Timothy W. Juliano, Christian P. Lackner, Bart Geerts, Branko Kosović, Lulin Xue, Peng Wu, Joseph B. Olson
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The observed BL structures are open cellular with high (∼3–5 km) and cold (−30 to −50 <span></span><math>\n <semantics>\n <mrow>\n <mo>°</mo>\n </mrow>\n <annotation> ${}^{\\circ}$</annotation>\n </semantics></math>C) cloud tops, and they often have pockets of high liquid water paths (LWPs; up to ∼1,000 g <span></span><math>\n <semantics>\n <mrow>\n <msup>\n <mi>m</mi>\n <mrow>\n <mo>−</mo>\n <mn>2</mn>\n </mrow>\n </msup>\n </mrow>\n <annotation> ${\\mathrm{m}}^{-2}$</annotation>\n </semantics></math>) associated with strong updrafts and enhanced turbulence. We use a high-resolution mesoscale model to explore how well four turbulence closure methods represent open cellular clouds. After applying a radar simulator to model outputs for direct evaluation, cloud top properties agree well with AMF1 observations (within ∼10%), but radar reflectivity and LWP agreement is more variable. 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引用次数: 0
摘要
海洋冷空气爆发(或 CAOs)是相对较冷的边界层(BL)空气在相对较暖的水域上空传输的气团转换。为了更深入地了解 CAO 条件下的边界层和混合相云特性,海洋边界层冷空气爆发实验(COMBLE)于 2019 年底至 2020 年初进行。在 COMBLE 期间,美国能源部的首个大气辐射测量移动设施(AMF1)被部署到了挪威的 Andenes,距离北极包冰很远(1000 千米)。本研究考察了在 AMF1 站点采样的两个最强烈的 CAO。观测到的BL结构是具有高(∼3-5千米)和冷(-30到-50 ° {}^{circ}$ C)云顶的开放蜂窝,它们通常具有与强上升气流和增强湍流相关的高液态水路径(LWPs;高达∼1,000 g m - 2 ${\mathrm{m}}^{-2}$ )。我们使用一个高分辨率的中尺度模型来探索四种湍流闭合方法对开放蜂窝云的代表性。在应用雷达模拟器对模型输出进行直接评估后,云顶特性与 AMF1 观测结果吻合得很好(在 10%以内),但雷达反射率和 LWP 的吻合程度变化较大。结果表明,湍流普朗特数可能对模拟的 BL 和云属性起重要作用。所有模拟都产生了增强的降水率,这些降水率与云的过渡密切相关。最后,涡度扩散/质量流方法产生了最深的云层,因此也产生了最大和最连贯的蜂窝结构。我们建议使用非局部湍流闭合方法,以更好地捕捉强 CAO 中的湍流过程。
Simulating Mixed-Phase Open Cellular Clouds Observed During COMBLE: Evaluation of Parameterized Turbulence Closure
Marine cold-air outbreaks, or CAOs, are airmass transformations whereby relatively cold boundary layer (BL) air is transported over relatively warm water. To more deeply understand BL and mixed-phase cloud properties during CAO conditions, the Cold-Air Outbreaks in the Marine Boundary Layer Experiment (COMBLE) took place from late 2019 into early 2020. During COMBLE, the U.S. Department of Energy's first Atmospheric Radiation Measurement Mobile Facility (AMF1) was deployed to Andenes, Norway, far downstream (∼1,000 km) from the Arctic pack ice. This study examines the two most intense CAOs sampled at the AMF1 site. The observed BL structures are open cellular with high (∼3–5 km) and cold (−30 to −50 C) cloud tops, and they often have pockets of high liquid water paths (LWPs; up to ∼1,000 g ) associated with strong updrafts and enhanced turbulence. We use a high-resolution mesoscale model to explore how well four turbulence closure methods represent open cellular clouds. After applying a radar simulator to model outputs for direct evaluation, cloud top properties agree well with AMF1 observations (within ∼10%), but radar reflectivity and LWP agreement is more variable. Results suggest that the turbulent Prandtl number may play an important role for the simulated BL and cloud properties. All simulations produce enhanced precipitation rates that are well-correlated with a cloud transition. Finally, the eddy-diffusivity/mass-flux approach produces the deepest cloud layer and therefore the largest and most coherent cellular structures. We recommend the use of a non-local turbulence closure approach to better capture turbulent processes in intense CAOs.
期刊介绍:
JGR: Atmospheres publishes articles that advance and improve understanding of atmospheric properties and processes, including the interaction of the atmosphere with other components of the Earth system.