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# Aerosol-Cloud-Precipitation Interactions in a Closed-cell and Non-homogenous MBL Stratocumulus Cloud

• A closed-cell marine stratocumulus case during the Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA) aircraft field campaign is selected to examine the heterogeneities of cloud and drizzle microphysical properties and the aerosol-cloud-precipitation interactions. The spatial and vertical variabilities of cloud and drizzle microphysics are found in two different sets of flight legs: Leg-1 and Leg-2, which are parallel and perpendicular to the cloud propagation, respectively. The cloud along Leg-2 was close to adiabatic, where cloud-droplet effective radius and liquid water content linearly increase from cloud base to cloud top with less drizzle. The cloud along Leg-1 was sub-adiabatic with lower cloud-droplet number concentration and larger cloud-droplet effective, but higher drizzle droplet number concentration, larger drizzle droplet median diameter and drizzle liquid water content. The heavier drizzle frequency and intensity on Leg-1 were enhanced by the collision-coalescence processes within cloud due to strong turbulence. The sub-cloud precipitation rate on Leg-1 was significantly higher than that along Leg-2. As a result, the sub-cloud accumulation mode aerosols and CCN on Leg-1 were depleted, but the coarse model aerosols increased. This further leads to a counter-intuitive phenomenon that the CCN is less than cloud-droplet number concentration for Leg-1. The average CCN loss rates are −3.89 $\mathrm{c}{\mathrm{m}}^{-3}\;{\mathrm{h}}^{-1}$ and −0.77 $\mathrm{c}{\mathrm{m}}^{-3}\;{\mathrm{h}}^{-1}$ on Leg-1 and Leg-2, respectively. The cloud and drizzle heterogeneities inside the same stratocumulus can significantly alter the sub-cloud aerosols and CCN budget. Hence it should be treated with caution in the aircraft assessment of aerosol-cloud-precipitation interactions.
摘要: 本文在北大西洋东部气溶胶和云实验（ACE-ENA）飞机外场实验中选择了一个海洋边界层内的封闭胞层积云案例，以研究云和细雨微物理特性的异质性和气溶胶-云-降水的相互作用。在Leg-1（平行于云传播路径方向）和Leg-2（垂直于云传播路径方向）两组不同的飞行航段中，发现了不同的云和细雨微物理的空间和垂直变化。沿着Leg-2的云层更接近绝热，云粒子的有效半径和液态水含量从云底到云顶呈线性增长，并伴随较少的细雨。沿着Leg-1的云是亚绝热的，伴随较低的云粒子数浓度，较大的云粒子有效半径，和较高的细雨粒子数浓度以及较大的细雨粒子中位直径和液体含水量。在Leg-1的云层内由强湍流增强的碰撞-合并过程加强了其产生细雨的频率和强度，因此Leg-1的云下降水率明显高于Leg-2的云下降水率，导致了leg-1云下的云凝结核和积聚模态气溶胶的减少，和粗粒子模态气溶胶的增加。这进一步造成了一个反直觉的现象，即Leg-1测得的云凝结核数浓度小于云粒子数浓度。Leg-1和Leg-2的平均云凝结核损失率分别为−3.89 cm−3 h−1和−0.77 cm−3 h−1。即使在同一层积云内，云和细雨的异质性亦可以显著地改变云下气溶胶和云凝结核数的收支，因此在使用飞机对气溶胶-云-降水相互作用进行评估时应被谨慎对待。
• Figure 1.  (a) 900 hPa geopotential height (contour) and wind (arrow, color denotes wind speed) in a 50° × 30° domain surrounding the ENA, and the red star denotes the position of ARM-ENA site; (b) the ARM-ENA ground-based radar reflectivity (contour) overlayed by the ceilometer measured cloud base (black dot) and RF0718 aircraft vertical flight track (purple line) between 0830 to 1200 UTC.

Figure 2.  Meteosat-9 measured Cloud Optical Depth over the 2° × 2° domain surrounding the RF0718 at (a) 0900 UTC; (b) 0930 UTC; (c) 1000 UTC; (d) 1030 UTC. The aircraft horizontal paths within each half hour are overlayed as purple lines with two flight directions: Leg-1 which is parallel to cloud propagation (fly from NW to SE) and Leg-2 which is perpendicular to cloud propagation (fly from SW to NE).

Figure 3.  Vertical profiles of (a) cloud-droplet number concentrations (${N}_{\mathrm{c}}$); (b) cloud-droplet effective radii (${r}_{\mathrm{c}}$); (c) cloud liquid water content ($\mathrm{L}\mathrm{W}{\mathrm{C}}_{\mathrm{c}}$) with dashed lines denoting adiabatic LWC; (d) drizzle-drop number concentration (${N}_{\mathrm{d}}$); (e) drizzle mass median diameter (${D}_{\mathrm{m},\mathrm{d}}$) and (f) drizzle liquid water content ($\mathrm{L}\mathrm{W}{\mathrm{C}}_{\mathrm{d}}$). Blue denotes sampling on Leg-1 side on L-shaped leg, and red denotes sampling on Leg-2 side on L-shaped leg. Dots show the mean values at each level, and the vertical bars from left to right represent 10%, 25%, 50%, 75%, and 90% values.

Figure 4.  Same as Fig. 3 except for profiles of (a) total aerosol number concentration (${N}_{\mathrm{a}}$); (b) cloud condensation nuclei number concentration at 0.35% supersaturation (${N}_{\mathrm{C}\mathrm{C}\mathrm{N}35}$); (c) accumulation mode aerosol number concentration (${N}_{\mathrm{A}\mathrm{C}\mathrm{C}}$) and (d) coarse mode aerosol number concentration (N>1 μm).

Figure 5.  Time series of (a) precipitation rate; (b) ${N}_{\mathrm{C}\mathrm{C}\mathrm{N}35}$; (c) ${N}_{\mathrm{A}\mathrm{C}\mathrm{C}}$ and (d) N> 1 μm for the sub-cloud aircraft horizontal legs.

Figure 6.  Log-normal aerosol size distributions from 0.1 μm to 3.2 μm for the sub-cloud aircraft horizontal legs.

Figure 7.  Chart plot of mass concentrations and relative percentages of PILS sampled submicron aerosol chemical components, on Leg-1 side of sub-cloud leg (left), and on Leg-2 side of sub-cloud leg (right).

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## Manuscript History

Manuscript revised: 18 May 2022
Manuscript accepted: 30 June 2022
###### 通讯作者: 陈斌, bchen63@163.com
• 1.

沈阳化工大学材料科学与工程学院 沈阳 110142

## Aerosol-Cloud-Precipitation Interactions in a Closed-cell and Non-homogenous MBL Stratocumulus Cloud

###### Corresponding author: Xiquan DONG, xdong@arizona.edu;
• 1. Department of Hydrology and Atmospheric Sciences, University of Arizona, Tucson 85721, AZ, USA
• 2. Pacific Northwest National Laboratory, Richland 99354, WA, USA
• 3. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena 91125, CA, USA

Abstract: A closed-cell marine stratocumulus case during the Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA) aircraft field campaign is selected to examine the heterogeneities of cloud and drizzle microphysical properties and the aerosol-cloud-precipitation interactions. The spatial and vertical variabilities of cloud and drizzle microphysics are found in two different sets of flight legs: Leg-1 and Leg-2, which are parallel and perpendicular to the cloud propagation, respectively. The cloud along Leg-2 was close to adiabatic, where cloud-droplet effective radius and liquid water content linearly increase from cloud base to cloud top with less drizzle. The cloud along Leg-1 was sub-adiabatic with lower cloud-droplet number concentration and larger cloud-droplet effective, but higher drizzle droplet number concentration, larger drizzle droplet median diameter and drizzle liquid water content. The heavier drizzle frequency and intensity on Leg-1 were enhanced by the collision-coalescence processes within cloud due to strong turbulence. The sub-cloud precipitation rate on Leg-1 was significantly higher than that along Leg-2. As a result, the sub-cloud accumulation mode aerosols and CCN on Leg-1 were depleted, but the coarse model aerosols increased. This further leads to a counter-intuitive phenomenon that the CCN is less than cloud-droplet number concentration for Leg-1. The average CCN loss rates are −3.89 $\mathrm{c}{\mathrm{m}}^{-3}\;{\mathrm{h}}^{-1}$ and −0.77 $\mathrm{c}{\mathrm{m}}^{-3}\;{\mathrm{h}}^{-1}$ on Leg-1 and Leg-2, respectively. The cloud and drizzle heterogeneities inside the same stratocumulus can significantly alter the sub-cloud aerosols and CCN budget. Hence it should be treated with caution in the aircraft assessment of aerosol-cloud-precipitation interactions.

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