Cloud and boundary layer interactions over the Arctic sea ice in late summer
Cloud and boundary layer interactions over the Arctic sea ice in late summer
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DOI：
10.5194/acp-13-9379-2013
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发表时间：
2013-01-01
影响因子：
6.3
通讯作者：
Leck, C.
中科院分区：
文献类型：
--
作者：
Shupe, M. D.;Persson, P. O. G.;Leck, C.
2008年夏末，北极夏季云海洋研究在北极中部海冰群进行观测，提供了海冰环境上空云-大气-地面相互作用和垂直混合过程的详细情况。从一套地面遥感器，近地面气象和气溶胶仪器，并从无线电探空仪和直升机配置文件的测量相结合，以表征为期一周的低层，混合相，层积云为主。详细的案例研究和统计分析被用来开发一个概念模型的云和大气结构及其相互作用在这种environment.Clouds是持续的研究期间，具有的品质，这表明他们是通过平流影响和云内过程相结合的持续，与地面的贡献很小。云顶附近的辐射冷却产生浮力驱动的湍流涡旋，有助于云的形成，并产生云驱动的混合层。该混合层的深度与湍流和凝结云水的量有关。这种云驱动的混合层的表面边界层的耦合主要是由接近。对于75%的研究期间，主要层积云云驱动的混合层与地面解耦，通常在一个温暖的潜在温度。由于近地表温度受到海洋-冰混合物的限制，高空的温暖温度表明这些空气团没有与海冰表面发生显着的相互作用。相反，反向轨迹分析表明，这些暖空气团从低纬度平流进入北极盆地中部。水汽和气溶胶粒子可能伴随着这些气团，为云的形成提供了必要的支持。在云-地面耦合确实发生的情况下，后向轨迹表明，这些气团在低层平流，而混合过程使混合层与近地面环境保持平衡。而不是贡献浮力强迫的混合层动力学，表面，而不是简单地出现，以响应混合层的过程。在这些情况下，云通常含有略高的冷凝水量，可能是由于来自下方的额外水分来源。
Observations from the Arctic Summer Cloud Ocean Study (ASCOS), in the central Arctic sea-ice pack in late summer 2008, provide a detailed view of cloud-atmosphere-surface interactions and vertical mixing processes over the sea-ice environment. Measurements from a suite of ground-based remote sensors, near-surface meteorological and aerosol instruments, and profiles from radiosondes and a helicopter are combined to characterize a week-long period dominated by low-level, mixed-phase, stratocumulus clouds. Detailed case studies and statistical analyses are used to develop a conceptual model for the cloud and atmosphere structure and their interactions in this environment.Clouds were persistent during the period of study, having qualities that suggest they were sustained through a combination of advective influences and in-cloud processes, with little contribution from the surface. Radiative cooling near cloud top produced buoyancy-driven, turbulent eddies that contributed to cloud formation and created a cloud-driven mixed layer. The depth of this mixed layer was related to the amount of turbulence and condensed cloud water. Coupling of this cloud-driven mixed layer to the surface boundary layer was primarily determined by proximity. For 75% of the period of study, the primary stratocumulus cloud-driven mixed layer was decoupled from the surface and typically at a warmer potential temperature. Since the near-surface temperature was constrained by the ocean-ice mixture, warm temperatures aloft suggest that these air masses had not significantly interacted with the sea-ice surface. Instead, back-trajectory analyses suggest that these warm air masses advected into the central Arctic Basin from lower latitudes. Moisture and aerosol particles likely accompanied these air masses, providing necessary support for cloud formation. On the occasions when cloud-surface coupling did occur, back trajectories indicated that these air masses advected at low levels, while mixing processes kept the mixed layer in equilibrium with the near-surface environment. Rather than contributing buoyancy forcing for the mixed-layer dynamics, the surface instead simply appeared to respond to the mixed-layer processes aloft. Clouds in these cases often contained slightly higher condensed water amounts, potentially due to additional moisture sources from below.