Coincidence Errors in a Cloud Droplet Probe (CDP) and a Cloud and Aerosol Spectrometer (CAS), and the Improved Performance of a Modified CDP

AbstractCentral to the aerosol indirect effect on climate is the relationship between cloud droplet concentrations Nd and cloud condensation nuclei (CCN) concentrations. There are valid reasons to expect a sublinear relationship between measured Nd and CCN, and such relationships have been observed for clouds in a variety of locations. However, a measurement artifact known as “coincidence” can also produce a sublinear trend. The current paper shows that two commonly used instruments, the cloud droplet probe (CDP) and the cloud and aerosol spectrometer (CAS), can be subject to significantly greater coincidence errors than are typically recognized, with an undercounting bias of at least 27% and an oversizing bias of 20%–30% on average at Nd = 500 cm−3, and with an undercounting bias of as much as 44% at Nd = 1000 cm−3. This type of systematic error may have serious implications for interpretation of in situ cloud observations. It is shown that a simple optical modification of the CDP dramatically reduces ov...

[1]  S. Twomey,et al.  The nuclei of natural cloud formation part II: The supersaturation in natural clouds and the variation of cloud droplet concentration , 1959 .

[2]  James E. Dye,et al.  Evaluation of the forward scattering spectrometer probe. Part II: Corrections for coincidence and dead-time losses , 1985 .

[3]  James E. Dye,et al.  The Drop-Size Response of the CSIRO Liquid Water Probe , 1987 .

[4]  W. Cooper,et al.  Effects of Coincidence on Measurements with a Forward Scattering Spectrometer Probe , 1988 .

[5]  B. Albrecht.  Aerosols, Cloud Microphysics, and Fractional Cloudiness , 1989, Science.

[6]  J. Brenguier,et al.  A Review and Discussion of Processing Algorithms for FSSP Concentration Measurements , 1994 .

[7]  J. W. Fitzgerald,et al.  Marine boundary layer measurements of new particle formation and the effects nonprecipitating clouds have on aerosol size distribution , 1994 .

[8]  George A. Isaac,et al.  Scale Effects on Averaging of Cloud Droplet and Aerosol Number Concentrations: Observations and Models , 1999 .

[9]  P. Mcmurry,et al.  Particle production near marine clouds: Sulfuric acid and predictions from classical binary nucleation , 1999 .

[10]  J. Seinfeld,et al.  CCN measurements during ACE-2 and their relationship to cloud microphysical properties , 2000 .

[11]  V. Ramanathan,et al.  Aerosols, Climate, and the Hydrological Cycle , 2001, Science.

[12]  A. Bandy,et al.  Measurements of enhanced H2SO4 and 3–4 nm particles near a frontal cloud during the First Aerosol Characterization Experiment (ACE 1) , 2001 .

[13]  Glenn E. Shaw,et al.  Indian Ocean Experiment: An integrated analysis of the climate forcing and effects of the great Indo-Asian haze , 2001 .

[14]  J. Seinfeld,et al.  Can chemical effects on cloud droplet number rival the first indirect effect? , 2002 .

[15]  Graham Feingold,et al.  Analysis of the Influence of Film-Forming Compounds on Droplet Growth: Implications for Cloud Microphysical Processes and Climate , 2002 .

[16]  J. Brenguier,et al.  Comparison between Standard and Modified Forward Scattering Spectrometer Probes during the Small Cumulus Microphysics Study , 2002 .

[17]  E. Emery,et al.  Wind Tunnel Measurements of the Response of Hot-Wire Liquid Water Content Instruments to Large Droplets , 2003 .

[18]  J. Seinfeld,et al.  Aerosol–cloud drop concentration closure in warm cumulus , 2004 .

[19]  A. Nenes,et al.  Chemical and dynamical effects on cloud droplet number: Implications for estimates of the aerosol indirect effect: CHEMISTRY, DYNAMICS, AND DROPLET NUMBER , 2004 .

[20]  J. Strapp,et al.  A Multiwire Hot-Wire Device for Measurment of Icing Severity, Total Water Content, Liquid Water Content, and Droplet Diameter , 2005 .

[21]  Melanie A. Wetzel,et al.  Evaluation of the aerosol indirect effect in marine stratocumulus clouds : droplet number, size, liquid water path, and radiative impact , 2005 .

[22]  J. Seinfeld,et al.  Evaluation of a new cloud droplet activation parameterization with in situ data from CRYSTAL‐FACE and CSTRIPE , 2005 .

[23]  J. Hudson,et al.  Aircraft measurements of the impacts of pollution aerosols on clouds and precipitation over the Sierra Nevada , 2006 .

[24]  V. Ramanathan,et al.  Investigation of aerosol–cloud interactions using a chemical transport model constrained by satellite observations , 2007 .

[25]  Graham Feingold,et al.  On the source of organic acid aerosol layers above clouds. , 2007, Environmental science & technology.

[26]  N. Holmes,et al.  A review of particle formation events and growth in the atmosphere in the various environments and discussion of mechanistic implications , 2007 .

[27]  C. O'Dowd,et al.  Flood or Drought: How Do Aerosols Affect Precipitation? , 2008, Science.

[28]  Rodney J. Weber,et al.  Enhanced secondary organic aerosol formation due to water uptake by fine particles , 2008 .

[29]  P. Chuang,et al.  Can aerosol decrease cloud lifetime? , 2009 .

[30]  Raymond A. Shaw,et al.  Homogeneous and Inhomogeneous Mixing in Cumulus Clouds: Dependence on Local Turbulence Structure , 2009 .

[31]  Ernst Strüngmann Forum,et al.  Clouds in the perturbed climate system : their relationship to energy balance, atmospheric dynamics, and precipitation , 2009 .

[32]  B. Stevens,et al.  Untangling aerosol effects on clouds and precipitation in a buffered system , 2009, Nature.

[33]  R. Wood,et al.  Observational Strategies from the Micro- to Mesoscale , 2009 .

[34]  J. K. Ayers,et al.  Effect of biomass burning on marine stratocumulus clouds off the California coast , 2009 .

[35]  Hongli Jiang,et al.  The Influence of Entrainment and Mixing Assumption on Aerosol–Cloud Interactions in Marine Stratocumulus , 2009 .

[36]  Joshua A. Gordon,et al.  Water droplet calibration of the Cloud Droplet Probe (CDP) and in-flight performance in liquid, ice and mixed-phase clouds during ARCPAC , 2010 .

[37]  Q. Min,et al.  Aerosol concentration and size distribution measured below, in, and above cloud from the DOE G-1 during VOCALS-REx , 2011 .

[38]  Hailong Wang,et al.  Modeling chemical and aerosol processes in the transition from closed to open cells during VOCALS-REx , 2011 .