Observational evidence of horizontal transport-driven dehydration in the TTL

Analysis of this data set verifies key hypotheses in Lagrangian simulations of TTL transport and freeze drying. Furthermore, the observations provide a number of new insights into the transport process: In the layer below the lapse rate tropopause, vertical transport from upward motion dominates the relative humidity structure; final dehydration, dominated by large-scale horizontal advection, occurs in the layer transacting the cold point tropopause that is often above the lapse rate tropopause, resulting in water vapor mixing ratios with corresponding frost points consistent with the coldest temperatures of the region, lower than the temperatures of the local cold points.