Climatic change in mixed-layer trajectories over large regions

Summary Using a modified version of the NOAA ARL/ATAD model, a series of over 300,000 mixed-layer back trajectories were calculated in eighteen hour time steps through the period 1948–1985 for seventeen trajectory endpoints in and around the state of Virginia. Results of these trajectory runs were aggregated both seasonally and annually to a spatial grid system covering approximately the eastern two-thirds of the United States. From this were generated plots of trajectory frequencies, residence times and transport times. A principal components analysis was performed on the spatial distribution of the gridded trajectory frequency data. The first principal component is dominated by mixed-layer-flow from the Ohio Valley and the Upper Midwest. A time-series plot of this component indicates a dramatic increase in this northwesterly flow over the study period, especially in the 1950s and early 1960s. A possible link between this observed phenomenon and anthropogenic climate alteration is discussed.With 7 Figures