Drivers of Cloud Condensation Nuclei in the Eastern North Atlantic as Observed at the ARM Site.

Autor: Ghate, Virendra P.1 (AUTHOR) vghate@anl.gov, Surleta, Thomas2 (AUTHOR), Magaritz‐Ronen, Leehi3 (AUTHOR), Raveh‐Rubin, Shira3 (AUTHOR), Gallo, Francesca4 (AUTHOR), Carlton, Annmarie G.5 (AUTHOR), Azevedo, Eduardo B.6 (AUTHOR)
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Zdroj: Journal of Geophysical Research. Atmospheres. 11/27/2023, Vol. 128 Issue 22, p1-21. 21p.
Abstrakt: Seven years of data collected at the Atmospheric Radiation Measurement's Eastern North Atlantic (ENA) site are analyzed to understand the controls of Cloud Condensation Nuclei (CCN) concentrations in the region. Day‐night differences in the aerosol data as segregated by wind direction demonstrate the aerosol observations to be impacted by local emissions when the wind direction (wdir) is between 90° and 310° (measured clockwise from the North where air is coming from). Data collected during marine conditions (wdir <90° or wdir >310°) show the CCN concentrations to be higher in the summer months as compared to the winter months. CCN budget analysis revealed advection and precipitation scavenging being primarily responsible for modulating the CCN concentrations at the site on monthly timescales, with rain rates driving the precipitation scavenging term. High (greater than 75th percentile) and low (lower than 25th percentile) CCN events were identified for each month to characterize the sub‐monthly variability of CCN concentrations. Low CCN events had thicker clouds, stronger rain rates, and lower reanalysis reported free‐tropospheric aerosol pseudo number concentration at the ENA site as compared to the high CCN events. Analysis of satellite data of air‐parcels 48 hr prior to their arrival at the ENA site demonstrated the air parcels during low CCN events to encounter higher cloudiness, stronger rain rates, and higher cloud top heights as compared to the high CCN events. The results presented herein provide key constraints for model evaluation studies and climatological studies conducted at the ENA site. Plain Language Summary: Aerosols on which water vapor condenses to form cloud droplets are commonly referred to as cloud condensation nuclei (CCN). The mechanisms responsible for changes in CCN concentrations over the open oceans are not fully known. The variability in the CCN concentrations over the Eastern North Atlantic region is examined. Analysis of day‐night differences in aerosol properties with wind direction show the aerosol measurements to be affected by human activity during certain wind conditions. Seven years of data collected when conditions were not impacted by human activity show higher CCN concentrations during summer months as compared to the winter month, and substantial variability within each month. CCN can be locally produced through wave‐breaking, transported to the location, and subsequently removed from the atmosphere as they transition into cloud or rain drops. Causes of seasonal and sub‐monthly changes in these CCN concentrations are examined. The analysis show transport of CCN to the site along with removal due to cloud processing to be the primary mechanisms for causing seasonal changes. In addition, air associated with low CCN concentration conditions at the site encountered higher cloudiness and rain prior to its arrival at the site as compared to that with high CCN concentrations. Key Points: Data suggest aerosol measurements at the Atmospheric Radiation Measurement Eastern North Atlantic site are affected by local emissions when the wind direction is between 90° and 310°Lower ambient wintertime Cloud Condensation Nuclei (CCN) concentrations compared to summer are primarily driven by advection and precipitationCCN variability at sub‐monthly timescales is driven by clouds and precipitation upstream of the site [ABSTRACT FROM AUTHOR]
Databáze: GreenFILE
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