It is becoming increasingly evident that clouds and precipitation play a critical role in many of the environmental or so-called ``strategic'' issues facing our society today, such as the ``ozone hole'' problem, climate change, ocean-atmospheric interactions and acid rain. Clouds and precipitation also play an important role in many applied problems such as aircraft icing and short-term forecasting. Solutions to these and other problems will require a deeper understanding of how clouds form, evolve and impact their surroundings. Scales associated with cloud formation range from the size of a sub-micron aerosol particle to the scale of a large hurricane. Scientific studies during the last four years have reaffirmed the notion that in order to adequately understand the role of clouds in these strategic and applied problems, fundamental studies on all scales important to cloud formation and evolution are required.
Papers in cloud physics during the last four years have been nearly equally divided between fundamental studies, applied studies, and studies related to strategic problems, and have spanned the range of scales mentioned above. As a result, a review of cloud physics will cover a wide range of topics and a large number of papers. In order to keep this review to a reasonable size and yet reflect the balance mentioned above, it was necessary to exclude some studies. The papers presented represent the key papers in theoretical and observational cloud physics in the opinion of this author published during the last four years. Studies conducted by U.S. scientists have been emphasized, although some important non-U.S. work has also been included as appropriate. The format followed is similar to that of the last review by Cooper [1991] in order to provide some continuity.
Laboratory cloud physics during the last four years is reviewed by Hallett [1995] in this issue. The reviews by Businger, Smull, Moeng and Lemone, Stephens, Cyzs, Kreidenweiss, Penner, Toohey, and Beasley contain additional information on aspects of cloud physics related to cold and warm mesoscale systems, boundary layer processes, radiation, weather modification, aerosols, tropospheric chemistry, stratospheric chemistry and lightning, respectively.