Description of Nowcasting Algorithm Celltrack and Evaluation of its Performance

CELLTRACK algorithm, that will be described in this contribution is member of category of radar cell-tracking nowcasting algorithms. Meteorological radar measures radar reflectivity, therefore the term reflectivity core is more appropriate instead of the term convective cell. Reflectivity core identification is based on single minimum thresholding of maximum reflectivity data. Wind field from area-tracking nowcasting algorithm COTREC is used as a first guess by reflectivity core assignment in subsequent images. Splitting and merging of cores are also considered within the reflectivity core assignment algorithm. Simple calculation of core motion vector from reflectivity core centres displacement is too inaccurate. Thus, to calculate core motion vector, special local similarity algorithm is applied on each assigned reflectivity core pair. The paper describes algorithm CELLTRACK, typical difficulties in reflectivity core identification and shows evaluation of the algorithm performance. Comparison with algorithm COTREC operationally implemented in the Czech Hydrometeorological Institute is showed.