Can the slowing of autoconversion result in increasing precipitation

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Can the slowing of auto-conversion result in
increasingprecipitation?

• Daniel Rosenfeld
• The Hebrew University of Jerusalem, Israel

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LWC gm-3 mm-1
Drop Diameter
Drop Diameter
Drop Diameter
Pristine Smoky
Pyro
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More cloud drops ?deeper cloud for onset of rain
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Andreae, M. O., D. Rosenfeld, P. Artaxo et
al., 2004 Smoking rain clouds over the Amazon.
Science, 303, 1337-1342.
Precipitation threshold
Aircraft measured Modal LWC cloud drop diameter
as a function of height above cloud base, for the
various aerosol regimes in Brazil Thailand.
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Cloud physics aircraft in clouds,
measuring Cloud drop size distributions and
liquid water contents Hydrometeor shapes and size
distributions Thermodynamics and winds
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Cloud physics aircraft 2005 03 02, Sierra Nevada
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Aerosol aircraft 2006 03 01 0103Z 900 m
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CCN40 cm-3
CCN100 cm-3
CCN800 cm-3
1
2
3
800
600
1
800
300
100
70
2
100
3
40
2
1
3
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Aircraft measured Modal LWC cloud drop diameter
as a function of height above cloud base, for the
various aerosol regimes in the world. Rosenfeld
et al., 2008, submitted.
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Open Questions

• For convective clouds, how general is the
  relation between concentrations of small CCN,
  cloud base drop number concentration and the
  depth above base for onset of warm rain?
• What is the role of normally observed variations
  in giant CCN?

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Aerosol effects on precipitation
Aerosols (not including GCCN) inhibit
precipitation Kaufman and Nakajima 1993 Borys
et al, 1998 2000 Rosenfeld and Lensky
1998 Rosenfeld 1999, 2000 Givati and Rosenfeld
2004 Tao et al (1995), Ferrier et al (1996( Khain
et al, 2001 Khain and Pokrovsky (2004) Khain
et al (2004a,b) Axel et al (2004) Tao et al
(2004) Teller and Levin(2006) Margaritz et al
(2006) Lynn et al (2006) Jirak and Cotton
(2006)
Aerosols can increase precipitation Ohashi and
Kida 2002 Shepherd and Burian 2003 Amiranashvili
et al 2004 Filho et al (2004) Khain et al
(2004a,b) Khain et al (2005-QJRMS) Axel et al
(2004) Axel and Beheng (2004) Tao et al
(2004) Van den Heever et al (2004) Lynn et al
(2005a,b) Lynn et al (2006) Khain et al (2005,
2006) Khain and Pokrovsky (2006)
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Open Questions

• How can we validate the conceptual model?
• Under what conditions the added aerosols induce
  greater amount of rainfall?
• What are the physical causes for that?

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• Factors determining the impact of aerosols on
  surface precipitation from clouds
• P. Khain, N. BenMoshe, A. Pokrovsky
• Department of Atmospheric Sciences, The Hebrew
  University of Jerusalem, Jerusalem, 91904, Israel
• Submitted to the Journal of the Atmospheric
  Sciences
• May 2007

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Precipitation
LOSS (evaporationsublimation)
GAIN (condensationdeposition)
-

Precip
Precipitation is often a small difference of
large values
Aerosols affect both generation and loss of
hydrometeor mass
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Smoky and Green-Ocean Clouds, t240 min
HS
Aerosols increase both generation and loss of
hydrometeor mass If DLossgtDGain -gtdecrease in
precipitation If DGaingtDLoss -gtincrease in
precipitation
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The role of atmospheric humidity
Aerosols (not including GCCN) inhibit
precipitation Rosenfeld 1999, 2000 (small
cloudsdroplets are small) Givati and Rosenfeld
2004 (Dry atmosphere, orographis clouds) Tao et
al (1995), Ferrier et al (1996( Khain et al, 2001
(very dry atmosphere, high instability) Khain
and Pokrovsky (2004) (very dry atmosphere, high
instability) Khain et al (2004a,b)(dry
atmosphere , single clouds) Axel et al (2004)
(dry atmosphere, single clouds) Tao et al
(2004)(dry atmosphere) Teller and Levin(2005)
(single cloud) Lynn et al (2006)(orographic
clouds, dry atmosphere) Borys et al
(2000)(orographic clouds, dry atmosphere) Jirak
and Cotton (2006 )(orographic clouds, dry
atmosphere)
Aerosols can increase precipitation Ohashi and
Kida 2002 (breeze, wet conditions) Shepherd and
Burian 2003 (wet conditions) Amiranashvili et al
2004 (wet conditions, deep thunderstorms) Filho
et al (2004) (wet conditions, breeze
circulation) Khain et al (2005-QJRMS) (Wet air,
tropical clouds) Axel et al (2004) (wet
air) Axel and Beheng (2004) Tao et al (2004)
(wet air, squall line) Van den Heever et al
(2004) (cloud system) Lynn et al (2005a,b-
Florida wet air, squall line) Lynn et al (2005 in
preparation Florida wet air, squall line) Khain
et al (2005-comparatively wet, convective storm)
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Classification diagram of sub-micron aerosols
effects on precipitation
DLOSSgtDGAIN Added small CCN decrease
precipitation
Deep convection in dry air
Organization
Single cells
Orographic clouds
Tropical squall lines
Small cumulus
Cloud ensembles, storms
Increase in Wind shear
Stratocumulus
D LOSS to Evaporation
Increase in air humidity
Tropical clouds
Deep convection in moist air

• LOSSltD GAIN
• Added small CCN increase precipitation

D Gain, CONDENSATES
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Conceptual model
HAIL
Graphics by Robert Simmon, NASA
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Conceptual model
HAIL
Graphics by Robert Simmon, NASA
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Conceptual model
Hygro-seeded
Williams, E., D. Rosenfeld, M. Madden et al.,
2002 Contrasting convective regimes over the
Amazon Implications for cloud electrification.
J. Geophys. Res., 107 (D20), 8082,
doi10.1029/2001JD000380. M. O. Andreae, D.
Rosenfeld, P. Artaxo, A. A. Costa, G. P. Frank,
K. M. Longo, and M. A. F. Silva-Dias, 2004
Smoking rain clouds over the Amazon. Science,
303, 1337-1342. Rosenfeld D., 2006 Aerosol-Cloud
Interactions Control of Earth Radiation and
Latent Heat Release. Space Science Reviews.
Springer, 9p. 6 December 2006. DOI
10.1007/s11214-006-9053-6. A. Khain, D. Rosenfeld
and A. Pokrovsky, 2005 Aerosol impact on the
dynamics and microphysics of convective clouds.
The Quarterly Journal of the Royal Meteorological
Societ, 131, 1-25.
HAIL
Graphics by Robert Simmon, NASA
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Simulation of extremely continental high base
(11oC) clouds (West Texas, August 1999)
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Vertical profiles of maximum values of (a) cloud
water content (CWC), (b) the mean volume diameter
and (c) droplet concentration observed in the
control run at 250 m below the growing cloud top,
presented on the background of the aircraft
observations (Rosenfeld and Woodley, 2000), shown
in green (CWCgt0.2 gm-3 and black (CWClt0.2 gm-3).
The blue and red squares denote model calculated
values for the low and high CCN concentrations.
The black square in the concentration panel (c)
denotes the model ice concentrations.
Rosenfeld and Woodley, Nature, 2000 Khain et
al., GRL 2001.
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West
Khain et al., QJRMS, 2005
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West
Khain et al., QJRMS, 2005
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Simulation of warm base Alabama squall
line (PRESTORM )
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Khain et al., QJRMS, 2005
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Khain et al., QJRMS, 2005
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Height (km)
Distance (km)
Distance (km)
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Scheme of aerosol effects on precipitation
Maritime moderate (wet) continental
clouds (like GATE and PRESTORM)
Accumulated rain
Dry unstable situation (like Texas clouds)
Aerosol concentration
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Weekly Cycle of Large-Scale Averages
T.L. Bell, D. Rosenfeld, K.M. Kim, J.M. Yoo,
M.I. Lee, M. Hahnenberger, 2007 Midweek
Increase in U.S. Summer Rain and Storm Heights
Suggests Air Pollution Invigorates Rainstorms. To
appear in JGR.
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Open Questions

• When added aerosols induce greater convective
  overturning?
• How much more heat is transferred upward for the
  same amount of rainfall when warm rain is
  suppressed?
• What is the manifestation of the enhanced
  vertical heat transport on the local, regional
  and global circulation systems?

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What do we need to measure?

• Vertical evolution of cloud microstructure and
  hydrometeors from base to anvil in various
  aerosol conditions.
• Sensible and latent convective heat fluxes in the
  clouds.
• Aerosol formation and sinks, and their CCN and IN
  activity.
• Regional vertically stratified heat and
  hydrological budgets.
• Closure of all measurable fluxes at the scale of
  a GCM grid, say, 5x5 degrees.

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What do we need to simulate?

• Simulate the observed processes for validation.
• Use the validated simulations for calculating the
  overall vertically stratified box budgets of heat
  (sensible, latent, radiative), water in its
  various forms, aerosols and their precursors, air
  mass transport and convergence.
• Quantify the sensitivity of the convective fluxes
  to the aerosols.
• Simulate the response of the local, regional and
  global circulation systems to the aerosol impacts
  on the convection, as well as the direct effects.

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What does it mean practically?

• A major INDOEX scale field campaign in an area
  with warm base deep convective clouds that has
  both pristine and polluted conditions alternating
  during the duration of the campaign.
• To be discussed in this workshop

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Conclusions

• Sub-micron CCN slow precipitation forming
  processes in all clouds.
• In shallow and short lived clouds, such as
  orographic, this is manifested as a net decrease
  in precipitation amount.
• In deep convective clouds net decrease occur in
  dry environments and cold-base clouds.
• The delay of precipitation in warm base clouds
  invigorates them and produces more rainfall
  despite of lower precipitation efficiency.
• The IAPSAG report is un-necessarily ambiguous and
  vague, because it fails to take into account
  systematically these physical considerations.