Kinetic limitations on cloud droplet formation and impact on cloud albedo
Kinetic limitations on cloud droplet formation and impact on cloud albedo
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DOI：
10.3402/tellusb.v53i2.16569
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发表时间：
2001-01
期刊：
影响因子：
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通讯作者：
A. Nenes;S. Ghan;Hayder Abdul-Razzak;P. Chuang;J. Seinfeld
中科院分区：
文献类型：
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作者：
A. Nenes;S. Ghan;Hayder Abdul-Razzak;P. Chuang;J. Seinfeld
在某些条件下，对云凝结核（CCN）生长的质量传递限制可能对云中可以形成的液滴的数量具有显著影响。因此，颗粒在被激活之前保持平衡的假设可能并不总是适合于大气中存在的气溶胶群体。这项工作确定了三种机制，导致动力学的限制，其对激活云滴数和云滴的影响进行了评估，使用一个一维的云块模型，详细的微物理的各种气溶胶的大小分布和上升气流速度。在评估动力学限制的影响时，我们不仅假设那些严格激活的云滴（如经典科勒理论所规定的），而且假设那些未激活的云滴大到足以影响云的光学特性。气溶胶数浓度被认为是控制动力学效应显著性的关键参数。模拟结果表明，平衡假设导致海洋气溶胶的液滴数超过10%的预测，城市类型的气溶胶，这种过度预测可以超过40%。总的来说，动力学限制对云凝结的影响可以被认为是重要的，当平衡激活理论始终高估液滴数超过10%。在海洋气溶胶等情况下，由于动力学限制，云的最大变化小于0.005;然而，在污染更严重的情况下，云的最大变化可能超过0.1。因此，预计动力学限制在全球范围内不会对气候产生重大影响，但在区域范围内会对云的可持续性产生重大影响。
Under certain conditions mass transfer limitations on the growth of cloud condensation nuclei (CCN) may have a significant impact on the number of droplets that can form in a cloud. The assumption that particles remain in equilibrium until activated may therefore not always be appropriate for aerosol populations existing in the atmosphere. This work identifies three mechanisms that lead to kinetic limitations, the effect of which on activated cloud droplet number and cloud albedo is assessed using a one-dimensional cloud parcel model with detailed microphysics for a variety of aerosol size distributions and updraft velocities. In assessing the effect of kinetic limitations, we have assumed as cloud droplets not only those that are strictly activated (as dictated by classical Köhler theory), but also unactivated drops large enough to have an impact on cloud optical properties. Aerosol number concentration is found to be the key parameter that controls the significance of kinetic effects. Simulations indicate that the equilibrium assumption leads to an overprediction of droplet number by less than 10% for marine aerosol; this overprediction can exceed 40% for urban type aerosol. Overall, the effect of kinetic limitations on cloud albedo can be considered important when equilibrium activation theory consistently overpredicts droplet number by more than 10%. The maximum change in cloud albedo as a result of kinetic limitations is less than 0.005 for cases such as marine aerosol; however albedo differences can exceed 0.1 under more polluted conditions. Kinetic limitations are thus not expected to be climatically significant on a global scale, but can regionally have a large impact on cloud albedo.