Estimation of melody line in homophonic music audio signals is a challenging subject of study. Some of the difficulties are derived from presence of accompanying components. To overcome those difficulties, we propose a method to enhance melodic components in music audio signals. The enhancement algorithm uses fluctuation and shortness of melodic components, which we call temporal-variability. We also discuss a melody tracking algorithm, which can be simple thanks to the preprocessing. In this paper, we describe the enhancement method and tracking method, and show the experimental results that supports the efficiency of our methods.