HIGH-LATITUDE COLD SEASON FRONTAL CLOUD SYSTEMS AND THEIR PRECIPITATION EFFICIENCY

A weak high-latitude warm-frontal precipitation system was simulated b y using a 2D cloud-resolving model. It was found that many of the stru ctural characteristics of the system were consequences of the subfreez ing temperatures and enhanced planetary rotation in the region. The co upling of cloud microphysical processes to frontal scale dynamics caus ed the precipitation efficiency (defined as the ratio of integrated su rface precipitation rate to the net water vapor influx into the storm) of the model storm to exhibit strong sensitivity to low-level humidit y conditions. A relatively high (zero) precipitation efficiency is ass ociated with a storm if it develops over regions having near surface r elative humidity with respect to ice greater than or equal to(<) 80%. In addition, the model results show that the precipitation efficiency of a system is decreased (increased) when the background static stabil ity is increased (decreased) or when the Coriolis parameter is increas ed (decreased). These model results may have great implications for th e Arctic water cycle as well as for the parameterization of Arctic clo uds and precipitation in GCMs.