Probing the Response of Tropical Deep Convection to Aerosol Perturbations Using Idealized Cloud-Resolving Simulations with Parameterized Large-Scale Dynamics
Probing the Response of Tropical Deep Convection to Aerosol Perturbations Using Idealized Cloud-Resolving Simulations with Parameterized Large-Scale Dynamics
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DOI：
10.1175/jas-d-18-0351.1
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发表时间：
2019-09
影响因子：
3.1
通讯作者：
U. Anber;Shuguang Wang;P. Gentine;M. Jensen
中科院分区：
文献类型：
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作者：
U. Anber;Shuguang Wang;P. Gentine;M. Jensen
介绍了一个框架，调查气溶胶加载对热带深对流的间接影响，使用三维有限域理想化的云系统解析模式模拟耦合大尺度动力学在固定的海面温度。大尺度环流参数化使用光谱弱温度梯度（WTG）近似，利用绝热冷却和非绝热加热在热带地区之间的主导平衡。气溶胶加载效应是通过在30 - 5000 cm−3的大范围环境中改变可用于形成云滴的云凝结核（CCN）的数量来检验的。辐射加热保持在恒定的规定速率，以隔离微物理效应。在对流和大尺度环境之间达到平衡后的一段时间内进行分析。平均降水量的减少温和和单调的气溶胶数浓度增加时，对流变弱，尽管增加云液态水在暖雨区和高空冰晶。这种减少可以追溯到减少表面焓通量作为能源的大气柱引起的耦合的大尺度运动，虽然总湿稳定度保持不变。CCN浓度的增加导致：1）由于非绝热加热的减少，自由对流层较冷; 2）由于蒸发冷却的抑制，边界层较暖。这种偶极温度结构与边界层上方的大尺度垂直运动和低层的上升运动有关。敏感性试验表明，对流和平均降水量的变化是不太可能造成的云滴和微物理特性的气溶胶的影响，而是通过占对流调整与大尺度动力学的反馈。此外，一个简单的缩放参数推导出的垂直综合湿静态能量预算的基础上，这使得已知的变化，表面焓通量和恒定的总湿稳定性的降水变化的估计。对云水凝物和微物理性质的影响也进行了研究，这是一致的宏观物理图片。
A framework is introduced to investigate the indirect effect of aerosol loading on tropical deep convection using three-dimensional limited-domain idealized cloud-system-resolving model simulations coupled with large-scale dynamics over fixed sea surface temperature. The large-scale circulation is parameterized using the spectral weak temperature gradient (WTG) approximation that utilizes the dominant balance between adiabatic cooling and diabatic heating in the tropics. The aerosol loading effect is examined by varying the number of cloud condensation nuclei (CCN) available to form cloud droplets in the two-moment bulk microphysics scheme over a wide range of environments from 30 to 5000 cm−3. The radiative heating is held at a constant prescribed rate in order to isolate the microphysical effects. Analyses are performed over the period after equilibrium is achieved between convection and the large-scale environment. Mean precipitation is found to decrease modestly and monotonically when the aerosol number concentration increases as convection gets weaker, despite the increase in cloud liquid water in the warm-rain region and ice crystals aloft. This reduction is traced down to the reduction in surface enthalpy fluxes as an energy source to the atmospheric column induced by the coupling of the large-scale motion, though the gross moist stability remains constant. Increasing CCN concentration leads to 1) a cooler free troposphere because of a reduction in the diabatic heating and 2) a warmer boundary layer because of suppressed evaporative cooling. This dipole temperature structure is associated with anomalously descending large-scale vertical motion above the boundary layer and ascending motion at lower levels. Sensitivity tests suggest that changes in convection and mean precipitation are unlikely to be caused by the impact of aerosols on cloud droplets and microphysical properties but rather by accounting for the feedback from convective adjustment with the large-scale dynamics. Furthermore, a simple scaling argument is derived based on the vertically integrated moist static energy budget, which enables estimation of changes in precipitation given known changes in surfaces enthalpy fluxes and the constant gross moist stability. The impact on cloud hydrometeors and microphysical properties is also examined, and it is consistent with the macrophysical picture.