摘要
基于POST观测计划中获得的海洋性层积云顶边界层内高频气象资料和云微物理资料,在选取解耦个例基础上研究解耦边界层湍流和云微物理特征及成因。结果表明,过渡层的大气静力稳定度较强,抑制向上浮力做功,使得湍流动能迅速消耗殆尽,实现边界层解耦。湍流动能最大值出现在云内,主要与云顶降温、大云滴下落沉降拖曳带来的下沉气流增强及云底之上附近凝结增长潜热释放产生向上浮力作用有关。近地面层的浮力项和切变项对湍流动能都起到增强作用,并以切变项的贡献更为显著,云内的湍流动能是以浮力项贡献为主。过渡层附近存在向下的热通量,抑制了热量向上输送和向上浮力项的增强,促进解耦发生。云内存在向上感热通量,其最大值及其出现高度主要与云顶冷却和云中下部的凝结潜热加热有关。云顶之上湿层促进了潜热通量的向下输送,增强了云内水汽含量,为解耦边界层云的发展起到正反馈作用。云顶浮力倒转引起的云中湍流混合呈现非均匀性,并进一步导致绝热或超绝热液滴出现,促进凝结和碰并增长的增强,同时云顶之上湿层进一步对云中的微物理增长起到了重要的推动作用。云底因夹卷混合表现为均匀混合特征。
This study investigates turbulence and cloud microphysical characteristics within the decoupled boundary layer,focusing on selected decoupling cases.High-frequency meteorological data and cloud microphysics data from stratocumulus-topped boundary layers,obtained during the POST(Physics of Stratocumulus Top)observation campaign,form the basis of our analysis.Results reveal that atmospheric static stability strengthens in the transition layer,inhibiting upward buoyancy work and rapidly depleting turbulent kinetic energy,leading to boundary layer decoupling.Maximum turbulent kinetic energy occurs within the cloud,driven primarily by cooling at the cloud top,enhanced downdraft from falling and sinking large cloud droplets,and latent heat release from condensation above the cloud base.Buoyancy and shear contributions augment turbulent kinetic energy in the near-surface layer,with shear playing a more prominent role,while within-cloud turbulent kinetic energy is mainly buoyancy-driven.Downward heat flux near the transition layer hinders upward heat transport and buoyancy enhancement,further promoting decoupling.Upward sensible heat flux within the cloud correlates with cloud top cooling and latent heat release from condensation in the lower cloud region.Increased moisture at the cloud top facilitates downward latent heat flux transport,amplifying water vapor content within the cloud,fostering positive feedback role in decoupled boundary layer cloud development.Cloud-top buoyancy reversal induces inhomogeneous mixing,leading to the appearance of adiabatic or super-adiabatic droplets and promoting condensation and coalescence growth.Additionally,enhanced moisture at the cloud top drives microphysical growth within the cloud.The cloud base exhibits homogeneous mixing characteristics due to entrainment.
作者
关铭
杨素英
丛春华
朱燕南
仲益君
杨怡伟
GUAN Ming;YANG Suying;CONG Chunhua;ZHU Yannan;ZHONG Yijun;YANG Yiwei(School of Emergency Management,Nanjing University of Information Science and Technology,Nanjing 210044,China;Key Laboratory for Aerosol-Cloud-Precipitation of China Meteorological Administration,Nanjing University of Information Science and Technology,Nanjing 210044,China;Shandong Meteorological Bureau,Jinan 250031,China;School of Environmental Science and Engineering,Nanjing University of Information Science and Technology,Nanjing 210044,China)
出处
《大气科学学报》
CSCD
北大核心
2024年第4期629-642,共14页
Transactions of Atmospheric Sciences
基金
山东省自然科学基金重大基础研究项目(ZR2020ZD21)
国家自然基金资助项目(41575133
U2242212)。
关键词
解耦
层积云顶边界层
湍流
夹卷
云微物理
decoupled
stratocumulus-topped boundary layer
turbulence
entrainment
cloud microphysics
