Aerosols as CCN, IN and their effects on CDNC

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Aerosols as CCN, IN and their effects on CDNC

• Sandro Fuzzi
• Institute of Atmospheric Sciences and Climate
• National Research Council
• Bologna, Italy

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Detection of human influence on 20th century
precipitation trends
Zhang et al., Nature (2007)
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Aerosol and precipitation over Asia
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Biomass burning aerosols and precipitation over
Amazonian basin

• Biomass-burning aerosols
• reduce droplet size and so delay the onset of
  precipitation in deep convective clouds (Andreae
  et al., Science, 2004)
• inhibit the formation of scattered cumulus clouds
  (Koren et al., Science, 2004)

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Polluted aerosol and orographic precipitation
RO the orographic enhancement factor of the
precipitation, which is the ratio between the
hill and the upwind plains precipitation. Ro
reflect the trend of increasing air pollution
since 1954 to present. Visibility is a proxy to
CCN concentrations.

• aerosol decreased precipitation by 30 to 50 at
  Mt. Hua near Xian, in central China from 1954 to
  present (Rosenfeld et al., Science, 2007)
• during the period of 19502002, the Ro of the
  hilly areas decreased by 15 in Israel (Givati
  and Rosenfeld, J. Appl. Meteor., 2005)
• ratio of upslope precipitation for elevated sites
  west of Denver and Colorado Springs, Colorado, to
  upwind urban sites has decreased by approximately
  30 over the past half-century (Jirak and Cotton,
  J. Appl. Meteor., 2005)

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Aerosol effect on precipitation

• The extent of precipitation change due to aerosol
  effect is different in different regions
• Aerosol can affect cloud formation and
  precipitation in two ways
• Effects on cloud microphysics (e.g. forming
  smaller and more numerous droplets)
• Aerosol dynamic-hydrological effect (direct,
  semi-direct and indirect effects modulate
  radiation thus perturbing atmospheric
  circulation)

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Aerosol-cloud-precipitation feedbacks
AEROSOLS
CCN Activation
IN Activation
Cloud Radiative Transfer
Cloud Microphysics
Aerosol Wet Removal
PRECIPITATION
Cloud Dynamics
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Key issues for aerosol effects on cloud
microphysics

• Physical vs. chemical aerosol properties on CCN
  and CDNC
• Natural vs. anthropogenic aerosols
• Aerosols as CCN vs. IN

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Key issues for aerosol effects on cloud
microphysics

• Physical vs. chemical aerosol properties on CCN
  and CDNC
• Natural vs. anthropogenic aerosols
• Aerosols as CCN vs. IN

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Chemical composition of CCNErvens et al., JGR
(2005)
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CCN closure
Broekhizen et al., ACP (2006)
Medina et al., JGR (2007)
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Microphysics vs. chemical composition
Concerning the title of Dusek et al. (2006)
Size matters more than chemistry for
cloud-nucleating ability of aerosol particles
Hudson et al. (2007) point out that the Moon
matters more for ocean tides than the Sun but
neglecting the gravity of the Sun could put one
into deep water neglecting particle chemistry
could often produce inaccurate estimates of CCN
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Chemical composition of aerosolin different areas
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Chemical composition of aerosolin different
periods
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Model parametrization oforganic aerosols
Decesari et al., EST (2007)
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Key issues for aerosol effects on cloud
microphysics

• Physical vs. chemical aerosol properties on CCN
  and CDNC
• Natural vs. anthropogenic aerosols
• Aerosols as CCN vs. IN

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Aerosol long term measurements
Koch et al., JGR, 2007
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Natural aerosol
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Biological source affectingcloud microphysics
Southern Ocean Meskhidze and Nenes, Science (2006)
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Key issues for aerosol effects on cloud
microphysics

• Physical vs. chemical aerosol properties on CCN
  and CDNC
• Natural vs. anthropogenic aerosols
• Aerosols as CCN vs. IN

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Ice nuclei

• Little is still known on IN properties
• IN are chemically very different from CCN
• Known natural ice nuclei are mainly dust and
  biological particles, contribution of
  anthropogenic ice nuclei is still a matter of
  debate
• Laboratory studies evidenced the ice-forming
  activity of soot particles of various sizes as
  contact nuclei for temperatures ranging from -5
  to -20 C (Gorbunov et al., J. Aerosol Sci.,
  2001).

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Field campaign on heterogeneous IN
Storm Peak Laboratory, Colorado Richardson et
al., JGR (2007)
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One overall point for discussion

• Which level of information is needed to describe
  (and use in models) the effect of CCN (and IN) on
  cloud formation and structure and, consequently,
  which tools do we have available?
• microphysics vs. chemistry
• in situ vs. remote sensing
• vertical profiles
• local-regional-global scale