Clouds, Aerosols and Precipitation

GRP Meeting August 2011GRP Meeting August 2011

Susan C van den HeeverSusan C van den Heever

Department of Atmospheric Department of Atmospheric ScienceScience

Colorado State UniversityColorado State University

Fort Collins, COFort Collins, CO

GRP Team MembersGRP Team Members

Tom AckermanTom Ackerman Hiro MasunagaHiro Masunaga Jim MatherJim Mather Sue van den HeeverSue van den Heever

Cloud-Aerosol-Cloud-Aerosol-Precipitation Precipitation

Interactions (CAPI)Interactions (CAPI) Cloud-Aerosol-Precipitation Cloud-Aerosol-Precipitation

InteractionsInteractions More general term than Aerosol More general term than Aerosol

Indirect Effects (Twomey, 1977; Indirect Effects (Twomey, 1977; Twomey et al., 1984; Albrecht, 1989)Twomey et al., 1984; Albrecht, 1989)

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

GEWEX ObjectivesGEWEX Objectives

CAPICAPI impacts on both the energy and water cycle impacts on both the energy and water cycle

processes through cloud and precipitation forcingprocesses through cloud and precipitation forcing regarded as one of the most uncertain aspects of regarded as one of the most uncertain aspects of

climate change through radiative effectsclimate change through radiative effects Enhancing our understanding of these Enhancing our understanding of these

processesprocesses directly in keeping with basic GEWEX objectivesdirectly in keeping with basic GEWEX objectives Improve model parameterization schemes with Improve model parameterization schemes with

CRMs and GCMsCRMs and GCMs

Question 1Question 1

Are aerosol responses different Are aerosol responses different under different environments? under different environments? What is the relative role of CAP What is the relative role of CAP interactions versus environment?interactions versus environment?

=> modulated by different => modulated by different environmental characteristicsenvironmental characteristics lower tropospheric static stabilitylower tropospheric static stability lower tropospheric relative humiditylower tropospheric relative humidity CAPECAPE

Question 1 Required Question 1 Required DataData

Aerosol concentrationsAerosol concentrations Surface precipitationSurface precipitation Base state variablesBase state variables

Question 2Question 2

Do precipitation responses to Do precipitation responses to aerosol indirect forcing differ aerosol indirect forcing differ based on storm type?based on storm type? Suppression in shallow clouds but Suppression in shallow clouds but

enhanced precipitation in more enhanced precipitation in more convectively active clouds?convectively active clouds?

Isolated clouds versus organized cloud Isolated clouds versus organized cloud systems? systems?

Question 2 Required Question 2 Required DataData

Aerosol concentrationsAerosol concentrations Surface precipitationSurface precipitation Cloud top heightCloud top height

Question 3Question 3

How does the raindrop size How does the raindrop size distribution vary as a function of distribution vary as a function of aerosol concentration?aerosol concentration? Modeling studies suggest that under enhanced Modeling studies suggest that under enhanced

aerosol concentrations => greater number of aerosol concentrations => greater number of smaller cloud droplets => reduced warm rain smaller cloud droplets => reduced warm rain efficiency => more cloud water available in efficiency => more cloud water available in cloud => greater collection efficiencies once cloud => greater collection efficiencies once rain drops forms => larger raindropsrain drops forms => larger raindrops

DSDs => impacts on precipitation estimation DSDs => impacts on precipitation estimation from remote sensorsfrom remote sensors

Question 3 Required Question 3 Required DataData

Aerosol concentrationsAerosol concentrations Drop size distributions Drop size distributions

Question 4Question 4 Is there a dynamic response to Is there a dynamic response to

aerosol indirect forcing?aerosol indirect forcing? Enhanced CCN concentrations => Enhanced CCN concentrations =>

suppressed warm rain processes => more suppressed warm rain processes => more cloud water lofted => enhanced ice cloud water lofted => enhanced ice formation and latent heat release => formation and latent heat release => enhanced buoyancy => deeper convection enhanced buoyancy => deeper convection => enhanced precipitation=> enhanced precipitation

Impacts on drop size distributions => cold Impacts on drop size distributions => cold pool response => impacts on secondary pool response => impacts on secondary convection => impacts on integrated rainfallconvection => impacts on integrated rainfall

Question 4 Required Question 4 Required DataData

Aerosol concentrationsAerosol concentrations Surface precipitationSurface precipitation Cloud top heightCloud top height Ice water contentIce water content Surface temperatureSurface temperature

Proposed Data Set 1Proposed Data Set 1

Combine the following:Combine the following:

1.1. TRMM 3 hour precipitation productTRMM 3 hour precipitation product

2.2. SPRINTARS aerosol informationSPRINTARS aerosol information Information on next slideInformation on next slide

3.3. ECMWF Meteorological dataECMWF Meteorological data Reanalysis and realtime products available Reanalysis and realtime products available

Allows for assessment of Question 1, as well Allows for assessment of Question 1, as well as basic aerosol indirect effects on as basic aerosol indirect effects on precipitationprecipitation

SPRINTARS (Takemura et al., 2000)SPRINTARS (Takemura et al., 2000) Global product with varying vertical and Global product with varying vertical and

horizontal resolutionhorizontal resolution Natural and anthropogenic sources (black carbon, Natural and anthropogenic sources (black carbon,

organic matter, sulfate, soil dust, and sea salt)organic matter, sulfate, soil dust, and sea salt) Aerosol transport processes (emission, advection, Aerosol transport processes (emission, advection,

diffusion, wet deposition, dry deposition, and diffusion, wet deposition, dry deposition, and gravitational settling)gravitational settling)

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

Proposed Data Set 2Proposed Data Set 2

Combine the following:Combine the following:

1.1. CloudSat, TRMM and AMSR-E CloudSat, TRMM and AMSR-E precipitationprecipitation

2.2. MODIS, CALIPSO and SPRINTARS MODIS, CALIPSO and SPRINTARS aerosol informationaerosol information

Allows for assessment of Questions 2 Allows for assessment of Questions 2 and 4 although sampling is limitedand 4 although sampling is limited

Proposed Data Set 3Proposed Data Set 3 Combine numerous aerosol and cloud properties Combine numerous aerosol and cloud properties

from the DOE ARM (ASR) SGP sitefrom the DOE ARM (ASR) SGP site Aerosol concentrationsAerosol concentrations Cloud base and top heightsCloud base and top heights Cloud typeCloud type Meteorological variablesMeteorological variables Cloud ice and liquid waterCloud ice and liquid water Vertical velocityVertical velocity Latent heat fluxLatent heat flux

Allow for assessment on Question 3 and Question Allow for assessment on Question 3 and Question 4 although only on a limited regional basis4 although only on a limited regional basis