Details

Autor(en) / Beteiligte

• Gong, Xianda
• Wang, Yang
• Xie, Hua
• Zhang, Jiaoshi
• Lu, Zheng
• Wood, Robert
• Stratmann, Frank
• Wex, Heike
• Liu, Xiaohong
• Wang, Jian

Titel

Maximum Supersaturation in the Marine Boundary Layer Clouds Over the North Atlantic

Ist Teil von

• AGU advances, 2023-12, Vol.4 (6), p.n/a

Ort / Verlag

Hoboken: John Wiley & Sons, Inc

Erscheinungsjahr

2023

Link zum Volltext

Quelle

Free E-Journal (出版社公開部分のみ）

Beschreibungen/Notizen

• The maximum supersaturation (Sx) in clouds is a key parameter affecting the cloud's microphysical and radiative properties. We investigate the Sx of the marine boundary layer clouds by combining airborne and surface observations in the Eastern North Atlantic. The cloud droplet number concentration (Nc) in the least diluted cloud cores agrees well with the number concentration of particles larger than the Hoppel Minimum (HM) (N>HM) below clouds, indicating that the HM represents the average size threshold above which particles are activated to form cloud droplets. The Sx values derived from surface observations vary from 0.10% to 0.50% from June 2017 to June 2018, with a clear seasonal variation exhibiting higher values during winter. Most of the Sx variance (∼60%) can be explained by the cloud condensation nuclei (CCN) concentration and updraft velocity (w), with the CCN concentration playing a more important role than w in explaining the variation of Sx. The influence of CCN concentration on Sx leads to a buffered response of Nc to aerosol perturbations. The response of Nc to low aerosol concentration during winter is further buffered by the high w. The global Community Earth System Model (CESM) simulated Sx values in the Azores have a positive bias compared to measured Sx, likely due to overestimated w and underestimated CCN concentration. The CESM simulated Sx exhibits higher values further north over the North Atlantic Ocean, which is attributed to stronger w. The suppression of Sx by aerosol is also evident in regions with high CCN concentrations. Plain Language Summary Aerosols influence Earth's radiation budget and climate indirectly by modifying the properties and lifetime of clouds. The maximum supersaturation is one of the most important parameters affecting the cloud's microphysical and radiative properties. However, due to the difficulty of directly measuring the supersaturation in clouds, at present, very few studies have examined maximum supersaturation and its variation. Here, the maximum supersaturation in marine boundary layer clouds over the Eastern North Atlantic is derived from June 2017 to June 2018 using an approach validated by in situ airborne measurements. A clear summer low and winter high of the maximum supersaturation are found. The influences of the cloud condensation nuclei (CCN) population and synoptic conditions on the maximum supersaturation are investigated. The derived year‐long maximum supersaturation values allow us to evaluate simulations by the Community Earth System Model, which are then used to examine the temporal‐spatial variations of maximum supersaturation over the North Atlantic Ocean. The variation of maximum supersaturation on a regional scale is positively correlated with updraft velocity, and the suppression of maximum supersaturation by aerosol is evident in locations with high CCN concentrations. Our results can help to constrain the evaluation of aerosol indirect effects and climate changes on a global scale. Key Points Maximum cloud‐base supersaturations are derived from 1‐year measurements at a marine site in the North Atlantic Maximum supersaturations are high in winter, consistent with the low aerosol loading and synoptic conditions Variability in maximum supersaturation and updraft velocity lessens the sensitivity of clouds to seasonal changes in aerosol concentrations