Tropical aerosol in the Aleutian High

Stratospheric aerosol profiles at high northern latitudes from the Stratospheric Aerosol Measurement (SAM) II experiment are used to document the aerosol maxima that occur in the major wintertime anticyclones. Fourteen years (1978-1991) of 1 mu m extinction are used to calculate median values for each season in bins of 5 degrees latitude by 30 degrees longitude by 1 km altitude. Longitude-altitude sections of estimated surface area density show that tropical, aerosol rich air tends to accumulate in the Aleutian High from 15 to above 30 km, and in the North Atlantic High in the 15-25 km layer. A trajectory case study with winds from the European Center for Medium-Range Weather Forecasting is used to investigate the hypothesis that the observed aerosol maxima are maintained by episodic poleward surges of high aerosol air from the tropical stratospheric reservoir. Lagrangian trajectories are initialized and run backward in time, from both a high-resolution grid and SAM II occultations, for selected days when high aerosol is found in the Aleutian High. Results show that during the case study provided, a deep sheet of aerosol rich air originating over Africa is advected poleward and eastward around the polar vortex and entrained into the Aleutian High.