第二章显式隐式格式.pptVIP

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 realistic numerical models, based on the primitive equations (PE). Increases were also made in the number of vertical levels and the horizontal resolution of the models. 1962: A 3-level baroclinic filtered-equation (geostrophic) model became operational. 1966: A 6-level, hemispheric, primitive equation (PE) model became operational. The first global PE model began operating in 1966 at NMC Washington, with a 300 km grid and six-layer vertical resolution. 1971: The Limited-area Fine-Mesh (LFM) model was introduced in NMC. The horizontal resolution in North America is significantly increased. The Nested-Grid Model (NGM) also became operational later. The late 1970s and the 1980s saw the introduction of the use of spectral coordinates and advances in methods of data assimilation and more accurate representation of physical processes in the atmosphere such as the formation of clouds and precipitation.? During the 1990s, models of finer and finer scales were developed.? ensemble modeling(集合预报) A more recent addition to the numerical weather prediction suite of products is “ensemble modeling.”? With ensemble modeling, many forecasts are run with slightly varying initial conditions from different models and an average, or ensemble mean, of the different forecasts is created.? This ensemble mean can extend forecast skill to the two-week range because it averages over the many possible initial states, to essentially “smooth” the chaotic nature of the atmosphere. In addition, this technique provides information about the level of uncertainty for different conditions because of the large ensemble of forecasts available.