Cloud-to-ground lightning-precipitation relationships in the South Central United States

Abstract

Despite the general coexistence of cloud-to-ground (CG) lightning and precipitation, there have been few studies on the nature of the relationship between these two phenomena. This study endeavors to explore this relationship, concentrating on three facets: the strength and variability of the linear correlation between the two parameters, and the possible benefits of including additional parameters to this relationship; the differences in several atmospheric and lightning parameters corresponding to differences in the precipitation-to-CG lightning ratio, and the search for an optimal radius for inclusion of CG lightning flashes when comparing them to point precipitation values. Six regions (each on the order of I' latitude by I' longitude) from the states of Nebraska, Kansas, Oklahoma, Texas, and Louisiana are examined. The parameters are examined on daily and/or monthly time scales. This study uses CG lightning data which were recorded by the National Lightning Detection Network (NLDN) during the months of April through October in the years 1989 to 1993. Precipitation data are included from all available first-order, second-order, and cooperative stations. Atmospheric parameters are computed from soundings in the region. A primary tool used in the analyses is the linear regression model for examining linear relations among CG lightning, precipitation, and other parameters. In addition, the t-test and Wilcoxon Rank Sum test are used to discern statistically significant differences in atmospheric and lightning parameters between groups of days categorized by the precipitation-to-CG lightning ratio. The results show that linear correlations between CG lightning and precipitation for a region are highly varied; there are generally higher correlations in regions further away from the Gulf of Mexico. The only parameter which is a significantly beneficial addition to the model which included CG lightning and precipitation is a measure of the amount of positive CG flashes. When days are categorized by a precipitation-to-CG lightning ratio, the percent positive shows the most dramatic differences, with values on "high precipitation-to-lightning" days from roughly five to twelve times the value on "low precipitation-to-lightning" days. Several other parameters show statistically significant differences as well. Lastly, tests on several different radii suggest that there is no consistent optimal radius for CG lightning-precipitation comparisons.