Response to Reviewers 1-3
The authors would like to express their appreciation for the detailed comments of the
three reviewers, who clearly devoted a lot of time reading the manuscript carefully. We
have addressed all the comments, questions and recommendations and incorporated the
majority of them. In those cases where we chose not to implement a suggested
modification or addition, we have offered our justification for not doing so.
We would also like to emphasize that the primary focus of this chapter is on measurement
of ice particle properties, although many of the uncertainties that are discussed are
equally applicable to water droplets. To better clarify this point, we have retitled the
chapter: “Cloud Ice Properties: In Situ Measurement Challenges”
Our response follows each reviewer comment and is highlighted in bold italics.
Response to Reviewer #1
I see no discussion of the difficulty in obtaining good overlaps between the size
distributions obtained by large drops measured with scattering probes and small drops
measured with optical array probes. Do you consider this a solved problem, and if so,
then state it. Otherwise this "grey zone" deserves thorough mentioning in the chapter.
The chapter discusses the measurement errors due to sample volume and coincidence,
but not due to beam inhomogeneity. Again, a thorough discussion is required to examine
the impact.
A figure and accompanying discussion has been added to address the overlap
issue in a new section “2.2.5 Impact of Uncertainties on Combining Sensor
Measurements”.
In general, there are only discussion of coincidence, Mie wiggles and their impact on missizing, but just as importantly, do you believe the droplet spectral width obtained
previously, now or with the Fast-FSSP?
We believe that the reviewer is referring to a long standing concern that the width
of droplet spectra measured with the FSSPs was not physically accurate since
models of droplet growth produce narrower spectra than is measured. Many
papers have been written on this subject, with a number on entrainment and mixing
that showed that such broadening was physically possible. Given that this chapter
focuses on ice, not water droplets, the point is mute here since the sensitivity and
uncertainties associated with ice crystals will clearly produce broader size
distributions.
Do you believe the small droplet tail that these probes always give? If so, is this tail
instrumental or the result of physical/chemical factors such as entrainment, aerosol
composition, etc.?
As with the reviewer’s previous comment, that deals with water droplets,
measurements in ice crystal or mixed phased clouds will often have a small particle
tail, as illustrated in the figure below. We don’t know, however, if this is the “tail”
to which the reviewer refers.
Minor comments:
Line 12: Add "in-situ".
Added
Line 69: Give references to prior studies that measured the differences in angles for actual
scattering probes. Is this now a solved problem? State.
We have now added the reference to Hovenac and Hirlman, 1991. They measure
scattering angles using a pin hole and demonstrate the variability in FSSP
scattering angles.
Line 104: Spell out MVD first time.
We have now spelled out MVD and LWC here.
Line 111: See comment also for line 69.
We have added the Hovenac and Hirlman, 1991.
Line 137: The Borrmann et al study may have used the wrong T-matrix code, thus
artificially smoothening their results.
The reviewer doesn’t give a reference for this but more importantly, the work by
Um and McFarquhar that we reference is a much more detailed shape analysis that
is probably more accurate given the technique applied.
Line 218: What about Baker and Lawson?
We assume that the reviewer is referring to Baker et al. (JTECH2009), we have now
added that reference
Line 221: I suggest adding " for ice particles" after the Vidaurre and Hallett paranthesis.
Their arguments hold for a stiff ice particle, but not necessarily for a spreading torroidal
ring after impact of a drop. For drop impact situations, splashing is less likely as the
correct surface to use is the surface of the torroidal ring at maximum spreading, not the
surface of the drop upstream of impact.
We added “for ice crystals” as suggested by the reviewer but remind the reviewer
that the monograph is focused on ice measurements and not liquid precipitation.
Lines 230-231: Arguably this minimization of shattering was not very successful, as
particle breakup is often seen with this instrument. Basically, the size of the detector
component is huge in comparison to many particle probes with small arms.
We have added the following: “Both SID-2 and SID-3 where designed prior to the
development of the Korolev style tips and in order to reduce the effect of shattering,
the inlet-tube of SID-1 was replaced with an open-path design where the placement
of the sample volume is well away from the probe laser and detector housing. The
probe housing design successfully reduces shattering effects only in cirrus where
small ice particles dominate (Cotton et al., 2010 show non-bimodal inter-arrival time
distribution for observations in cirrus).”
Line 260: Jensen and Granek reference, as first 2-D Fresnel with time constants.
Jensen and Granek, 2002 have been added to the list of references on imaging
probe limitations.
Line 383: If U with subscript "inlet", why not E with subscript "max"?
Subscripted as recommended.
Lines 450-453: Give reference, numbers look grabbed out of thin air otherwise.
There is not a formal reference for this source of uncertainty but we have added
(A. Korolev, personal communication)
Line 458: Again, give references. And is it really temperature dependent, or IWC/LWC
dependent? How exactly does temperature affect accuracy of vapor measurements?
We don’t understand the reviewer’s comment here. Neither on line 458 or in this
paragraph are we referring to temperature dependency and in this paragraph we
already have provided two references.
Line 527: Fig. 9.6.
Changed Fig. 6 to Fig. 9.6.
Line 533: Fig. 9.7.
Changed Fig. 9.6 to Fig. 9.7
Line 651: (?) ???
Replaced this sentence with: “Droplets and ice crystals larger than 100-200 um and
measured with OAPS can be sized to ±20% and concentrations better than ±50%
with appropriate corrections made to remove artifacts.”
Line 1007: Most frequently deployed "in-situ" cloud "particle" instruments.
Replaced “Most frequently deployed cloud instruments” with “In-situ cloud particle
instruments.”. We have added more instruments to the table to be all inclusive.
Line 1041: Explain what "A" is in figure. (I think I know, but this is a general monograph).
Have added: “where A is the sensitive area of the instrument”
Response to Reviewer #2:
Some key aspects of corrections involved in these observations are illustrated. However,
there is no attention paid for the sampling frequency and how to define accuracy of the
measurements.
Section 5 already discusses sample size but does not specifically talk about
sampling frequency. We are not sure what the reviewer wishes to be discussed.
Perhaps something about high frequency sampling to look at small scale
structure? We don’t think that this falls within the theme of the chapter about
uncertainties, unless it would be talking about aliasing. With respect to defining
accuracy, this is a valid point and we have now added a paragraph in the
introduction that discusses how we define accuracy.
The recommendations for practical use and list of corrections and procedures available
could be given in a table for easy reference.
Practical use, corrections and procedures are the topic of Chapter 11, a separate
chapter that will be available at the same time as Chapter 9.
The recommended steps mentioned in Page 30 correspond to the ones undertaken by
instrument developers and those who have access to some of the laboratory facilities.Ln
641-642 statements focus on the end user of the instruments and data.
This is correct. We don’t know if the reviewer intended that we add or change
something or is just asking confirmation.
Ln 650-651 especially ends with a question mark.
The question mark has been removed.
It is important to illustrate the suite of instruments in combination to derive complete
particle size distribution with least uncertainty.
This was already pointed out in section 6.1 on hybrid sensors. We have also added
a figure, 9.5, in a new section (2.2.5) showing issues with matching up overlapping
size ranges.
Abstract line 13-16 is very lengthy, small sentences are better here. Similarly for Ln 1820
In the abstract, these lines now read: “There are many outstanding challenges.
These are summarized and accompanied by recommendations for moving forward.
with new developments that fill the remaining information gaps. Filling these gaps
will remove the obstacles that hinder our understanding of cloud processes in
general and ice evolution in particular.”
Lines 18-20 now read: “Since the early 1960s there have been many field programs
conducted with instrumented research aircraft. These programs focused on
measuring ice cloud properties; however, significant gaps remain in our
understanding of fundamental processes. These gaps are primarily a result of the
inherent limitations and uncertainties associated with the instruments that make
the measurements.”
Ln 71: Hereafter
“From here forward” has been replace by “Hereafter”.
Line 104: Define MVD, LWC
Done
Ln 149: Particle number concentration
Done
Ln 151: Use of word ‘bias’ for overestimation of size. This wording is confusing. This is a
characterization issue and could be addressed in the data processing stage.
We have now added in the introduction a discussion about types of error. A
systematic error in statistics is also commonly referred to as a “bias” error. Hence,
our use of it with respect to sizing is correct.
Ln 178: Only to accept particles
Corrected
Line 187: sample are? I think it should be sample area
Corrected
Line 193: Check Figure number
Corrected
Ln 202: by estimating
Corrected
Ln 221: of satellites ? Reference (Vidaurre and Hallett, 2009 ?)
Changed to: “fragments per ice crystal collision”
Changed 2007 to 2009.
Line 352: change attitude to altitude
We actually mean attitude, as in angle of attack, yaw and roll. Environmental factors
take into account the temperature, pressure and humidity.
Line 418: the King probe will underestimate
Corrected
Line 458: check unit (-10C) correct it to -10oC
Corrected
Line 460: TWC (use either italics or no italics)
Corrected
Ln 478: IWC cannot be differentiated from LWC, is it pertaining to the specific probe ?
We have added “..in the PVM”
Line 527: Check Figure number
Corrected
Ln 585: Integrated measuring systems
We don’t understand the comment.
590: discussed earlier
Changed
645: Effectively
Corrected
Line 648: Check sentence (can be rewritten as??? - show promise to a great deal but
more effort is needed to characterize……)
Corrected
Ln 653: do not take crystal shattering in to account.
We think that the sentence is correct and understandable as written
Ln 654-656: Sentence is not clear
This has been rewritten
Line 656: Fullstop and space after ±20%.
Corrected
Line 657: correct 100um to 100 um
Corrected
Response to Reviewer #3:
Major issues to be addressed:
1. Completeness: There is one class of instrument completely missing in the manuscript
and Table I. The in situ light scattering probes measuring fundamental light scattering
properties of cloud particles like the Polar Nephelometer (PN, Gayet et al., 1997) or the
Cloud Integrating Nephelometer (CIN, Gerber et al., 2000) are missing. These
instruments are important for assessing cloud radiative effects and have a long history in
aircraft deployments. The limitations and uncertainties of these instruments should be
discussed in the manuscript as a separate class of instruments. This could be done for
instance by adding the measurement parameter "Particle Light Scattering Properties" in
Table I.
This is an excellent suggestion about a class of measurements that we overlooked.
We have added a new section: “5.0 Direct measurement of Cloud Particle Optical
Properties” that discusses the uncertainties in measurements by the Polar
Nephelometer and Cloud Integrating Nephelometer.
2. Classification: I have a problem with the classification "most frequently flown
instrument". There is no justification given in the manuscript why instruments (if selected
at all) make it into the "most frequently flown" class and into Table I. With such an arbitrary
term the authors can freely include and exclude instruments, which is misleading to the
reader. For instance, the HOLODEC instrument is presented in the manuscript under
"next generation sensors" and is listed in Table I as "most frequently deployed cloud
instrument", while PHIPS-HALO, also a "next generation sensor", cannot be found in
Table 1, although it might have similar flight hours as the HOLODEC. I suggest that all
instruments discussed in the manuscript are included in Table 1 and instead of the "most
frequently flown" class the authors should add a column titled "available since" to Table
1.
Agreed. We no longer refer to “most frequently used” as we do not want to exclude
any instrument that has gone beyond the prototype stage. All instruments,
including the most recently introduced that have flown on at least one field project,
are now in the Table I.
3. Presentation: It seems to me that the authors are not always aware of the recent
contributions to instrument characterization and deployment, which is vital for a review
article. This is specifically the case when discussing the SID instrument family. The SID3 capabilities for discriminating and classifying ice particles in mixed phase clouds are
thoroughly discussed in the paper by Vochezer et al. (2016), a paper that needs to be
included in the discussion. Another example is the discussion of the polarization based
detection of aspherical particles. Here, the authors state that "The polarization
measurements, although potentially able to provide more detailed information on the
morphology of small ice crystals, need much more detailed studies in the laboratory and
cloud chambers to determine the thresholds separating water droplets from ice crystals
as a function of size and shape complexity." This statement is even repeated in the
summary. This is misleading as the reader gets the impression that no specific laboratory
or cloud chamber studies have been conducted in this respect. The manuscript would
benefit a lot by including and discussing the results from the recent AIDA cloud chamber
study by Järvinen et al. (2016). In this study, two CAS-POL instruments were deployed in
well-defined mixed-phase and ice cloud simulation experiments to study the sensitivity of
polarimetric measurements to ice particle shape, size and complexity, and in comparison
to other methods (e.g. SID-3).
Yes, these two papers clearly need to be referenced and we now have done so in
the revision, as the reviewer recommends, by adding to the discussion that the
AIDA chamber has been successfully used to evaluated the polarization response.
Detailed comments:
Section 2.1.2, line 131: Include "in the respective angular detection range" after "… the
same intensity of light".
Added
Section 2.1.2, lines 137 - 145: This sizing error strongly depends on the detection angular
range. One can even have an oversizing of ice particles in cases when light is detected
in side scattering angular ranges. So, the authors should clearly state which sizing error
corresponds to what instrument.
The Um and McFarquhar (2015) study was done for collection angles similar to the
FSSP and CDP. We have added that qualifier to the discussion. In addition, we have
noted that the error can be negative or positive depending on the size range a is
seen in Fig. 9.3.
Section 2.1.2, line 132: "When the particle is quasi-spherical the resulting EOD will
represent the size within the expected uncertainties associated with Mie theory (Gayet,
1996)." This is a general statement that is no longer valid as recent cloud chamber studies
by) Järvinen et al. (2016 have shown that also geometrically spherical ice particles but
with a rough surface texture can have light scattering properties that significantly differ
from those of smooth spheres.
We disagree with the reviewer that what we have stated is incorrect. Järvinen et al.
(2016) show that the roughness of a spherical ice particle will affect its scattering
properties but nowhere in that paper do they discuss how the derived size is
affected. That is unfortunate as it would have been interesting to compare the sizes
derived by the two CAS-POL and PPD-2K. Since that wasn’t done, it doesn’t
disqualify our statement that the derived EOD will represent the size “within the
expected uncertainties”
Section 2.1.2, lines 160 - 168: The authors should include the coincidence consideration
and artifacts given in Vochezer et al. (2016) for the SID-3 instrument. This is important as
the high resolution patterns acquired by SID-3 can be used as a reference of the
coincidence patterns that can be expected in the low resolution versions of the SID
family.
We have added the following: “Vochezer et al. (2016) observe the high-resolution
scattering patterns from the SID-3 and predict a lower coincidence rate. The
difference is that Cotton et al. (2010) and Johnson et al. (2014) use the worst case
scenario for coincidence by assuming that after a trigger, a second particle in the
extended main-detector sensing volume adds to the scattered image. Vochezer et
al (2016) calculate the coincidence probability assuming the second particle has
to be in the much smaller trigger volume.”
Section 4, lines 520 - 529: Determining the ice particle complexity and surface roughness
with the SID-3 scattering pattern method is a novel tool, which is not yet widely applied.
Currently only two papers exist, which discuss this method in case of ice particles. In the
manuscript only one of these papers, namely the deployment of SID-3 in an aircraft study
by Ulanowski et al. (2014), is presented. The authors thereby ignore the more
fundamental cloud chamber work by Schnaiter et al. (2016) that is essential to understand
the sensitivity, the limits and the capabilities of this method for a detailed analysis of the
ice particle small-scale complexity.
The reviewer is correct and this was an unfortunate oversight. We now include the
Schnaiter et al (2016) paper in our discussion.
Section 6.2, line 618: Abdulmonem -> Abdelmonem
Corrected
Section 6.2, line 625: insert same after "… with the image of the". Change PHIPS to
PHIPS-HALO
Modified as recommended.