Explanations for simultaneous laminae in water vapor and aerosol profiles found during the SESAME experiment

Abstract

An instrumented balloon launched from Kiruna during the SESAME experiment displayedsimultaneous local decreases of water vapor and aerosol at 2 different potential temperaturelevels 410 K and 364 K. Despite the similar characteristics present at both levels, 2 differentexplanations are given for these laminae. At the highest level, the air mass showing the watervapor and aerosol decrease is found when the balloon travels in the vortex edge region. A backtrajectory shows that this air mass was trapped in the vortex edge region for several days andprocessed by a PSC causing the water vapor and aerosol decreases. On the other hand, thelowest level air mass was found to be in the sub-vortex region. No local conditions can explainthe observed decreases of water vapor and aerosol. Back trajectories show that this air massoriginates from middle latitudes. Although the back trajectories calculated in these conditionsare more subject to caution, comparison of several characteristics at the measurement pointand at the middle latitude sites corroborates the explanation of the decrease of water vaporand aerosol by the origin of the air mass.