The NASA ACTIVATE Mission
Armin Sorooshian, Leong Wai Siu, Kelly M. Butler, Michael A. Brunke, Brian Cairns, Seethala Chellappan, Jingyi Chen, Yonghoon Choi, Ewan Crosbie, Lauren Cutler, Joshua P. DiGangi, Glenn S. Diskin, R. A. Ferrare, Johnathan W. Hair, C. A. Hostetler, Simon Kirschler, Mary M. Kleb, Xiangyu Li, Hongyu Liu, Allison McComiskey, Soodabeh Namdari, David Painemal, Joseph S. Schlosser, Taylor Shingler, Michael A. Shook, Sam J. Silva, Kenneth Sinclair, William L. Smith, Cassidy Soloff, Snorre Stamnes, Shuaiqi Tang, Kenneth L. Thornhill, Florian Tornow, George Tselioudis, Bastiaan van Diedenhoven, Christiane Voigt, Holger Vömel, Hailong Wang, Edward L. Winstead, Yike Xu, Xubin Zeng, Bo Zhang, Luke D. Ziemba, Paquita Zuidema
Abstract
Abstract The NASA Aerosol Cloud Meteorology Interactions over the Western Atlantic Experiment (ACTIVATE) conducted 162 joint flights with two aircraft over the northwest Atlantic to study aerosol–cloud interactions (ACIs), which represent the largest uncertainty in estimating total anthropogenic radiative forcing. The combination of a high-flying King Air and low-flying HU-25 Falcon, equipped with remote sensing and in situ instruments, characterized trace gases, aerosol particles, clouds, and meteorological variables with data collected nearly simultaneously below, within, and above marine boundary layer (MBL) clouds. Flights spanning warm and cold seasons across 3 years (2020–22) provided a broad range of conditions associated with aerosol particles, cloud properties (including particle size and phase), and meteorology, ideally suited for robust ACI calculations and assessing how well models simulate a wide range of MBL clouds from stratiform to cumulus. ACTIVATE data suggest that drivers of cloud droplet number concentration N d , including aerosol particles and MBL dynamics, vary between winter and summer months with a stronger potential to convert aerosol particles into cloud droplets in winter. Models of varying complexity not only highlight some skills in simulating winter and summer cloud types but also identify challenges that still need to be addressed such as treatment of turbulence, wet scavenging, and mesoscale organization. Remote sensing advances range from new retrieval methods for N d , cloud phase classification, vertically resolved aerosol and cloud condensation nuclei number concentration, and ocean surface wind speed. This work describes these scientific and technological advances along with efforts in outreach and open data science. Significance Statement Depending on the number and type of aerosol particles there are in the air, the properties of cloud droplets can vary in number concentration, size, and lifetime, and this leads to varying effects of clouds on climate and weather. We took an ambitious approach to investigate aerosol–cloud interactions, which represent the largest uncertainty in estimating human impacts on climate change. The NASA ACTIVATE mission conducted 162 joint airborne flights over the northwest Atlantic with two spatially coordinated planes making measurements relevant to understanding clouds spanning the continuum from stratiform to cumulus clouds. Along with newfound knowledge of how clouds evolve and interact with aerosol particles, extensive technological advancements were made assisted by the carefully designed sampling strategy.