North Atlantic Ocean SST-gradient-driven variations in aerosol and cloud evolution along Lagrangian cold-air outbreak trajectories
Authors: Sanchez Kevin J. , Zhang Bo , Liu Hongyu , Brown Matthew D. , Crosbie Ewan C. , Gallo Francesca , Hair Johnathan W. , Hostetler Chris A. , Jordan Carolyn E. , Robinson Claire E. , Scarino Amy Jo , Shingler Taylor J. , Shook Michael A. , Thornhill Kenneth L. , Wiggins Elizabeth B. , Winstead Edward L. , Ziemba Luke D. , Saliba Georges , Lewis Savannah L. , Russell Lynn M. , Quinn Patricia K. , Bates Timothy S. , Porter Jack , Bell Thomas G. , Gaube Peter , Saltzman Eric S. , Behrenfeld Michael J. , Moore Richard H. 
Published: March 2022

Abstract. Atmospheric marine particle concentrations impact cloud
properties, which strongly impact the amount of solar radiation reflected
back into space or absorbed by the ocean surface. While satellites can
provide a snapshot of current conditions at the overpass time, models are
necessary to simulate temporal variations in both particle and cloud
properties. However, poor model accuracy limits the reliability with which
these tools can be used to predict future climate. Here, we leverage the
comprehensive ocean ecosystem and atmospheric aerosol–cloud dataset
obtained during the third deployment of the North Atlantic Aerosols and
Marine Ecosystems Study (NAAMES3). Airborne and ship-based measurements were
collected in and around a cold-air outbreak during a 3 d (where d stands for day) intensive
operations period from 17–19 September 2017. Cold-air outbreaks are of keen
interest for model validation because they are challenging to accurately
simulate, which is due, in part, to the numerous feedbacks and sub-grid-scale processes that influence aerosol and cloud evolution. The NAAMES
observations are particularly valuable because the flight plans were
tailored to lie along Lagrangian trajectories, making it possible to
spatiotemporally connect upwind and downwind measurements with the
state-of-the-art FLEXible PARTicle (FLEXPART) Lagrangian particle dispersion
model and then calculate a rate of change in particle properties. Initial
aerosol conditions spanning an east–west, closed-cell-to-clear-air
transition region of the cold-air outbreak indicate similar particle
concentrations and properties. However, despite the similarities in the
aerosol fields, the cloud properties downwind of each region evolved quite
differently. One trajectory carried particles through a cold-air outbreak,
resulting in a decrease in accumulation mode particle concentration
(−42 %) and cloud droplet concentrations, while the other remained outside
of the cold-air outbreak and experienced an increase in accumulation mode
particle concentrations (+62 %). The variable meteorological conditions between these two adjacent trajectories result from differences in the local sea surface temperature in the Labrador Current and surrounding waters, altering the stability of the marine atmospheric boundary layer. Further
comparisons of historical satellite observations indicate that the observed
pattern occurs annually in the region, making it an ideal location for
future airborne Lagrangian studies tracking the evolution of aerosols and
clouds over time under cold-air outbreak conditions.