño–Southern Oscillation (ENSO) returns. In the twenty-first century, such an expectation is unrealistic in regions where global warming induces an increase in terrestrial aridity larger than the changes in aridity driven by ENSO variability. This premise is also flawed in areas where precipitation supply cannot offset the global warming–induced increase in evaporative demand. Here, atmosphere-only experiments are analyzed to identify land regions where aridity is currently sensitive to ENSO and where projected future changes in mean aridity exceed the range caused by ENSO variability. Insights into the drivers of these changes in aridity are obtained using simulations with the incremental addition of three different factors to the current climate: ocean warming, vegetation response to elevated CO2 levels, and intensified CO2 radiative forcing. The effect of ocean warming overwhelms the range of ENSO-driven temperature variability worldwide, increasing potential evapotranspiration (PET) in most ENSO-sensitive regions. Additionally, about 39% of the regions currently sensitive to ENSO will likely receive less precipitation in the future, independent of the ENSO phase. Consequently aridity increases in 67%–72% of the ENSO-sensitive area. When both radiative and physiological effects are considered, the area affected by arid conditions rises to 75%–79% when using PET-derived measures of aridity, but declines to 41% when an aridity indicator for total soil moisture is employed. This reduction mainly occurs because plant stomatal resistance increases under enhanced CO2 concentrations, resulting in improved plant water-use efficiency, and hence reduced evapotranspiration and soil desiccation. Imposing CO2-invariant stomatal resistance may overestimate future drying in PET-derived indices.

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Thomas P. Ackerman, Amy J. Braverman, David J. Diner, Theodore L. Anderson, Ralph A. Kahn, John V. Martonchik, Joyce E. Penner, Philip J. Rasch, Bruce A. Wielicki, and Bin Yu

Given the breadth and complexity of available data, constructing a measurement-based description of global tropospheric aerosols that will effectively confront and constrain global three-dimensional models is a daunting task. Because data are obtained from multiple sources and acquired with nonuniform spatial and temporal sampling, scales, and coverage, protocols need to be established that will organize this vast body of knowledge. Currently, there is no capability to assemble the existing aerosol data into a unified, interoperable whole. Technology advancements now being pursued in high-performance distributed computing initiatives can accomplish this objective. Once the data are organized, there are many approaches that can be brought to bear upon the problem of integrating data from different sources. These include data-driven approaches, such as geospatial statistics formulations, and model-driven approaches, such as assimilation or chemical transport modeling. Establishing a data interoperability framework will stimulate algorithm development and model validation and will facilitate the exploration of synergies between different data types. Data summarization and mining techniques can be used to make statistical inferences about climate system relationships and interpret patterns of aerosol-induced change. Generating descriptions of complex, nonlinear relationships among multiple parameters is critical to climate model improvement and validation. Finally, determining the role of aerosols in past and future climate change ultimately requires the use of fully coupled climate and chemistry models, and the evaluation of these models is required in order to trust their results. The set of recommendations presented here address one component of the Progressive Aerosol Retrieval and Assimilation Global Observing Network (PARAGON) initiative. Implementing them will produce the most accurate four-dimensional representation of global aerosols, which can then be used for testing, constraining, and validating models. These activities are critical components of a sustained program to quantify aerosol effects on global climate.

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Thomas L. Delworth, Anthony Rosati, Whit Anderson, Alistair J. Adcroft, V. Balaji, Rusty Benson, Keith Dixon, Stephen M. Griffies, Hyun-Chul Lee, Ronald C. Pacanowski, Gabriel A. Vecchi, Andrew T. Wittenberg, Fanrong Zeng, and Rong Zhang

Abstract

The authors present results for simulated climate and climate change from a newly developed high-resolution global climate model [Geophysical Fluid Dynamics Laboratory Climate Model version 2.5 (GFDL CM2.5)]. The GFDL CM2.5 has an atmospheric resolution of approximately 50 km in the horizontal, with 32 vertical levels. The horizontal resolution in the ocean ranges from 28 km in the tropics to 8 km at high latitudes, with 50 vertical levels. This resolution allows the explicit simulation of some mesoscale eddies in the ocean, particularly at lower latitudes.

Analyses are presented based on the output of a 280-yr control simulation; also presented are results based on a 140-yr simulation in which atmospheric CO2 increases at 1% yr−1 until doubling after 70 yr.

Results are compared to GFDL CM2.1, which has somewhat similar physics but a coarser resolution. The simulated climate in CM2.5 shows marked improvement over many regions, especially the tropics, including a reduction in the double ITCZ and an improved simulation of ENSO. Regional precipitation features are much improved. The Indian monsoon and Amazonian rainfall are also substantially more realistic in CM2.5.

The response of CM2.5 to a doubling of atmospheric CO2 has many features in common with CM2.1, with some notable differences. For example, rainfall changes over the Mediterranean appear to be tightly linked to topography in CM2.5, in contrast to CM2.1 where the response is more spatially homogeneous. In addition, in CM2.5 the near-surface ocean warms substantially in the high latitudes of the Southern Ocean, in contrast to simulations using CM2.1.

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David J. Diner, Thomas P. Ackerman, Theodore L. Anderson, Jens Bösenberg, Amy J. Braverman, Robert J. Charlson, William D. Collins, Roger Davies, Brent N. Holben, Chris A . Hostetler, Ralph A. Kahn, John V. Martonchik, Robert T. Menzies, Mark A. Miller, John A. Ogren, Joyce E. Penner, Philip J. Rasch, Stephen E. Schwartz, John H. Seinfeld, Graeme L. Stephens, Omar Torres, Larry D. Travis, Bruce A . Wielicki, and Bin Yu

Aerosols exert myriad influences on the earth's environment and climate, and on human health. The complexity of aerosol-related processes requires that information gathered to improve our understanding of climate change must originate from multiple sources, and that effective strategies for data integration need to be established. While a vast array of observed and modeled data are becoming available, the aerosol research community currently lacks the necessary tools and infrastructure to reap maximum scientific benefit from these data. Spatial and temporal sampling differences among a diverse set of sensors, nonuniform data qualities, aerosol mesoscale variabilities, and difficulties in separating cloud effects are some of the challenges that need to be addressed. Maximizing the longterm benefit from these data also requires maintaining consistently well-understood accuracies as measurement approaches evolve and improve. Achieving a comprehensive understanding of how aerosol physical, chemical, and radiative processes impact the earth system can be achieved only through a multidisciplinary, interagency, and international initiative capable of dealing with these issues. A systematic approach, capitalizing on modern measurement and modeling techniques, geospatial statistics methodologies, and high-performance information technologies, can provide the necessary machinery to support this objective. We outline a framework for integrating and interpreting observations and models, and establishing an accurate, consistent, and cohesive long-term record, following a strategy whereby information and tools of progressively greater sophistication are incorporated as problems of increasing complexity are tackled. This concept is named the Progressive Aerosol Retrieval and Assimilation Global Observing Network (PARAGON). To encompass the breadth of the effort required, we present a set of recommendations dealing with data interoperability; measurement and model integration; multisensor synergy; data summarization and mining; model evaluation; calibration and validation; augmentation of surface and in situ measurements; advances in passive and active remote sensing; and design of satellite missions. Without an initiative of this nature, the scientific and policy communities will continue to struggle with understanding the quantitative impact of complex aerosol processes on regional and global climate change and air quality.

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Mary C. Barth, Christopher A. Cantrell, William H. Brune, Steven A. Rutledge, James H. Crawford, Heidi Huntrieser, Lawrence D. Carey, Donald MacGorman, Morris Weisman, Kenneth E. Pickering, Eric Bruning, Bruce Anderson, Eric Apel, Michael Biggerstaff, Teresa Campos, Pedro Campuzano-Jost, Ronald Cohen, John Crounse, Douglas A. Day, Glenn Diskin, Frank Flocke, Alan Fried, Charity Garland, Brian Heikes, Shawn Honomichl, Rebecca Hornbrook, L. Gregory Huey, Jose L. Jimenez, Timothy Lang, Michael Lichtenstern, Tomas Mikoviny, Benjamin Nault, Daniel O’Sullivan, Laura L. Pan, Jeff Peischl, Ilana Pollack, Dirk Richter, Daniel Riemer, Thomas Ryerson, Hans Schlager, Jason St. Clair, James Walega, Petter Weibring, Andrew Weinheimer, Paul Wennberg, Armin Wisthaler, Paul J. Wooldridge, and Conrad Ziegler

Abstract

The Deep Convective Clouds and Chemistry (DC3) field experiment produced an exceptional dataset on thunderstorms, including their dynamical, physical, and electrical structures and their impact on the chemical composition of the troposphere. The field experiment gathered detailed information on the chemical composition of the inflow and outflow regions of midlatitude thunderstorms in northeast Colorado, west Texas to central Oklahoma, and northern Alabama. A unique aspect of the DC3 strategy was to locate and sample the convective outflow a day after active convection in order to measure the chemical transformations within the upper-tropospheric convective plume. These data are being analyzed to investigate transport and dynamics of the storms, scavenging of soluble trace gases and aerosols, production of nitrogen oxides by lightning, relationships between lightning flash rates and storm parameters, chemistry in the upper troposphere that is affected by the convection, and related source characterization of the three sampling regions. DC3 also documented biomass-burning plumes and the interactions of these plumes with deep convection.

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Robert J. H. Dunn, Freya Aldred, Nadine Gobron, John B. Miller, Kate M. Willett, Melanie Ades, Robert Adler, R. P. Allan, John Anderson, Orlane Anneville, Yasuyuki Aono, Anthony Argüez, Carlo Arosio, John A. Augustine, Cesar Azorin-Molina, Jonathan Barichivich, Aman Basu, Hylke E. Beck, Nicolas Bellouin, Angela Benedetti, Kevin Blagrave, Stephen Blenkinsop, Olivier Bock, Xavier Bodin, Michael G. Bosilovich, Olivier Boucher, Gerald Bove, Dennis Buechler, Stefan A. Buehler, Laura Carrea, Kai-Lan Chang, Hanne H. Christiansen, John R. Christy, Eui-Seok Chung, Laura M. Ciasto, Melanie Coldewey-Egbers, Owen R. Cooper, Richard C. Cornes, Curt Covey, Thomas Cropper, Molly Crotwell, Diego Cusicanqui, Sean M. Davis, Richard A. M. de Jeu, Doug Degenstein, Reynald Delaloye, Markus G. Donat, Wouter A. Dorigo, Imke Durre, Geoff S. Dutton, Gregory Duveiller, James W. Elkins, Thomas W. Estilow, Nava Fedaeff, David Fereday, Vitali E. Fioletov, Johannes Flemming, Michael J. Foster, Stacey M. Frith, Lucien Froidevaux, Martin Füllekrug, Judith Garforth, Jay Garg, Matthew Gentry, Steven Goodman, Qiqi Gou, Nikolay Granin, Mauro Guglielmin, Sebastian Hahn, Leopold Haimberger, Brad D. Hall, Ian Harris, Debbie L. Hemming, Martin Hirschi, Shu-pen (Ben) Ho, Robert Holzworth, Filip Hrbáček, Daan Hubert, Petra Hulsman, Dale F. Hurst, Antje Inness, Ketil Isaksen, Viju O. John, Philip D. Jones, Robert Junod, Andreas Kääb, Johannes W. Kaiser, Viktor Kaufmann, Andreas Kellerer-Pirklbauer, Elizabeth C. Kent, Richard Kidd, Hyungiun Kim, Zak Kipling, Akash Koppa, Jan Henning L’Abée-Lund, Xin Lan, Kathleen O. Lantz, David Lavers, Norman G. Loeb, Diego Loyola, Remi Madelon, Hilmar J. Malmquist, Wlodzimierz Marszelewski, Michael Mayer, Matthew F. McCabe, Tim R. McVicar, Carl A. Mears, Annette Menzel, Christopher J. Merchant, Diego G. Miralles, Stephen A. Montzka, Colin Morice, Leander Mösinger, Jens Mühle, Julien P. Nicolas, Jeannette Noetzli, Tiina Nõges, Ben Noll, John O’Keefe, Tim J. Osborn, Taejin Park, Cecile Pellet, Maury S. Pelto, Sarah E. Perkins-Kirkpatrick, Coda Phillips, Stephen Po-Chedley, Lorenzo Polvani, Wolfgang Preimesberger, Colin Price, Merja Pulkkanen, Dominik G. Rains, William J. Randel, Samuel Rémy, Lucrezia Ricciardulli, Andrew D. Richardson, David A. Robinson, Matthew Rodell, Nemesio J. Rodríguez-Fernández, Karen H. Rosenlof, Chris Roth, Alexei Rozanov, This Rutishäuser, Ahira Sánchez-Lugo, Parnchai Sawaengphokhai, Verena Schenzinger, Robert W. Schlegel, Udo Schneider, Sapna Sharma, Lei Shi, Adrian J. Simmons, Carolina Siso, Sharon L. Smith, Brian J. Soden, Viktoria Sofieva, Tim H. Sparks, Paul W. Stackhouse Jr., Ryan Stauffer, Wolfgang Steinbrecht, Andrea K. Steiner, Kenton Stewart, Pietro Stradiotti, Dimitri A. Streletskiy, Hagen Telg, Stephen J. Thackeray, Emmanuel Thibert, Michael Todt, Daisuke Tokuda, Kleareti Tourpali, Mari R. Tye, Ronald van der A, Robin van der Schalie, Gerard van der Schrier, Mendy van der Vliet, Guido R. van der Werf, Arnold. van Vliet, Jean-Paul Vernier, Isaac J. Vimont, Katrina Virts, Sebastiàn Vivero, Holger Vömel, Russell S. Vose, Ray H. J. Wang, Markus Weber, David Wiese, Jeanette D. Wild, Earle Williams, Takmeng Wong, R. I. Woolway, Xungang Yin, Ye Yuan, Lin Zhao, Xinjia Zhou, Jerry R. Ziemke, Markus Ziese, and Ruxandra M. Zotta
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