The Cloud Spectrometer and Impactor CSI

1
The Cloud Spectrometer and Impactor (CSI) Greg L.
Kok1, Cynthia H. Twohy2 and Darrel Baumgardner3
1Droplet Measurement Technologies, 2Oregon State
University, 3Universidad Nacional Autónoma de
México

• Objectives
• To develop an airborne instrument that measures
  both cloud particle size distribution and bulk
  condensed water content over a broad size range
• To achieve a small package that can be mounted on
  the aircraft wing where airflow distortion is
  minimal

Flight Testing
High altitude autonomous (NASA WB-57F)
Low altitude w/ operator (NCAR C-130)
High altitude w/ operator (UND Citation)
CVI
CDP
Cloud particle trajectories around aircraft
fuselage, showing how concentrations may be
distorted. From King et al., (1984), J. Atmos.
Ocean. Tech., 1, 5-13.
Airflow Modeling
Counterflow Virtual Impactor (CVI)

• The CVI tip samples water drops and ice particles
  in a cloud, while rejecting interstitial vapor
  and particles
• Hydrometeors are impacted into dry air and
  evaporated
• Resulting water vapor is measured directly with a
  tunable diode laser absorption hygrometer

Computational modeling was performed to select
locations around the canister for the CVI and CDP
that were least distorted relative to freestream
conditions. Trajectories of different-sized
particles were also computed.
Calculations also assessed different shroud
designs, in order to straighten airflow while
maintaining flow velocities near freestream.
Validation of Technique
Cloud Droplet Probe (CDP)
Comparison with ice water content (IWC) measured
with an isokinetic inlet system and Lyman-alpha
fluorescence yielded excellent agreement, within
uncertainty of measurements. We gratefully
acknowledge Elliot Weinstock and David Sayres of
Harvard University for sharing preliminary data.
Testing in NASA's Icing Research Tunnel indicates
good agreement with reference icing blade liquid
water content (30 ?m median volume diameter).
From Twohy et al. (2003), J. Atmos. Ocean. Tech.,
20, 781-790.

• Open path sampling minimizes potential for
  breakup aritifacts
• Lightweight, miniaturized electronics
• Flexible mounting location
• Size range 2-60 ?m

• Specifications
• Length 1.60 m (including inlet and shroud)
• Weight 42 kg (not including small pump)
• Power 45 A of 28 Vdc if de-iced
• Water Content Range 0.001-1 g m-3 (5-2000
  ?m)
• Uncertainty 15
• varies with operating conditions

Acknowledgements This work was funded by the
National Science Foundation under a Small
Business-Technology Transfer award
DMI-0110358. John Ogren, Jost Heintzenberg and
Robert Charlson were the original inventors of
the CVI Ogren et al. (1985). "In situ sampling
of clouds with a droplet to aerosol converter."
Geophys. Res. Lett. 12 (3), 121-124. .