CN -- TSI Condensation Counter (0.005 -> > 1 µm)

PCASP -- PMS Passive Cavity Aerosol Spectrometer Probe (0.1 - 3.0 µm)

FSSP-300 -- PMS Forward Scattering Spectrometer Probe (Model 300) (0.3 - 20 µm)

FSSP-100 -- PMS Forward Scattering Spectrometer Probe (Model 100) (2 - 50 µm)

260-X -- PMS One Dimensional Optical Array Probe Model 260-X (40 - 840 µm)

2D-C -- PMS Two Dimensional Optical Array Cloud Probe (25 - 800 µm)

2D-P -- PMS Two Dimensional Optical Array Precipitation Probe (200 - 6400 µm)

PLWCC -- Left Wing Hot wire Liquid Water Probe
(Operating principles and characteristics)

PLWCC1 -- Right Wing Hot Wire Liquid Water Probe
(Operating principles and characteristics)

PVM -- Particle Volume Monitor

RICE -- Rosemount Icing Detector
(Operating principles and characteristics)

The operating principles and characteristics were written by Darrel Baumgardner.

The flight-by-flight tabulation of how each of the eleven cloud and aerosol microphysical instruments performed on the 16 research flights is summarized in Table I. The performance is categorized as good, bad, or intermittent. Good means that the instrument operated within expected performance characteristics throughout the flight, Bad means that some malfunction prevented the instrument from working throughout the flight, and Intermittent means that there were period in which the data is suspect due to either environmental (icing or vibration) or instrumental problems.

A detailed second by second evaluation has not been made of the measurements. Each of the instrumentÆs performance is summarized below with guidelines provided to assist the investigator in evaluating specific measurements, e.g., hints are provided for detecting questionable data or for selecting one instrument over another when there are redundant measurements.

Figures 1-32 provide visual summaries that compare comparable measurement techniques and to illustrate potential problems. Figures 1-16 are scatter plots of the sixteen flights that compare the LWCs from the two hot wire probes and the PVM with LWC derived from the FSSP-100. The straight lines represent 1^st order, least square fits to each of the three comparisons. The correlation coefficients are also given to represent the amount of scatter.

Figures 17-32 have three plots on each figure that show vertical profiles from the concentration measurements made from the CN, PCASP, and the FSSP-300, the three instruments whose primary function is to measure aerosols and that should respond more or less in a similar fashion as they go through aerosol layers. Their differences in size range, however, will appear as large differences (sometimes) in relative concentrations. Normally, FSSP300 < PCASP < CN. The exception to this will be in clouds when it is sometimes possible for the PCASP to measure less than the FSSP-300 because of the inlet heating of the PCASP and subsequent volatilization of some fraction of the particles. The other two scatter plots compare FSSP-300 and FSSP-100 concentrations and 2D-C and 2D-P concentrations, respectively.

Flight 1 LWC Comparisons
Flight 2 LWC Comparisons
Flight 3 LWC Comparisons
Flight 4 LWC Comparisons
Flight 5 LWC Comparisons
Flight 6 LWC Comparisons
Flight 7 LWC Comparisons
Flight 8 LWC Comparisons
Flight 9 LWC Comparisons
Flight 10 LWC Comparisons
Flight 11 LWC Comparisons
Flight 12 LWC Comparisons
Flight 13 LWC Comparisons
Flight 14 LWC Comparisons
Flight 15 LWC Comparisons
Flight 16 LWC Comparisons
Flight 1 Concentration Comparisons
Flight 2 Concentration Comparisons
Flight 3 Concentration Comparisons
Flight 4 Concentration Comparisons
Flight 5 Concentration Comparisons
Flight 6 Concentration Comparisons
Flight 7 Concentration Comparisons
Flight 8 Concentration Comparisons
Flight 9 Concentration Comparisons
Flight 10 Concentration Comparisons
Flight 11 Concentration Comparisons
Flight 12 Concentration Comparisons
Flight 13 Concentration Comparisons
Flight 14 Concentration Comparisons
Flight 15 Concentration Comparisons
Flight 16 Concentration Comparisons

The CN counter had a leak in the internal plumbing during the first two flights and the data are unusable. The remainder of the data are good, although in cloud data might be contaminated by spurious particle formation from droplet or ice crystal breakup.

The PCASP was operational except for flights 14-16 when it was not operated due to a broken pump that could not be repaired in time to complete the project. In flights 5 and 6 the measurements should be used with caution as they appear to be occasionally contaminated with noise and have values larger than the CN, an occurrence that should not happen. The concentrations from this instrument will not reflect accurate values and size distributions will be biased towards smaller sizes when in cloud because of particle volatilization. There is also some evidence, occasionally, or particle breakup contamination. The first size channel of this instruments has been excluded from the total concentration calculation because of evidence that it becomes contaminated from electronic noise occasionally.

The FSSP-300 was completely operational throughout the project. In clouds, it may undersize larger particles but this has yet to be quantified. Its performance in the presence of irregular, non-spherical ice particles is also unquantifiable and the data showed be viewed with caution when the 2D-C is showing significant concentrations. In addition, the first channel of this instrument is seen to occasionally be contaminated by electronic noise. For this reason, the concentrations calculated from this probe have had channel 1 counts removed.

The FSSP-100 failed on flights 9 and 13 and no data is available for those flights from this instrument. During those flights, however, a large fraction of the time the majority of water droplets were smaller than 20 m m, so the FSSP-300 can be used as a proxy for the 100, though caution must be used because of the response of the FSSP-300 to aerosols as well as water droplets. On flights 1 and 5, and maybe on other flights, there was significant buildup of ice on the inlet of the FSSP that cause intermittent dropouts in the data. In addition, data system failures during the first flight introduced large spikes in the data.

As with the FSSP-300, non-spherical ice particle are incorrectly sized and some limited research has indicated that the result is an oversizing of particles and subsequent overestimate of water content.

The 260-X data must be viewed with great caution. It suffered from alignment problems throughout the project because of the temperature extremes and vibration of the C-130. The data have been filtered by eliminating the first three channels from the concentration calculations, since these channels reflect the alignment problems most often. In addition, the end diode voltages should be monitored when selecting 260X data for analysis. If either of the end diode values are below 0.5 volts, then the probability of erroneous data is high.

With the exception of the first flight when the interface card failed, these instruments worked without fail. There are generally very low 2D-P concentrations as ice particles were normally quite small and below the detection range of this instrument.

These are virtually identical instruments that are located on the left and right wings, respectively. PLWCC stopped working after Flight 7 and was not repaired until flight 14. PLWCC1 operated to expected performance throughout the project.

The hot wire probes begin losing their sensitivity when droplets exceed 30 m m or so and these instruments will subsequently underestimate LWCs when significant fractions of water mass are in droplets greater than this size. The hot wire probes respond very little to ice crystals.

The PVM was operated on the C-130 for the first time on the SHEBA project. This was a new instrument that was purchased after the SCMS project. In the first two flights, the data are intermittent because of defective wiring and solder connections in the instrument that apparently was a result of poor workmanship at the manufacturer. Once the RAF technical staff thoroughly touched up questionable solder connections, the instrument operated as expected.

The PVM has an upper limit somewhere between 40-50 um and will underestimate LWCs in larger droplets. Its response to non-spherical particles is also not quantified.

The manufacturer (Gerber Inc.) has notified the RAF that the calibration that was supplied with the instrument is incorrect due to problems with a laboratory standard, used to calibrate the RAF instrument, that apparently was malfunctioning. The manufacturer plans to send the RAF a new calibration coefficient for the probe once he establishes a new standard, but at this time indicates that the RAF probe is most likely underestimating the LWC. He could not estimated the amount of underestimation; however, this would most like move the PVM values closer to those of the FSSP.

The Rosemount icing probe was inoperational in the first three flights but worked well thereafter. This instrument responds very little to ice crystals, but is a very good indicator of supercooled water. At this time it can only be used qualitatively to tell when water is liquid or frozen.

Figures 1-16 show that the correlation is generally good in the comparison of the FSSP with the other three measurements of LWC. It can be seen however, that the FSSP is usually a factor of 2-3 larger than the hot wire probes, and about 40% higher than the PVM. It is not clear at this time as to which LWC best represents the actual cloud water. It is likely that the FSSP measurements are biased by ice particles and the diameter-cubed relationship of the derived LWC will cause large bias errors if the sizing is incorrect. The FSSP was calibrated carefully with particles of known size, however, so there remains a question of where additional errors might be introduced. The hot wire probes are showing nearly identical results, but their location close to the leading edge of the wings are cause for concern. As a test, one hot-wire was mounted in a more extended position during SHEBA, but there are no apparent differences in response. The PVM likely provides the most accurate measurement of LWC, even though it might have biases introduced by ice crystals, or may be underestimating the water mass in larger droplets.

Additional information on all of the cloud passes are available by looking at the RAF SHEBA field program web site and selecting "cloudpasses". Each of the vertical profiles and horizontal transects through clouds during every research flight are documented as plots of particle concentration and LWC, as well as the meteorological parameters of temperature, water vapor mixing ratio, potential temperature, and the wind speed and direction.

The location of each of the instruments on the aircraft may be found at this same web site by selecting "instrumentation".