Arctic stratospheric dehydration - Part 1: Unprecedented observation of vertical redistribution of water
We present high-resolution measurements of water vapour, aerosols and\nclouds in the Arctic stratosphere in January and February 2010 carried\nout by in situ instrumentation on balloon sondes and high-altitude\naircraft combined with satellite observations. The measurements provide\nunparalleled evidence of dehydration and rehydration due to\ngravitational settling of ice particles. An extreme cooling of the\nArctic stratospheric vortex during the second half of January 2010\nresulted in a rare synoptic-scale outbreak of ice polar stratospheric\nclouds (PSCs) remotely detected by the lidar aboard the CALIPSO\n(Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation)\nsatellite. The widespread occurrence of ice clouds was followed by\nsedimentation and consequent sublimation of ice particles, leading to\nvertical redistribution of water inside the vortex. A sequence of\nballoon and aircraft soundings with chilled mirror and Lyman-ff\nhygrometers (Cryogenic Frost-point Hygrometer, CFH; Fast In Situ\nStratospheric Hygrometer, FISH; Fluorescent Airborne Stratospheric\nHygrometer, FLASH) and backscatter sondes (Compact Optical Backscatter\nAerosol Detector, COBALD) conducted in January 2010 within the LAPBIAT\n(Lapland Atmosphere-Biosphere Facility) and RECONCILE (Reconciliation of\nEssential Process Parameters for an Enhanced Predictability of Arctic\nStratospheric Ozone Loss and its Climate Interactions) campaigns\ncaptured various phases of this phenomenon: ice formation, irreversible\ndehydration and rehydration. Consistent observations of water vapour by\nthese independent measurement techniques show clear signatures of\nirreversible dehydration of the vortex air by up to 1.6 ppmv in the\n20-24 km altitude range and rehydration by up to 0.9 ppmv in a 1 km\nthick layer below. Comparison with space-borne Aura MLS (Microwave Limb\nSounder) water vapour observations allow the spatiotemporal evolution of\ndehydrated air masses within the Arctic vortex to be derived and\nupscaled.