PDI Concentration Data Chuang, Patrick Earth and Planetary Sciences Department University of California, Santa Cruz Earth and Marine Sciences Building 1156 High St Santa Cruz, Ca 95064 831-459-1501 pchuang@pmc.ucsc.edu http://people.ucsc.edu/~pchuang/ Rossiter, Dione Earth and Planetary Sciences Department University of California, Santa Cruz Earth and Marine Sciences Building 1156 High St Santa Cruz, Ca 95064 831-459-1724 drossite@es.ucsc.edu 1.0 DATA SET OVERVIEW: This data set is comprised of time and Liquid Water Content (LWC) data. LWC was calculated using data collected by the Phase Doppler Interferometer and is in units of g/m^3. Time period covered by the data = start: 16 July 2008; end: 15 August 2008 Physical location: left inboard of Twin Otter aircraft. 2.0 INSTRUMENT DESCRIPTION: The Artium Flight Phase Doppler Interferometer is based on the phase-Doppler interferometry technique. One advantage of the PDI over other standard cloud probes in the same size range is the independence of drop sizing from light intensity, making the measurement more robust under conditions of optics contamination and electronic noise. The PDI fundamentally measures the diameter, velocity and arrival time of individual cloud drops. Drops are assumed to be spherical with known refractive index, assumptions that are typically satisfied in warm clouds. From the fundamental quantities, we derive drop size distributions at fixed frequency by determining the instrument view volume. Although the full size range of the PDI during POST is ~3 to 150 microns diameter, counting statistics limit the practical size range to 3 to 100 microns diameter. Coincidence is theoretically predicted to be a very minor issue (less than 1% of events should suffer from coincidence), and no attempt to correct such a small effect is made. For POST, we will not report velocity distributions but they are available on request. For more information, see a recently published paper that describes the instrument principle and treatment of data in great detail: Chuang, P. Y., E. W. Saw, J. D. Small, R. A. Shaw, C.M. Sipperley, G. A. Payne, and W. D. Bachalo, .Airborne phase Doppler interferometry for cloud microphysical measurements,. Aerosol Sci. Tech., 42, 685-703, 2008. Specifications: Size range: 3 to 100 microns diameter Size accuracy: ~1 to 2 microns Size bins: 128 log-spaced bins Concentration accuracy: ~5% for each size bin + counting uncertainty View volume: approx. 0.5 mm^2 typical (depends on drop size and can be varied) 3.0 DATA COLLECTION AND PROCESSING: The ARTIUM AIMS software provides raw measurements of individual drops measured by the PDI. This includes the arrival time, size, velocity, PVC weight, signal to noise ratio and the rejection criteria. This data is fed into a processing code written primarily by Jennifer D. Small (UCSC). This program reads the PDI data and calculates a corrected PDI view volume for each measured droplet event using the AIMS correction equation and a probe volume diameter equation created and provided by Patrick Y. Chuang (UCSC). The data is binned into 128 logarithmically spaced size bins and a number distribution file is created. The number distribution file is then used with the probe volume diameter calculations and information from plane measurements (the Twin Otter) to calculate the concentration of drops within each size bin. The concentration file is then used to calculate the liquid water content, volume, surface area, spectral widths, and equivalent radar reflectivity. Several quality control procedures take place before data is posted. Before a research mission, the PDI is inspected by ARTIUM Technologies to ensure the instrument is working properly. Before each flight, a basic evolution of instrument is also preformed. During these evaluations, drops of an approximately known sizes and speeds are sent through the PDI beam intersection. Drop size, speed, and rejection rate are inspected to ensure measured values are reasonable. Droplets are rejected during collection if their trajectory or other qualities are not validated. During flight, drop size, speed, and rejection rates are also inspected periodically to ensure in-cloud values are reasonable. A data intercomparison is preformed after PDI data has been processed. Derived PDI LWC data is compared to Gerber Probe LWC data. This is our main method for post-processing quality control and is a final check for ensuring the data is in its most accurate form. 4.0 DATA FORMAT: Data file structure = Tab delimited ASCII Data format, layout, parameters with units Column Nr: Description: 1 UTC time given in seconds since midnight 2 PDI total liquid water content (g/m^3) for each second 3 PDI total lwc (g/m^3) corrected using the fssp roll-off efficiency curve 4 PDI total lwc (g/m^3) corrected using the gerber roll-off efficiency curve 5 PDI total lwC (g/m^3) corrected for the king probe roll-off efficiency curve 6 Gerber lwc (g/m^3) for each second The second column within the data file is the PDI calculated LWC derived from the PDI concentration file. The next three columns are the same PDI calculated LWC but which include corrections based on differen instruments and their roll-off diameters. Meaning columns 3-5 LWC calculations only account for the PDI bin sizes which correspond to the FSSP, Gerber,or King Probe size range. The calculations will eliminate that liquid water that was measured by the PDI system that was "out of range" of the different probes due to efficiency issues. In those cases the liquid water content will be lower than without the efficiency correction. Column 3 considers the FSSP size range being 0.70 to 45.75 microns. Column 4 considers the gerber probe efficiency curve of y = 0.8545 + 0.2142x - 0.00068x^2 where x is the geomean bin size. We have found that the orginal Gerber probe efficiency equation needed to be shifted by 7 microns in diameter. Column 5 considers the King Probe Response Curve from Biter et. al 1987, J. Atmos. Ocean. Tech. of y = 1.0034 - 0.0041x + .000006x^2 where x is the geomean bin size. Column 5 is the Gerber LWC data pulled directly from PVMdata Version 1.0, 12/1/08. Sampling interval: continuous Frequency: binned to 1 Hz Range: 0-8000 Data version (number and date): 1.0; 5, November 2009 5.0 DATA REMARKS: During the Flight 1, an autosetup (a processor feature) was preformed during flight. In short, this feature will allow the PDI to sample cloud air and, from the range of drops measured during a particular time range, determine the most appropriate processor settings to use. These settings should stay the same throughout the remainder of the mission. Sometime during Flight 2, the processor settings changed. This change was not noticed until after Flight 6. All of these days were reprocessed using an “updater” supplied to us by ARTIUM Technologies. This updater read the old data and corrected it using the appropriate processor settings. More information and details regarding these changes can be accessed by contacting Dione L. Rossiter. Flights 7 through 11 preceded with correct processor settings and went normally. During Flight 12, autosetup was run again. During this day, we also began to see drop velocities forming 3 groups. We came to determine that these velocities were due to the PDI containing a laser which would unpredictably change intensities. Drops velocity should match the velocity of the Twin Otter during flight (45-65 m/s) therefore, the code was re-written to ignore all drops which were measured outside of this velocity range. The measured velocities within this range are considered accurate data. 6.0 REFERENCES: Chuang, P. Y., E. W. Saw, J. D. Small, R. A. Shaw, C.M. Sipperley, G. A. Payne, and W. D. Bachalo, Airborne phase Doppler interferometry for cloud microphysical measurements,. Aerosol Sci. Tech., 42, 685-703, 2008.