Negative Index Of Mid-latitude Circulation And Blocking The Process Of Research

A new regional circulation index is defined in this dissertation. It is calculated at daily 500hpa height field. The transition of the index of certain regions from positive to negative means the changing of the mid-latitude atmosphere circulation from zonal flow pattern to meridianal circulation pattern. So the new index is a development of those zonal index/annular mode index. While the new index not only concerns the situation of the whole latitude circle, but also it can reflect the regional pattern of the meridianal circulation by the negative index area in the index field. The experience of a certain region from positive index to negative index then back to positive index is called as "negative index process". The process begins at the first appearance of negative index on a certain grid point and terminates at the last time the negative index occurring at that grid point. According to the conception of negative index process, one could take out a collection of local circulations from the profound mid-latitude westly band atmosphere motions.Firstly, the whole collection of the mid-latitude regional circulations is considered. A statistic is made about the geographical distribution, strength/amplitude, persistence properties and the annual cycle of the negative process around the whole north hemisphere mid-latitude area. Analysis shows that of the whole collection of the negative process one main kind of the negative index process has a certain long duration and considerably big magnitude, and negative index process longer than 5 days has a good resemble to atmospheric blocking.Then, based on the conception of negative index, a new blocking index is put forward. A Comparison has been done between the new blocking index and the others blocking index defined by former researchers, which shows that the new blocking index can depicture blocking events better at many aspects than the former ones. By means of the new blocking index, all blocking events are selected from the 42-year long data, a statistic of the strength, occurrence perturbation and the long term variations is done.Since the negative index can discover the key area of blocking region, a case study of the persistent negative index pattern process or blocking event has been performed, which studied the flow field and temperature field characters and fluxing properties of the key area and the four directions around area, gives a clear picture of the blocking, and tells the location of the sensitive heat and vorticity sources.Besides, a mechanical study of the interactions between the planetary-scale part of blocking flow and the synoptical-scale transient eddies has also done to study the role of the topography forcing induced type blocking in causing the pole-ward deflection of storm-track.A diagnose has also been done to discus the different roles played by different interactions between large scale and small scale waves in effecting the life cycle of blocking.