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Dehydration in the Antarctic winter stratosphere is a well-known phenomenonthat is annually observed by satellites and occasionally observed byballoon-borne measurements. However, in situ measurements of dehydrated airmasses in the Antarctic vortex are very rare. Here, we present detailedobservations with the in situ and GLORIA remote sensing instrument payloadaboard the German aircraft HALO. Strongly dehydrated air masses down to1.6 ppmv of water vapor were observed as far north as 47° S inan altitude between 12 and 13 km in the lowermost stratosphere. Thedehydration can be traced back to individual ice formation events above theAntarctic Peninsula and Plateau, where ice crystals sedimented out and watervapor was irreversibly removed. Within these dehydrated stratospheric airmasses, filaments of moister air reaching down to the tropopause are detectedwith the high-resolution limb sounder, GLORIA. Furthermore, dehydrated airmasses are observed with GLORIA in the Antarctic lowermost stratosphere downto 7 km. With the help of a backward trajectory analysis, a midlatitudeorigin of the moist filaments in the vortex can be identified, while the dryair masses down to 7 km have stratospheric origins. Antarcticstratosphere–troposphere exchange (STE) and transport of dehydrated airmasses into the troposphere are investigated. Further, it is shown that theexchange process can be attributed to several successive Rossby wave eventsin combination with an isentropic exchange of air masses across the thermaltropopause. The transport into the troposphere is caused by air masses thatare detached from the potential vorticity (PV) structure by Rossby wave breaking events andsubsequently transported diabatically across the dynamical tropopause. Oncetransported to the troposphere, air masses with stratospheric origin canreach near-surface levels within several days

Transport of Antarctic stratospheric strongly dehydrated air into the troposphere observed during the HALO-ESMVal campaign 2012