Studies of cloud microphysics in Arctic mixed-phase cloud: long ARM observational time-series take us beyond case studies

Description

Mixed-phase clouds occur in the Arctic for a large part of the year. Because the partitioning between ice and liquid water in these clouds—and hence their radiative properties—can vary widely, their correct representation in climate models is an urgent problem. The North Slope of Alaska (NSA) site of the ARM Climate Research Facility in Barrow, Alaska, has collected well over a decade of cloud property and radiation measurements with the aim of testing and refining climate model parameterizations of mixed-phase Arctic cloud. In this work, we classify the existing observations into four major meteorological regimes in two ways: (1) inspection of NCEP reanalysis data, and (2) k-means clustering on surface meteorological data. We show that cloud properties, as derived from radiometry, lidar, radar, and balloon-borne sensors, differ significantly between the four meteorological regimes. These regimes can therefore serve as ensembles of test cases for cloud properties that can be used to robustly test climate model parameterizations, exposing models to physically relevant atmospheric states spanning the full range of meteorological variability found in nature. We present this technique as a potentially valuable supplement to the more common method of testing climate model parameterizations against individual case studies from intensive aircraft field campaigns. To illustrate the utility of this approach, we use over a decade of ARM observations to show that model success differs significantly between meteorological regimes in comparisons between observed and modeled cloud properties in a single-column and a regional climate model with a variety of microphysical parameterizations, ranging from strong underprediction of cloud optical thickness when high pressure to the north prevails to strong overprediction during low-pressure systems to the south.