By using NCEP/NCAR reanalysis products to forecast the nonlinear evolution of the spatial and temporal characteristics, the results shows that on the Spatial dimensions, NCEP ensemble forecast that the products of nonlinear evolution have obvious zonal features. The overall distribution situation is the nonlinear evolution of the southern hemisphere, which is larger than that of the northern hemisphere. In the same hemisphere, low value area is near the equator, and high value area for middle and high latitude area. On the time dimension, the nonlinear evolution of NCEP ensemble prediction products will increase with the extension of the forecast period. In addition, the nonlinear evolution of NCEP ensemble forecast products in North America is greater than the Asian region.
Ensemble forecast can convert traditional deterministic prediction to multiple values of probability forecast, and provide a method that can be used to estimate the uncertainty of forecasts. NECP ensemble forecasts show that the atmosphere has an initial value of uncertainty. This concept breaks the traditional concept of numerical prediction to the initial value. Ensemble forecast not only can estimate the uncertainty of the initial value, but also can use patterns which are better than the method of physical process and numerical model on the estimation of uncertainty. In a word, ensemble forecast can effectively compensate the defects of single deterministic prediction [
The nonlinear Evolution of NCEP ensemble forecast products will affect the effect of forecast based on the above products [
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To calculate the nonlinear evolution characteristics and save computing resources, in this section, the NCEP/GEFS early 500 hpa height field forecast data every day are selected, and selecting only data of forecast starting time is day 00 to analysis. For each forecast starting moment, forecast memberships are 12, No. 1 - 12. Among them: No. 1 member of GFS hi res ens_control; No. 2 member of GFS low res ens_control; No. 3 ~ 12 members of 5 disturbance forecast (ens_perturbation = + 1, 1, +, − 2, + 3, 2 − 3, + 4, 4, + 5, 5), forecast step and resolution of this 10 ensemble members are same as the No. 2 member. The research objects of this section for the collection of disturbance forecast members, are named 3 - 12 members. In order to facilitate for statistical analysis, trailer step of Members are united to 12 hours in this section. Prediction time of Members are united to 0 - 384 hours (i.e., 0 - 16 days). Horizontal resolution is united to 2.5˚ × 2.5˚ latitude and longitude. In this way, to forecast the starting moment, each set disturbance forecast members have 33 times forecast fields around the world. Each global forecast field is 144 × 73 = 10,512 grid points.
In NECP Ensemble Prediction System, undisturbed field adding and subtracting the perturbation field can constitute a set composed of members of the initial field. In the process of forecast, it will work with members of a collection of the initial field in pairs and corresponding pairs of two prediction field in arithmetic average. Their linear growth will be offset; the rest will remove forecast average field again; then we can get the results of the nonlinear [
The annual average nonlinear evolution of global range forecast for the 3 day (
in the northern hemisphere near to the Bering strait, Alaska and the North Pacific and North Atlantic near to Iceland, the British Isles, high value area in the southern hemisphere is mainly located in the ocean near the Antarctic continent, and to the north and south on both sides of the decreasing. In other areas, the northern hemisphere is a more uniform zonal distribution. The southern hemisphere is obvious zonal zonal distribution. Also it can be seen from the picture. When forecasting aging for 3 days, the nonlinear evolution of the southern hemisphere is larger than that of the northern hemisphere.
Then looking at the global annual average 7 days forecast limitation of nonlinear evolution (
Above, the global scale nonlinear evolution feature analysis found that different regions of nonlinear evolution characteristics were not the same, which were largely in the southern hemisphere ocean nonlinear evolution of maximum, but the regions as a result of forecast service object are little than NCEP set focused on the application of forecast products area. NCEP ensemble forecast products in the northern hemisphere are more densely populated, which aggregate large Asian and North America and are used most widely. Therefore, the analysis and comparison of NCEP ensemble prediction products in the two regions of nonlinear evolution are very necessary.
First of all, from the 3 days of the forecast period for the Asian region of the nonlinear evolution of the annual average distribution of the situation (
Asian region is from the southwest to the northeast direction. Most of our country is located in low value areas, only in North China and Northeast China. North America annual average forecast period for 3 days of nonlinear evolution of distribution (
Forecast time for 7 days in Asia nonlinear evolution of annual average distribution (
parts of the south the evolution of nonlinear is located in low value area. For North America forecast period for 7 days, the annual average nonlinear evolution is shown in
In order to make a more intuitive analysis of the nonlinear evolution in different regions of the world, this section will use the nonlinear evolution to calculate and draw a one-dimensional curve (
In this paper, the NCEP/NCAR reanalysis data are used to predict the nonlinear evolution of its spatio-temporal features. At present, the development of ensemble forecasting system is at a relatively preliminary stage all over the world. The results of this paper are of great theoretical significance not only for the understanding of the initial and lateral boundary perturbation methods for ensemble forecasting of convective scales, but also for the future development of this type of business System providing a certain basis. The results are as follows:
1) In space dimension, the NCEP ensemble prediction shows that the nonlinear evolution products have obvious zonal characteristics. The overall distribution is the nonlinear evolution in the southern hemisphere, larger than the
northern hemisphere. In the same hemisphere, the low value region is near the equator and the high value region is at the middle and high latitude region.
2) In the time dimension, the nonlinear evolution of NCEP ensemble forecasting products will increase with the forecasting period. In addition, the nonlinear evolution of NCEP ensemble forecasting products is smaller in North Asia than in North America, and the non-linear evolution in summer in Asia and North America is small.
3) The NCEP set average forecast has better forecast consistency than the corresponding control forecast. Aggregate average forecast can effectively reduce the occurrence of forecast jump. When the forecasting time exceeds 240 h, the average forecast jump index of the set average forecast is usually only 25% - 50% of the control forecast, which greatly increases the forecast stability. The frequency of forecast jumping in summer fluctuated at 17.5%, which was not significantly different from the annual frequency range (10% - 20%).
Li, Y. and Zhang, X.K. (2018) Nonlinear Evolution Characteristics of the NCEP Ensemble Forecast Products. Atmospheric and Climate Sciences, 8, 337-343. https://doi.org/10.4236/acs.2018.83022