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 Tom Ackerman Hiro Masunaga Hiro Masunaga Jim Mather Jim Mather Sue van den Heever Sue van den Heever

Cloud-Aerosol-Precipitation Interactions (CAPI) Cloud-Aerosol-Precipitation Interactions Cloud-Aerosol-Precipitation Interactions More general term than Aerosol Indirect Effects (Twomey, 1977; Twomey et al., 1984; Albrecht, 1989) 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 Allows for inclusion of a range of related responses such as cloud dynamic forcing

GEWEX Objectives CAPI CAPI impacts on both the energy and water cycle processes through cloud and precipitation forcing 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 regarded as one of the most uncertain aspects of climate change through radiative effects Enhancing our understanding of these processes Enhancing our understanding of these processes directly in keeping with basic GEWEX objectives directly in keeping with basic GEWEX objectives Improve model parameterization schemes with CRMs and GCMs Improve model parameterization schemes with CRMs and GCMs

Question 1 Are aerosol responses different under different environments? What is the relative role of CAP interactions versus environment? Are aerosol responses different under different environments? What is the relative role of CAP interactions versus environment? => modulated by different environmental characteristics => modulated by different environmental characteristics lower tropospheric static stability lower tropospheric static stability lower tropospheric relative humidity lower tropospheric relative humidity CAPE CAPE

Question 1 Required Data Aerosol concentrations Aerosol concentrations Surface precipitation Surface precipitation Base state variables Base state variables

Question 2 Do precipitation responses to aerosol indirect forcing differ based on storm type? Do precipitation responses to aerosol indirect forcing differ based on storm type? Suppression in shallow clouds but enhanced precipitation in more convectively active clouds? Suppression in shallow clouds but enhanced precipitation in more convectively active clouds? Isolated clouds versus organized cloud systems? Isolated clouds versus organized cloud systems?

Question 2 Required Data Aerosol concentrations Aerosol concentrations Surface precipitation Surface precipitation Cloud top height Cloud top height

Question 3 How does the raindrop size distribution vary as a function of aerosol concentration? 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 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 DSDs => impacts on precipitation estimation from remote sensors

Question 3 Required Data Aerosol concentrations Aerosol concentrations Drop size distributions Drop size distributions

Question 4 Is there a dynamic response to aerosol indirect forcing? 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 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 Impacts on drop size distributions => cold pool response => impacts on secondary convection => impacts on integrated rainfall

Question 4 Required Data Aerosol concentrations Aerosol concentrations Surface precipitation Surface precipitation Cloud top height Cloud top height Ice water content Ice water content Surface temperature Surface temperature

Proposed Data Set 1 Combine the following: Combine the following: 1. TRMM 3 hour precipitation product 2. SPRINTARS aerosol information Information on next slide Information on next slide 3. ECMWF Meteorological data Reanalysis and realtime products available Reanalysis and realtime products available Allows for assessment of Question 1, as well as basic aerosol indirect effects on precipitation Allows for assessment of Question 1, as well as basic aerosol indirect effects on precipitation

SPRINTARS (Takemura et al., 2000) SPRINTARS (Takemura et al., 2000) Global product with varying vertical and horizontal resolution Global product with varying vertical and horizontal resolution Natural and anthropogenic sources (black carbon, organic matter, sulfate, soil dust, and sea salt) 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) Aerosol transport processes (emission, advection, diffusion, wet deposition, dry deposition, and gravitational settling) An example of SPRINTARS output – total aerosol optical thickness on 4 July 2010

Proposed Data Set 2 Combine the following: Combine the following: 1. CloudSat, TRMM and AMSR-E precipitation 2. MODIS, CALIPSO and SPRINTARS aerosol information Allows for assessment of Questions 2 and 4 although sampling is limited Allows for assessment of Questions 2 and 4 although sampling is limited

Proposed Data Set 3 Combine numerous aerosol and cloud properties from the DOE ARM (ASR) SGP site Combine numerous aerosol and cloud properties from the DOE ARM (ASR) SGP site Aerosol concentrations Aerosol concentrations Cloud base and top heights Cloud base and top heights Cloud type Cloud type Meteorological variables Meteorological variables Cloud ice and liquid water Cloud ice and liquid water Vertical velocity Vertical velocity Latent heat flux Latent heat flux Allow for assessment on Question 3 and Question 4 although only on a limited regional basis Allow for assessment on Question 3 and Question 4 although only on a limited regional basis