Simulation of Late Summer Arctic Clouds during ASCOS with Polar WRF
Simulation of Late Summer Arctic Clouds during ASCOS with Polar WRF
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DOI：
10.1175/mwr-d-16-0079.1
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发表时间：
2017-02-01
影响因子：
3.2
通讯作者：
Bromwich, David H.
中科院分区：
文献类型：
--
作者：
Hines, Keith M.;Bromwich, David H.
低层云在北极分布广泛，对区域气候变化的反馈理解不足。对于实时天气预报和气候模式来说，夏季和秋季北冰洋上空低层云（包括混合相云）的模拟仍然是一个挑战。本文采用最新极地优化版本（3.7.1）的天气研究与预报（Polar WRF）模式，采用先进的两矩Morrison微物理方案，对2008年8月至9月的北极夏季云海研究（ASCOS）进行高分辨率中尺度模拟，寻求改进的云表示。对2008年8月10日至9月3日的几个天气系统进行了模拟，其中包括27公里网格间距的外部域和9公里和3公里网格间距的嵌套域。这些是常见中尺度应用的实际水平网格间距。控制模拟在低层云中产生过多的云液态水，导致模拟的入射短波辐射在地面出现较大的亏缺。入射长波辐射则不那么敏感。在ASCOS期间，海冰反照率向较大观测值的变化导致了更真实的模拟。更重要的是，灵敏度测试表明，将规定的液滴数减少到非常原始的状态，增加了液体降水，大大减少了模拟低层云中液态水的过剩，并改善了模拟地面入射短波和长波辐射。
Low-level clouds are extensive in the Arctic and contribute to inadequately understood feedbacks within the changing regional climate. The simulation of low-level clouds, including mixed-phase clouds, over the Arctic Ocean during summer and autumn remains a challenge for both real-time weather forecasts and climate models. Here, improved cloud representations are sought with high-resolution mesoscale simulations of the August-September 2008 Arctic Summer Cloud Ocean Study (ASCOS) with the latest polar-optimized version (3.7.1) of the Weather Research and Forecasting (Polar WRF) Model with the advanced two-moment Morrison microphysics scheme. Simulations across several synoptic regimes for 10 August-3 September 2008 are performed with three domains including an outer domain at 27-km grid spacing and nested domains at 9- and 3-km spacing. These are realistic horizontal grid spacings for common mesoscale applications. The control simulation produces excessive cloud liquid water in low clouds resulting in a large deficit in modeled incident shortwave radiation at the surface. Incident longwave radiation is less sensitive. A change in the sea ice albedo toward the larger observed values during ASCOS resulted in somewhat more realistic simulations. More importantly, sensitivity tests show that a reduction in specified liquid cloud droplet number to very pristine conditions increases liquid precipitation, greatly reduces the excess in simulated low-level cloud liquid water, and improves the simulated incident shortwave and longwave radiation at the surface.