第2章显式隐式格式.ppt

4、时间的显隐，时间层数;迎风格式（时间向前差，空间向后差）;蛙跳格式（跳背格式）时间、空间均为中央差;隐式差分格式;初边值问题 ;相容性 Consistency ;收敛性convergence ;稳定性 ;;;;拉克斯（LAX）等价定理;CFL判据;五、数值天气预报的概念和历史回顾 ;An initial- and boundary- value problem;An initial- and boundary- value problem;The accuracy of the numerical weather prediction;The inaccuracy of numerical weather prediction ;The accuracy of a numerical method;Another challenge of numerical weather prediction;The early history of Numerical Weather Prediction;Lewis Fry Richardson 1920;forecast factory;后来，有些小进展;1928 Courant, Friedricks and Lewy -- Found that space and time increments in integration of differential equations have to meet a certain stability criterion. 1939 Rossby -- Simplified the governing equations for large scale motion.;John von Neumann and the ENIAC computer.;Charney et al., 1950;The first one-day, nonlinear weather prediction was made in April, 1950. Its completion required the round-the-clock services of the modelers, and, because of several ENIAC breakdowns, more than 24 hours to execute. due to the limited computer capacity, only the most simple of Charneys models could be used, the barotropic equation of atmospheric motion. However, this first forecast was successful in proving to the meteorological community that numerical weather prediction was feasible. ;On July 1, 1954, the Joint Numerical Weather Prediction Unit (JNWPU) was organized, staffed, and funded by the U.S. Weather Bureau, the U.S. Air Force, and the U.S. Navy. for developing operational versions of research model. Using a newly purchased IBM 701, by mid-1955, the JNWPU was issuing numerical weather predictions twice a day.? ;;during the 50s the first operationally useful NWP forecasts were barotropic: in Sweden in 1954 in the US in 1958 in Japan in 1959. Only in 1962 could the US launch the first operational quasi-geostrophic baroclinic model, followed by Britain in 1965. By that time, work was already under way, to introduce more rea