Transport of Mt. Pinatubo aerosol by tropospheric synoptic-scale and stratospheric planetary-scale waves

The isentropic transport of stratospheric air from the tropics into northern hemisphere mid-latitudes is examined using Mt. Pinatubo aerosol observed by the Improved Stratospheric and Mesospheric Sounder (ISAMS). The technique of contour advection is used to produce high-resolution aerosol gelds which are used to help diagnose transport processes. By sampling the high-resolution contour-advection fields at the satellite measurement points, we show that the small-scale information present in the contour-advection calculation is consistent with the ISAMS measurements. Results of this study indicate that transport from the tropics into mid-latitudes is strongly dependent on altitude. In the lowest regions of the stratosphere, the upward influence of the subtropical jet and the synoptic-scale waves that form on the storm tracks are important in transporting air from the tropics and in the distribution of aerosol in mid-latitudes. Synoptic-scale spirals form in the aerosol field on the 500 K isentrope at the end of storm tracks associated with LCl baroclinic life-cycle behaviour. At altitudes near the 600 K isentrope, direct tropospheric effects diminish and intrusions of air from the tropics to mid-latitudes weaken. At altitudes approaching the middle stratosphere, planetary-wave activity becomes stronger and the associated displacements of the polar vortex to low latitudes produce transport from the tropics, particularly during mid-winter warming events.