DOI: 10.35097/1935
title: PPD-2K Ice Fog Particle Size and Shape Distributions from ALPACA

description: This data set contains particle size distributions of spherical and aspherical cloud particles between 7.9 and 107 microns with a 300-second time resolution calculated using the Particle Phase Discriminator Mark. 2 Karlsruhe Edition (PPD-2K). The PPD-2K detects individual cloud particles passing a 532 nm laser beam using two nested trigger detectors. The trigger signal is recorded with a maximum rate of 11 kHz that can be used to derive particle size distributions by using the procedure described in Vochezer et al. (2016), doi:10.5194/amt-9-159-2016. For a sub-set of triggered particles a two-dimensional (2-D) scattering pattern is recorded that can be analysed for particle sphericity, shape and complexity by a specifically developed image analysis software. More information on the analysis of particle complexity using the k-value can be found in Schnaiter et al., 2016, doi.org/10.5194/acp-16-5091-2016.
From the numbers of observed spherical and aspherical 2-D scattering patterns the fractions of spherical and aspherical particles are derived. Multiplication of those number-based fractions with the total particle size distribution yields phase-specific particle size distribution. The uncertainty due to the fact that the imaged particles are a subset of all sampled particles can be estimated from the Clopper–Pearson confidence limits. The data was collected during the ALaskan Pollution And Chemical Analysis (ALPACA) field project, where PPD-2K was operated by the University of Alaska Fairbanks between January 28th and February 3rd, 2022. The measurement location was 64.83025°N and 147.66654°W.

Funding statement:
The PPD-2K instrument was provided by Karlsruhe Institute of Technology and funded by the German Helmholtz Association, through its research program “Atmosphere and Climate (ATMO)”.
These data were collected by the University of Alaska, Fairbanks researchers as part of a project supported by the Broad Agency Announcement Program from the U.S. Army Cold Regions Research and Engineering Laboratory (ERDC-CRREL) under Contract No. W913E521C0017 from the U.S. Army Basic Research Program (Program Element 0603119A, Ground Advanced Technology).
description: This netCDF file contains PPD-2K measurements taken during the ALPACA field project. The variables in the file are:
- Time: seconds after midnight 
- Dp: bin midpoint diameters in microns
- dNdlogDp: Total particle size distribution normalised with bin width as a function of time and Dp in cm-3
- N: Total concentration as a function of time in cm-3
- N_column: Concentration of particles classified as column as a function of time in cm-3 (contains confidence intervals)
- N_droplets: Concentration of particles classified as spherical as a function of time in cm-3 (contains confidence intervals)
- N_ice: Concentration of particles classified as aspherical as a function of time in cm-3 (contains confidence intervals)
- N_plate: Concentration of particles classified as plates as a function of time in cm-3 (contains confidence intervals)
- N_rough_column: Concentration of particles classified as roughened columns as a function of time in cm-3 (contains confidence intervals)
- N_rough_plate: Concentration of particles classified as roughened plates as a function of time in cm-3 (contains confidence intervals)
- Column_fraction: Size segregated fraction of columns as a function of time and Dp
- Plate_fraction: Size segregated fraction of plates as a function of time and Dp
- Rough_column_fraction: Size segregated fraction of roughened columns as a function of time and Dp
- Rough_plate_fraction: Size segregated fraction of roughened plates as a function of time and Dp
- Kvalue: Median size segregated k-value as a function of time and Dp
- Variance: Median size segregated variance as a function of time and Dp
See more information on the data products from Vochezer et al. (2016), doi:10.5194/amt-9-159-2016, and Schnaiter et al., 2016, doi.org/10.5194/acp-16-5091-2016.