Comparison of LWC measurements on the NCAR C-130 in AIRS-2

The Alliance Icing Research Study - II (AIRS-2) occurred October to December 2003 and used several instrumented research aircraft, including the NSF/NCAR C-130. It was equipped with a variety of instruments to measure cloud particles and liquid water content (LWC) and made fifteen research flights through stratiform and stratocumulus clouds over the Great Lakes region from Ohio to Montreal, Quebec. These clouds included liquid, ice, and mixed-phase types.

The LWC instruments included four hot-wire type devices (PMS King, Nevzorov, DRI large and small T-probes), optical scattering probes (FSSP-100), optical array probes (PMS 2D-C, 2D-P, 260-X), HVPS (High Volume Precipitation Spectrometer), Cloud Particle Imaging probe (CPI), and a counter-flow virtual impactor (CVI). The Nevzorov and DRI T-probes also measure ice water content (IWC). A Rosemount icing detector (RICE) detected supercooled liquid water. These instruments were on the fuselage and under-wing locations as shown in the top of Figure 1.

This paper describes the instrumentation, shows examples of the measurements, and identifies regimes where there were systematic differences in the LWC measurements. These differences arise from the range of drop sizes, the affect of probe location on the aircraft (fuselage, under-wing, wing-tip, pod), time response, and sub-cloud scale structure. The bottom of Figure 1 shows an example of observations from ten minutes of level flight (2.8 km MSL). It illustrates both the relative agreement and discrepancies among probe types.