Wesley Berg, Tristan LEcuyer, and Sue van den Heever

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Evaluating the impact of aerosols on the onset
and microphysical properties of rainfall off the
coast of China

• Wesley Berg, Tristan LEcuyer, and Sue van den
  Heever
• Department of Atmospheric Science
• Colorado State University

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Differences in TRMM Rainfall Detection February
1, 2000
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Impact of Aerosols on Rainfall Detection?
TMI-PR Rain Detection Differences
SPRINTARS Sulfate AOD
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Coincident TRMM/CloudSat Case3 April 2007
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Coincident TRMM/CloudSat Case3 April 2007
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Rain Rate Histograms3 April 2007
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Differences in Radar SensitivityTRMM PR (13.8
GHz) vs. CloudSat (94 GHz)
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Coincident TRMM/CloudSat Case3 April 2007
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Cloud Resolving Model SimulationsCSU RAMS
Transect of Cloud Liquid Water
3-D Cloud Structure
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Cloud Resolving Model SimulationsEffect of
Variations in Sulfate Aerosol Optical Depth
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Cloud Resolving Model SimulationsEffect of
Variations in Sulfate Aerosol Optical Depth
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Probability of Precipitation versus Liquid Water
Path
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Summary

• Differences in rain fraction between PR and TMI
  off the coast of China point to a modification of
  cloud microphysical properties by aerosols.
• Magnitude is substantial (i.e. the frequency of
  occurrence leads to large differences in the
  total rain (up to 50 or 2 mm/day) locally.
• Results from 3 April 2007 Case and Idealized
  CRM Simulations
• Consistency in rain area between TMI and CloudSat
  indicate the presence of large-scale light rain
  and/or drizzle below the PR detection threshold
  (17 dBZ)
• High AOD CRM simulation has substantially more
  cloud water and the onset of rain is delayed.
• This is consistent with the observations as
  higher cloud water paths may lead to an
  overestimate of the rain rate by TMI/CloudSat and
  possible underestimate by the PR as a result of
  smaller drops initially. In addition, the delay
  in the development of rain drops may be a factor
  leading to the underestimate of the rain area by
  PR.
• Results from Statistical Analysis (Global ocean
  analysis from 2007)
• Probability of precipitation decreases
  significantly in high sulfate aerosol
  environment.
• Aerosol effect is evident in both stable and
  unstable environments.
• Results are consistent using either SPRINTARS
  sulfate AOD or MODIS aerosol index.

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The CloudSat Mission
Primary Objective To provide, from space, the
first global survey of cloud profiles and cloud
physical properties, with seasonal and
geographical variations needed to evaluate the
way clouds are parameterized in global models,
thereby contributing to weather predictions,
climate and the cloud-climate feedback problem.
The Cloud Profiling Radar

• Nadir pointing, 94 GHz radar
• 3.3?s pulse ? 500m vertical res.
• 1.4 km horizontal res.
• Sensitivity -28 dBZ
• Dynamic Range 80 dB
• Antenna Diameter 1.85 m
• Mass 250 kg
• Power 322 W

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Tropical Rainfall Measuring Mission (TRMM)
TRMM Sensors
Nov. 1997 launch, 35 inclination 402 km
Precipitation radar (PR) 13.8 GHz 4.3 km
footprint 0.25 km vertical res. 215 km
swath Microwave radiometer (TMI) 10.7, 19.3,
21.3, 37.0 85.5 GHz (dual polarized except for
21.3 V-only) 10x7 km FOV at 37 GHz 760 km
swath Visible/infrared radiometer (VIRS) 0.63,
1.61, 3.75, 10.8, and 12 at 2.2 km
resolution Lightning Imaging Sensor (LIS )
Cloud Earth Radiant Energy System (CERES)