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Gerald D. Bell, Michael S. Halpert, Russell C. Schnell, R. Wayne Higgins, Jay Lawrimore, Vernon E. Kousky, Richard Tinker, Wasila Thiaw, Muthuvel Chelliah, and Anthony Artusa

The global climate during 1999 was impacted by Pacific cold episode (La Niña) conditions throughout the year, which resulted in regional precipitation and atmospheric circulation patterns across the Pacific Ocean and the Americas that are generally consistent with those observed during past cold episodes. The primary La Niña-related precipitation anomalies included 1) increased rainfall across Indonesia, and a nearly complete disappearance of rainfall across the east-central and eastern equatorial Pacific; 2) above-normal rains across northwestern and northern Australia; 3) increased monsoon rains across the Sahel region of western Africa; 4) above-average rains over southeastern Africa, 5) above-average rains over the Caribbean Sea and portions of Central America, and 6) below-average rains in southeastern South America.

The La Niña also contributed to persistent cyclonic circulation anomalies in the subtropics of both hemispheres, which flanked the area of suppressed convective activity over the eastern half of the equatorial Pacific. In the Northern Hemisphere this anomaly feature contributed to a pronounced westward retraction of the wintertime East Asian jet stream, which subsequently impacted precipitation and storm patterns across the eastern North Pacific and western North America. The La Niña-related pattern of tropical rainfall also contributed to a very persistent pattern of anticyclonic circulation anomalies in the middle latitude of both hemispheres, extending from the eastern Pacific across the Atlantic and Africa eastward to Australasia. This anomaly pattern was associated with an active Atlantic hurricane season, an inactive eastern North Pacific hurricane season, above-average rains in the African Sahel, and an overall amplification of the entire southeast Asian summer monsoon complex.

The active 1999 North Atlantic hurricane season featured 12 named storms, 8 of which became hurricanes, and 5 of which became intense hurricanes. The peak of activity during mid-August–October was accompanied by low vertical wind shear across the central and western Atlantic, along with both a favorable structure and location of the African easterly jet. In contrast, only 9 tropical storms formed over the eastern North Pacific during the year, making it one of the most inactive years for that region in the historical record. This relative inactivity was linked to a persistent pattern of high vertical wind shear that covered much of the main development region of the eastern North Pacific.

Other regional aspects of the short-term climate included: 1) above-average wintertime precipitation and increased storminess in the Pacific Northwest, United States; 2) above-average monsoonal rainfall across the southwestern United States; 3) drought over the northeastern quadrant of the United States during April–mid-August; 4) hurricane-related flooding in the Carolinas during September; 5) drought over the south-central United States during July–November; 6) below-average rainfall in the Hawaiian Islands throughout the year, with long-term dryness affecting some parts of the islands since October 1997; 7) a continuation of long-term drought conditions in southeastern Australia, with most of Victoria experiencing below-average rainfall since late 1996; and 8) above-average rainfall in central China during April–August.

Global annual mean surface temperatures during 1999 for land and marine areas were 0.41°C above the 1880–1998 long-term mean, making it the fifth warmest year in the record. However, significant cooling was evident in the Tropics during 1999 in association with a continuation of La Niña conditions. In contrast, temperatures in both the Northern Hemisphere and Southern Hemisphere extratropics were the second warmest in the historical record during 1999, and only slightly below the record 1998 anomalies.

The areal extent of the Antarctic ozone hole remained near record levels during 1999. The ozone hole also lasted longer than has been observed in past years.

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Fedor Mesinger, Geoff DiMego, Eugenia Kalnay, Kenneth Mitchell, Perry C. Shafran, Wesley Ebisuzaki, Dušan Jović, Jack Woollen, Eric Rogers, Ernesto H. Berbery, Michael B. Ek, Yun Fan, Robert Grumbine, Wayne Higgins, Hong Li, Ying Lin, Geoff Manikin, David Parrish, and Wei Shi

In 1997, during the late stages of production of NCEP–NCAR Global Reanalysis (GR), exploration of a regional reanalysis project was suggested by the GR project's Advisory Committee, “particularly if the RDAS [Regional Data Assimilation System] is significantly better than the global reanalysis at capturing the regional hydrological cycle, the diurnal cycle and other important features of weather and climate variability.” Following a 6-yr development and production effort, NCEP's North American Regional Reanalysis (NARR) project was completed in 2004, and data are now available to the scientific community. Along with the use of the NCEP Eta model and its Data Assimilation System (at 32-km–45-layer resolution with 3-hourly output), the hallmarks of the NARR are the incorporation of hourly assimilation of precipitation, which leverages a comprehensive precipitation analysis effort, the use of a recent version of the Noah land surface model, and the use of numerous other datasets that are additional or improved compared to the GR. Following the practice applied to NCEP's GR, the 25-yr NARR retrospective production period (1979–2003) is augmented by the construction and daily execution of a system for near-real-time continuation of the NARR, known as the Regional Climate Data Assimilation System (R-CDAS). Highlights of the NARR results are presented: precipitation over the continental United States (CONUS), which is seen to be very near the ingested analyzed precipitation; fits of tropospheric temperatures and winds to rawinsonde observations; and fits of 2-m temperatures and 10-m winds to surface station observations. The aforementioned fits are compared to those of the NCEP–Department of Energy (DOE) Global Reanalysis (GR2). Not only have the expectations cited above been fully met, but very substantial improvements in the accuracy of temperatures and winds compared to that of GR2 are achieved throughout the troposphere. Finally, the numerous datasets produced are outlined and information is provided on the data archiving and present data availability.

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Wayne Higgins, Dave Ahijevych, Jorge Amador, Ana Barros, E. Hugo Berbery, Ernesto Caetano, Richard Carbone, Paul Ciesielski, Rob Cifelli, Miguel Cortez-Vazquez, Art Douglas, Michael Douglas, Gus Emmanuel, Chris Fairall, David Gochis, David Gutzler, Thomas Jackson, Richard Johnson, Clark King, Timothy Lang, Myong-In Lee, Dennis Lettenmaier, Rene Lobato, Victor Magaña, Jose Meiten, Kingtse Mo, Stephen Nesbitt, Francisco Ocampo-Torres, Erik Pytlak, Peter Rogers, Steven Rutledge, Jae Schemm, Siegfried Schubert, Allen White, Christopher Williams, Andrew Wood, Robert Zamora, and Chidong Zhang

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 scientific objectives of NAME are to promote a better understanding and more realistic simulation of warm-season convective processes in complex terrain, intraseasonal variability of the monsoon, and the response of the warm-season atmospheric circulation and precipitation patterns to slowly varying, potentially predictable surface boundary conditions.

During the summer of 2004, the NAME community implemented an international (United States, Mexico, Central America), multiagency (NOAA, NASA, NSF, USDA) field experiment called NAME 2004. This article presents early results from the NAME 2004 campaign and describes how the NAME modeling community will leverage the NAME 2004 data to accelerate improvements in warm-season precipitation forecasts for North America.

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Suranjana Saha, Shrinivas Moorthi, Hua-Lu Pan, Xingren Wu, Jiande Wang, Sudhir Nadiga, Patrick Tripp, Robert Kistler, John Woollen, David Behringer, Haixia Liu, Diane Stokes, Robert Grumbine, George Gayno, Jun Wang, Yu-Tai Hou, Hui-ya Chuang, Hann-Ming H. Juang, Joe Sela, Mark Iredell, Russ Treadon, Daryl Kleist, Paul Van Delst, Dennis Keyser, John Derber, Michael Ek, Jesse Meng, Helin Wei, Rongqian Yang, Stephen Lord, Huug van den Dool, Arun Kumar, Wanqiu Wang, Craig Long, Muthuvel Chelliah, Yan Xue, Boyin Huang, Jae-Kyung Schemm, Wesley Ebisuzaki, Roger Lin, Pingping Xie, Mingyue Chen, Shuntai Zhou, Wayne Higgins, Cheng-Zhi Zou, Quanhua Liu, Yong Chen, Yong Han, Lidia Cucurull, Richard W. Reynolds, Glenn Rutledge, and Mitch Goldberg

The NCEP Climate Forecast System Reanalysis (CFSR) was completed for the 31-yr period from 1979 to 2009, in January 2010. The CFSR was designed and executed as a global, high-resolution coupled atmosphere–ocean–land surface–sea ice system to provide the best estimate of the state of these coupled domains over this period. The current CFSR will be extended as an operational, real-time product into the future. New features of the CFSR include 1) coupling of the atmosphere and ocean during the generation of the 6-h guess field, 2) an interactive sea ice model, and 3) assimilation of satellite radiances by the Gridpoint Statistical Interpolation (GSI) scheme over the entire period. The CFSR global atmosphere resolution is ~38 km (T382) with 64 levels extending from the surface to 0.26 hPa. The global ocean's latitudinal spacing is 0.25° at the equator, extending to a global 0.5° beyond the tropics, with 40 levels to a depth of 4737 m. The global land surface model has four soil levels and the global sea ice model has three layers. The CFSR atmospheric model has observed variations in carbon dioxide (CO2) over the 1979–2009 period, together with changes in aerosols and other trace gases and solar variations. Most available in situ and satellite observations were included in the CFSR. Satellite observations were used in radiance form, rather than retrieved values, and were bias corrected with “spin up” runs at full resolution, taking into account variable CO2 concentrations. This procedure enabled the smooth transitions of the climate record resulting from evolutionary changes in the satellite observing system.

CFSR atmospheric, oceanic, and land surface output products are available at an hourly time resolution and a horizontal resolution of 0.5° latitude × 0.5° longitude. The CFSR data will be distributed by the National Climatic Data Center (NCDC) and NCAR. This reanalysis will serve many purposes, including providing the basis for most of the NCEP Climate Prediction Center's operational climate products by defining the mean states of the atmosphere, ocean, land surface, and sea ice over the next 30-yr climate normal (1981–2010); providing initial conditions for historical forecasts that are required to calibrate operational NCEP climate forecasts (from week 2 to 9 months); and providing estimates and diagnoses of the Earth's climate state over the satellite data period for community climate research.

Preliminary analysis of the CFSR output indicates a product that is far superior in most respects to the reanalysis of the mid-1990s. The previous NCEP–NCAR reanalyses have been among the most used NCEP products in history; there is every reason to believe the CFSR will supersede these older products both in scope and quality, because it is higher in time and space resolution, covers the atmosphere, ocean, sea ice, and land, and was executed in a coupled mode with a more modern data assimilation system and forecast model.

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