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David S. Battisti, Daniel J. Vimont, and Benjamin P. Kirtman

to the north of the equator in the Atlantic ( Fig. 8-1 ) is presumably the asymmetry in the geometry of Africa and South America ( Privé and Plumb 2007b ). The extraordinary surface heating of the Sahara in summer forces a monsoon circulation that is barotropically and baroclinically unstable ( Burpee 1972 ; see Wu et al. 2012 , and references therein), spawning easterly waves across sub-Saharan Africa that (along with other synoptic disturbances) sum to make a well-defined Atlantic ITCZ in the

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George A. Isaac

Abstract

Any observing program studying summer cumulus clouds should attempt to measure cloud lifetime. This parameter is important for determining whether a cloud will last long enough for precipitation to form by either natural or artificially stimulated mechanisms. When reporting cloud lifetime, the definition used and the method of calculation should be clearly specified. In North America, after a summer cumulus cloud has been identified and selected, lifetimes, at temperatures below –5°C, of approximately 10 to 12 min are being reported. This lifetime must be considered marginal for static mode seeding to produce precipitation by artificial ice nucleants.

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Randall M. Dole

Abstract

Historically, the atmospheric sciences have tended to treat problems of weather and climate separately. The real physical system, however, is a continuum, with short-term (minutes to days) “weather” fluctuations influencing climate variations and change, and, conversely, more slowly varying aspects of the system (typical time scales of a season or longer) affecting the weather that is experienced. While this past approach has served important purposes, it is becoming increasingly apparent that in order to make progress in addressing many socially important problems, an improved understanding of the connections between weather and climate is required.

This overview summarizes the progress over the last few decades in the understanding of the phenomena and mechanisms linking weather and climate variations. The principal emphasis is on developments in understanding key phenomena and processes that bridge the time scales between synoptic-scale weather variability (periods of approximately 1 week) and climate variations of a season or longer. Advances in the ability to identify synoptic features, improve physical understanding, and develop forecast skill within this time range are reviewed, focusing on a subset of major, recurrent phenomena that impact extratropical wintertime weather and climate variations over the Pacific–North American region. While progress has been impressive, research has also illuminated areas where future gains are possible. This article concludes with suggestions on near-term directions for advancing the understanding and capabilities to predict the connections between weather and climate variations.

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Eric G. Hoffman

Abstract

In the last decade, Fred Sanders was often critical of current surface analysis techniques. This led to his promoting the use of surface potential temperatures to distinguish between fronts, baroclinic troughs, and non-frontal baroclinic zones, and to the development of a climatology of surface baroclinic zones. In this paper, criticisms of current surface analysis techniques and the usefulness of surface potential temperature analyses are discussed. Case examples are used to compare potential temperature analyses and current National Centers for Environmental Prediction analyses.

The 1-yr climatology of Sanders and Hoffman is reconstructed using a composite technique. Annual and seasonal mean potential temperature analyses over the continental United States, southern Canada, northern Mexico, and adjacent coastal waters are presented. In addition, gridpoint frequencies of moderate and strong potential temperature gradients are calculated. The results of the mean potential temperature analyses show that moderate and strong surface baroclinic zones are favored along the coastlines and the slopes of the North American cordillera. Additional subsynoptic details, not found in Sanders and Hoffman, are identified. The availability of the composite results allows for the calculation of potential temperature gradient anomalies. It is shown that these anomalies can be used to identify significant frontal baroclinic zones that are associated with weak potential temperature gradients. Together the results and reviews in this paper show that surface potential temperature analyses are a valuable forecasting and analysis tool allowing analysts to distinguish and identify fronts, baroclinic troughs, and nonfrontal baroclinic zones.

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John S. Theon

Abstract

By 1984, more than a decade had passed since the National Aeronautics and Space Administration (NASA) weather and climate program had won approval for a new research mission. There was concern that it would be difficult to justify the budget of the program, so ideas were requested for a new research mission aimed at advancing our understanding of the weather and/or climate. More than a dozen proposals were submitted, including one by North, Wilheit, and Thiele for a mission to observe rainfall directly from space. They called it the Tropical Rainfall Measuring Mission (TRMM).

Studies were conducted to demonstrate that the proposal was feasible by deploying airborne versions of the proposed precipitation radar, microwave radiometer, and visible-infrared radiometer over carefully documented ground-based observations of rainfall. Sampling studies were undertaken to assure that one satellite could adequately sample precipitation events, and advanced mission studies were undertaken to define the mission as well as its cost.

When it became obvious that the cost of the mission would severely limit chances of winning approval, it was decided to invite an international partner to share the cost. With the support of Dr. Bert Edelson, the NASA associate administrator, and through the cooperation of Dr. Nobuyoshi Fugono of Japan, it was possible to study the mission as a joint enterprise. Although the one-year joint mission study concluded that the mission was feasible, obtaining the funding in both countries was anything but simple. When Dr. North decided to leave NASA, Dr. Simpson was suggested as his successor as project scientist. Dr. Simpson's energy and determination were key to winning approval of TRMM by the U.S. Congress. Dr. Simpson had, as President of the American Meteorological Society, briefed Congressman Green of New York on the enormous potential scientific benefits of TRMM. The fiscal year 1991 NASA budget was amended, mandating a new start for TRMM. Once NASA had approval for the mission, Japan agreed to share the costs, and the rest is history. TRMM was launched in 1997 and continues to acquire unprecedented rainfall data on a global scale.

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This appendix is the executive summary of the 2004 Atmospheric Radiation Measurement Program Science Plan: Current Status and Future Directions of the ARM Science Program (DOE/ER-ARM-0402; available online at https://www.arm.gov/publications/programdocs/doe-er-arm-0402.pdf ) sponsored by the U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research. The text has been edited to conform to the style of the American Meteorological Society, but the content is

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J. Verlinde, B. D. Zak, M. D. Shupe, M. D. Ivey, and K. Stamnes

energy imbalance suggested a polar site, an Arctic location was preferred, because the Arctic plays a stronger role in the general circulation than does the Antarctic ( Crowley and North 1991 ). As far back as 1896, the Swedish scientist Svante Arrhenius suggested that changes in Earth’s atmospheric composition would lead to faster changes in the Arctic compared to the rest of the globe ( Arrhenius 1896 ), a process confirmed by general circulation models and now called Arctic amplification [e

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This appendix is the executive summary of the 1996 Science Plan for the Atmospheric Radiation Measurement Program (ARM) (DOE/ER-0670T, UC-402; available online at https://www.arm.gov/publications/programdocs/doe-er-0670t.pdf ) sponsored by the U.S. Department of Energy, Office of Energy Research, Office of Health and Environmental Research, Environmental Sciences Division. The text has been edited to conform to the style of the American Meteorological Society, but the content is otherwise

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John E. Walsh, David H. Bromwich, James. E. Overland, Mark C. Serreze, and Kevin R. Wood

. Using these data, Barry (1967) examined the location of the Arctic frontal zone over North America for January, April, July, and October. Shapiro et al. (1987) more recently presented clear evidence in winter of Arctic jet streams with tropopause folds between the lower Arctic troposphere to the north and the higher Arctic troposphere to the south. These fields are associated with what are now known as tropopause polar vortices ( Cavallo and Hakim 2009 , 2010 , 2012 ). A prominent

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Harold E. Brooks, Charles A. Doswell III, Xiaoling Zhang, A. M. Alexander Chernokulsky, Eigo Tochimoto, Barry Hanstrum, Ernani de Lima Nascimento, David M. L. Sills, Bogdan Antonescu, and Brad Barrett

distances between workers grew. Any work done pre–World War II in Australia, for example, would be unlikely to be noticed by researchers in North America or Europe. 2. The importance of severe convective storm science The impetus for funding abstract research is attributable to the immense societal impact of severe convective storms, in both the damage such storms do and the fatalities and injuries that are inflicted when humans are in the path of severe convective storms. Only part of the economic

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