Application of a Three-Dimensional Model to the Calculation of Trajectories: A Case Study

Abstract

A complex winter storm occurred in eastern United States on 14–15 January 1980. During its passage, five sequential samples of precipitation were collected at State College, Pennsylvania as part of an intensive study of the storm by the Dept. of Meteorology at the Penn State University. Twenty four-hour back trajectories from State College were calculated for each precipitation sample, using the horizontal and vertical winds predicted by a 3D numerical primitive equation model. The source regions of the precipitating atmosphere were then compared with some chemical properties of the rainfall. The rainfall samples were analyzed for the following ions: hydronium (H₃O⁺), sulfate (SO₄ ⁼), nitrate (NO₃ ⁻), chloride (Cl⁻) and sodium (Na⁺) among others. Some of the concentrations changed significantly during the period of the precipitation event. Of perhaps greatest interest is the ratio of Cl⁻ to Na⁺ (Cl⁻/Na⁺) which decreased from values of 0.9 and 1.15 near the beginning of the event to less than 0.6 during the sampling period of about 12 h. Because the Cl⁻/Na⁺ ratio in the sea water is 1.18, the data suggest a source region which changes from maritime to continental during the observation period. The transport model results support this hypothesis.