Evidence of mineral dust altering cloud microphysics and precipitation Qilong Min Atmospheric Science Research Center, State University of New York Rui Li, Lee Harrison, Bing Lin, Everette Joseph, Yong Hu, Vernon Morris, Shuyu Wang

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Evidence of mineral dust altering cloud
microphysics and precipitationQilong
MinAtmospheric Science Research Center, State
University of New York Rui Li, Lee Harrison,
Bing Lin, Everette Joseph, Yong Hu, Vernon
Morris, Shuyu Wang
2
Aerosol-cloud interaction Qilong
MinAtmospheric Science Research Center, State
University of New York Rui Li, Lee Harrison,
Bing Lin, Everette Joseph, Yong Hu, Vernon
Morris, Shuyu Wang
3
IPCCs Fourth Assessment Report (2007)
IPCC (2007)

• The total direct aerosol RF as derived from
  models and observations is estimated to be 0.5
  0.4 W m2, with a medium-low level of
  scientific understanding.
• The RF due to the cloud albedo effect (also
  referred to as first indirect or Twomey effect),
  in the context of liquid water clouds, is
  estimated to be 0.7 1.1, 0.4 W m2, with a
  low level of scientific understanding.

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• Aerosol indirect effects on clouds and
  precipitation

IPCC (2007)
Only few studies focus on the aerosol indirect
effects on ice clouds and precipitation,
particularly on the deep convective cloud systems
More than 50 of the earths precipitation
originates in the ice phase, it is critical to
understand the processes of ice nucleation and
their implication on clouds and precipitation
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• Aerosol indirect effects on clouds and
  precipitation

• Mineral dust CCN, Giant CCN, IN
• One of the main natural sources of atmospheric
  aerosol particles and has been observed in the
  most remote regions in the world (Prospero,
  1999).
• A significant climate forcing due to their direct
  effects on scattering and absorption of solar and
  thermal radiation as well as indirect effects on
  clouds and precipitation (as well as Hurricanes).
  
• Model studies show that dust may enhance the
  collision and coalescence of droplets and
  therefore increase warm precipitation formation
  and decrease the clouds albedo Yin et al, 2000,
  van den Heever et al, 2006 Teller and Levin
  2006.
• Some observations show that dust suppress clouds
  and precipitation Rosenfeld 2000, Rosenfeld et
  al. 2001

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Aerosol Indirect Effect (AIE) and Semi-direct
Inconsistent evidence of AIE
?dynamic and thermodynamic conditions
?observation limitations

• A-Train
• AMSR-E WV, Cloud and ice water and precipitation
• MODIS Aerosol and cloud optical properties
• CERES Radiation and climate forcing
• AIRS/AMSU/HSB Temperature and humidity
• CloudSat and CLIPASO active radar and lidar
• TRMM
• TMI WV, Cloud water and precipitation
• PR Precipitation
• VIRS Aerosol and cloud optical properties
• CERES Radiation
• GOES and METSAT
• Surface network NOAA RHB Ship , AMMA, and AERNET
• Re-analysis data

Where
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Observations from METSAT Visible image (Mar
310, 1 frame / day)
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Measured aerosol size distribution and
composition on AEROSE 2004
NOAA RHB Ship

Mineral dust
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A partial dust case UT 911, March 8, 2004
METSAT
TRMM

MODIS
AIRS
Dust
Dust-free
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Statistic study
North
South
Mar 1 2004
Mar 7 2004
Mar 10 2004
Mar 4 2004
Dust-free period
Dust period
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Deep convective clouds
Convective Rain Stratiform Rain
advection
The young, active and violent convection-related
rains
The older, inactive and weak convection-related
rains
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Precipitation size growth CFADs of PR
Reflectivity
More precipitation-size ice here!
Weaker near surface radar reflectivity
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Deep convective clouds
Convective Rain Stratiform Rain
advection
Mineral dust act as ice forming nuclei to produce
more, small size ice particles. Due to
insufficient water vapor supply and short life
time, some particles dont grow too much? Too
small to be detected by PR because their
reflectivity is below the PR size detection
threshold (about 17dBz)
Sufficient time has elapsed to allow the growth
of ice crystals to sizes detectable by the PR as
evident by the high reflectivity observed in the
stratiform dust region.
Mineral Dust Layer suppress the water vapor
supply and increase ice forming nuclei.
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Precipitation size growth CFADs of PR
Reflectivity
Dynamic impacts ?
Stronger convection is associated with higher
reflective startiform rain tops.
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Dynamic impacts ?
Detailed sensitivity study at 8 km
There are substantial differences of convective
core-stratiform rain ratio between the DS and DF
sectors. The difference is not due to dynamics
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Precipitation particle size information
PCT85 small ice (several hundred microns)
particle PCT37 large ice (millimeter) particle,
Tb19 liquid water ? More small ice particles
and less large ice particles in the stratiform
rain area under dust conditions for a given
convection strength or rain intensity
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IWP and Re for non-rain clouds from VIRS
Suppressing homogeneous Nucleation
Enhancing Heterogeneous Nucleation
Smaller sizes with less dependence on temperature
Large sizes and increasing with decreasing
temperature
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PR, TMI, and AMSR rain rate profiles and surface
rain Overall mean PR rainfall profiles
Suppressed convective rains
Enhanced stratiform rains
Suppressed warm rains

• A mild increase at above 6 km and a steep
  increase between 4-6 km, reflecting two possible
  raindrop growth mechanisms of water vapor
  deposition and aggregation of ice.
• The enhancement of precipitation at high
  altitudes was contributed as the consequence of
  aerosol IN effects of enhancing ice phase
  hydrometeors

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PR, TMI, and AMSR rain rate profiles and surface
rain dynamic impacts
Surface rain statistics
Convective rain
Stratiform rain

• Given a constraint on dynamics, mineral dust
  suppress rain rates (and the surface rain
  amounts) at mid and low layers for convective
  rains
• But enhance rain rate at upper layers for
  stratiform rains.
• Suppress warm rains

Warm rain
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TMI AMSR Precipitation efficiency index
Rain Water / Total Water
A low PEI suggests that more small sized cloud
particles and precipitating hydrometeors are
formed in the cloud system, inhibiting the
formation of drizzle and rain and reducing the
coalescence efficiency Mineral dust tends to
decrease the precipitation efficiency for given
condensed water in the atmosphere, an evidence of
the second aerosol indirect effects.
TMI
AMSR
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TMI and AMSR Evaporation rate

• The evaporation rates between the DS and DF
  sectors in the convective rain regime are not
  significantly different.
• The drier and warmer dust layer enhances
  evaporation in the stratiform rain regime.

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• A new aerosol indirect effect
• Mineral dust LW indirect radiation
  forcing

IPCC (2007)
LW emission
-38 C
Heterogeneous Nucleation
Homogeneous Nucleation
Mineral dust
Background aerosols
Macrophysical changes in clouds as a consequence
of heterogeneous nucleation process of mineral
dust exert a strong cooling effect of thermal
infrared radiation on cloud system.
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• A new aerosol indirect effect
• Mineral dust LW indirect radiation
  forcing

Ice Cloud properties De WP CET Outgoing LW
Radiation flux From CERES SSF (Res. 20km)
Aerosol Optic Depth From MODIS MYD08 (Res.
1ºx1º)
Data Collocation
Sea Surface Temperature Column water vapor From
AMSR-E (Res. 0.25ºx0.25º)
CAPE Vertical Velocity RH From NCEP NFL (Res.
1ºx1º)
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• A new aerosol indirect effect
• Mineral dust LW indirect radiation
  forcing

Ice cloud top temperature (CTT) distribution
between clouds developed over northeast Atlantic
Ocean
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• A new aerosol indirect effect
• Mineral dust LW indirect radiation
  forcing

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• A new aerosol indirect effect
• Mineral dust LW indirect radiation
  forcing

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• A new aerosol indirect effect
• Mineral dust LW indirect radiation
  forcing

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• A new aerosol indirect effect
• Mineral dust LW indirect radiation
  forcing

Enhancement of outgoing LW (up to 16 Wm-2)
Observation from CERES
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• A new aerosol indirect effect
• Mineral dust LW indirect radiation
  forcing

• A model sensitive study
• Cloud top temperature (or height)
• Ice water path (IWP),
• Ice particle size,
• Sea surface temperature,
• Water vapor amount and profile
• Another layer of cloud or dust aerosol below the
  ice cloud

• When the ice clouds are optically thick enough,
  IWP gt 40 gm-2, the OLR is insensitive to the
  changes of atmospheric conditions
• Size (Re) matters only for a thin cloud (IWP lt 40
  gm-2)

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• A new aerosol indirect effect
• Mineral dust LW indirect radiation
  forcing

• Macrophysical changes in ice cloud top
  distributions as a consequence of heterogeneous
  nucleation process of mineral dust exert a strong
  cooling effect (up to 16 wm-2) of thermal
  infrared radiation on cloud systems.
• Induced changes of ice particle size by mineral
  dusts influence cloud emissivity and play a minor
  role in modulating the outgoing longwave
  radiation for optically thin ice clouds.
• Such a strong cooling forcing of thermal infrared
  radiation would have significant impacts on cloud
  systems and subsequently on climate.

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Mineral dust indirect effect Warm
clouds dynamic issues and constraints

1
3

• Precipitation as a proxy to classify the relative
  convection intensity of cloud.
• Convective rain clouds
• ---strong convection
• Stratiform rain cloud
• ---moderate convection
• Non-rain cloud
• ---weak convection

• Stratify clouds based on LWP
• Use the regression slope of LWP and TAU to
  replace Re.

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2

• Cloud top temperature as an additional
  constraint
• -20 ? -10 ?,
• -10? 0 ?,
• 0? 10?,
• 10? 20 ?.

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Mineral dust indirect effect Warm clouds

• The sharp gradient of aerosol concentration from
  its northern dust sector to its southern
  dust-free sector provides us an ideal case to
  investigate the aerosol indirect effect.
• Red convective rain clouds
• Blue stratiform rain clouds
• Gray non-rain clouds

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Mineral dust indirect effect Warm clouds
Twomey effect at different layers

• Scatterplots of cloud LWP and cloud optical
  thickness for convective rain clouds (left
  panel), stratiform rain clouds (central panel)
  and non-rain clouds (right panel) with four cloud
  top temperature ranges (upper to lower) -20 ?
  -10 ?, -10? 0 ?, 0? 10?, 10?-20 ?.

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Rain Cloud Non-Rain Cloud
Mineral dust indirect effect Warm clouds

Weak Transport Of dust
Strong Transport Of dust
Weak AIE
Strong AIE
Strong AIE
Wet scavenging
Weak AIE
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Mineral dust indirect effect Warm clouds AIE
at different layers
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• Mineral dust radiation forcing
• direct and indirect SW forcing for
  this case

• At SZA of 21.6
• Mineral dust direct forcing is 53.48 8.56 Wm-2
  per unit AOD
• Mineral dust indirect forcing with LWP of 100
  gm-2 is 29.882.42 (8.1) Wm-2 per unit AOD.
• The magnitude of indirect SW forcing is about 56
  of direct SW forcing of mineral dust in this case.

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Summary

• The observational evidence that mineral dust
  alter cloud microphysics and precipitation
• Dusts, transported up by the strong convection
  updraft, act as additional ice nuclei. Mineral
  dust enhance heterogeneous nucleation process and
  suppress homogeneous nucleation process,
  resulting small cloud particle size.
• Some of ice particles are grown and contributed
  to convective precipitation, and others were
  advected into the neighboring stratiform region
  and slowly grown to precipitate in stratiform
  region. Thus dusts enhance stratiform
  precipitation.
• Consequences of microphysical effects of dusts
  were shifting precipitation size spectrum from
  heavy precipitation to light precipitation and
  suppressing precipitation. Dusts also enhanced
  evaporation processes, which further reduced the
  precipitation reaching surfaces
• A new aerosol indirect effect LW cooling effect
  (up to 16 wm-2)
• Macrophysical changes in ice cloud top
  distributions as a consequence of heterogeneous
  nucleation process of mineral dust exert a strong
  cooling effect (up to 16 wm-2) of thermal
  infrared radiation on cloud systems.
• Induced changes of ice particle size by mineral
  dusts influence cloud emissivity and play a minor
  role in modulating the outgoing longwave
  radiation for optically thin ice clouds.
• Such a strong cooling forcing of thermal infrared
  radiation would have significant impacts on cloud
  systems and subsequently on climate.
• Twomey effect of mineral dust (CCN)--- on the
  cloud precipitation regime and cloud top height.
• Our estimated aerosol indirect effect (AIE) for
  convective rain clouds with cloud top height
  above the freezing level is -0.14 (r0.67,
  plt0.03)
• In contrast, for non-rain clouds, clouds that
  directly interact with the dust layer show strong
  Twomey effects with AIE of -0.24 (r0.94, plt0.01)
• Mineral dust direct forcing is 53.48 8.56 Wm-2
  per unit AOD
• Mineral dust indirect forcing with LWP of 100
  gm-2 is 29.882.42 (8.1) Wm-2 per unit AOD.

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Other results of dynamic analysis(not included
in the paper)
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• A new aerosol indirect effect
• Mineral dust LW indirect radiation
  forcing

Ice cloud top temperature (CTT) distribution
between clouds developed in the dust free (DF)
and dust period (DS) over northeast Atlantic Ocean
MODIS
CERES