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1 Introduction In September 1980, in response to a need expressed by the Associate Admin- istrator of the National Oceanic and Atmospheric Administration, an Ad Hoc Panel on Mesoscale Processes was appointed by the Committee on Atmo- spheric Sciences of the National Research Council. The charge to the panel was to "conduct a brief survey of the current mesoscale meteorological research being conducted throughout the federal government and to develop a preliminary assessment of the adequacy of this research in terms of the important opportunities that exist in this area of scientific endeavor." The panel met twice, once in Princeton, New Jersey, on October 2, 1980, and a second time in Boulder, Colorado, on January 15-16, 1981, and heard exten- sive presentations by representatives of various federal agencies (Appendix A) concerning ongoing and planned mesoscale research. The panel decided to summarize the activities in mesoscale meteorology by agency and by general topic (Chapter 2) to make an assessment of the adequacy of current research, emphasizing the areas that stand out as especial- ly important for more concentrated efforts in the 1980's (Chapter 3) and to make recommendations for the organization of future efforts in this field (Chapter 4). These assessments and recommendations are based on the pre- sentations to the panel during its two meetings and on recent reports of work- shops and panels, especially the following: The Atmospheric Sciences: National Objectives for the 1980's, NRC Commit- tee on Atmospheric Sciences (National Academy of Sciences, Washington, D.C., 1980), 130pp. Atmospheric Precipitation: Prediction and Research Problems, NRC Commit-

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Introduction 3 tee on Atmospheric Sciences (National Academy of Sciences, Washington, D.C., 1980), 63 pp. Extratropical Cyclones: Progress and Research Needs (Report of a Workshop on Extratropical Cyclones held in Seattle, Washington, September 10-12, 1979). Technological and Scientific Opportunities for Improved Weather and Hydro- logical Services in the Coming Decade, Select Committee on the National Weather Service (National Academy of Sciences, Washington, D.C., 1980), 87 pp. An important recommendation from the first report concerned short-range prediction of precipitation and severe weather: Recent technological developments provide opportunities to improve both special and general local weather forecasts, from less than an hour to 12 hours in advance, which are of particular value during periods of weather that threaten life and property or disrupt normal commerce and transporta- tion. These developments include higher-resolution satellite imagery, Doppler radar, acoustical probes, and other remote sensing devices; improved methods of communicating and analyzing these observations; and emerging techniques for the rapid dissemination of forecasts and warnings to special users and the general public. This new technology can and should be used simultaneously for intensive study of fundamental meteorological processes occurring on the local scale and for the development of kinematic, dynamic, and statistical methods for local forecasting that can lead to additional benefits to the public. A well- focused, coordinated program, involving research, development, and pilot operations, should be conducted by government operational and research groups and those university groups that are involved in research in this area. Prediction of wind and temperature fields up to 48 hours over the United States have steadily improved over the past two decades. There has been some improvement in predicting the areas in which precipitation will occur during the next 24 hours; this improvement has come most recently from develop- ment and use of high-resolution numerical models over limited geographical regions. However, there has been less success in predicting amounts of pre- cipitation or the times of onset and cessation. Research should now be con- centrated on (a) theoretical and modeling studies, using existing observing capabilities and special field programs to investigate the mesoscale structure and dynamics of midlatitude winter cyclones and to determine the extent to which prediction of amounts of rain or snow can be improved, and (b) major field experiments, with special observing networks of finer scale than are rou- tinely provided by the National Weather Service, to identify the factors that force the outbreak and control the intensity of severe convective storms and

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4 CURRENT MESOSCALE METEOROLOGICAL RESEARCH storm systems that occur most often in spring and summer. These two research areas will require expanded computing and graphical display capabilities. In support of the above assessment, the second report concluded: WE RECOMMEND A MAJOR, COORDINATED NATIONAL MESO- SCALE RESEARCH PROJECT TO STUDY MECHANISMS INVOLVED IN THE FORMATION OF PRECIPITATION IN BOTH SUMMER ANDWINTER STORMS IN VARIOUS REGIONS OF THE NATION. Many of the problems involved in the understanding and forecasting of pre- cipitation that are highlighted in this report are concerned with mesoscale processes. The frequency of occurrence and relative importance of various physical mechanisms that produce mesoscale precipitation phenomena vary over the United States and with the seasons. A central feature of a national mesoscale research project should be comprehensive field observational studies to take place periodically at selected sites. While emphasis should be placed on the mesoscale, associated synoptic and microscale studies will be necessary. We envision the national mesoscale research project to be a closely coordinated research endeavor involving federal agencies, universities, and other research establishments and carried out over the next decade. Finally, the workshop on extra tropical cyclones recommended a long-term effort consisting of coordinated basic and applied research to achieve the above objectives: In view of the range of problems hindering progress in our understanding and prediction of the weather (particularly precipitation) associated with extra- tropical cyclones, the workshop recommended the establishment of a NA- TIONAL CYCLONE PROJECT to extend over a period of ten years. Encour- agement that a national program dedicated to the cyclone problem would be profitable in terms of improved understanding and better weather forecasts stems from several considerations. Firstly, there are powerful observational techniques that could be more effectively directed toward the mesoscale pre- diction problem. Secondly, the progress that has been made in recent years in mesoscale and microscale studies and in fine-mesh numerical modeling is such that a more concentrated and coordinated effort in these areas is likely to produce impressive results. Thirdly, the availability of faster communication systems and more adequate displays of information permit more detailed in- formation to be assimilated, utilized and passed on to the public, than ever before. The NATIONAL CYCLONE PROJECT should involve the federal, univer- sity, and private sectors of the meteorological community and the National Center for Atmospheric Research. It should be assured of consistent support on a level commensurate with the tasks it would undertake.

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Introduction 5 These reports provide details of important mesoscale meteorological prob- lems, with scientific justification that the time is ripe for significant progress in areas that will provide important economic and safety benefits to the United States in the near future. In general, we endorse their recommenda- tions and urge the relevant government agencies and the other sections of the scientific community to work together in an efficient way to solve the im- portant problems. An overriding property of the atmosphere is its indivisibility, which leads to difficulties in subdividing atmospheric research. Thus, an attempt to sepa- rate mesoscale meteorology from other parts of atmospheric science cannot be fully justified, since many of the processes that control mesoscale events also affect larger- and smaller-scale processes. In addition, atmospheric scien- tists are inclined to separate themselves more by the techniques that they have mastered than by the phenomena to which they apply the techniques. Finally, there is the usual dichotomy, especially strong in the geophysical sciences, between those who divide a problem into conquerable bits and those who approach it holistically. However, no field of science progresses uniform- ly, and we believe that some current trends can be defined fairly unambigu- ously. The next chapter summarizes the types of mesoscale meteorological re- search that are necessary to mount a coordinated effort to solve the com- plicated scientific and technological problems that stand in the way of pro- viding the public with information they can effectively use to save life and property when severe weather threatens or make economically profitable de- cisions in the more common situations of daily weather events. Current, major research efforts in mesoscale meteorology are summarized according to the organization supporting or conducting the research and also by the type of research.