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Derek J. Posselt, Bruce Fryxell, Andrea Molod, and Brian Williams

Abstract

Parameterization of processes that occur on length scales too small to resolve on a computational grid is a major source of uncertainty in global climate models. This study investigates the relative importance of a number of parameters used in the Goddard Earth Observing System Model, version 5 (GEOS-5), atmospheric general circulation model, focusing on cloud, convection, and boundary layer parameterizations. Latin hypercube sampling is used to generate a few hundred sets of 19 candidate physics parameters, which are subsequently used to generate ensembles of single-column model realizations of cloud content, precipitation, and radiative fluxes for four different field campaigns. A Gaussian process model is then used to create a computationally inexpensive emulator for the simulation code that can be used to determine a measure of relative parameter sensitivity by sampling the response surface for a very large number of input parameter sets. Parameter sensitivities are computed for different geographic locations and seasons to determine whether the intrinsic sensitivity of the model parameterizations changes with season and location. The results indicate the same subset of parameters collectively control the model output across all experiments, independent of changes in the environment. These are the threshold relative humidity for cloud formation, the ice fall speeds, convective and large-scale autoconversion, deep convection relaxation time scale, maximum convective updraft diameter, and minimum ice effective radius. However, there are differences in the degree of parameter sensitivity between continental and tropical convective cases, as well as systematic changes in the degree of parameter influence and parameter–parameter interaction.

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Johnny C-L. Chan, Brian J. Williams, and Russell L. Elsberry

Abstract

A detailed analysis of the performance of the U.S. Navy Nested Tropical Cyclone Model (NTCM) for western North Pacific tropical cyclones is made based on five storm-related factors: latitude, longitude, intensity, 12-h intensity change and size (radius of 15 m s−1 (30 kt) winds). The error measures used to assess the accuracy of the NTCM forecasts include: mean and median forecast errors, the systematic errors in the zonal and meridional directions, and the cross-track and along-track components relative to a climatology-persistence (CLIPER) track. These different measures provide insights into the different characteristics of the NTCM forecasts. Although the mean forecast errors are widely reported, they provide no indication of directionality. The zonal and meridional systematic errors provide additional information, but are difficult to interpret since both eastward and westward moving storms are included. Referencing the cross-track and along-track components to a standard forecast technique (CLIPER) provides directions information on the NTCM forecast errors that will be useful to the forecaster.

The analyses based on the latitude and longitude stratifications suggest that the NTCM predictions are most accurate for low-latitude storms and those in the western region of the western North Pacific. However, the model does not perform very well for storms north of 17° or east of 129°E. The NTCM provides better guidance when the observed intensity is close to that of the bogus vortex inserted in the NTCM. For cyclones with a radius of 15 m s−1 winds ≥ 389 km, the NTCM forecasts do not have good skill relative to those from the CLIPER scheme. Intensity changes in the past 12 h do not appear to affect to affect significantly the performance of the NTCM. Most of the results from these analyses may be attributed to a slow bias in the NTCM. Other potential sources of error include the fixed intensity and size of the bogus vortex and the domain size of the nested grid.

The study is intended as a prototype for evaluating an objective track forecast aid based on storm-related factors. Results from such an evaluation can be used not only by the forecasters but also in future modifications of the forecast aid. The results of this study indicate strongly a need to improve specification of the initial conditions in the NTCM, and especially to introduce a bogus storm that is more representative of the storm.

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William J. Koshak, Kenneth L. Cummins, Dennis E. Buechler, Brian Vant-Hull, Richard J. Blakeslee, Earle R. Williams, and Harold S. Peterson

Abstract

Changes in lightning characteristics over the conterminous United States (CONUS) are examined to support the National Climate Assessment (NCA) program. Details of the variability of cloud-to-ground (CG) lightning characteristics over the decade 2003–12 are provided using data from the National Lightning Detection Network (NLDN). Changes in total (CG + cloud flash) lightning across part of the CONUS during the decade are provided using satellite Lightning Imaging Sensor (LIS) data. The variations in NLDN-derived CG lightning are compared with available statistics on lightning-caused impacts to various U.S. economic sectors. Overall, a downward trend in total CG lightning count is found for the decadal period; the 5-yr mean NLDN CG count decreased by 12.8% from 25 204 345.8 (2003–07) to 21 986 578.8 (2008–12). There is a slow upward trend in the fraction and number of positive-polarity CG lightning, however. Associated lightning-caused fatalities and injuries, and the number of lightning-caused wildland fires and burn acreage also trended downward, but crop and personal-property damage costs increased. The 5-yr mean LIS total lightning changed little over the decadal period. Whereas the CONUS-averaged dry-bulb temperature trended upward during the analysis period, the CONUS-averaged wet-bulb temperature (a variable that is better correlated with lightning activity) trended downward. A simple linear model shows that climate-induced changes in CG lightning frequency would likely have a substantial and direct impact on humankind (e.g., a long-term upward trend of 1°C in wet-bulb temperature corresponds to approximately 14 fatalities and over $367 million in personal-property damage resulting from lightning).

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David C. Fritts, Ronald B. Smith, Michael J. Taylor, James D. Doyle, Stephen D. Eckermann, Andreas Dörnbrack, Markus Rapp, Bifford P. Williams, P.-Dominique Pautet, Katrina Bossert, Neal R. Criddle, Carolyn A. Reynolds, P. Alex Reinecke, Michael Uddstrom, Michael J. Revell, Richard Turner, Bernd Kaifler, Johannes S. Wagner, Tyler Mixa, Christopher G. Kruse, Alison D. Nugent, Campbell D. Watson, Sonja Gisinger, Steven M. Smith, Ruth S. Lieberman, Brian Laughman, James J. Moore, William O. Brown, Julie A. Haggerty, Alison Rockwell, Gregory J. Stossmeister, Steven F. Williams, Gonzalo Hernandez, Damian J. Murphy, Andrew R. Klekociuk, Iain M. Reid, and Jun Ma

Abstract

The Deep Propagating Gravity Wave Experiment (DEEPWAVE) was designed to quantify gravity wave (GW) dynamics and effects from orographic and other sources to regions of dissipation at high altitudes. The core DEEPWAVE field phase took place from May through July 2014 using a comprehensive suite of airborne and ground-based instruments providing measurements from Earth’s surface to ∼100 km. Austral winter was chosen to observe deep GW propagation to high altitudes. DEEPWAVE was based on South Island, New Zealand, to provide access to the New Zealand and Tasmanian “hotspots” of GW activity and additional GW sources over the Southern Ocean and Tasman Sea. To observe GWs up to ∼100 km, DEEPWAVE utilized three new instruments built specifically for the National Science Foundation (NSF)/National Center for Atmospheric Research (NCAR) Gulfstream V (GV): a Rayleigh lidar, a sodium resonance lidar, and an advanced mesosphere temperature mapper. These measurements were supplemented by in situ probes, dropsondes, and a microwave temperature profiler on the GV and by in situ probes and a Doppler lidar aboard the German DLR Falcon. Extensive ground-based instrumentation and radiosondes were deployed on South Island, Tasmania, and Southern Ocean islands. Deep orographic GWs were a primary target but multiple flights also observed deep GWs arising from deep convection, jet streams, and frontal systems. Highlights include the following: 1) strong orographic GW forcing accompanying strong cross-mountain flows, 2) strong high-altitude responses even when orographic forcing was weak, 3) large-scale GWs at high altitudes arising from jet stream sources, and 4) significant flight-level energy fluxes and often very large momentum fluxes at high altitudes.

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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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