Analysis of regional visibility in the Southwest using principal-component and back-trajectory techniques

Abstract Approximately 3 years of visibility data from a 13-station teleradiometer network in the southwest desert is the basis for the analysis presented. Principal component analysis is employed to identify regions of similarly varying visibility for the enitre data set and by seasons. ‘North’, ‘Center’ and ‘South’ regions are identified in each of the four seasons. These regions change their size, shape and location somewhat through the seasons and thus are referred to as groups with each group containing four seasonal regions. Distinctive mean visibility levels and variations characterize the three groups. Back trajectoryanalysis techniques are developed to infer the nature and extent of influence of upwind areas on the three visibility groups. Two years of four daily back trajectories indicate primary detrimental influence from the southwest for the ‘North’ group and from the southeast for the ‘South’. Areas influencing the ‘Center’-group visibility are a combination of those affecting the other two groups. A method to calculate transport extinction budgets is demonstrated for the three visibility groups.