Measurement of Condensed Water Content in Liquid and Ice Clouds Using an Airborne Counterflow Virtual Impactor

Abstract

Condensed water content (CWC) measured using a counterflow virtual impactor (CVI) with a Lyman-␣ hygrometer downstream is compared with that measured by other airborne instruments (a hot-wire probe, a PMS FSSP, and a PMS 2D-C). Results indicate that the CVI system provides a reliable measurement of CWC in both liquid-and ice-phase clouds and that the CVI measures CWC contained in both large and small hydrometeors; this means that the condensed water present in both phases and virtually all hydrometeor sizes can be measured with a single device. Small ice contents of a few milligrams per cubic meter present in cirrus clouds can also be measured by the technique.

Chemical characteristics of ice residual nuclei in anvil cirrus clouds: evidence for homogeneous and heterogeneous ice formation

“…Several aircraft flew in anvils generated from thunderstorms that usually were located over the Florida landmass, at a latitude of about 26 • N. The particles described here were collected using the University of North Dakota Citation aircraft, which flew at cloud levels between about six and twelve km, spanning environmental temperatures between −8 to −56 • C. Particles from ambient clear air near the convection were sampled at generally lower altitudes, at temperatures between about +7 to −32 • C. Using a counterflow virtual impactor (CVI; Noone et al, 1988;Twohy et al, 1997), cirrus crystals larger than about 5 µm diameter were virtually impacted into dry nitrogen where the water was removed through drying and heating of the sample stream to 50 • C. Non-volatile residual nuclei were then impacted onto carbon-coated nickel electron microscope grids using a two-stage jet impactor. The 50% cut sizes of the two impactor stages were about 0.56 and 0.10 µm diameter for unit density spherical particles or 0.38 and 0.07 µm diameter for 1.7 g cm −3 density particles at typical sampling pressures of 350 mb.…”

Parameterizing Size Distribution in Ice Clouds

“…Given that these are two very different methods for estimating the IWC, the agreement is quite good (within ~20% usually). The CVI uncertainty in IWC is estimated to be 13% at water contents of 0.05 to 1.0 g m -3 , and increases to 16% at 0.01 g m -3 and to 40% at 0.0025 g m -3 (Heymsfield et al 2007b;Twohy et al 1997Twohy et al , 2003. The data in Fig.…”

A fiber-coupled laser hygrometer for airborne total water measurement

“…Alternately, authors working with evaporative hygrometers refer to the measured sum of condensed water plus ambient water vapor as the "total water" (e.g., Brown and Francis, 1995;Wood and Field, 2000;Davis et al, 2007b). Also complicating interpretation of the literature is the diversity of terms used to denote the sum of ice plus liquid water excluding water vapor; these terms include "condensed water content" (e.g., Twohy et al, 1997), "total condensed water content" (e.g., Hogan et al, 2002), "cloud water content" (Strom and Heintzenberg, 1994), and "total condensate content" (Gultepe and Isaac, 1997). Because the term "total" in its general usage is suggestive of a complete sum, we choose to use the phrase "total water content" (TWC; g m −3 ) to refer to the mass concentration of water in all phases, including vapor.…”

“…As an independent check on the accuracy of CLH-2, a laboratory comparison was performed with the first-generation CLH, an instrument that itself has been previously compared (Davis et al, 2007a) with multiple total water instruments, including the Harvard University Lyman-α total water photofragment-fluorescence hygrometer (Weinstock et al, 2006) and the Droplet Measurement Technologies Cloud Spectrometer and Impactor (Twohy et al, 1997). As in the calibration, this laboratory intercomparison was performed using vapor-only mixtures: the undiluted output of the dewpoint generator was split in parallel and passed through the CLH and CLH-2 at atmospheric pressure (843 hPa).…”