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

1. Introduction and background The North American monsoon system (NAMS) is the large-scale atmospheric circulation system that drives the dramatic increase in rainfall experienced in the desert southwest United States and northwestern Mexico during the summer months of July, August, and September. These summer thunderstorms typically begin in early July and last until mid-September and can account for as much as 50%–70% of the annual precipitation in the arid region ( Carleton et al. 1990

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Wayne Higgins and David Gochis

1. The NAME Process Study The North American Monsoon Experiment (NAME) is an internationally coordinated process study aimed at determining the sources and limits of predictability of warm season precipitation over North America. The NAME program is jointly sponsored by the Climate Variability and Predictability (CLIVAR) and Global Energy and Water Cycle Experiment (GEWEX) interdisciplinary research efforts. NAME seeks improved understanding of the key physical processes that must be

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X. Gao, J. Li, and S. Sorooshian

1. Introduction This study investigated the capacity of a regional climate model (RCM) to reproduce the major elements of the 2004 North American monsoon (NAM) system. The modeling time period is from 0000 UTC 1 June to 0000 UTC 1 September, which overlaps with the North American Monsoon Experiment (NAME) 2004 Enhanced Observation Period. The NAME project aims to determine the sources and limits of predictability of warm-season precipitation over North America, and has proposed to achieve its

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Mekonnen Gebremichael, Enrique R. Vivoni, Christopher J. Watts, and Julio C. Rodríguez

1. Introduction The North American monsoon (also referred to as the southwest, Mexican, or Arizona monsoon) is a subcontinental-scale climate feature that produces a significant increase in rainfall during the summer months in northwestern Mexico and the southwestern United States ( Douglas et al. 1993 ; Adams and Comrie 1997 ; Fuller and Stensrud 2000 ). It is the most important source of water in the region, as it accounts for 50%–70% of the annual precipitation. The monsoon impacts

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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

1. Introduction The North American monsoon (NAM) is the primary climate phenomenon controlling summer precipitation in northwestern Mexico and the southwestern United States (e.g., Douglas et al. 1993 ; Adams and Comrie 1997 ). Convective storms during the monsoon period can account for a large percentage of the total annual precipitation in the region ( Sheppard et al. 2002 ) and lead to significant impacts on the local climate, ecosystem function, and water resources ( Higgins et al. 2003

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J. Craig Collier and Guang J. Zhang

1. Introduction During the twentieth century, the North American monsoon system became recognized as a significant climate regime in the southwestern United States and northwestern Mexico. Among the earliest written reports of a monsoonlike climate in this region are those of Campbell (1906) and Blake (1923) , who document the existence of “Sonora storms” that prevail over the mountains and deserts of southern California from July into early October. As early as there have been

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Michelle Hallack-Alegria and David W. Watkins Jr.

North American monsoon (NAM), occurring in the summer (July–September). The NAM is the northernmost portion of a more extensive region of heavy precipitation that first develops over southern Mexico during the spring and then spreads northward along the western slopes of the Sierra Madre Occidental ( Douglas et al. 1993 ; Stensrud et al. 1995 ). The monsoon circulation brings warm, humid air from the south, and short-lived thunderstorms result from convection as the air is lifted by orographic

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Chunmei Zhu and Dennis P. Lettenmaier

1. Background Northwestern Mexico, a region that is strongly affected by the North American monsoon system (NAMS), receives between 60% and 80% of its annual precipitation during the June–September (JJAS) monsoon season ( Douglas et al. 1993 ). Understanding the genesis of warm season rainfall in northwestern Mexico has strong implications for warm season precipitation predictability over the NAMS region as well as much of the southern tier of U.S. states (which effectively are the northwestern

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John E. Janowiak, Valery J. Dagostaro, Vernon E. Kousky, and Robert J. Joyce

behavior such as the nighttime maxima over the central United States and over parts of central South America that are associated with low-level jet streams and orographic features. The main purpose of this paper addresses the second concern and thus we present an evaluation of the ability of the National Oceanic and Atmospheric Administration’s (NOAA) Global Forecast System model (GFS) and the regional Eta Model [currently referred to as the North American Mesoscale model (NAM)] to characterize the

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Andrea J. Ray, Gregg M. Garfin, Margaret Wilder, Marcela Vásquez-León, Melanie Lenart, and Andrew C. Comrie

1. Introduction The goal of the multinational, multiyear North American Monsoon Experiment (NAME) program is to improve our understanding of monsoon dynamics to improve prediction skill ( NAME Project Science Team 2004 ). A larger goal for monsoon research is to enhance society’s ability to cope with climate variability and therefore reduce its vulnerability by providing monsoon information and predictions. Lemos and Morehouse (2005) recently described models to facilitate the “co

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