Simulation of a Stratospheric Intrusion Using the Lagrangian Particle Transport Model FLEXPART, Combined With Observed Surface Impacts Over the United States in Early May 1999

This paper reports observations and a model simulation of an exceptionally-strong tropopause fold in early May 1999 which impacted the surface of Colorado and the south-central United States. The model simulation was performed using a special version of the Lagrangian particle dispersion model FLEXPART, which revealed the evolution of the fold eastward across the United States during the subsequent week. This intrusion was recorded by the NOAA Fritz Peak (40N, 105W) DIAL ozone lidar on May 6. Its subsequent path has been inferred from high ozone values in the AIRS data network, and using altered water vapor (AWV) imagery, a linear modification of the GOES water vapor channel which depicts specific humidity in the mid- and upper troposphere.