Abstract
Polar clouds are, as a consequence of the paucity of in situ observations, poorly understood compared to their lower latitude analogs, yet highly climate-sensitive through thermal radiation emission. The prevalence of Thin Ice Clouds (TIC) dominates in cold Polar Regions and the Upper Troposphere Lower Stratosphere (UTLS) altitudes. They can be grouped into 2 broad categories. The first thin ice cloud type (TIC1) is made up of high concentrations of small, non-precipitating ice crystals. The second type (TIC2) is composed of relatively small concentrations of larger, precipitating ice crystals. In this study, we investigate the ability of a developmental version of the Canadian Regional Climate Model (CRCM6) in simulating cold polar-night clouds over the Arctic Ocean, a remote region that is critical to atmospheric circulation reaching out to the mid-latitudes. The results show that, relative to CloudSat-CALIPSO vertical profile products, CRCM6 simulates high-latitude and low spatial frequency variations of Ice Water Content (IWC), effective radius (re) and cooling rates reasonably well with only small to moderate wet and dry biases. The model can also simulate cloud type, location, and temporal occurrence effectively. As well, it successfully simulated higher altitude TIC1 clouds whose small size evaded CloudSat detection while being visible to CALIPSO.
Highlights
The Arctic is one of the most climate-sensitive regions on Earth [1]
He found mainly positive surface temperature trends in summer, spring, and autumn broadly over the Arctic Ocean associated with sea ice retreats, but noted some negative trends during the winter, with some cooling observed over large areas of the Bering Sea and parts of Russia
An important legacy of the 15 years of satellite-based LiDAR and radar data acquired to date, is that during the polar night, Thin Ice Clouds (TIC) are known to be dominant over the High Arctic
Summary
The Arctic is one of the most climate-sensitive regions on Earth [1]. Surface observations demonstrate a warming trend over the 1954–2003 climate period and still increasing to this date, especially in continental areas during winter with some cool anomalies predominantly oceanic areas, such as southern Greenland. An important legacy of the 15 years of satellite-based LiDAR and radar data acquired to date, is that during the polar night, TICs are known to be dominant over the High Arctic These very cold and semi-transparent clouds emit longwave radiation, from their boundaries but within their large cloud volume, depleting thermal energy very effectively from their large cloud volume rather than only from their edges. The formation and dehydrating precipitation of TIC2s results in the significant aforementioned radiative cooling of the cloud volume as well as a significant reduction in water vapor concentration This process could arguably contribute to systematic regional cooling as well as the increased variability and cold-winter anomalies that have been observed at mid-latitudes in recent decades. These are essential for performing complete analyses of the energy cycle [25]
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