ATMOSPHERIC TRANSPORT PROCESSES 451 Fig. 1—Pattern of radioactive fallout intensities (pe/m* of dry air) observed over the United States ina 24-hyr sampling period ending at approximately 15 GCT,Nov. 25, 1962. Lightly hatched regions indicate precipitation during the 24-hr period ending at 0600 GCT of the same day, as reported in the “Daily Weather Map’’ of the U. S. Weather Bureau. The dark belts outline vegions in which the reported debris age is less than 15 days. contaminated air was traced along isentropic surfaces for the period of time for which diabatic effects were assumed to be negligible. TRANSPORT OF DEBRIS BY LARGE-SCALE ATMOSPHERIC MOTIONS Mechanism of Downward Transport For adiabatic flow conditions in a coordinate system with potential temperature, 6, as the vertical coordinate, the vorticity equation aw ow =— — Q=-DQ +4, — 55 t Way where Q = the vertical component of absolute vorticity D = the divergence q, and q, = the horizontal components of relative vorticity w = the vertical displacement 1 (1)