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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