Arctic stratospheric dehydration - Part 2: Microphysical modeling
Large areas of synoptic-scale ice PSCs (polar stratospheric clouds)\ndistinguished the Arctic winter 2009/2010 from other years and revealed\nunprecedented evidence of water redistribution in the stratosphere. A\nunique snapshot of water vapor repartitioning into ice particles was\nobtained under extremely cold Arctic conditions with temperatures around\n183K. Balloon-borne, aircraft and satellite-based measurements suggest\nthat synoptic-scale ice PSCs and concurrent reductions and enhancements\nin water vapor are tightly linked with the observed de-and rehydration\nsignatures, respectively. In a companion paper (Part 1), water vapor and\naerosol backscatter measurements from the RECONCILE (Reconciliation of\nessential process parameters for an enhanced predictability of Arctic\nstratospheric ozone loss and its climate interactions) and LAPBIAT-II\n(Lapland Atmosphere-Biosphere Facility) field campaigns have been\nanalyzed in detail. This paper uses a column version of the Zurich\nOptical and Microphysical box Model (ZOMM) including newly developed NAT\n(nitric acid trihydrate) and ice nucleation parameterizations. Particle\nsedimentation is calculated in order to simulate the vertical\nredistribution of chemical species such as water and nitric acid.\nDespite limitations given by wind shear and uncertainties in the initial\nwater vapor profile, the column modeling unequivocally shows that (1)\naccounting for small-scale temperature fluctuations along the\ntrajectories is essential in order to reach agreement between simulated\noptical cloud properties and observations, and (2) the use of recently\ndeveloped heterogeneous ice nucleation parameterizations allows the\nreproduction of the observed signatures of de- and rehydration.\nConversely, the vertical redistribution of water measured cannot be\nexplained in terms of homogeneous nucleation of ice clouds, whose\nparticle radii remain too small to cause significant dehydration.