Cloud Property Measurements from Commercial Aircraft

A compact (500 cm3), lightweight (500 g), near-field, single particle backscattering optical spectrometer is described that mounts flush with the skin of an aircraft and measures the concentration and optical equivalent diameter of particles from 5 to 75 μm. The backscatter cloud probe (BCP) was designed as a real-time qualitative cloud detector initially only for data quality control of trace gas instruments developed for the climate monitoring instrument packages that are being installed on commercial passenger aircraft as part of the European Union In-Service Aircraft for a Global Observing System (IAGOS) program (http://www.iagos.org/). Subsequent evaluations of the BCP measurements on a number of research aircraft, however, revealed that it is capable of delivering semi-quantitative dust and cloud particle data products including size distributions, liquid water content and other information on dust and cloud properties. We demonstrate the instrument's capability for delivering useful long-term climatological, as well as aviation performance information, across a wide range of environmental conditions.

The BCP has been evaluated by comparing its measurements with those from other cloud particle spectrometers on research aircraft and six BCPs are currently flying on European and Asian commercial A340/A330 Airbus passenger airliners. The design of the BCP is described in this presentation, along with an evaluation of measurements made on the research and commercial aircraft. Results from more than 8,000 hours of airborne measurements by the BCP on five Airbus A-340s (Lufthansa, China Airlines, Air France and Iberia) operating on routine global traffic routes show that more than 700 hours of cloud data, in > 20000 clouds wider than 25 km, have been recorded at normal cruise altitudes (> 10 km) since September, 2011. These data are a valuable contribution to data bases of cloud properties, including sub-visible cirrus, in the upper troposphere and useful for validating satellite retrievals of cloud water and effective radius as well as providing a broader, geographically and climatologically relevant view of cloud microphysical variability useful for improving parameterizations of clouds in climate models. They are also useful for monitoring the vertical climatology of clouds over airports, especially those over mega-cities where pollution emissions may be impacting local and regional climate.