An Intercomparison of In Situ Observations of Cloud Water Content from the NSF Gulfstream V Aircraft During IDEAS 2013
Wednesday, 17 December 2014
Cloud water contents (CWC) were measured in situ during the IDEAS 2013 campaign by direct absorption infrared laser instruments that employ two different sampling methods on the NCAR Gulfstream-V aircraft. The University of Colorado CLH-2 instrument, mounted under the wing in a canister, employs a fiber-coupled distributed feedback laser (DFL) and direct absorption to quantify total water concentrations within a closed path of known pressure and temperature downstream of a heated inlet. Similarly, the NCAR CVI instrument uses a MayCom compact tunable diode laser (TDL) hygrometer mounted inside the aircraft cabin to measure condensed water evaporated in a counterflow virtual impactor (CVI) inlet. These two CWC measurements, which have similar sub-isokinetic particle enhancement characteristics, should differ primarily by the amount of ambient water vapor that is admitted by the CLH-2 inlet, but rejected by the dry counterflow in the CVI. We measured that ambient water vapor with a Picarro cavity ringdown spectrometer sourced by a backward-facing inlet. During a series of flights through a variety of clouds near Broomfield, CO, we were able to intercompare these two methods for measuring CWCs, both of which are capable of high accuracy sampling over a wide range of CWCs from the lower atmosphere to the tropopause. The results help characterize the accuracy, time-response, and precision of the two methods, and they improve our understanding of the new approach for measuring CWC using the canister-mounted CLH-2 instrument on the Gulfstream-V aircraft.