New and Updated Cloud Droplet Number Concentration Data Available

Published: 8 April 2025

The plot shows calculated droplet number concentration for two different periods. The droplet number concentration is generally seen between 0.0 and 0.4 m-3. There is also a box showing quality check results on the calculated droplet number concentration variable. — This sample plot shows droplet number concentration from the EPCAPE ARM Mobile Facility site in La Jolla, California. Image is provided by Chitra Sivaraman, Pacific Northwest National Laboratory.

The Droplet Number Concentration value-added product (NDROP VAP) has been processed for the 2023–2024 Eastern Pacific Cloud Aerosol Precipitation Experiment (EPCAPE) in La Jolla, California. In addition, the VAP has been updated to use reprocessed multifilter rotating shadowband radiometer data from the Eastern North Atlantic (ENA) atmospheric observatory in the Azores.

Cloud droplet number concentration is an important factor in understanding aerosol-cloud interactions. NDROP provides an estimate of cloud droplet number concentration for overcast liquid water clouds retrieved using cloud optical depth from the Atmospheric Radiation Measurement (ARM) User Facility’s multifilter rotating shadowband radiometers and liquid water path from ARM’s microwave radiometers.

When cloud-layer information is available from vertically pointing lidar and radar in the Active Remote Sensing of CLouds (ARSCL) VAP, NDROP also provides estimates of the adiabatic liquid water path, which is calculated assuming the cloud is formed by adiabatic cooling, and an adiabatic parameter that indicates how divergent the liquid water path is from the adiabatic case.

NDROP data are now available for the full duration of the EPCAPE campaign—February 15, 2023, to February 14, 2024—at the ARM Mobile Facility site on the Ellen Browning Scripps Memorial Pier.

The ENA data are from June 1, 2014, to April 14, 2021. VAP code did not change when the data were reprocessed. The reprocessing occurred as the input data for the ENA were reprocessed.

Scientists can begin using the new and updated droplet number concentration data now.

More information about NDROP can be found on the VAP web page.

For questions or to report data problems, please contact ARM translator Damao Zhang or developer Chitra Sivaraman.

Access the NDROP data in the ARM Data Center. (To download the data, first create an ARM account.)

To cite the data, please use doi:10.5439/1131339.

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ARM is a DOE Office of Science user facility operated by nine DOE national laboratories.