Advancing Aerosol-Cloud-Meteorology Knowledge through ACTIVATE

Advancing Aerosol-Cloud-Meteorology Knowledge through ACTIVATE

Despite the crucial role of clouds in maintaining the Earth’s energy balance and water cycle, their formation and evolution processes still have large uncertainties among the international scientific research community. Expanding knowledge on the relationships between aerosols and clouds is key to understanding different cloud properties and their resulting impact on climate and weather. The Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) aims to provide a unique dataset of aerosol-cloud-meteorology interactions for international model intercomparison and improvement, in addition to process-based studies. In an innovative approach based upon the results of numerous previous field studies, ACTIVATE generates statistics of aerosols and clouds under a wide range of meteorological conditions to address its scientific objectives. ACTIVATE will quantify aerosol and cloud relationships, reduce model uncertainty, improve understanding of the factors governing cloud micro/macro-physical properties and their relationships to cloud effects on aerosol, and improve remote sensing capabilities. ACTIVATE’s approach more effectively exploits the airborne sampling advantages and mitigates the previous known limitations. To achieve the sampling objectives, ACTIVATE employs two aircraft, the King Air and the HU-25. The King Air aircraft is equipped with remote sensing instrumentation and dropsondes while the HU-25 is equipped with an extensive instrument payload for in-situ measurements of aerosol, cloud properties, and meteorological parameters, as well as several trace gas measurements. The dual aircraft approach allows more comprehensive characterization of aerosol and cloud properties in a single atmospheric column at the same time and enables a sampling strategy consisting of “statistical surveys” (Figure 1) and mechanistic process studies. This research will advance knowledge of atmospheric composition, the Earth’s water and energy cycle, climate variability and change, and weather.

ACTIVATE Nominal Profile Figure

Figure 1. Nominal profile of a single cloud ensemble conducted with ACTIVATE’s dual aircraft approach. The HU-25 Falcon conducts in situ measurements of gases, aerosols, clouds, and meteorological parameters in the lower troposphere where boundary layer clouds evolve, whereas the King Air flies higher, at ~9 km, in a coordinated fashion to provide remote sensing data in the same vertical column while launching dropsondes along the flight track. A single flight including multiple ensembles of this approach are called “statistical survey” flights, which amount to about 90% of all ACTIVATE flights with the rest being process study flights with different flight designs. Image Source: ACTIVATE Science Team

The Atmospheric Science Data Center (ASDC) at NASA Langley Research Center will archive ACTIVATE data throughout the campaign. At this time, all current publication-quality data from the first and second deployments of ACTIVATE can be accessed via the ASDC ACTIVATE project landing page. Additional publication-quality data will become available in the near future.


Image Source:


Spatial Coverage:

(25°–50°N, 60°–85°W)

Temporal Coverage:


Scientific Objectives

  1. Quantify relationships between number concentrations of aerosol (Na), cloud condensation nuclei (CCN), and cloud droplets (Nd) and reduce uncertainty in model cloud droplet activation parameterizations.
  2. Expand process-level understanding and model representation of factors controlling cloud properties and their relationships with cloud effects on aerosol.
  3. Improve remote sensing capabilities in the retrieval of aerosol and cloud properties that relate to aerosol-cloud interactions.

Instruments Used

Two aircraft, the HU-25 Falcon and the King Air, are used to collect data for ACTIVATE. Each aircraft is equipped with an extensive suite of instrumentation detailed in the table below.

Platform Type Platform Relevant Instrument Study Area

Airborne  Platform

HU-25 Falcon

TSI Condensation Particle Counters

TSI Scanning Mobility Particle Sizer (SMPS)

TSI Laser Aerosol Sizer (LAS)

TSI Nephelometer (TSI Neph)

f(RH) System: TSI 3563 Nephelometers and RH Controlled Humidifier

Particle Soot Absorption Photometer (PSAP)

Particle Into Liquid Sampler (PILS)

High-Resolution Time-of-Flight Aerosol Mass Spectrometer (AMS)

DMT Cloud Condensation Nuclei Spectrometer (CCN)

DMT Cloud Droplet Probe (CDP) and Cloud and Aerosol Spectrometer (CAS)

DMT Cloud Imagery Probe (CIP)

Axial Cyclone Cloud water Collector and offline chemistry (AC3)

Turbulent Air Motion Measurement System (TAMMS)

Rosemount Total Temperature Sensor 102 (TTS)

IR Sensor for Sea Surface Temperature


Diode Laser Hygrometer (DLH)

Edgetech frostpoint Hygrometer (cryo)

PICARRO Cavity Ring-Down Spectrometer

2B Technologies Ozone Monitor

Applanix POS AV

Aerosol properties

Cloud properties

Meteorological state parameters

Trace gases

Aircraft geolocation and attitude parameters

Airborne  Platform

King Air

High Spectral Resolution Lidar 2 (HSRL-2)

Research Scanning Polarimeter (RSP)


Applanix POS AV

Aerosols and cloud properties

Atmospheric profiling

Aircraft parameters

Access Data

The ASDC archives and distributes all currently available publication-quality data from the first and second deployments of ACTIVATE. In the future, the ASDC will distribute additional publication-quality data from the first two deployments, as well as the remaining deployments scheduled for 2021 and 2022. Data from ACTIVATE can be accessed on the ASDC ACTIVATE landing page, as well as on Earthdata Search.

Events of Interest

This section highlights events within the field campaign of particular scientific interest.


The first deployment of ACTIVATE was conducted in the winter of 2020 between February 14, 2020 and March 12, 2020. Several interesting events occurred during the first deployment, including a flight on February 29, 2020 in which forecasts suggested clear air sampling, but instead scientists encountered low clouds during the flight; this event demonstrated the importance of ACTIVATE in improving modeling of marine boundary layer clouds. The winter flights sampled cold air outbreak conditions, which are of special importance as climate models struggle to simulate the postfrontal clouds associated with these conditions. Flights in March included the first coordinated underflight with a satellite overpass that targeted the Advanced Spaceborne Thermal Emission and Reflected Radiometer (ASTER) aboard the TERRA satellite.

The first deployment was cut short due to the evolving COVID-19 situation, and the second deployment had to be postponed to the August/September time frame rather than the May/June time frame originally planned. During the second deployment, ACTIVATE flights encountered the impacts of the western United States wildfires, particularly those in California. Several flights were conducted in coordination with satellites including the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite and ASTER. Forty flights were conducted during these two deployments, including 35 joint flights.

The third ACTIVATE deployment began in January 2021 and, at the point of publication, is still in progress. The first science flight of the deployment was conducted on January 27th, and the first joint flight was conducted on February 3rd.

Major Findings

Though ACTIVATE is still in progress, intriguing information already is beginning to result from the data collected thus far. Early data has sampled a wide array of conditions that may impact cloud formation and evolution including different seasons, wildfires from the western United States in the summer of 2020, varying wind directions, varying cloud cover conditions, and varying precipitation conditions. The collection of data from such wide-ranging sources contributes to a vast dataset that will improve statistics in the international scientific research community. One example of ACTIVATE’s early findings is that cloud droplet concentration measured by the HU-25 appears to decrease moving away from the coast, confirming satellite observations. These cloud droplet concentrations cover a wide range in values, spanning several orders of magnitude. Additionally, in-situ cloud imaging data from early flights illustrate many different ice shapes such as column-like needle structures. Increasing cloud ice likely accelerates transitions from overcast cloud decks to broken cloud fields in cold air outbreaks (more information available in this publication by ACTIVATE scientists). The HSRL-2 lidar has detected unusual aerosol particle properties for the marine boundary layer (more information available in this poster presentation from the American Geophysical Union Fall Meeting of 2020), which has major implications for satellite aerosol typing from the Cloud-Aerosol LIdar with Orthogonal Polarization (CALIOP) instrument aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite.

Members of the ACTIVATE team have delivered a number of presentations at conferences such as those of the American Geophysical Union (AGU), with some listed below.

Relevant Publications

ACTIVATE Publications

ACTIVATE AGU Presentations:

Cairns, B., Alexandrov, M., van Diedenhoven, B., Crosbie, E., Hu, Y., Scarino, A. J., Shook, M., orooshian, A., Hair, J., Sinclair, K., Wasilewski, A., Hostetler, C., Moore, R., Shingler, T., & Ziemba, L. (2020). Using remotely sensed cloud top properties to look at drizzle formation [Conference presentation]. AGU Fall Meeting 2020, virtual location.

Ferrare, R., Hair, J., Hostetler, C., Harper, D., Seaman, S., Shingler, T., Cook, A., Vaughan, M., Diskin, G., DiGangi, J., Nowak, J., Moore, R., Ziemba, L., Winker, D., Shook, M., Fenn, M., Scarino, A. J., Crosbie, E., Thornhill, K. L., Robinson, C., Choi, Y., Liu, H., Zhang, B., Choi, H., Zuidema, P., Chellappan, S., Schlosser, J., & Sorooshian, A. (2020). Airborne HSRL2 Measurements of Enhanced Depolarization in Marine Aerosols [Poster presentation]. AGU Fall Meeting 2020, virtual location.

Sorooshian, A., & ACTIVATE Science Team (2020). The Aerosol Cloud meTeorology Interactions over the western ATlantic Experiment (ACTIVATE): Concept and First Results [Poster presentation]. AGU Fall Meeting 2020, virtual location.

Chellappan, S., Zuidema, P., Painemal, D., Li, X., Wang, H., Thornhill, K. L., Robinson, C., Chen, G., Shook, M., & Sorooshian, A. (2020). Investigating Cold Air Outbreaks over the Western North Atlantic Ocean [Poster presentation], AGU Fall Meeting 2020, virtual location.

Li, X., Wang, H., Ackerman, A. S., Cairns, B., Chellappan, S., Chen, G., Chen, J., Crosbie, E., Endo, S., Ferrare, R. A., George, G., Hair, J.W., Kirschler, S., Kleb, M. M., Moore, R., Painemal, D., Scarino, A. J., Shook, M., Shingler, T. J., Sorooshian, A., Thornhill, K. L., Tornow, F., Voigt, C., Zeng, X., & Zuidema, P. (2020). Large-eddy Simulations of Marine Boundary-layer Clouds during the ACTIVATE Campaign: Sensitivities to Large-scale Forcings [Poster presentation], AGU Fall Meeting 2020, virtual location.

Tornow, F., Ackerman, A. S., Fridlind, A. M., Cairns, B., Crosbie, E., Kaufmann, S., Kirschler, S., Li, X., Moore, R., Robinson, C. E., Shingler, T. J., Shook, M., Sorooshian, A., Thornhill, K.L., van Diedenhoven, B., Voigt, C., Wang, H., Winstead, E., & Ziemba, L. D. (2020). Cold air outbreaks during ACTIVATE: Observationally constrained large-eddy simulations of microphysically-mediated cloud regime transitions [Poster presentation], AGU Fall Meeting, 2020, virtual location.

Liu, H., Zhang, B., Moore, R., Ziemba, L., Choi, H., Painemal, D., Wang, H., Sorooshian, A., Hair, J., Ferrare, R., Crosbie, E., Shook, M., Scarino, A. J., Fenn, M., Hostetler, C., Chen, G., Kleb, M., Fairlie, D., Luo, G., Yu, F., Tackett, J., Vaughan, M., Diskin, G., Nowak, J., & DiGangi, J. (2020). Distribution and Sources of Tropospheric Aerosols Over the Western North Atlantic During ACTIVATE [Poster presentation], AGU Fall Meeting 2020, virtual location.

Dixon, R. D., Zhang, S., Zeng, X., Wan, H., & Holland, M. (2020). Extreme supersaturation in CESM2 and E3SM simulations: sensitivity to time-stepping and impact on model climate [Poster presentation], AGU Fall Meeting 2020, virtual location.

Brunke, M. A., Dixon, R. D., Cutler, L., Zeng, X., Sorooshian, A., & Thornhill, L. (2020). Evaluating the Roles of Dynamics, Physics, and Dynamics-Physics Interactions in CAM6 Simulated Clouds and Aerosols over the Western North Atlantic Ocean [Poster presentation]. AGU Fall Meeting, 2020, virtual location.

Ouyed, A., Zeng, X., Longtao, W., Posselt, D., & Su, H. (2020). Two-Stage Artificial Intelligence Algorithm for Calculating Atmospheric Motion Vectors [Poster presentation]. AGU Fall Meeting 2020, virtual location.