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

studies. Briefly, there are two main avenues for the warm season moisture supply from the IAS: the southerly Great Plains low-level jet (LLJ) on the east side of the Rocky Mountains and a southerly flow of moisture over a wider region across the Gulf of Mexico coast farther east, punctuated by surges associated with summer frontal passages. During boreal summer ( Fig. 3 , bottom), the easterly trade winds carry moisture from the Atlantic into the Caribbean Sea where the flow intensifies forming the

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Kingtse C. Mo, Eric Rogers, Wesley Ebisuzaki, R. Wayne Higgins, J. Woollen, and M. L. Carrera

precipitation. Areas with negative P anomalies are warmer ( Fig. 6f ). The coarse-resolution CDAS model does not resolve the Gulf of California (GoC) ( Schmitz and Mullen 1996 ). It is interesting to examine whether the assimilation of soundings along the GoC improves the representation of the low-level jet from the Gulf of California (GCLLJ). The vertically integrated moisture fluxes from the operational GDAS ( Fig. 7a ) clearly show two low-level jets: one from the Gulf of Mexico to the Great Plains

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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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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

Mitchell 1994 ; Carbone et al. 2002 ); and 3) large-scale or subcontinental controls such as the nocturnal low-level jet ( Rasmusson 1967 ; Helfand and Schubert 1995 ; Higgins et al. 1997 ; Schubert et al. 1998 ), atmospheric tides ( Dai and Deser 1999 ; Dai et al. 1999 ; Lim and Suh 2000 ), thermally driven large-scale land–ocean circulation and regional subsidence ( Silva Dias et al. 1987 ; Figueroa et al. 1995 ; Gandu and Silva Dias 1998 ; Dai and Deser 1999 ; Dai 2001 ), and the seasonal

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Paquita Zuidema, Chris Fairall, Leslie M. Hartten, Jeffrey E. Hare, and Daniel Wolfe

Depression Blas to the south and southwest of the Altair and an upper-level trough to the northeast of the Gulf of California (GoC) ( Johnson et al. 2007 ). Outflow from Blas helped delay the northward migration of the climatological westerly jet, but after 17 July the upper-level winds at the location of the Altair were easterly and stayed that way, signifying an established summer monsoon. The sea surface temperature (SST) and water vapor path (WVP) fields at the onset of the ship cruise are shown

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Wayne Higgins and David Gochis

California low-level jet. Additional studies of the impacts of the NAME 2004 enhanced observations (e.g., rain gauge, SSTs, and various combinations thereof) on atmospheric analyses are needed to determine if NAME science has the potential to improve large-scale simulations and predictions of North American climate variability. To achieve its goals, NAME will need to improve numerical simulations of the monsoon circulation and its large-scale effects. A driving hypothesis of NAME is that the community

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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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Timothy J. Lang, David A. Ahijevych, Stephen W. Nesbitt, Richard E. Carbone, Steven A. Rutledge, and Robert Cifelli

, which then force gulf convection later (e.g., Mapes et al. 2003 ). This study will establish the timing, evolution, and propagation of convective systems, thus testing both of these hypotheses. b. Intraseasonal variability of precipitation A major goal of NAME is to better understand regimes associated with intraseasonal variability of convection during July–August in the tier I region and its linkages to precipitation in the southwestern United States, including the influences of surges, jets

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

et al. 1998 ; Higgins et al. 1997 ); the ENSO–NAM precipitation relationship and NAM interannual variability ( Ropelewski and Halpert 1996 ; Higgins et al. 1999 ; Higgins et al. 2000 ); onset and northward extension of NAM precipitation and the “tripole” interaction among summer precipitation regimes over the continental United States ( Higgins et al. 1999 ; Mo 2000 ); moisture surges over the Gulf of California and the low-level jet (LLJ) from the northern end of the gulf to the southwest

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

from the relatively cooler ocean in over the land. The combination of moist air and warm land surfaces causes convective instability, thus producing frequent summer precipitation events ( Adams and Comrie 1997 ; Barlow et al. 1998 ). The seasonal shift in the winds depends primarily upon the relative location of the subtropical jet, which typically migrates northward during the summer months. Several studies have shown that a more northward displacement of the subtropical ridge is associated with

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