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

An instrumented balloon launched from Kiruna during the SESAME experiment d isplayed simultaneous local decreases of water vapor and aerosol at 2 diffe rent potential temperature levels 410 K and 364 K. Despite the similar char acteristics present at both levels, 2 different explanations are given for these laminae. Ar the highest level, the air mass showing the water vapor a nd aerosol decrease is found when the balloon travels in the vortex edge re gion. A back trajectory shows that this air mass was trapped in the vortex edge region for several days and processed by a PSC causing the water vapor and aerosol decreases. On the other hand, the lowest level air mass was fo und to be in the sub-vortex region. No local conditions can explain the obs erved decreases of water vapor and aerosol. Back trajectories show that thi s air mass originates from middle latitudes. Although the back trajectories calculated in these conditions are more subject to caution, comparison of several characteristics at the measurement point and at the middle latitude sires corroborates the explanation of the decrease of water vapor and aero sol by the origin of the air mass.