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John M. Peters, Christopher J. Nowotarski, and Gretchen L. Mullendore

dimensions were 100.8, 100.8, and 22 km in the x , y , and z directions, respectively (the extra 0.8 km in the x and y directions was included to satisfy the multithreading requirements of the model). Horizontal and vertical grid spacing was isotropic at 100 m, and a nonacoustic time step of 0.9 s was necessary to ensure numerical stability. Radiation and surface physics were turned off, and free-slip bottom and top boundary conditions were used. Microphysical processes were parameterized using

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Jason A. Otkin, Martha C. Anderson, Christopher Hain, Iliana E. Mladenova, Jeffrey B. Basara, and Mark Svoboda

, to infer the surface energy budget. Use of time-differential observations reduces model sensitivity to errors in absolute temperature retrievals resulting from sensor calibration and atmospheric correction. A simple model of atmospheric boundary layer (ABL) growth ( McNaughton and Spriggs 1986 ) is used to provide closure to the time-integrated energy balance equations over the morning period, alleviating the need for specifying near-surface boundary conditions in air temperature, which often

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M. Hoerling, J. Eischeid, A. Kumar, R. Leung, A. Mariotti, K. Mo, S. Schubert, and R. Seager

stabilization that accompanied anomalous upper-tropospheric high pressure over the region. The drought can thus be seen as a symptom of classical meteorological conditions that control the region's warm season rains. The 2012 summertime central Great Plains drought resulted mostly from natural variations in weather. The assessment did not find substantial evidence for underlying causes associated with the effects of long-lived boundary forcings. Retrospective climate simulations identify a mean dry signal

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Richard Seager, Lisa Goddard, Jennifer Nakamura, Naomi Henderson, and Dong Eun Lee

droughts is important but more important from the point of view of planning ahead for, and possibly preventing, damaging impacts is development of an ability to predict droughts. Prediction of drought on the seasonal-to-interannual time scale will depend on the ability to predict slowly evolving boundary conditions that, by forcing the atmospheric circulation, can create tendencies toward drought-inducing patterns of sufficient amplitude that they can emerge amidst the internal atmospheric variability

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Martha C. Anderson, Christopher Hain, Jason Otkin, Xiwu Zhan, Kingtse Mo, Mark Svoboda, Brian Wardlow, and Agustin Pimstein

systems such as the USDM. Recent “flash drought” events, where surface moisture conditions declined rapidly because of high temperatures and enhanced evaporative losses, have highlighted the need for rapid response indicators. Vegetation cover condition, as sampled by remotely sensed shortwave vegetation indices (VIs), is a relatively slow response variable, typically adjusting only after notable crop damage has already occurred. Remote sensing indices based primarily on VI data include the vegetation

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Hailan Wang, Siegfried Schubert, Randal Koster, Yoo-Geun Ham, and Max Suarez

Feng 2012 ; Dai 2013 ) and atmospheric general circulation model (AGCM) simulations (e.g., Hoerling and Kumar 2003 ; Schubert et al. 2004a , b ; Seager et al. 2005 ; Wang et al. 2010 ). An important finding from such studies is that ENSO and the PDO in their cold phases, and the AMO in its warm phase, produce a tendency for drought conditions over the United States, with the Pacific playing the dominant role (e.g., Mo et al. 2009 ; Schubert et al. 2009 ). In addition, the impact of SST

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Eric F. Wood, Siegfried D. Schubert, Andrew W. Wood, Christa D. Peters-Lidard, Kingtse C. Mo, Annarita Mariotti, and Roger S. Pulwarty

parameterizations (and features such as resolution and reductions in overall model structural uncertainty including initial and boundary conditions) are most likely to lead to more skillful models is limited. This highlights the challenges in developing multimodel ensemble systems. Fig . 4. Correlation between (left) first PC of SST [labeled S1(SST)] and SST and (right) S1(SST) and ensemble mean precipitation for JJA 1982–2012. Top row contains observations. Lower rows contain NMME models. See text for the

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Paul A. Dirmeyer, Jiangfeng Wei, Michael G. Bosilovich, and David M. Mocko

such as large-scale subsidence, increased entrainment of dry air at the top of an otherwise favorable boundary layer, or a change in coupled land–atmosphere feedbacks caused by anomalous land surface conditions. Further diagnoses would be helpful to better understand the combination of events that contribute to precipitation extremes around the globe. Acknowledgments This research was supported by National Aeronautics and Space Administration Grant NNX09AI84G. Much of the data used in this effort

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Shahrbanou Madadgar and Hamid Moradkhani

, represents the marginal distribution of the i th variable, and is the copula cumulative distribution function. A copula satisfies the “boundary” and “increasing” conditions, which is expressed as follows in the case of bivariate copulas: If is absolutely continuous, the copula density is written as follows: and the joint density function can be decomposed using the copula density function: Hence, Eq. (3) can be rewritten as where is the product operator, and is the density function of a

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Youlong Xia, Michael B. Ek, David Mocko, Christa D. Peters-Lidard, Justin Sheffield, Jiarui Dong, and Eric F. Wood

for improving the land initial conditions for numerical weather predictions. Since then, the system has expanded its scope to include model intercomparison studies ( Xia et al. 2012a , b ), evaluation of NLDAS products ( Peters-Lidard et al. 2011 ; Xia et al. 2012c ), and development of a near-real-time NLDAS drought monitoring system ( Ek et al. 2011 ; Sheffield et al. 2012 ; Xia et al. 2013 ). The drought monitoring system provides a range of drought indices, including daily, weekly, and

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