Low‐CCN concentration air masses over the eastern North Atlantic: Seasonality, meteorology, and drivers
Low‐CCN concentration air masses over the eastern North Atlantic: Seasonality, meteorology, and drivers
复制标题
北大西洋东部的低 CCN 空气浓度团：季节性、气象和驱动因素
DOI：
10.1002/2016jd025557
复制
发表时间：
2017
期刊：
影响因子：
--
通讯作者：
A. Jefferson
中科院分区：
文献类型：
--
作者：
R. Wood;J. Stemmler;J. Rémillard;A. Jefferson
来自北大西洋偏远格拉西奥萨岛（北纬 39°，西经 28°）的 20 个月云凝结核浓度 (NCCN) 数据集用于表征具有低云凝结核 (CCN) 浓度的气团。低 CCN 事件定义为平均 NCCN<20 cm−3（0.1% 过饱和）的 6 小时周期。总共识别出 47 个低 CCN 事件。地面、卫星和再分析数据用于探索低 CCN 气团的气象和云环境。低CCN事件在所有季节都会发生，但12月至5月的频率是6月至11月的3倍。复合材料显示，许多低 CCN 事件具有共同的气象基础，包括南风低层气流和格拉西奥萨相当低的风速。在这些事件期间，异常低压位于格拉西奥萨以西，但向后轨迹和滞后的 SLP 合成表明，低 CCN 气团通常起源于格拉西奥萨北部和西部的冷空气爆发。格拉西奥萨的低 CCN 事件与低云滴浓度 (Nd) 相关，但低 CCN 事件期间的液态水路径 (LWP) 与其他时间没有系统性的不同。来自 MODIS 的卫星 Nd 和 LWP 估计与拉格朗日背向轨迹显示，在到达格拉西奥萨前几天，Nd 和 LWP 系统地降低，LWP 升高，这与观察到的低 CCN 气团通常是由厚厚的暖云中的合并清除形成的假设一致，通常是在冷空气爆发时。
A 20 month cloud condensation nucleus concentration (NCCN) data set from Graciosa Island (39°N, 28°W) in the remote North Atlantic is used to characterize air masses with low cloud condensation nuclei (CCN) concentrations. Low‐CCN events are defined as 6 h periods with mean NCCN<20 cm−3 (0.1% supersaturation). A total of 47 low‐CCN events are identified. Surface, satellite, and reanalysis data are used to explore the meteorological and cloud context for low‐CCN air masses. Low‐CCN events occur in all seasons, but their frequency was 3 times higher in December–May than during June–November. Composites show that many of the low‐CCN events had a common meteorological basis that involves southerly low‐level flow and rather low wind speeds at Graciosa. Anomalously low pressure is situated to the west of Graciosa during these events, but back trajectories and lagged SLP composites indicate that low‐CCN air masses often originate as cold air outbreaks to the north and west of Graciosa. Low‐CCN events were associated with low cloud droplet concentrations (Nd) at Graciosa, but liquid water path (LWP) during low‐CCN events was not systematically different from that at other times. Satellite Nd and LWP estimates from MODIS collocated with Lagrangian back trajectories show systematically lower Nd and higher LWP several days prior to arrival at Graciosa, consistent with the hypothesis that observed low‐CCN air masses are often formed by coalescence scavenging in thick warm clouds, often in cold air outbreaks.
影响因子：
6.3
作者：
Mauritsen, T.;Sedlar, J.;Swietlicki, E.
通讯作者：
Swietlicki, E.