A Preliminary Study Of Climate Dynamics Of Summer Subtropical Vortices

Subtropical vortices are multiscale and diverse. Recently, its climate dynamics isgiven more and more attentions. In order to understand the comprehensive climatedynamics of subtropical vortices, this thesis will make investigations on theclimatology of subtropical vortices, the observations and the dynamics of subtropicalvortex self-orgnization.First of all, using a modified vortex detection method which is based onstreamline geometry, the datasets of 1985-2002 summer subtropical vortices at850hPa level are extracted from the ECMWF 40 years re-analysis (ERA40) and theNCEP/NACR re-analysis (NRA) data in four regions, which are the western NorthPacific (NWP), the eastern North Pacific (NEP), the western North Atlantic (NWA)and the eastern North Atlantic (NEA). By utilizing this datasets, we analyzed thespatial and temporal characteristics of subtropical vortex activities. It is shown that: (1)the spatial distributions of ERA40 vortices are well consistent with those of NRAvortices in four regions, especially in the NWP. (2) The vortices spread over wideareas and have the largest mean intensity in the NWP, with two high active centersthere. (3) In all regions, vortices mainly cruise along the coast and in the adjacent seas,from where to the land or to the open sea, vortex activities are decreased gradually. (4)The annual variations of vortex activities are different in four regions. (5) Vortices aredivided into strong and weak types, and the investigations show that: most weakvortices occur in the land and low-latitude areas, while most strong vortices take placein the adjacent seas; except for the NWP, the number of strong vortices has increasingtrend in three other regions; the mean intensity of strong vortices in the NWP andNEP region has an increasing trend, so do the weak vortices in the NEP, NWA andNEA regions.Furthermore, using twelve layers of ERA40 data, the three dimensionaldistributions of vortices in the NWP are explored. The 400hPa level is found to be adivision interface. Blow 400hPa level: the spatial distribution and annual variations of vortex activities just like those at 850hPa level; the 950h～850hPa vortices are themost energetic; except the South China Sea, the rest areas have decreasing vortexactivities; the mean vortex intensity at 1000hPa level has an increasing trend. Abovethe 400 level: the 250h～200hPa vortices are the most vigorous; at all levels above400hPa, vortices mainly spread in the 15°～25°N belt, with the most active areas inthe central Pacific; from 300hPa to 150hPa, the mean vortex intensity has adecreasing trend.Secondly, the self-oganization processes of typhoon "Matsa" are investigatedthrough TBB datasets in genesis periods. The results show that there are multiscaleinteractions betweenγ-scale vortices, betweenβ-scale vortices, betweenγ-scale andβ-scale vortices, or betweenβ-scale vortices and tropical cyclones.Basing on the observations of self-organization and using the Gerris flow solver,which is an adaptive mesh model, the influences of a small system on theself-organization of binary vortices are simulated, through changing three parameters.The three parameters are the position, intensity and structure of the small sytem. Theresults show that: when the initial position of a small vortex is located in a "Z" shapesensitive region, the final state of binary interaction could be altered; the "Z" shapearea is close correlated with the intensity and structure of the small vortex; in order tochange the final state of binary interaction, the small vortex should satisfy fournecessary conditions, which are an initial position in the "Z" shape sensitive region,sufficient intensity, proper distance to binary vortices and a longer life.In the end, by utilizing a high resolution barotropic pseudo-spectral model, thephysical mechanisms are investigated. For the vortex merging, the whole processesare as follows: when the heteroclinic hyperbolic points of the streamfunction in theco-rotating frame enter the vortices, filaments will be expelled in clockwise direction;these filaments form an antisymmetric vorticity field, which produces airflows insidethe vortices that push the vortices into merge. For the influences of a small system onthe binary interaction, the physical process are as follows: when the small system islocated in the positive influencing area of one vortex in initial period, an antisymmetric vorticity field comes into being and inspires airflows whose directionspoint to the other vortex; If those airflows are sufficient strong, they will make thetwo vortices moving to each other and reaching into the merging critical distance in ashort time, which finally cause the coalescence of two vortices and the inverse energycascade.