Estimates for the Probabilities of Surface-to-Air Cloud-Free Lines-of-Sight and Low Cloud Statistics from Ship Observations. Part 1. Fifteen Marine Locations.

Abstract : Estimates of the probability of cloud-free lines of sight (PCFLOS) were calculated for a set of nine angles using a modification of Lund and Shanklin's universal method from lower cloud weather data taken at fifteen marine locations. The data compilation covers periods from five to seven years (1964-1971) and provides statistics for seasonal variations of lower cloud base heights and cover and low cloud type and cover. Both the seasonal weather data (winter, spring, and summer) and the PCFLOS are tabulated for each location for nine different elevation angles from 10 to 90 degrees above the horizontal and for the heights for which lower cloud base data were available. The main assumption of the unmodified method, which is fully described in the text, is that the universal method can be applied successfully to the statistics for individual low cloud base height recording cells. Intermediate computational results corresponding to base height cells and the values of PCFLOS through all clouds, calculated by the unmodified method. Data from four selected locations were plotted for illustration and comparison purposes. PCFLOS statistics for various angles and cloud base heights were related to ability to visually detect targets at various ranges, altitudes, and elevation angles, by means of graphs that precalculated the slant range. A summary of the weather statistics and PCFLOS for all stations is also included. (Author)