Data from: Supersaturation and critical size of cloud condensation nuclei in marine stratus clouds
Cite this dataset
Svensmark, Henrik et al. (2024). Data from: Supersaturation and critical size of cloud condensation nuclei in marine stratus clouds [Dataset]. Dryad. https://doi.org/10.5061/dryad.cnp5hqccr
Abstract
Observations of marine stratus clouds in clean air off the Californian coast reveal a functional relationship between the number of cloud condensation nuclei (CCN) and supersaturation. Satellite-derived liquid droplet density estimates the number density of CCN. Combining the estimated supersaturation using Kohler theory, global maps of supersaturation and the critical activation size of CCN are estimated. Here, we show that high supersaturation >0.5% persists over the oceans with a critical CCN size of 25-30 nm, which is smaller than the conventional wisdom of 60 nm. Independent support for such high supersaturation in the marine cloud is obtained from CCN measurements provided by the "Atmospheric Tomography Mission". Higher supersaturation implies smaller activation size for CCN making cloud formation more sensitive to changes in aerosol nucleation.
README: Data from: Supersaturation and critical size of cloud condensation nuclei in marine stratus clouds
https://doi.org/10.5061/dryad.cnp5hqccr
The data set consists of four netCDF files, one with a critical mean diameter of Cloud Condensation Nuclei and a file of the corresponding supersaturation, in a 1x1 deg grid covering the oceans. In addition, two files where the supersaturation and critical diameter of Cloud Condensation Nuclei are within a 90% confidence interval. i.e., there is a 90% probability that the supersaturation is higher than the given values and the critical diameter of Cloud Condensation Nuclei is smaller.
The data files are the data used to produce the four panels of Fig. 3 of the GRL paper.
Description of the data and file structure
The files are:
Critical_d.nc contains 360 points of longitude (-179.5 to 179.5) and 180 points of latitude (-89.5 to 89.5), and a critical diameter in a (360,180) grid. Land pixel values are set to -99
Supersaturation.nc contains 360 points of longitude (-179.5 to 179.5) and 180 points of latitude (-89.5 to 89.5), and an effective supersaturation in a (360,180) grid. Land pixel values are set to -99
Critical_d90%.nc contains 360 points of longitude (-179.5 to 179.5) and 180 points of latitude (-89.5 to 89.5) and a critical diameter in a (360,180) grid. Land pixel values are set to -99. The critical diameter is 90% likely to be smaller than the given value.
Supersaturation90%.nc contains 360 points of longitude (-179.5 to 179.5) and 180 points of latitude (-89.5 to 89.5), and an effective supersaturation in a (360,180) grid. Land pixel values are set to -99. The supersaturation is 90% likely to be larger than the given value.
Methods
The present data set is the critical size of cloud condensation nuclei of low clouds over the oceans and the corresponding supersaturations.
Satellite retrieval of Liquid Water Path, Optical Thickness, and cloud fraction makes it possible to estimate the average number density of warm cloud droplets over the oceans. An empirical relationship between effective supersaturation and cloud number density allows for determining the effective supersaturation in a 1x1 deg pixel. Finally, Kohler's theory and the obtained supersaturation give a critical CCN size.
Funding
Technical University of Denmark