Automatic recognition of mid-altitude radial convergence and study on the relationship between the convergence and strong convective weather based on Doppler weather radar data

Abstract

To identify the mid-altitude radial convergence of a strong convective weather automatically, we propose a method based on recognition of ‘positive-negative velocity region-pairs’ (region-pairs)in a single elevation angle of the Doppler radar radial velocity image. First of all, according to the principle of the radar detection, this paper explains the phenomenon that the convergence field formed by the airflow must produce a local maximum in positive or negative velocity region in the radial velocity image.The algorithms for recognizing these regions and matching the positive-negative pair are then devised.By searching a set of region-pairs with longitudinal extension, which are obtained from the multiple single elevation radial velocity images, we can judge whether there is a mid-altitude radial convergence in the convective storm, and estimate important parameters, such as the strength and extended thickness of the mid-altitude radial convergence.Finally, we determine the position of optimal section and present the cross-sectional view of the mid-altitude radial convergence. We have tested 384 samples with obvious mid-altitude radial convergence and 365 heavy rainfall samples without obvious mid-altitude radial convergence. Experimental results show that the recognition rate of obvious mid-altitude radial convergence is 100% and the false alarm rate is 0.Compared with the manual way by means of the cross-sectional view, the proposed method in this paper can more rapidly recognize the mid-altitude radial convergence (and reduce the recognition time from minutes to seconds). At the same time, it can present a great deal of quantitative information, including the strength, height, thickness, and position of the mid-altitude radial convergence.Furthermore, it shows the cross-sectional view automatically.We can obtain good results from the comparison between the mid-altitude radial convergence and strong convective weather by using the given parameters.We test and verify the strong correlation between the mid-altitude radial convergence and severe surface wind.Moreover, the height of the strongest mid-altitude radial convergence plays an important role in discrimination of strong hail and torrential rain. Also the strength of the mid-altitude radial convergence can be used to estimate the maximum dimensions of the hail.