North Atlantic Ocean SST-gradient-driven variations in aerosol and cloud evolution along Lagrangian cold-air outbreak trajectories

Abstract

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.

Investigating the development of clouds within marine cold-air outbreaks

“…Previous work has found that some air masses can travel over the sea ice for extended periods before reaching the ocean (Silber and Shupe, 2022); however, a full investigation is beyond the scope of this study. Previous work has found a similarly steep decline in N d concentration following an MCAO (Abel et al, 2017;Sanchez et al, 2022). Two main drivers of this N d gradient in MCAOs have been proposed: the dilution of aerosol concentration through entrainment of air from the free troposphere and precipitation scavenging of aerosol from the below-cloud layer, which are considered further below.…”

Marine Cold‐Air Outbreak Snowfall in the North Atlantic: A CloudSat Perspective

“…Globally, MCAOs are most frequent in the North Atlantic and the associated unique cloud regime can often be identified in visible satellite imagery (e.g., Abel et al., 2017; Brümmer, 1999; Geerts et al., 2022; Renfrew & Moore, 1999; Sanchez et al., 2022; Terpstra et al., 2021). More specifically, Fletcher et al.…”

“…The advent of satellite meteorology has evolved our understanding of MCAOs, as its unique cloud regime can often be identified in visible imagery (e.g., Abel et al., 2017; Brümmer, 1999; Geerts et al., 2022; Renfrew & Moore, 1999; Sanchez et al., 2022; Terpstra et al., 2021). Beyond the visible spectrum, clouds and precipitation in remote locations can now be observed via retrievals by CloudSat, a polar‐orbiting satellite with a W‐band radar onboard and measurement capabilities up to |82$${}^{\circ}$$| latitude (Stephens et al., 2002).…”

“…Globally, MCAOs are most frequent in the North Atlantic and the associated unique cloud regime can often be identified in visible satellite imagery (e.g., Abel et al, 2017;Brümmer, 1999;Geerts et al, 2022;Renfrew & Moore, 1999;Sanchez et al, 2022;Terpstra et al, 2021). More specifically, Fletcher et al (2016a) identified that the highest frequency and strength (via lapse rate) of North Atlantic MCAOs occur along the Gulf Stream or western continental boundary, Labrador Sea, south of Greenland, and in the Norwegian Sea (Fletcher et al, 2016a).…”

Long-range transported continental aerosol in the Eastern North Atlantic: three multiday event regimes influence cloud condensation nuclei

“…Changes in specific aerosol properties caused by the arrival of continental air masses over the ENA region have been described in previous literature. Namely, increased concentrations of submicron aerosol particles have been reported in the Western and Eastern North Atlantic by a number of previous studies (Garrett and Hobbs, 1995;Logan et al, 2014;Pennypacker and Wood, 2017;Sanchez et al, 2022).…”