IMPACTS Cloud Microphysics This archive consists of data collected from five instruments on the NASA P-3 aircraft, the SPEC Hawkeye Cloud Particle Imager (CPI) and Fast Cloud Droplet Probe (FastCDP), the SPEC Two-Dimensional Stereo probe (2D-S), and two SPEC High Volume Precipitation Spectrometers (HVPS3). The 2D-S and HVPS3 are two- dimensional optical array probes which record images of particles that travel through their sampling area. The recorded images are then analyzed to produce particle size distributions from 20 microns to 3 centimeters in diameter. The FastCDP is a forward scattering instrument designed to measure the size and concentration of cloud droplets between 2 and 50 microns in diameter. The CPI is a high-resolution imager with a 256-level color depth. No particle concentration estimates have been attempted with the CPI. ----Probe specifications---- 2D-S: Two 128-element diode arrays, 10 microns per pixel HVPS3: 128-element diode array, 150 microns per pixel Hawkeye CPI: 1280x1024 element CCD, 2.3 microns per pixel Hawkeye FCDP: Forward scattering instrument The 2D-S records particles from two separate arrays, one with a vertical (top view) orientation, and one with a horizontal (side view) orientation. They are treated as two separate instruments in this dataset. There were two HVPS-3 instruments on this payload. The probe named "HVPS3A" was oriented horizontally, and the probe named "HVPS3B" was oriented vertically. ----Processing details---- Particle size distributions are given in terms of particle maximum dimension, which is defined as the diameter of the smallest circle than can completely enclose the particle image. Images that touch a side of the array are counted if the center of the particle is deemed to be within the array. The technique described in Field et al. (2006) has been applied to mitigate shattering artifacts on the 2D-S. The 2D-S and HVPS-3 had probe tips designed to minimize the amount of shattering. Optical depth of field for the 2D-S and HVPS-3 follows Lawson et al. (2006). "MergedHorizontal" and "MergedVertical" files have been produced for each flight, which are a combination the 2D-S for particles smaller than 1mm in diameter, the HVPS3 for particles larger than 1mm in diameter. Merged files are only available when both the 2D-S and HVPS3 are available at the specified orientation (horizontal or vertical). Bulk ice water content (IWC) is available in the size distribution files for the convenience of data users, which has been derived using a mass-size parameterization of mass=0.0061*(D^2.05) from Heymsfield et al. (2004). Note that this has been indiscriminately applied, and will not be valid in cases of rain, graupel, or ice habits that are not well represented by this mass-size parameterization. Other derived parameters are available in the files, including total number concentration (Nt), mean diameter (MND), median mass-weighted diameter (MMD), and median volume diameter (MVD). All derived parameters are computed using particles larger than 100 microns in diameter in order to avoid uncertainties with very small particles. Particle shape information is available in mean area ratio distributions and mean aspect ratio distributions. The area ratio is defined as the area of the particle divided by the area of a circle with the particle's maximum dimension. Aspect ratio uses the method described in Korolev and Isaac (2003). Droplet size distributions from the FastCDP were processed using software provided by the manufacturer. Particle images and shape information are not available from this instrument, all measured particles are assumed to be liquid in the derived variables. Periods of missing or poor data have been marked with a value of -999 in all variables. A probe quality flag is available to indicate where difficult probe conditions existed, such as low end-diode voltages, significant probe dead time, probe malfunction, or a high proportion of rejected particles. ----File naming convention---- Size distributions, shape distributions, and derived parameters are written in netCDF-4 files for all instruments. The two arrays on the 2D-S are identified by an 'H' for the horizontal array, and a 'V' for the vertical array. Files are named with the following convention: IMPACTS_PROBENAME-P3_YYYYMMDD_sizedistributions_v01.nc Particle image files for the HVPS3, 2D-S, and CPI are named with the following convention: IMPACTS_PROBENAME-P3_YYYYMMDD-HHMMSS_images_v01.png There is one image file available for each minute that a probe was in operation and collecting valid particles. ----Probe performance---- There were a total of 10 science flights during the IMPACTS 2020 campaign. The CPI, FastCDP, and HVPS3-A were operational for all flights. The HVPS3-B was operational for six flights between Feb 7th and Feb 25th. The 2D-S was operational for all flights except Feb 25th. ----Contacts---- Data Processing: Aaron Bansemer, bansemer@ucar.edu Data Collection: Michael Poellot, michael.poellot@und.edu ----References---- Field, P. R., A. J. Heymsfield, A. Bansemer, 2006: Shattering and Particle Interarrival Times Measured by Optical Array Probes in Ice Clouds. J. Atmos. Oceanic Technol., 23, 1357–1371. Heymsfield, A.J, Aaron Bansemer, Carl Schmitt, Cynthia Twohy, and Michael R. Poellot, 2004: Effective Ice Particle Densities Derived from Aircraft Data. J. Atmos. Sci., 61, 982–1003. Korolev, A., and G. Isaac, 2003: Roundness and Aspect Ratio of Particles in Ice Clouds. J. Atmos. Sci., 60, 1795–1808. Lawson, R.P., Darren O’Connor, Patrick Zmarzly, Kim Weaver, Brad Baker, Qixu Mo, and Haflidi Jonsson, 2006: The 2D-S (Stereo) Probe: Design and Preliminary Tests of a New Airborne, High-Speed, High-Resolution Particle Imaging Probe. J. Atmos. Oceanic Technol., 23, 1462–1477.