Comments on "Effective Radius of Ice Cloud Particle Populations Derived from Aircraft Probes"

In the recent paper by Heymsfield et al. (2006, hereafter H06) I am thanked for being a reviewer of their paper. I was not an American Meteorological Society reviewer of their paper, but instead was a co–principal investigator who, along with some of the H06 authors, participated in the Cirrus Regional Study of Tropical Anvils and Cirrus Layers-Florida Area Cirrus Experiment (CRYSTAL-FACE, hereafter C-F) cumulus field study in 2002. Some of the authors fielded cloud probes and I fielded my cloud-integrating nephelometer (CIN; Gerber et al. 2000; see also Garrett et al. 2003) on the University of North Dakota Citation research aircraft. I was also responsible for calculating and placing in the National Aeronautics and Space Administration (NASA) Ames data archive C-F values of the optical extinction coefficient ( ) and asymmetry parameter (g) measured by this CIN on all Citation flights, as well as values of the effective radius (re) of the cloud particles obtained by ratioing the total liquid and solid water measured by the counterflow virtual impactor (CVI; Twohy et al.1997) and the extinction measured by the CIN (the archived data can be found in files EC*.CIT, RE*.CIT, and CV*.CIT online at http://espoarchive. nasa.gov/archive/arcs/crystalf/data/citation). The comments made here are limited to describing the performance and evaluation of this particular CIN used on the Citation, topics that H06 deals with at length. It was already noticed at the Key West, Florida, field site for the C-F study and reported by Gerber (2003) that there was a factor of 2 difference in Citation measured by the CIN versus calculated from particle size distributions measured by the forward spectrometer scattering probe (FSSP) and the 2D-C probes on the Citation. Remarkably, this factor of 2 was found to be independent of the nature of the particles observed in the various C-F clouds, be they small drops found in warm clouds or ice crystals of various shapes and sizes in the colder clouds. H06 states that this difference is a result of the CIN overestimating by a similar factor of 2.5. H06 further states that the agreement between CVI, FSSP, and King hot-wire probe measurements of liquid water content (LWC) on the Citation indicated that the CVI was operating accurately, so that the problem in calculating re from the CVI/CIN ratio was the measured by the CIN. Clearly, either the CIN was overestimating or the CVI was underestimating LWC and ice water content (IWC) to cause this consistent factor of 2 difference. To test these conclusions in H06 I take another close look at the C-F microphysics data for several Citation flights that flew through clouds with only liquid water droplets. Here the various probes should give the best agreement with respect to LWC, , and re, because the additional complexity of ice crystal shape does not enter in. Only three such clouds were found in the data archive; however, they are sufficient to provide new insight on the performance of the probes and the validity of the archived values of re. In the following I look at the preliminary microphysical data originally submitted to the NASA Ames data archive as well as the final revised data, conclude if the revised data improved agreement between the probes, discuss potential ice crystal breakup on the CIN thought to be a possibility by H06, describe the calibration of the CIN, and come to some new conclusions as to the validity of the Citation data collected during C-F.