Impacts of long-range transport of aerosols on marine-boundary-layer clouds in the eastern North Atlantic

Creators: Wang, Yuan; Zheng, Xiaojian; Dong, Xiquan; Xi, Baike; Wu, Peng; Logan, Timothy; Yung, Yuk L.

Abstract

Vertical profiles of aerosols are inadequately observed and poorly represented in climate models, contributing to the current large uncertainty associated with aerosol–cloud interactions. The US Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA) aircraft field campaign near the Azores islands provided ample observations of vertical distributions of aerosol and cloud properties. Here we utilize the in situ aircraft measurements from the ACE-ENA and ground-based remote-sensing data along with an aerosol-aware Weather Research and Forecast (WRF) model to characterize the aerosols due to long-range transport over a remote region and to assess their possible influence on marine-boundary-layer (MBL) clouds. The vertical profiles of aerosol and cloud properties measured via aircraft during the ACE-ENA campaign provide detailed information revealing the physical contact between transported aerosols and MBL clouds. The European Centre for Medium-Range Weather Forecasts Copernicus Atmosphere Monitoring Service (ECMWF-CAMS) aerosol reanalysis data can reproduce the key features of aerosol vertical profiles in the remote region. The cloud-resolving WRF sensitivity experiments with distinctive aerosol profiles suggest that the transported aerosols and MBL cloud interactions (ACIs) require not only aerosol plumes to get close to the marine-boundary-layer top but also large cloud top height variations. Based on those criteria, the observations show that the occurrence of ACIs involving the transport of aerosol over the eastern North Atlantic (ENA) is about 62 % in summer. For the case with noticeable long-range-transport aerosol effects on MBL clouds, the susceptibilities of droplet effective radius and liquid water content are −0.11 and +0.14, respectively. When varying by a similar magnitude, aerosols originating from the boundary layer exert larger microphysical influence on MBL clouds than those entrained from the free troposphere.

Additional Information

© Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License. Received: 22 Jun 2020 – Discussion started: 27 Jul 2020 – Revised: 05 Oct 2020 – Accepted: 09 Oct 2020 – Published: 02 Dec 2020. This article is part of the special issue "Marine aerosols, trace gases, and clouds over the North Atlantic (ACP/AMT inter-journal SI)". It is not associated with a conference. This study was primarily supported by the collaborative NSF grant (award nos. AGS-1700727, 1700728). We acknowledge helpful discussions on the model setup with Zheng Lu at Texas A&M University. We thank the instrument mentors of the AMS, SP2, and CPC instruments and the individuals collecting measurements during the ACE-ENA field campaign. We also acknowledge high-performance computing support from Pleiades provided at NASA Ames. All requests for materials in this paper should be addressed to Yuan Wang (yuan.wang@caltech.edu). This research has been supported by the National Science Foundation, Directorate for Geosciences (grant nos. AGS-1700727, AGS-1700728, and AGS-1700796). Author contributions. YW conceived and designed the research. YW performed the WRF simulations. YW and XZ performed the data analyses and produced the figures. YW wrote the paper. All authors contributed to the scientific discussions and preparation of the manuscript. Data availability. All the WRF model simulation output used for this research can be downloaded from the corresponding author's website at http://web.gps.caltech.edu/~yzw/share/Wang-2020-ACP-Azores (Wang, 2020). The aircraft and ground-based measurements used in this study were obtained from the Atmospheric Radiation Measurement (ARM) program sponsored by the US Department of Energy (DOE) Office of Energy Research, Office of Health and Environmental Research, and Environmental Sciences Division. The data can be downloaded from https://adc.arm.gov/discovery/#/results/site_code::ena (Atmospheric Radiation Measurement Data Center, 2020). The CAMS global aerosol reanalysis product at pressure level used in this study can be downloaded at https://apps.ecmwf.int/datasets/data/cams-nrealtime/levtype=pl/ (European Centre for Medium-Range Weather Forecasts, 2020). ERA5 data are available for download via the data archive at the National Center for Atmospheric Research, Computational and Information Systems Laboratory (https://doi.org/10.5065/D6X34W69) (European Centre for Medium-Range Weather Forecasts, 2017). The authors declare that they have no conflict of interest. Review statement. This paper was edited by Hailong Wang and reviewed by Michael Diamond and one anonymous referee.

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