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Clouds, Aerosols and Precipitation. GRP Meeting August 2011 Susan C van den Heever Department of Atmospheric Science Colorado State University Fort Collins, CO. GRP Team Members. Tom Ackerman Hiro Masunaga Jim Mather Sue van den Heever. Cloud-Aerosol-Precipitation Interactions (CAPI).

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clouds aerosols and precipitation

Clouds, Aerosols and Precipitation

GRP Meeting August 2011

Susan C van den Heever

Department of Atmospheric Science

Colorado State University

Fort Collins, CO

grp team members
GRP Team Members

Tom Ackerman

Hiro Masunaga

Jim Mather

Sue van den Heever

cloud aerosol precipitation interactions capi
Cloud-Aerosol-Precipitation Interactions (CAPI)

Cloud-Aerosol-Precipitation Interactions

More general term than Aerosol Indirect Effects (Twomey, 1977; Twomey et al., 1984; Albrecht, 1989)

Allows for inclusion of a range of related responses such as cloud dynamic forcing

gewex objectives
GEWEX Objectives
  • CAPI
    • impacts on both the energy and water cycle processes through cloud and precipitation forcing
    • regarded as one of the most uncertain aspects of climate change through radiative effects
  • Enhancing our understanding of these processes
    • directly in keeping with basic GEWEX objectives
    • Improve model parameterization schemes with CRMs and GCMs
question 1
Question 1
  • Are aerosol responses different under different environments? What is the relative role of CAP interactions versus environment?
  • => modulated by different environmental characteristics
    • lower tropospheric static stability
    • lower tropospheric relative humidity
    • CAPE
question 1 required data
Question 1 Required Data
  • Aerosol concentrations
  • Surface precipitation
  • Base state variables
question 2
Question 2
  • Do precipitation responses to aerosol indirect forcing differ based on storm type?
    • Suppression in shallow clouds but enhanced precipitation in more convectively active clouds?
    • Isolated clouds versus organized cloud systems?
question 2 required data
Question 2 Required Data
  • Aerosol concentrations
  • Surface precipitation
  • Cloud top height
question 3
Question 3
  • How does the raindrop size distribution vary as a function of aerosol concentration?
    • Modeling studies suggest that under enhanced aerosol concentrations => greater number of smaller cloud droplets => reduced warm rain efficiency => more cloud water available in cloud => greater collection efficiencies once rain drops forms => larger raindrops
    • DSDs => impacts on precipitation estimation from remote sensors
question 3 required data
Question 3 Required Data
  • Aerosol concentrations
  • Drop size distributions
question 4
Question 4
  • Is there a dynamic response to aerosol indirect forcing?
    • Enhanced CCN concentrations => suppressed warm rain processes => more cloud water lofted => enhanced ice formation and latent heat release => enhanced buoyancy => deeper convection => enhanced precipitation
    • Impacts on drop size distributions => cold pool response => impacts on secondary convection => impacts on integrated rainfall
question 4 required data
Question 4 Required Data
  • Aerosol concentrations
  • Surface precipitation
  • Cloud top height
  • Ice water content
  • Surface temperature
proposed data set 1
Proposed Data Set 1
  • Combine the following:
  • TRMM 3 hour precipitation product
  • SPRINTARS aerosol information
    • Information on next slide
  • ECMWF Meteorological data
    • Reanalysis and realtime products available
  • Allows for assessment of Question 1, as well as basic aerosol indirect effects on precipitation

An example of SPRINTARS output – total aerosol optical thickness on 4 July 2010

  • SPRINTARS (Takemura et al., 2000)
    • Global product with varying vertical and horizontal resolution
    • Natural and anthropogenic sources (black carbon, organic matter, sulfate, soil dust, and sea salt)
    • Aerosol transport processes (emission, advection, diffusion, wet deposition, dry deposition, and gravitational settling)
proposed data set 2
Proposed Data Set 2
  • Combine the following:
  • CloudSat, TRMM and AMSR-E precipitation
  • MODIS, CALIPSO and SPRINTARS aerosol information
  • Allows for assessment of Questions 2 and 4 although sampling is limited
proposed data set 3
Proposed Data Set 3
  • Combine numerous aerosol and cloud properties from the DOE ARM (ASR) SGP site
    • Aerosol concentrations
    • Cloud base and top heights
    • Cloud type
    • Meteorological variables
    • Cloud ice and liquid water
    • Vertical velocity
    • Latent heat flux
  • Allow for assessment on Question 3 and Question 4 although only on a limited regional basis