INSTRUMENT PERFORMANCE FOOTNOTES


Lawson probe performance footnote (Lawson): The PI- (Particle Imaging) Nephelometer digitally records images of particles as well as recording the particle's scattering phase function. Throughout the SUCCESS project the operation of the PI- Nephelometer was being refined and hardware and software problems were being sorted out. Much of the data recorded during the SUCCESS field project (especially the early missions) still has to be analyzed to get a more complete picture of the overall quality of the data. As mentioned above, the PI-Nephelometer records a particle's digital image as well as its scattering phase function. More emphasis was initially placed on the imaging system. When the probe was installed and operating, images were almost always recorded in the presence of particles. However, image detection efficiency and image quality varied, generally improving as the field season progressed. Scattered light from a particle is collected by optical fibers at 28 discreet angles. These data are used to define the scattering phase function. We are currently doing lab work to remove the effects of the electrical and optical systems on the light recorded at the 28 angles. Therefore, this report does not include the status of the scattered light data; that information will be forthcoming. The report (above) is a preliminary summary sheet of the opperational status of the PI-Nephelometer instrument during each of the DC-8 missions. We have included our own alpha-numeric classification scheme to describe the status of the PI-Nephelometer for the DC-8 flights. Hopefully, this will give a more complete picture of the operational status of the instrument. Gerber-Probe performance footnote (DeMott): The performance and data quality of the PVM on the DC-8 during SUCCESS, although quite good overall, was affected significantly by its interaction with the fairing in which it was mounted. A preliminary look at the PVM data suggests the following: 1) Mechanical interference of probe and fairing caused the loss of laser alignment in the earlier flights resulting in nearly total loss of data, 2) the fairing exposed to rain while the DC-8 was on the ground caused the optics of the probe to be adversely coated when the trapped water vented on the subsequent flight; some data was lost as a result, 3) laminar flow through the fairing was apparently lost during certain maneuvers of the DC-8; this condition appeared when the DC-8 was descending and caused significant noise in the outputs of the probe, 4) a small sine wave noise signal of about 1.47 Hz is superimposed on the IWC channel, and 5) the probe operated best when the DC-8 was flying horizontally. CVI (Counterflow Virtual Impactor) performance footnote (Twohy): The CVI was WORKING for all missions. There were some time segments (usually outside of clouds) when the CVI was used as a standard aerosol inlet. During these times, only total particle number (not ice water content) was available. These times are noted in the archive files. All CVI data are in the SUCCESS archive ("CV96????.DA1" files) Here are a few comments for investigators, who want to use CVI data:
  • This is still preliminary data. We don't anticipate any major changes, but there may be some despiking and improved baselining at a later date. Please let me know if you see anything that looks odd.
  • Please note that there were a few time periods when we were taking whole air or interstitial aerosol samples, rather than cloud samples. These are noted with a "1" or "2" in the "INLET" column. These were mostly clear air time periods, with a few exceptions (notably periods of 960508). Ice water content (IWC) is forced to 0 during these periods. These periods are listed at the end of this message, in addition to being noted in the arhive. If you really need IWC during one of these periods, contact me and we may be able to retrieve it with more involved processing. Also, note that IWC is really condensed water content, and so may include liquid contributions in mixed or liquid-phase clouds. We believe the IWC data are quite accurate (within about 10%), barring uncertainty due to mounting location on the aircraft. We are still waiting for airflow analysis from NASA/Ames to quantify this.
  • We have included a column, "N", that is the number of residual particles left after evaporating the ice crystals. Some of these values are quite high (> 100/cm3) in cirrus clouds. When large crystals are present, one crystal may produce more than one residual, either through crystal breakup or if crystals are aggregates with several nuclei or scavenged particles attached. We need to compare these data with those from a variety of other microphysical probes to determine exactly when this occurs, so stay tuned. Concentrations in contrails, wave clouds, and cirrus tops where primarily small (<100 micron) crystals are present DO reflect the actual ice crystal concentration above the cut size (given in archive file in column "CVRAD"), and can be used with confidence.
  • You may notice that none of the concentrations in the archive files go below 0.10/cm3, since concentrations smaller than this were set to 0.0 in the processing. We occasionally had spurious (out of cloud) counts, especially at low altitudes, that were due either to a leak or flow disturbance with certain aircraft attitudes. This did not generally affect data at high altitudes and in straight and level flight, so very low in-cloud concentrations can be recovered with special processing. I have already done this for a few people for the wave cloud cases, and would be willing to reprocess specific time periods if you need access to these very low concentrations.
  • Other data we collected include volatility of ambient aerosol (during time periods mentioned below) and impactor samples for transmission electron microscopy (including some cirrus and contrail residuals). These data are not compiled yet, but should be available in six months or so. Please contact Cynthia Twohy (twohy@ucar.edu) with comments and questions. CSU aerosol measurements (Rogers): Colorado State University made 4 types of measurements on the DC-8 (IN, CN, IN-impactions and size-sorted total aerosol impactions). Ice nuclei (IN) and condensation nuclei (CN) measurements are continuous, whereas impactor samples were made only during selected time periods. The IN instrument is new, and we made minor changes and improvements to it throughout SUCCESS. It had a persistent problem showing evidence of an air leak. There was an electronics error that was fixed 4/30; we believe the earlier data can be corrected. The CN counter operated very reliably throughout the project. The only problems with it were (1) reduced performance at highest altitudes (lowest pressures) and (2) a change in response that correlates with aircraft pitch and roll. We believe this effect is due to the angle of attack of the sample inlet probe, and we are looking into it further.

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