Spatial-Temporal Characteristics Analysis For The Possibility Of Extended-range Forecast

In this thesis,36 years of data including 200hPa,500hPa and 850hPa geopotential height fields and sea surface temperature fields from NCEP/NCAR are utilized to analyze the seasonal change characteristics and spatial distribution characteristics of contribution percentages made by disturbed quantity variations in two bands of 11 to 25 days and 29 to 59 days globally in different seasons; and EOF method is utilized to analyze the correlation between the seasonal changes of the disturbances of the two bands over Eurasia continent and North American continent and the northern hemisphere SST. The analyses show clear temporal changes in the contribution rate made by the disturbance energy of the two bands to total variance, and preliminary SST anomalies in different sea areas corresponding to the disturbance energy in different seasons. It is concluded in the study that there is a close relationship between the weather changes in extended-range time scale and the abnormal thermal forcing of certain sea areas in different seasons. Results of this study are conducive to a deeper understanding of the physical mechanism of extended-range weather forecast changes and can provide valuable analytical thinking for actual forecasting and referenced key sea areas for forecasting. The main findings are as follows:1. At the same height level, the variance contribution of geopotential height disturbance in the time scale of 11 to 25 days is greater than that in the time scale of 29 to 59 days. In the same season, the spatial distribution pattern of variance contribution of intermediate level and high level is similar, with near-barotropic structure. High-latitude variance contribution is greater than that in low-and-middle latitude regions. The variance proportion of tropical and subtropical regions in equatorial north and south is minimum, the main differences between the lower atmosphere and middle and upper atmospheres are shown in areas near the equator. In lower atmosphere, the variance of some areas on both sides of the equator contributes greatly. In the same meteorological element field, the variance contribution of different band disturbances in middle and high latitudes is generally greater than that in low latitudes. The distribution of variance contribution is closely related to forced weather system. And the variance contributions of Alaska forced ridge area are obvious.2. Northern Hemisphere sea surface temperature anomalies is significantly correlated with atmospheric low-frequency disturbances. In different seasons, the locations of sea areas affecting atmospheric low-frequency oscillations of different areas are different. The correlation of the band of 11 to 25 days with SST anomalies is significantly better than the band of 29 to 59 days; the relationship between the marine factors in the fall" and the low-frequency disturbances in North American is obviously stronger than Eurasian continent; but in winter and spring, ocean thermal anomaly and low-frequency disturbances in Eurasian continent are closely associated.3. The analysis on the average disturbance energy of the two bands for years showed that the strength of disturbance amplitude at different stages of different seasons varies, which hinted at a possible close relationship between the activity of disturbances with seasonal changes.By analyzing the spatial and temporal variation characteristics of energy contribution made by atmospheric low-frequency waves and analyzing the relationship between the low frequency disturbance energy over the land of Northern Hemisphere in different seasons with the prophase SST anomalous field, the suggestions can be obtained that for extended-range forecasts, not only the internal dynamic process of the atmosphere but also the impact of abnormal marine thermal forcing should be considered. That is, in addition to the full consideration of the dynamic processes in the atmosphere, the impact of seasonal factors on low-frequency oscillations, characteristics of spatial location, and the impact of thermal forcing of key sea areas in different seasons should be taken into account for making forecasts in extended range.Although the work in this thesis yet give specific forecast indicators, qualitative estimation of the spatial distribution characteristics and seasonal changes of extended-range forecast effects can be made by studying the temporal and spatial variation of atmospheric low-frequency signals in different seasons. And according to the key sea areas affecting the extended-range time scale of Eurasian continent and North American continent, valuable research foundation for further research on the physical mechanism of the marine influence on extended-range time scale changes can be provided. The application values of the study in the thesis are to determine the possible forecasting effect of extended-range time scale with seasons, to make forecasts of output products with a combination of numerical model, to comprehensively analyze forcing factors, and to improve the effect of weather forecasts in extended range.