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

. Clark , and J. Pitlick , 2005 : Seasonal cycle shifts in hydroclimatology over the western United States. J. Climate , 18 , 372 – 384 . Reiter , E. R. , and M. Tang , 1984 : Plateau effects on diurnal circulation patterns. Mon. Wea. Rev. , 112 , 638 – 651 . Ropelewski , C. F. , and M. S. Halpert , 1986 : North American precipitation and temperature patterns associated with El Niño/Southern Oscillation (ENSO). Mon. Wea. Rev. , 114 , 2352 – 2362 . Sheppard , P. R. , A. C

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

European Centre for Medium-Range Weather Forecasts (ECMWF) 15-yr global reanalysis (ERA15, Gibson et al. 1997 ). They examine uncertainties arising from choices of area boundaries, calculation algorithms, spatial and temporal resolutions, as well as a combination of these effects. Their main conclusion is that these uncertainties are smaller than the large annual and interannual variabilities in moisture flux divergence estimated from the NCEP–NCAR reanalysis. The implication is that the NCEP

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Michelle Hallack-Alegria and David W. Watkins Jr.

present analyses of seasonal drought predictability and discuss ways in which these results may be used by water managers and other decision makers in Sonora. 2. Data and methods Due to the far-reaching effects of drought, in a wide range of social, environmental, and economic contexts, and due to the range of spatial and temporal scales associated with drought, it is difficult to develop a concise definition of drought or an index to measure it. All definitions seem to agree that drought is a

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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

and Colima (around 20°N) before gradually moving northward, reaching southern Arizona in early July (around 35°N) ( Douglas et al. 1993 ). Thus, the core monsoon region ( Higgins et al. 2006 ), where the largest effects of the monsoon have been observed, has been roughly identified as the region between latitudes 20°–35°N and longitudes 100°–115°W with its center in the Sierra Madre Occidental (SMO), although there are also significant effects in other areas [e.g., monsoon onset is associated with

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

al. 2005 ). The onset of seasonal rains in these regions is critical to the function and sustenance of ecosystems as well as supplying water resources for domestic and agricultural purposes. This fact is particularly true for the region encompassing the Sierra Madre Occidental (SMO) in western Mexico, which receives, on average, between 50% and 80% of its annual water resource from monsoon precipitation ( Gochis et al. 2006 ). The general climatology of daily and subdaily precipitation in the

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

“monsoon outlook.” 2. State of monsoon forecasting Currently, monsoon-related forecasts include the official National Oceanic and Atmospheric Administration/National Weather Service (NOAA/NWS) monthly and seasonal U.S. precipitation forecasts issued by the Climate Prediction Center (CPC). These forecasts are issued midmonth, and an updated monthly forecast is issued on the last day of the month (information online at http://www.cpc.ncep.noaa.gov/products/forecasts/month_to_season_outlooks.shtml ). The

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Chunmei Zhu, Tereza Cavazos, and Dennis P. Lettenmaier

relationship between JJAS rainfall and antecedent winter and spring P , T s , S m , SWE, and Z500. A Student’s t test is used to test the significance of spatial correlations, assuming one degree of freedom per year. 4. Classification of extreme years To remove the seasonal mean and local rainfall effects, we first calculated standardized rainfall anomalies for each grid point of the domain and then calculated an average over the MSa region ( Fig. 5 ). Wet (dry) monsoon years in MSa are defined as

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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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Wanqiu Wang and Pingping Xie

1. Introduction Observational studies have revealed that sea surface temperatures (SSTs) have strong local effects in the seasonal evolution and interannual variation of the North American monsoon (NAM) system. Mitchell et al. (2002) showed that the timing, intensity, and regional extent of the NAM rainfall are strongly related to the Gulf of California (GoC) SSTs. Monsoon rainfall did not occur until GoC SSTs became warmer than 26°C and about 75% of the rainfall in the Arizona–New Mexico

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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

properties, in particular soil moisture and vegetation, have received much less attention. Theoretically, soil wetness and plant cover can influence the surface energy balance through changes to the albedo, temperature, and partitioning into sensible and latent heat fluxes. Eltahir (1998) hypothesized that variations in surface conditions caused by soil moisture and vegetation dynamics can have a direct impact on the moist static energy in the boundary layer with subsequent effects on rainfall

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