Tropical aerosol in the Aleutian High

Stratospheric aerosol profiles at high northern latitudes from the Stratosp heric Aerosol Measurement (SAM) II experiment are used to document the aero sol maxima that occur in the major wintertime anticyclones. Fourteen years (1978-1991) of 1 mu m extinction are used to calculate median values for ea ch season in bins of 5 degrees latitude by 30 degrees longitude by 1 km alt itude. Longitude-altitude sections of estimated surface area density show t hat tropical, aerosol rich air tends to accumulate in the Aleutian High fro m 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-Rang e Weather Forecasting is used to investigate the hypothesis that the observ ed aerosol maxima are maintained by episodic poleward surges of high aeroso l air from the tropical stratospheric reservoir. Lagrangian trajectories ar e initialized and run backward in time, from both a high-resolution grid an d 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 she et of aerosol rich air originating over Africa is advected poleward and eas tward around the polar vortex and entrained into the Aleutian High.