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Page 13 1 Introduction We live in an atmosphere that shapes our activities and states of mind, an atmosphere whose storms threaten our lives and property, and whose climate and composition influence the nature and vitality of our societies. Today we see accelerating progress as the atmospheric sciences develop improved understanding of the atmosphere and thus an increasing capability to help society anticipate atmospheric events. Observational technology and strategies are advancing to provide improved understanding of interactions between the atmosphere, ocean, and land. Enhanced physical and mathematical understanding allows use of increasingly powerful computers to organize observations and convert them into predictions of weather, climate, and air quality. These advances will enable the atmospheric sciences to develop notable new and improved capabilities for serving society these and lead to a vision for the science entering the twenty-first century: Improvements in atmospheric observations, further understanding of atmospheric processes, and advances in technology will continue to enhance the accuracy and resolution of atmospheric analysis and prediction. As a consequence, society will enjoy greater confidence in atmospheric information and forecasts and will be able to act more decisively and effectively. Realizing this vision requires a focus on the observational and modeling infrastructure, on research tasks with the greatest promise, and on mechanisms to ensure that federal investments in atmospheric research and operations are effective and produce results significant to the nation in the early decades of the twenty-first century.

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Page 14 Four Centuries of Progress The theoretical bases of the contemporary atmospheric sciences have been established over the past four centuries, beginning in the seventeenth century with the study of gases and the formulation of Newton's laws of motion and continuing in the late nineteenth century with the formalization of thermodynamics and radiation theory. In North America, the study of meteorology and climate began in the colonial period with Benjamin Franklin's investigation of the passages of large-scale fronts and storms on the East Coast and the relationship of lightning to electricity. Early in the twentieth century, telegraphic transmission of observations and the demands of aviation, agriculture, and other activities stimulated meteorological research and the development of conceptual models of storm and frontal systems that made crude short-range predictions possible. Steady progress ensued, with important advances often arising from technological developments. Contemporary technologies being applied to atmospheric analysis and prediction include remote sensing satellites, radars that measure precipitation and wind, laser systems, and powerful digital computers. The classical cycle continues: observations stimulate theory, and, in turn, theory and new understanding stimulate new observations and new capabilities for understanding and prediction. In recent decades, the emphases in the atmospheric sciences have moved simultaneously in two directions: toward the smaller space and time scales involved with physical processes and toward the larger scales involved in the evolution and prediction of climate and environmental change. Moreover, there is an increasing emphasis on atmospheric chemistry and on the prediction of upper atmosphere processes. In all cases, observations, theory, and computer models combine to provide new understanding and prediction. The Atmospheric Sciences and Other Disciplines To appreciate the key role of the atmospheric sciences in understanding our world, imagine a planet without an atmosphere. The surface is rough and torn, battered by meteor impacts. Ultraviolet radiation and streams from solar flares impinge freely on the surface, making life there impossible. The temperature contrasts between day and night, between equator and pole, are astonishingly large. The differences between this stark planet and our own blue and green Earth arise from the presence of a substantial atmosphere. The atmosphere shelters life on Earth from the hazards of space and provides the global transport system that maintains the resources necessary for life. In addition to addressing their own scientific challenges, the atmospheric sciences illuminate important issues in a range of disciplines, while in turn drawing on these disciplines to create more realistic portraits of the forces and constraints that shape atmospheric behavior.

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Page 15 Oceanography is perhaps the closest scientific partner of the atmospheric sciences. The ocean surface is a critical boundary for the atmosphere, which in turn provides a critical boundary for the oceans. Across their common interface, the atmosphere and ocean exchange energy, momentum, and some important chemical constituents, most notably water in various forms. Because the ocean and atmosphere interact so intimately in shaping and controlling the planetary environment, many major initiatives today concerned with climate and climate change are collaborative efforts between the two sciences. Improved understanding of atmospheric and oceanic circulations has opened new areas of research for the geological sciences by providing independent, physically based climate estimates that stimulate new ideas and validate conclusions. Research in atmospheric chemistry provides new understanding of chemical reactions, sources, and sinks that enhance understanding of the chemical evolution of the planet. Climate conditions shape the distribution of life and must be taken into account by scientists defining optimum conditions and limits of flora and fauna, as species or as ecosystems. Today, human health responses to weather and climate are becoming apparent. Direct connections related to heat stress and respiratory problems are augmented by climate variations that modify disease vectors and affect carriers of infectious diseases. Moreover, both the occurrence of skin cancer and the vigor of immune systems appear to be related to the intensity of ultraviolet radiation reaching the Earth's surface and hence are subject to variations in atmospheric chemical constituents. In 1963, the noted physicist Alvin M. Weinberg argued that the relative scientific merit of disciplines could be assessed by their impact on other disciplines, saying ''that field has the most scientific merit which contributes most heavily to and illuminates most brightly its neighboring scientific disciplines.'' On this basis, the atmospheric sciences stand high among the disciplines that study the Earth and its biological systems. Looking Forward to the Twenty-First Century As the century turns, new areas of emphasis are enriching the atmospheric sciences and sharpening their contributions to society. At the same time, fundamental and worldwide changes in economic activity and public policy are being driven at unprecedented rates by the information revolution. Some aspects of contemporary society are increasingly sensitive to atmospheric events. Thus, timely and accurate information to support critical decisions is increasingly valuable. Moreover, as the Earth's population grows and its economic engines accelerate, human activities may force the atmosphere-ocean-land system in ways and directions that we do not yet completely comprehend. As atmospheric issues become more complex and interdisciplinary, the implications more critical, and federal funds more scarce, it becomes especially

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Page 16 pressing to set priorities for the atmospheric sciences so that they simultaneously develop fundamental understanding and serve national needs effectively. The improved benefits of atmospheric science achieved through the synergy of increasing capability and greater user confidence will be the measure of success as the twenty-first century unfolds.