A modeling case study of mixed-phase clouds over the Southern Ocean and Tasmania

Anthony Edward Morrison, Steven Thomas Siems, Michael John Manton, Alex Nazarov

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18 Citations (Scopus)

Abstract

The cloud structure associated with two frontal passages over the Southern Ocean and Tasmania is investigated. The first event, during August 2006, is characterised by large quantities of supercooled liquid water and little ice. The second case, during October 2007, is more mixed phase. The Weather Research and Forecasting (WRFV2.2.1) model is evaluated using remote sensed and in-situ observations within the post frontal airmass. The Thompson microphysics module (Thompson et al. 2007) is used to describe in-cloud processes, ice is initiated using the Cooper parameterisation (Cooper 1986) at temperatures lower than -8?C, or at ice supersaturations greater than 8 . The evaluated cases are then used to numerically investigate the prevalence of supercooled and mixed phase clouds over Tasmania and the ocean to the west. The simulations produce marine stratocumulus like clouds with maximum heights of between 3 and 5km. These are capped by weak temperature and strong moisture inversions. When the inversion is at temperatures warmer than -10?C, WRF produces wide spread supercooled cloud fields with little glaciation. This is consistent with the limited in-situ observations. When the inversion is at higher altitudes, allowing cooler cloud tops, glaciated (and to a lesser extent mixed phase) clouds are more common. The simulations are further explored to evaluate any orographic signature within the cloud structure over Tasmania. No consistent signature is found between the two cases.
Original languageEnglish
Pages (from-to)839 - 862
Number of pages23
JournalMonthly Weather Review
Volume138
DOIs
Publication statusPublished - 2010

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