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首页> 外文期刊>Journal of the Atmospheric Sciences >A FIRE-ACE/SHEBA Case Study of Mixed-Phase Arctic Boundary Layer Clouds: Entrainment Rate Limitations on Rapid Primary Ice Nucleation Processes
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A FIRE-ACE/SHEBA Case Study of Mixed-Phase Arctic Boundary Layer Clouds: Entrainment Rate Limitations on Rapid Primary Ice Nucleation Processes

机译：FIRE-ACE / SHEBA混合相北极边界层云的案例研究：快速一次冰成核过程的夹带率限制

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Observations of long-lived mixed-phase Arctic boundary layer clouds on 7 May 1998 during the First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE)–Arctic Cloud Experiment (ACE)/Surface Heat Budget of the Arctic Ocean (SHEBA) campaign provide a uN_ique opportuN_ity to test understanding of cloud ice formation. Under the microphysically simple conditions observed (apparently negligible ice aggregation, sublimation, and multiplication), the only expected source of new ice crystals is activation of heterogeneous ice nuclei (IN) and the only sink is sedimentation. Large-eddy simulations with size-resolved microphysics are iN_itialized with IN number concentration N_(IN) measured above cloud top, but details of IN activation behavior are unknown. If activated rapidly (in deposition, condensation, or immersion modes), as commonly assumed, IN are depleted from the well-mixed boundary layer within minutes. Quasi-equilibrium ice number concentration N_i is then limited to a small fraction of overlying N_(IN) that is determined by the cloud-top entrainment rate we divided by the number-weighted ice fall speed at the surface υ_f. Because wc , 1 cm s~(-1) and υ_f . 10 cm s~(-1), N_i/N_(IN)《1. Such conditions may be common for this cloud type, which has implications for modeling IN diagnostically, interpreting measurements, and quantifying sensitivity to increasing N_(IN) (when we/υ_f , 1, entrainment rate limitations serve to buffer cloud system response). To reproduce observed ice crystal size distributions and cloud radar reflectivities with rapidly consumed IN in this case, the measured above-cloud N_(IN) must be multiplied by approximately 30. However, results are sensitive to assumed ice crystal properties not constrained by measurements. In addition, simulations do not reproduce the pronounced mesoscale heterogeneity in radar reflectivity that is observed.
机译：1998年5月7日在第一个国际卫星云气候项目（ISCCP）区域实验（FIRE）–北极云实验（ACE）/北冰洋表面热收支（SHEBA）期间观测到的长寿命混合相北极边界层云运动提供了一次机会来测试对云冰形成的理解。在观察到的微观物理简单条件下（明显的冰凝集，升华和增殖可忽略不计），新冰晶的唯一预期来源是异质冰核（IN）的活化，唯一的汇是沉积。使用大小分辨的微观物理学对大涡模拟进行了iN_itialized，并在云顶以上测量了IN数浓度N_（IN），但是IN激活行为的细节未知。如果迅速激活（在沉积，冷凝或浸没模式下）（通常认为），IN将在数分钟内从充分混合的边界层中耗尽。然后将准平衡冰数浓度N_i限制在上覆N_（IN）的一小部分，该分数由云顶夹带率除以表面υ_f的数加权冰落速度确定。因为wc，1 cm s〜（-1）和υ_f。 10厘米s〜（-1），N_i / N_（IN）《 1。此类条件对于这种云类型可能很常见，这对诊断IN建模，解释测量结果以及量化对增加N_（IN）的敏感性有影响（当我们/υ_f为1时，夹带速率限制可用来缓冲云系统响应）。为了在这种情况下用快速消耗的IN来再现观测到的冰晶尺寸分布和云雷达反射率，必须将测得的云层以上N_（IN）乘以约30。但是，结果对不受测量约束的假定冰晶特性很敏感。另外，模拟没有在观察到的雷达反射率中重现明显的中尺度异质性。

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