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Michelle Hallack-Alegria and David W. Watkins Jr.

variability can result from shifts in these regimes. Orographic effects, and the state’s proximity to the Pacific Ocean and Gulf of California, also play a role in the temporal and spatial variabilities of climate across the region ( Sheppard et al. 2002 ). Average annual precipitation in Sonora ranges from 15 cm (6 in.) in the coastal zone to 100 cm (40 in) in the mountain regions. Most of the area has a biseasonal rainfall pattern, with a significant portion of the annual precipitation attributed to the

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Enrique R. Vivoni, Hugo A. Gutiérrez-Jurado, Carlos A. Aragón, Luis A. Méndez-Barroso, Alex J. Rinehart, Robert L. Wyckoff, Julio C. Rodríguez, Christopher J. Watts, John D. Bolten, Venkataraman Lakshmi, and Thomas J. Jackson

may provide a means for assessing land–atmosphere interaction at the regional scale and the effects of vegetation changes in recycling moisture back to the atmosphere. The subtropical scrub should be targeted as it occupies broad areas of the landscape and can sustain high specific humidity despite relatively low soil moisture contents. Capturing ecosystem dynamics and terrain controls on hydrologic response is critical for properly representing the role of the land surface in numerical models of

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Wayne Higgins and David Gochis

parameterized for more realistic simulations and accurate predictions with coupled ocean–atmosphere–land (O–A–L) models. A fundamental first step toward improved prediction is the clear documentation of the major elements of the monsoon system and their variability within the context of the evolving OAL annual cycle. NAME employs a multiscale (tiered) approach with focused monitoring, and diagnostic and modeling activities in the core monsoon region, on the regional and continental scales ( Fig. 1 ). An

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David J. Gochis, Christopher J. Watts, Jaime Garatuza-Payan, and Julio Cesar-Rodriguez

transition include the onset of strong, diurnally modulated convection over the semiarid regions of the southwestern United States and western Mexico (e.g., Douglas et al. 1993 ; Gochis et al. 2004 , Anderson and Kanamura 2005 ), a decrease in precipitation over the Great Plains region of the United States ( Higgins et al. 1997 ), and the dramatic invigoration of the regional terrestrial hydroecology (e.g., Brito-Castillo et al. 2003 ; Viramontes and Descriox 2003 ; Biondi et al. 2005 ; Matsui et

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Myong-In Lee, Siegfried D. Schubert, Max J. Suarez, Isaac M. Held, Arun Kumar, Thomas L. Bell, Jae-Kyung E. Schemm, Ngar-Cheung Lau, Jeffrey J. Ploshay, Hyun-Kyung Kim, and Soo-Hyun Yoo

cycle (e.g., Randall et al. 1991 ), and provide guidance on how to improve the representation of subgrid-scale processes in the model (e.g., Betts et al. 1996 ; Giorgi and Shields 1999 ; Lin et al. 2000 ; Groisman et al. 2000 ; Yang and Slingo 2001 ; Zhang 2003 ; Collier and Bowman 2004 ; Lee et al. 2007 ). Although current climate models simulate reasonably well the broad-scale characteristics of the diurnal cycle of warm season precipitation, there are still many features at the local/regional

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J. Craig Collier and Guang J. Zhang

located in mesh cell k , r ( g ∈ k ; t ) was summed to obtain mesh cell total R k ( t ). The mesh cell totals were then averaged onto the model’s T85 horizontal grid to obtain R ( t ). The phase and amplitude of the diurnal cycle were determined by fitting the regional-mean hourly mean precipitation rates R ( t ) to the diurnal harmonic, such that where and δ ( t ) is a residual. Estimates of the coefficients, â and b̂ , were determined by least squares regression, and formulas for the

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Christopher J. Watts, Russell L. Scott, Jaime Garatuza-Payan, Julio C. Rodriguez, John H. Prueger, William P. Kustas, and Michael Douglas

1. Introduction The North American monsoon (NAM) is an important regional phenomenon that provides the majority of annual rainfall over large parts of western Mexico and the southwestern United States. The premonsoon conditions in this region are of extreme dryness, with very high air temperatures and little or no rainfall occurring in the months before the arrival of the monsoon rains. The onset of the monsoon typically occurs in early June in the coastal areas of the Mexican states of Jalisco

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Katrina Grantz, Balaji Rajagopalan, Martyn Clark, and Edith Zagona

variability of the NAMS. Regionally, the intensity of the NAMS decreases as one moves northward of the Sierra Madre Occidental. Not only is the intensity of the monsoon much weaker in the southwestern United States, but the variability of the monsoon is also much larger in these regions, sometimes larger than the mean summer rainfall itself ( Higgins et al. 1998 ). The temporal variability of the NAMS ranges from diurnal to seasonal, to interannual, to interdecadal. Diurnal variability is dominated by

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Alberto M. Mestas-Nuñez, David B. Enfield, and Chidong Zhang

1. Introduction Mestas-Nuñez et al. (2005) have recently evaluated the uncertainties in estimating moisture flux divergences over the Intra-Americas Sea (IAS; composed of the Gulf of Mexico and the Caribbean Sea) using several datasets, which include sounding observations, the National Centers for Environmental Prediction (NCEP) Eta regional analysis ( Black 1994 ), the NCEP–National Center for Atmospheric Research (NCAR) global reanalysis ( Kalnay et al. 1996 ; Kistler et al. 2001 ), and the

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Richard H. Johnson, Paul E. Ciesielski, Brian D. McNoldy, Peter J. Rogers, and Richard K. Taft

systems (ships, aircraft, wind profilers, radars, and surface stations), was designed to study the complex and multifaceted properties of the North American summer monsoon: its onset, precipitation characteristics, the Gulf of California (GoC) low-level jet, gulf surges, easterly waves, tropical cyclone influences, orographic effects, mesoscale convective systems, and the diurnal cycle of convection ( Higgins et al. 2006 ). While the North American summer monsoon is not as dramatic as its Asian

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