November 2011

NASA/TM–2011-217192

A State‐of‐the‐Art Experimental Laboratory for Cloud and Cloud‐Aerosol Interaction Research

Need for a National Facility to Complement In Situ and Remote Field Measurements for Improved Atmospheric Modeling and Simulation—Background and Discussion

Charles M. Fremaux and Dennis M. Bushnell Langley Research Center, Hampton, Virginia

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November 2011

NASA/TM–2011-217192

A State‐of‐the‐Art Experimental Laboratory for Cloud and Cloud‐Aerosol Interaction Research

Need for a National Facility to Complement In Situ and Remote Field Measurements for Improved Atmospheric Modeling and Simulation—Background and Discussion

Charles M. Fremaux and Dennis M. Bushnell Langley Research Center, Hampton, Virginia

Available from:

NASA Center for AeroSpace Information 7115 Standard Drive

Hanover, MD 21076-1320 443-757-5802

“The importance of clouds in the climate system cannot be overemphasized”—Akio Arakawa, 2004

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TableofContents

Acknowledgments 2

Abstract 3

Introduction 4

Background 10

SummaryoftheStateoftheArtforGround‐BasedExperimentalLaboratories 14

SomeHigh‐LevelFacilityRequirementsforCloudResearchviaGround‐BasedLaboratories 18

APotentialApproachtoaLargeChamberforCloud‐AerosolResearch 22

NextSteps 24

Conclusions 25

References 26

Appendix 31

PartialListofExistingGround‐BasedAerosolandCloudChamberResearchFacilitiesandSummaryofCapabilities(fromRef.52) 31

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Acknowledgments

Theauthorswouldliketoacknowledgeorganizationsandindividualsthatprovidedreviewcomments that improved the final version of this report. From NASA Langley ResearchCenter, thefollowingorganizationscontributed:ResearchDirectorate,ScienceDirectorate,CenterOperationsDirectorate,andEngineeringDirectorate.Veryhelpfulexternalreviewswere provided by Dr. James D. Klett, Dr. Steven Ghan, and Dr. John H. Helsdon. ManyvaluableadditionalcommentsandideaswereprovidedbyindividualsinsideandoutsideofNASA prior to and during the writing of the paper. Special thanks goes to Mr. BradleyHallierof theLangleyAerospaceResearchSummerScholarsProgramforputting togethertheextensivelistoffacilitiesthatappearsintheAppendixofthisreport.

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Abstract

The state of the art for predicting future climate changes due to increasing greenhousegassesintheatmospherewithhighaccuracyisproblematic,notablyduetoneedforgreatersophistication in atmospheric modeling. Confidence intervals on current long‐termpredictions (on the order of 100 years) are so large that the ability to make informeddecisions with regard to optimum strategies for mitigating both the causes of climatechangeanditseffectsisindoubt.Thereisampleevidenceintheliteraturethatlarge,ifnotthe largest, sources of uncertainty in current climate models are various aerosol effects,withuncertaintylevelsrangingfrom50%to400%andgreater.Asignificantdeficiencyincurrent capabilities is the lack of high‐fidelity mathematical models for cloud‐aerosolinteractions.Asexaflop‐classcomputationalcapabilitybeginstocomeonlineoverthenextdecadeorso,muchbettermodelingoftheseinteractionswillbeneededtotakeadvantageof significantly increased computational power and enable the high fidelity climatepredictions needed by policy and decision makers in government and industry. Oneapproachtofurtheringdiscoveryaswellasmodeling,andverificationandvalidation(V&V)forcloud‐aerosolinteractionsisuseofa"cloudchamber"withasignificantlylargervolumethaniscurrentlyavailable.Suchalaboratoryfacilitywouldbeusedinacomplimentaryroleto in‐situ and remote sensing field campaignmeasurement approaches (e.g., airborne andspaceborneinstruments)toenableimprovedglobalclimatemodeling.Whileitisrecognizedthatreproducingallofthehighlycomplexphenomenaassociatedwiththeseinteractionsisnotfeasible,itissuggestedthatthephysicsofcertainkeyprocessescanbeestablishedinalaboratory setting so that relevant fluid‐dynamic and cloud‐aerosol phenomena (e.g.,turbulent many‐phase flow, convection, electrostatics, aerosol particle formation andgrowth,etc.)canbeexperimentallysimulatedandstudiedinacontrolledenvironmentusingsophisticated instrumentation in a facility that is large enough so that wall effects arereducedtoacceptable levels,andreasonable‐scaleclouddynamicscanbesimulated. Thisreportpresentsahigh‐levelargumentforsignificantlyimprovedlaboratorycapability,andismeant to serveasa startingpoint for stimulatingdiscussionwithin the climate scienceand other interested communities with regard to the need, requirements, and payoff forpursuing a large, state‐of‐the‐art experimental facility for improving prediction of futureclimatestates.

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Introduction

Currently, there iswideagreementwithin theclimatesciencecommunity that theEarth'smeanatmospherictemperaturehasrisenoverthelastcenturyrelativetohistoricalnorms,and that this rise is being driven primarily by increased concentrations of natural andanthropogenic greenhouse gasses, although there is some disagreement as to whetherincreased greenhouse gas concentrations are due to natural cycles or human‐inducedactivities. Water vapor is the most abundant greenhouse gas in the atmosphere, butincreasesprimarily in carbondioxide (CO2), but alsomethane (CH4), nitrousoxide (N2O),chlorofluorocarbons (CFCs), and others are most associated with the rise in globaltemperature.GloballyandwithintheU.S.,significantresourcesarebeingexpendedonmeasurementsofatmosphericphenomena,anddeveloping,testing,andrefiningclimatemodelsforpredictingclimate change and its impacts. Key policy‐ and decision‐makers in government andindustryrequirehigh‐confidenceprojectionsoffutureclimatestatesinordertomakegooddecisions with regard to deployment of resources for reducing greenhouse gas sources,dealingwith impacts due to climate change such as sea level rise, etc., andpossibly evendeveloping"engineeringsolutions"tomitigateundesirableclimatechanges.Whileanalysesofhistoricalclimatedataindicatewithfairlyhighcertaintythatmeanglobalatmospheric temperature has risen since the late nineteenth century (the consensusiestimateisintherangeof0.56oCto0.92oCoverthe100yearsbetween1906and2005(Fig.1)),andthatmeansealevelhasrisenoverthesametimeintervalbyapproximately15cm,thestateoftheartforpredictingfutureclimatechangeswithhighaccuracyismuchmoreproblematic.Infact,confidenceintervalsoncurrentlong‐termpredictions(e.g.,bytheendof the twenty‐first century) are so large that the ability tomake informeddecisionswithregardtooptimumstrategiesformitigatingboththecausesofclimatechangeanditseffectsis in doubt. For example, over the next century, IPCC best‐estimates1 for global surfacemeanatmospherictemperatureriserelativetothelasttwodecadesofthetwentiethcentury(Table1)varybyafactorgreaterthantwo(+1.8oCto+4.0oC).Iftheworst‐caseextremesof"likely"temperatureincrease(wherelikelyisdefinedinReference1as>66%probabilityofoccurrence)areused,thespreadisnearlyafactorofsix(+1.1oCto+6.4oC),asillustratedbythegray"bestestimate"bars to the rightofFigure2. Similarly, sea‐level risepredictionsvarybyafactorofgreaterthanthree(approximately+18cmto+59cm).Whilethereasonsforthespreadinthepredictionsarevariedandcomplex(differingunderlyingassumptions,uncertainties in themodeled values, etc.), depending on whether the outcome is on oneextremeofthepredictionsortheother,adifferent(likelysignificantlydifferent)responsebypolicy‐anddecisionmakerswillberequired.Makingthe"wrong"investmentsearlyoncouldhavesignificantnegativeimpactinthelongrun,rangingfromneedlessexpenditureof

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valuableresourcesononeextremetofailuretodealwiththeproblemsufficientlytopreventmajorenvironmentalconsequencesattheotherextreme. Figure 1. Observed historical change in global average surface temperatures,

average sea level, and northern hemisphere snow cover (from Ref. 1, Fig. 1.1, p. 31)

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Table 1. Projected Global Average Surface Warming and Sea Level Rise at the end of the 21st Century (from Ref. 1, Table 3.1, p. 45)

Figure 2. Change in average measured (1900-2000) and predicted (2000-2100) surface temperature relative to 1980-1999 (from Ref. 2, Fig. SPM.5, Summary for Policymakers section, p. 14)

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There isampleevidence in the literature (e.g. refs.2 ‐5,withmanyotherexamplescitedlater) that large, if not the largest, sources of uncertainty in current simulation climatemodelsarevariouscloudandcloud‐aerosoleffects,withvaluesrangingfrom50%to400%and greater. A significant deficiency in current capabilities is a lack of high‐fidelitymathematical models for cloud effects and cloud‐aerosol interactions. The followingexcerptfromthe2010DepartmentofEnergy(DOE)AtmosphericSystemResearchScienceandProgramPlan6executivesummarycapturestheissuesuccinctly:

Currentclimatemodelsshowalargespreadinthevaluesofprojectedclimateparameterslikesurfacetemperatureandprecipitation,andthisspreadmakesitdifficult forpolicymakers tousesuchprojections todevelopnationalandinternational energy policy. The spread in climatemodel projections arisesfrom two broad sources of uncertainty. First, scientists believe thatanthropogenic atmospheric aerosols partially offset the global warminginfluence due to enhanced greenhouse gas concentrations, but becauseclimatemodelsareuncertainhowtorepresentthecomplexaerosol lifecyclein the atmosphere, they are also uncertain about the impact of aerosols onclimate. Second, clouds are a large source of uncertainty in climatemodels,particularly how clouds will respond to and interact with changes inatmospheric composition. Bothaerosols and clouds influenceradiationandprecipitation,whichtogetherlargelydrivetheglobalatmosphericcirculation.

A primary cause of current high levels of uncertainty in future climate prediction bymodeling is a low level of understanding of the underlying physical processes related toatmosphericaerosolsandcloud‐aerosol interactionsattheypertaintoclimatechange. AsclearlynotedbytheIPCCinReference2:

Anthropogeniccontributionstoaerosols(primarilysulphate,organiccarbon,blackcarbon,nitrateanddust)togetherproduceacoolingeffect,withatotaldirect radiative forcing of –0.5 [–0.9 to –0.1] W m–2 and an indirect cloudalbedo forcing of –0.7 [–1.8 to –0.3]Wm–2. These forcings are nowbetterunderstood than at the time of the TAR (i.e., the third Technical AnalysisReportproducedby the IPCC in2001)due to improved insitu, satelliteandground‐basedmeasurementsandmorecomprehensivemodeling,butremainthedominantuncertaintyinradiativeforcing(emphasisadded).Aerosolsalsoinfluencecloudlifetimeandprecipitation.

The mechanisms contributing to radiative forcing are summarized in Figure 3 fromReference 2. Note that the total (direct + cloud albedo) impact of aerosols on radiativeforcing issecondonly toCO2,but that theuncertaintieson thesequantitiesareby far thelargestofanyofthecomponents,andthatthe"levelofscientificunderstanding"(LOSU)is"mediumto low" fordirecteffects, and "low" for cloudalbdeoeffects. Theclearneed forsignificantly better understanding of the physical mechanisms and processes underlying

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atmospheric aerosols and cloud‐aerosol interactions (as they relate to climage change) istheimpetusforproposingthathighlycontrolledexperimentsbeconductedinastate‐of‐the‐art laboratory. Onlywhen the relevantunderlyingphysical processes related to aerosolsand cloud‐aerosol interactions aremuch better understood, and those physical processesthat arewell understood are adequately accounted for,will uncertainties be significantlyreduced.Asmuchmorepowerfulsupercomputersbegintocomeonline

overthenextdecadeorso(likelyexaflop‐classcomputers,i.e.,1018floatingpointoperationspersecond),muchbettermodelingoftheseinteractionswillbeneededtotakeadvantageof

Figure 3. Anthropogenic and Natural Radiative Forcing Components Important to Climate Change (from Ref. 2, Fig. SPM.2, Summary for Policymakers section, p. 4)

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significantly increased computational power and deliver the high fidelity climatepredictionsneededbypolicyanddecisionmakersingovernmentandindustry.Thereare,inaddition,considerableandincreasingconcernsregardingthepotentialimpactof"positivefeedbacks”. Forexample,warming‐inducedreleaseofthemassiveamountsoffossilmethaneandmethaneclathrates(methaneiceor"fireice")presentinthetundraandocean sediments could have a major impact on temperature rise since methane is overtwenty times more effective than CO2 as a greenhouse gas. The tundra and oceans alsocontainmassiveamountsoffossilCO2thatisbeingreleasedaswarmingoccurs.Inaddition,the ability of the oceans to absorb excess atmospheric CO2 (i.e., "CO2 uptake") is beingreducedduetotemperaturerise,acidification,andreductionsinalgae.Anotherexampleofapositivefeedbackcycleisrelatedtotheplanet'salbedo,ortheamountofsolarradiationreflected back into space. As large ice sheets melt, albedo is reduced and averagetemperatureisincreased. Increasedtemperatureresults inmorewaterbeingevaporated,andwatervapor isadominantgreenhousegas. Taken together, thesepositive feedbackscouldevidently,fromcrudeestimates,greatlyacceleratetherateandincreasetheimpactsofclimatechange.Reference7providesadiscussionofthe"cloudpositivefeedback”thatisdirectlyrelatedtocloud‐aerosolinteractions.Oneapproach to furtheringdiscoveryaswell asmodeling,andverificationandvalidation(V&V)forcloud‐aerosolinteractionsistousea"cloudchamber"withasignificantlylargervolume than is currently available. Such a laboratory facility would be used in acomplimentary role to in‐situ field campaignmeasurement approaches (e.g., airborne andspaceborne instruments) to improve the fidelity of atmosphericmodels for climate changeprediction.Itisrecognizedthatreproducingallofthehighlycomplexphenomenaassociatedwiththeseinteractionsinalaboratorysettingisnotfeasible.However,itissuggestedthatthephysicsofcertainkeyprocessescanbeestablishedsothatimportantphenomena(e.g.,turbulent many‐phase flow, convection, turbulence, electrostatics, particle formation andgrowth,etc.)canbeexperimentallysimulatedandstudiedinacontrolledenvironmentusingsophisticated instrumentation in a facility that is large enough so that wall effects arereduced to acceptable levels, and reasonable‐scale cloud dynamics can be simulated. Asdiscussed and suggested herein, controlled laboratory experiments in large‐scale groundfacilities appear to be a "missing link" in the quest for truly high fidelity climate changepredictions going forward, but detailed analyses will have to be conducted in order toestimatethemagnitudeofuncertaintyreductionthatcanultimatelyberealizedrelativetothecurrentfieldcampaignstateoftheart.Overall,itisobviousthatprognosticationofclimatechangeoverthenextseveraldecadestoacenturymustbedonewithasmuchprecisionandaccuracyascanbemusteredduetothepotentiallymassiveimpactsgoingforwardonglobaleconometrics,humanhealth,standards

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oflivingandnationalsecurity.Thereisapossibilitythatglobalco‐operationwhilstworking“climate change” as a “common enemy” could lead to greater global consilience. NASALangleyResearchCenterisassessingtheneedandrequirementsforaground‐basedfacilityto experimentally simulate, both for discovery science and modeling, cloud‐aerosolinteractions with application(s) to their effects on climate change. Such a facility isenvisioned as a national resource for developing critical aspects of climate models,calibrating computationalmethods, and understanding the physical processes underlyingcloud‐aerosolinteractionsthroughthestudyofmeaningfulbutmanageable"unitproblems"at useful scales. This document outlines the impetus for considering the need for betterunderstanding and representation of cloud‐aerosol interactions in Global ClimateModels(GCMs), some initial high‐level requirements for a ground‐based experimental facility,possibleconceptualapproachestoitsdesign,andthenextstepsneededtoassessthelevelofconsensusforsuchafacilitywithintheclimatesciencecommunity. Background

Asearchofthepertinentliteraturerevealsthat,whilethemeanpredictedtrendsappeartobe consistent (e.g., that a rise in mean global temperature over a time scale of severaldecades will occur due to increasing levels of greenhouse gasses from a combination ofanthropogenic and natural sources) there is wide acceptance within the climate sciencecommunity that there are large uncertainties in these projections due to a number offactors. Oneof the largest sourcesofuncertainty appears tobe lackof sophistication forrepresenting cloud feedbacks (positive and negative) into the Earth's radiation budget inGlobalClimateModels4,5, including forcingeffectsofaerosolsas they interactwithclouds.Large Eddy Simulations (LES) and other computational approaches use modeling tosimulatecomplexatmosphericphysicsandchemistry, includingtheeffectsofaerosols, forpredicting climate states (e.g., Ref. 8). These aerosol (and other particulate) effects arebelieved tobe the sourceofphenomenaranging from"globaldimming" (the reductionofdirect solar radiation reaching the Earth's surface and thus reducing atmospherictemperature and partially counteracting temperature rise caused by greenhouse gaspollution), tochanges in theglobalprecipitationpattern. ThediscretizationscaleofmostGCMs(ontheorderof1degreeoflatitude,orroughly100km)isalsoproblematicintermsofpredictingphenomenathataremanifestatsmallerscalessuchascloudeffects,andthustheirimpacts.Currentpracticeistoparameterizecloudeffectsusingbulkpropertiesacrossagridcell,eventhoughthescaleofindividualclouds(andevencloudsystems)canbemanytimes smaller. While necessary due to the computational intensity of atmosphericsimulations relative to current computer power, this compromise clearly introduces asourceofuncertaintyintotheresults.However,somerecentsimulationshavebeenrunatresolutionsas lowas100minordertoresolve individualcloudswithencouragingresults

(Ref.9).Belowarerepresentativeexcerptsfromasamplingofthecontemporaryliterature

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with regard to cloud and cloud‐aerosol interactions and their impact on climate changepredictions:

"EstimatesofEarth'sclimatesensitivityareuncertain,largelybecauseofuncertaintyinthelong‐termcloudfeedback"‐(Ref.10)

“CloudshaveastronginfluenceontheEarth’sradiativebalancebutarepoorly

representedincurrentclimatemodels"‐(Ref.11)

“ManyoftheuncertaintiesinGlobalClimateModelsstemfrompoorrepresentationofcloudprocessesthatoperateatfinescales”‐(Ref.6)

“Wedonotknowhowmuchwarmingduetogreen‐housegaseshasbeencanceledby

coolingduetoaerosols”‐(Ref.12)

"Theuncertaintyinassessinganthropogenicaerosolimpactsonclimatemustbemuchreducedfromitscurrentleveltoallowmeaningfulprojectionsoffutureclimate"‐(Ref.13)

"Theinteractionsbetweenaerosolsandcloudsisprobablythebiggestuncertaintyof

allclimateforcing/feedbackprocesses”‐(Ref.13) “Modelingthecloudalbedoeffectfromfirstprincipleshasprovendifficultbecause

therepresentationofaerosol‐cloudinteractionsandofcloudsthemselvesinclimatemodelsarestillcrude”‐(Ref.14)

“Variationsofcloudinessby5%translatestoadegreeoftemperaturechange”‐(Ref.

15)

“Whether anthropogenic activity actually increases or decreases ice nucleiconcentrationisamatterofdebate"‐(Ref.16)

“Theuncertaintyinaerosolradiativeforcing istypicallygreaterthan100%andfor

someaerosolcomponents it ismore than200%. Theregional scale forcingcanbesignificantly greater than the global average, as can the associated uncertainty” ‐(Ref.17)

“The indirect radiative effects of aerosols also includes effects on ice and mixed

phasecloudsbutthemagnitudeofanyindirecteffectassociatedwiththeicephaseisnotknown”‐(Ref.3)

“Aerosols represent the largest uncertainty in understanding how humans are

changingourclimate”‐(Ref.18)

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“Evensmallchangesiniceformationcouldhaveasignificantimpactontheindirectforcingduetoaerosols”‐(Ref.3)

“Scientists have yet to untangle the interplay between pollution, clouds,precipitationandtemperature”‐(Ref.19)

“GlobalmodelssuggestthatsulfateaerosolsproduceadirectforcingintheNorthern

Hemisphereofthesameorderofmagnitudeasthatfromanthropogenicgreenhousegasesbutoppositeinsign.Thereissubstantialuncertaintyaboutthemagnitudeandspatialdistributionofthenegativeforcingbyaerosols.Itistheopinionofthispanel(theNRC)thattheuncertaintyinthemagnitudeoftheeffectsofaerosolsonclimateisseriouslyhinderingourabilitytoassesstheeffectofanthropogenicemissionsonclimate”‐(Ref.20)

“Anthropogenic aerosols have the potential to introduce complex anomalies in the

circulationandprecipitationclimatologytherebycreatinghazardousnewhotspotsinthewatercycle.”‐(Ref.21)

“Quantifying the indirect (cloud‐aerosol) effectsofaerosols ishighlyuncertainand

remainsoneofthelargestuncertaintiesinoureffortstocalculateradiativeforcing”‐(Ref.23)

“Thegreatestuncertaintyaboutaerosolclimateforcing,indeedthelargestofallthe

uncertaintiesaboutglobalclimateforcing–isprobablytheindirecteffectofaerosolsonclouds”‐(Ref.24)

"EstimatesofEarth’sClimatesensitivityareuncertainlargelybecauseofuncertainty

inlongtermcloudfeedback"‐(Ref.10)

“Accuraterepresentationofcirruscloudsremainsachallengetoclimatemodelinginpart becauseof an incompleteunderstandingof ice formationmechanisms” ‐ (Ref.25)

“Themagnitudeof the indirecteffects (ofaerosols)oncloudsremainsamystery” ‐

(Ref.26)

“Thecloud‐aerosol‐precipitationprocessesarenottakenintoaccountastheyshouldnotbecausewedonotrecognizetheirimportancebutratherbecauseweknowtoolittle on how to quantify them accurately in the weather and climate models, Itappearswecannotgettheclimatesystemrightwithoutproperlyaccountingfortheaerosol‐cloud‐precipitation processes, the dynamic response of the clouds and thecascadeoffeedbacks”‐(Ref.27)

“Aerosols and clouds play central roles in atmospheric chemistry and physics,

climate, air pollution and public health. The mechanistic understanding and

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predictability of aerosol and cloud properties, interactions, transformations andeffectsare,however,stillverylimited”‐(Ref.28)

InReference29,theissuethatwasmostuncertaintoallfourteenexpertswasclouds,

specifically whether or not clouds would exacerbate climate change by trappingmoreheatorameliorateitbyreflectingmoresunlight.

Basedonrecent reports (e.g.,Ref.2), typicaluncertainties forvarious impactsofaerosolsupon climate forcing are in the 50% to 100%range, butwith several atmuch greateruncertainties of up to 400%. The current state‐of‐the‐art for developing atmosphericsimulationmodelsreliesalmostprimarilyoninsituandremote‐sensingfieldmeasurementsofatmosphericstateusinggroundbased,airborne,orspaceborneinstruments. Theuseofhighly sophisticated instruments and sensing techniques in real‐world atmosphericmeasurements produces very high quality data for analysis andmodeling. However, theinformation produced by such field campaigns is, by its nature, “all inclusive” and“contemporary”,i.e.,theentirepanoplyofphysicalmechanismsandinteractionspresentintheatmospherelocallyandcurrentlyarerepresented,buttheabilitytoassesstheimpactofparticular constituents or processes in controlled and repeatable ways (i.e., as in alaboratory setting) is either very difficult or impossible. Thus, potential changes to suchphysicsandinteractionsthatmightbeinducedgoingforwardbyvariousimpactsofclimatechange are not accessed. Without accurate, validmodeling of the requisite physics writlarge these current field campaigns cannot be projected forward to yield what is reallyrequired–accurate“predictions”andimpactsofvariousmitigationapproaches.AsnotedinReference 3: “Projections of a future indirect effect are especially uncertain becauseempirical relationships between clouddroplet number and aerosolmassmaynot remainvalid for possible future changes in aerosol size distributions”. Although the empiricalformulationsnoted inReference3havebeensupersededby those thataremorephysics‐based in the current generation of climate models (as noted in Reference 4), significantwork remains to be done before the all of the relevant physics are captured. The fieldcampaigns are essential to studying the factors that control behavior of the currentatmosphere,butarefarfromwhatisrequiredtodevelopandcalibratehigh‐fidelityphysicalmodelsforpredictingfuturechanges.Forsuchmodeling,laboratorystudiesarerequiredsothatunitproblemsanddiscoverycanbeundertakenundercontrolledconditions inacosteffectiveandexpeditiousmanner."ThekeytoreducingaerosolRFuncertaintyestimatesisto understand the contributing processes well enough to accurately reproduce them inmodels” (Ref. 13). Currently in theU.S., ground‐based laboratory facilities (excluding theground‐basedatmosphericmeasurementfieldcampaigninstrumentsjustnoted)appeartobe primarily used for instrument calibration and some limited science for understandingfundamentalphysicsonasmallscale,e.g.,cloudmicrophysics.Examplesofsomeprocessesthatcouldbenefitfromhighlycontrolledlaboratoryexperimentsarebrieflysummarizedinalatersectionofthisreport.

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Summary of the State of the Art for Ground-Based Experimental Laboratories

Areviewoftheliteraturerevealsthatthestateofground‐basedfacilitiesforexperimentallysimulating and studying cloud phenomena (excluding those for instrument calibration,small‐scale experiments, and educational instruction) is at a low ebb, far moreconspicuously in the U.S. than in Europe. The appendix of this report summarizes thefacilities that were identified during a recent literature survey. While this list is notexhaustive,itdoesprovideagoodindicationofbreadth,location,andoverallcapabilitiesofcurrentfacilities.In the U.S., while fairly large facilities (e.g., cloud chambers) were in use during pastdecades,fewifanyoftheseappeartobeoperationaltoday.Inthemid20thcentury,cloudchamber laboratory facilities of various types and sizes were relatively common,contributingmuchtotheunderstandingofcloudmicrophysics.Inthelaterportionsofthe20thcentury,interestshiftedintotheemergingnumericalsimulationarenaasacompanionto field campaigns and, in the U.S., cloud chamber and other laboratory studies weredeemphasizedandmostweredecommissioned.Aworkshopon“TheFutureofLaboratoryResearch and Facilities for Cloud Physics and Cloud Chemistry” (Ref. 30) was held atBoulder, Colorado in 1985. The report from that workshop states that “...laboratoryresearchoverthepasttwodecades(i.e.,sincethe1960s)hasdeclinedtosuchanextentthatscientific progress toward understandingmany processes occurring in the atmosphere isbeingimpeded”. Additionallystatedinthatreportisthefollowingconclusion:“Triple(i.e.,two types of precipitation particles and cloud) and triple‐plus interactions need to beunderstood and facilities with new capabilities are required to carry out the necessarystudies;thesepointsarecertain.Manyoftheproblemsandcostsinvolvedintacklingtripleandtriple‐plusinteractionswithnewequipmentmaydemandaconsolidationofresourcesintoasingleNationalFacility,orasetoffacilitiesthatwouldbesuitableforawidevarietyofexperimentalworkthatcannotbeundertakenwithexistingfacilities.”Thereportgoesontorecommend facilities in the 80m to 120m‐size range to enable studies of cloud‐aerosolinteractions,asillustratedinFigure4.More recently, Reference 31 indicates that 10m clouds, a size that could be studied in a100mfacility,areofinteresttoatmosphericaerosol‐cloudinteractiondynamics. Also,"Tostudycloudsandaerosolsonemustdealwithprocessesoccurringandinteractinginmorethan12ordersofmagnitude,changesonthemicrophysicalclouds(6m‐10m)mayproducedramaticchangesontheregionalclimateandwholehydrologicalcycle”(Ref.32).

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Intheinterveningtwenty‐sixyearssincethelaboratoryworkshopcitedinReference30washeld, climate change concerns have become bothmore worrisome andmore immediate,withconcomitantrequirementsforever‐more‐accurateclimateprojectionsattheregionalandgloballevels. Alsoduringthistimeframe,cloudchamberlaboratoryclimatestudiesinthe U.S. have even further atrophied. The promise shown by advanced atmosphericsimulationtechniques(bothasapredictivetool,andasawaytomakethosepredictionsatlower cost than via ground‐based experiments), coupled with availability of "currentatmosphere"datafromsophisticatedinsituandremote‐sensingfieldmeasurements,wasaprimarydriverforthisshiftinemphasis.However,inhindsight,itisclearthathighfidelityclimate predictions must rely on a "three legged stool" of field measurements,modeling/simulation, and sophisticated laboratory experimentation, and that the de‐emphasisofthelatteroverthepastfewdecadeshasresultedinan"outofbalance"situationthatishamperingpredictivecapabilityjustwhenitisneededmost.A direct analogy to the situation in climate prediction is the imminent demise ofaerodynamic wind tunnels that was predicted with the advent of sophisticatedcomputational fluid dynamic (CFD) codes for solving the Navier‐Stokes equations thatbegan in the 1970s ("there will be no need for wind tunnels within ten years..."), andcontinuedinthedecadesthatfollowed. However, inthefortyyearssincethen,whileCFDhasmadegreat inroads intohigh‐fidelityaerodynamicpredictionandmanywind tunnelshave closed (more due to a significant reduction in the number of aircraft developmentefforts, e.g., due to the end of the ColdWar, than to a reduction in need for high‐fidelityexperimental data in any given project), it appears that the aerospace community is

1

2

Figure 4. Concept for a national cloud and precipitation research facility from 1985 facilities workshop. 1: diameter 80m, height 120m, 2: diameter 120m, height 60m. (Ref. 30)

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realizingthatthisassumptionwasprematureandshortsighted,andthatsomeminimumsetofwindtunnelswillberequiredfordecadestocomeforconductingcontrolledexperimentsforadvancedaerodynamicmodeling,validationandcalibrationofcomputationaltools,anddatabasedevelopmentforconfigurationsinflowregimesinwhichCFDisnotyetcapableofproviding the "final answer" prior to flight. So, while Boeing used CFD to significantlyreduce the number of wing sets that were wind tunnel tested for the 787 Dreamlinercomparedtoearlieraircraft,itcouldnothaveaccomplishedthetaskwithouttheconcurrentuseofhighqualityexperimentaldatafromlargewindtunnels,bothfordatagenerationandfor computational tool validation. Climate predictionmethods appear to have followed apathsimilar to thatof theaerospacecommunity,buthavegoneevenfarther in that therearefewifanylargeexperimentalfacilitiesinoperationtoday.Needless tosay, thesuggested100mclass facilitiescalled forat the1985workshopwerenever constructed. There have been attempts to secure funding for larger scale facilities(i.e., larger than contemporary facilities), but to‐date none of these proposals has beensuccessful (Ref. 33). Besides cloud chambers, other facilities such as specially designedvertical wind tunnels have been used to simulate the dynamics of raindrops and otherparticulates in the atmosphere (e.g., Refs. 34‐36). While not emphasized in this report,improvedwindtunnelcapabilityforstudying,e.g.,aerosolparticleandicecrystalformationandgrowth,shouldalsobeconsidered.In Europe the situation appears to be somewhat better (Ref. 37), with updated cloudchambersbeingbuiltandutilizedforclimateissues,butthesearefarsmallerthanthe100mclassfacilitiescalledoutinthe1985laboratoryworkshop.EuropeanSimulationChambersforInvestigatingAtmosphericProcesses(EUROCHAMP‐2)isahighlyintegratedconsortiumof sixteen chamber facilities operated by fourteen partner organizations from eightEuropean countries organized in 2009 as a follow‐on to EUROCHAM‐1 (2004 ‐ 2009).AlthoughtherearenoEUROCHAMPfacilitiesthatapproachthescaleofthatbeingdiscussedin this report, there are some relatively large chambers of recent vintage. The largestappearstobeAerosolsInteractionandDynamicsintheAtmosphere(AIDA)37,38inGermanyforstudyingclouddynamicsandcloud‐aerosolinteractionsonasmallscale.Thischamber(Fig.5)hasavolumeof85m3,atemperaturerangeof ‐90oCto+50oC,reducedpressurecapability, can introduce trace gasses, and has highly sophisticated instrumentation,allowingAIDAtocarryoutaerosolandcloudexperimentsoverafullrangeoftroposphericandstratospherictemperaturesandpressures.Another example of a modern facility is LACIS, or Leipzig Aerosol Cloud InteractionSimulatoroperatedbytheLeibnizInstituteforTroposphericResearchinGermany(Ref.39).This facility is highly specialized to study cloud‐aerosol interactions. LACIS consists of a

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large outer shell containg a highly instrumented flow tube. The exterior of the facility isshowninFigure6.Thetemperaturecapabiltyofthefacilityis‐60oCto+40oC.

 

Figure 5. AIDA cloud chamber (Ref. 38, public domain image courtesy of Karlsruhe Institute of Technology)

Figure 6. LACIS cloud-aerosol interaction facility (Ref. 39, public domain image courtesy of Dr. Frank Stratmann/EUROCHAMP)

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Some High-Level Facility Requirements for Cloud Research via Ground-Based Laboratories

Clearly,dependingontheintendeduseofthefacility,a"cloudchamber"cantakeononeofseveral incarnations. For example, as noted earlier, specialized vertical wind tunnels, or"cloudtunnels"havebeensuccessfullyusedtosimulateprocessessuchasraindropandicecrystal formation and dynamics within clouds. However, a ground facility forexperimentallysimulatinganactualcloud(evenasmallone)wouldnecessarilyhavetobequitelarge.Ifitisassumed,e.g.asinReference31,thatcloudswithlengthscalesassmallas10mplayanimportantroleinclimatephysics,thenafacilitywithdimensions5to10timesthe cloud scalemight be required to keepwall effects and other unwanted influences toacceptable levels during experiments. Also, wall temperatures would likely have to bepreciselyregulatedinordertoprovideconditionsforconductingmeaningfulexperiments.This high degree of temperature control could be accomplished via the use of super‐insulated walls, active temperature regulation, or a combination of the two methods.Additionally, the need for specialized instrumentation, possibly sophisticated flow (andphase)control,andotherconsiderationswouldhavetobetakenintoaccount.Asamplingofthe physical mechanisms and processes requiring improved discovery, quantification aswellasmodelingandV&V, individuallyand invariousconcertusing laboratorychambersincludes(butisnotlimitedto):

Gasphasephoto‐chemicalreactionsofvolatileorganiccompounds,includingeffectsof inorganic acids on secondaryorganic aerosol size andmass, andheterogeneouschemicalreactions

Effectsofinnatelyanisotropicturbulenceuponcloudcondensationnuclei(CCN)and

ice forming nuclei (IFN), i.e., micro‐scale turbulence accelerates cloud formation,changescollision frequencyand triggersprecipitation,and turbulencecausesrapidgrowthindropletsize.

Dampeningeffectsofaerosolsuponturbulence

Discoveryandmodelingregardingthephysics,etc.,associatedwiththeinitiationof

precipitation,especiallyforiceclouds

Ice nucleationmechanisms, including the inhibiting effects of organic content, theefficiencyoflead‐containingparticles,etc.

Tracegaseffects,includingconcentrationsofnitricacid(HNO3)onCCNnumberand

effectiveness,andimpactsuponhygroscopicity

Effects of dynamic motions, convection, and shear, at the cloud and larger scalesupon aerosol interactions and behavior, including coalescence, evaporation,

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collisions, coagulation, condensation, activation, glaciation, aggregation andsedimentation

Possibility ofmajor effects of cosmic rays and ion‐induced nucleation and electro‐

scavenging on ice formation, along with effects of solar radiation and photo‐chemistry

Effectsofsolarheatingofblackcarbonaerosolsupontheiractivationintodropsand

CCNeffectiveness Effectsoffilm‐formingcompoundsuponCCNeffectiveness

Atmosphericandself‐inducedelectric fieldeffects (including lightning)oncollision

frequency and ice nucleation. Some observations indicate greatly enhanced icenucleation.

Aerosoleffectsuponcloudcellularconvection

Aerosoleffectsuponcloudformationmechanisms(gravity,Parker‐Jeans,collisional,

etc.)andturbulenceinclouds

Aerosoleffectsuponcloudradiationinfluences,writlarg

Aerosoleffectsoncloud"edge"dynamicsanddetails

EffectsofbiologicsonCCNincludingsurfacechemistry,hygroscopicity,andcontactanglealterations

Methaneinfluencesonsulfateandproductionofotheraerosols

The major cloud‐aerosol interaction processes to be simulated include agglomeration,coagulation, coalescence, the various phase changes including areas with significantknowledgegapssuchasicecloudformation,nucleation,deposition,catalysis,electrification,chemicalchangeswritlarge,andconvection(includingturbulenceandprecipitation). Theindependent parameter spaces include altitude/pressure, temperature, moisture,convection/turbulence, radiation (including ultraviolet and cosmic rays), chemicalcomposition(s), initial aerosol compositions/size/geometry/number density, electrostaticfields, various “bio effects”, and doubtless others. Clearly, there are myriad physicalmechanisms and processes related to clouds, precipitation, aerosol interactions, etc., thatarenotasyetwellunderstoodwhichcouldbenefitgreatlyfromstudyinahighly‐capable,well‐designedlaboratory(whydoesprecipitationoccur?howdoicecloudsformandgrow?do we fully understand the impact of the biologics, e.g., bacteria, algae, pollen, onatmosphericchemistryanddynamics?).

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InReference40,itisstatedthat“Sinceiceformationincloudsisnotyetfullyunderstooditisrecommendedthatfurtherlaboratorystudiesandinsitumeasurementsbeconductedtoclarify the nucleation mechanisms” (emphasis added). Similarly, from Reference 18:“Obviously deconvoluting the relative impact of each property on CCN activation ismorestraight forward in well controlled laboratory experiments". Also, “In contrast to fieldobservations, laboratory studies allowone to examine (ice) crystal growthprocesses andthe effect of each environmental variable under controlled conditions” (Ref. 41). And“Significantadvancesinlaboratorydataandmodelingtechniquesareneededforanumberofimportantaerosolsystems”(Ref.17).Thus,laboratorystudiesareessentialforprovidingnecessaryinformationforinputintomoredetailedatmosphericmodels”.In their 2010 Atmospheric SystemResearch Science and Program Plan (Ref. 6), the DOEOfficeofSciencedevotedsignificantattentiontotheneedforbetterlaboratoryfacilitiesforcloudandaerosolstudies,suchas:“Laboratorystudiesareessentialtounravelingprocessesinvolvingchemicalreactionsandcomposition‐dependentaerosolmicrophysicalproperties”and“WhatisclearlyneededtoadvanceunderstandingofcloudaswellasaerosolformationisadedicatedconsolidatedlaboratoryfacilityintheU.S.capableofconductingexperimentsunder controlled conditions....such a facility would be a bold breakthrough‐science‐typeinitiative thatwould laya firm foundation forsystematically improvingcloudandaerosolprocesses/propertiesmodulesaswellasserveasanincubatorforthedevelopmentofnewcloudandaerosolinstrumentsdesignedforfielddeployment”.To the extent that the various scientific and modeling shortfalls and physical issuesdiscussedhereinareaffectedbycloud‐levelturbulenceandconvection,alarge‐scalecloudchamber/laboratoryappearstoberequiredtoconductcontrolledexperiments,asnotedinReference42: “Oneprinciple continuingdifficulty is thatof incorporating, inaphysicallyrealisticmanner,themicrophysicalphenomenainthebroadercontextofthehighlycomplexmacrophysical environment of natural clouds”. While it is recognized that a parametricapproach can become so far removed from the situation of interest that it is no longeruseful,thelonghistoryofground‐basedlaboratoryexperimentsinanynumberofscientificdisciplinesshowsthatmeaningfulresultsthatprovideabetterunderstandingofunderlyingphysicsareobtainableviathoughtfulexperimentdesign.The motion of air within clouds is in general turbulent, and the characteristics of thisturbulence are a function of the details of cloud formation, interactions, and internaldynamics. The literature concerning the effects of this turbulence upon cloud‐aerosolinteractionsindicatesthefollowing(refs.43to47):

Cloudturbulenceapplicabletodropletscalesissubstantiallyanisotropicduetolocalizedactionsofbuoyancy&evaporation

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Turbulenceaffectsparticle‐dropletcollisionandcoalescenceprocesses,greatlychangeslocalizedrelativevelocities,andtriggersrainshowers

Higherlevelsofturbulenceresultinfasterdropletgrowthandcondensation,wheretheincreasesareafunctionofturbulenceamplitudeandotherdetailedcharacteristics

Theverticaltransportofaerosolscanbedominatedbyturbulence

Turbulencebridgesdropletgrowthbycondensationandcoagulation

Turbulencecontributestotheformationofhighicecrystalconcentration

"Withoutturbulenceonly7%ofthetotalmasswasobservedindroplets

withsizesover100microns,whilewithmoderateturbulencethisincreasedto79%"(ref.43)

Overall,theinteractionsbetweencloudmicrophysicsandturbulencehavenotbeenstudiedindetail,andwouldbenefitfromtheavailabilityofahighlycapablegroundfacility.Basedonexistingtechniquesincurrentwindtunnelsandotherresearchfacilities,itisfeasibletogenerate and control air turbulence of varying scales, frequencies, amplitudes, etc., forparametric studies in a cloud chamber. Potential techniques include production of localshear/convection, “artifactual” turbulence (i.e., turbulence generatedoutside the chamberand "injected"), and utilization of other turbulence production approaches includingbuoyancy,localizedheating,chemicalreactions,andpossiblyapplicationofmagneticfields.Turbulence is generated in many ways in both nature and by technology, and thesemechanisms should be studied to identify and select the most promising candidates forprovidingdynamicfieldsintherangesrequired.Adetailedstudymustbeconductedwithregardtothetype(s)ofturbulencerequired(scaleranges,degreeofanisotropy,functionaldependenceonvelocityandtemperaturefields,discretedynamicfeatures,etc.‐allofwhichhavebeenfoundtobeimportantforunderstandingcloud‐aerosolinteractions)andthebestmethodsforgeneratingsuchturbulenceinachamber.Suchastudywouldbeafoundationalsteptowardrealizingalargelaboratoryforcloud‐aerosolresearch. 

Clearly, the literature has many examples of major gaps in the knowledge necessary toadaquatelymodelcloud‐aerosoleffectsforbothregionalandglobalclimateprojections.Itisrecognized that no single ground facility can duplicate the myriad complex interactionsfoundinnature,orevensomeofthemostdifficultphenomenaindividually(e.g.,cloud‐topradiativecoolingasadrivingmechanismforturbulence),butwiththestillambitousgoalofconductinghigh‐fidelityexperimentsonunitproblems ina largechamber, there isaverydetailedsetofcapabilitiesrequired,includingthecapacitytoindependentlyvaryturbulencedynamics(shear,level,scale,etc.)andahostofotherparameters.Additionalmajor“issues”

22

thatneedtobeaddressedtoenablerelevantunitexperimentsincludewalleffects(thermal,radiation, convection) and reconciling dynamic interactions at scales (Reynolds number)beyondthoseachieveableinevena100mclasschamber.However,itisworthnotingthatatremendousamountof therequisiteresearchregardingthese issuescouldbe,andshould,be,conductedinsmall(er)scalechambers.

APotentialApproachtoaLargeChamberforCloud‐AerosolResearch

Although a ground facility for simulating even small clouds could bemassive, precedentexistsfortheconstructionofthebasicshellofsuchafacility.Clearlywalleffects(thermal,fluid boundary, etc.) would need to be minimized. It is assumed that fluid boundaryconditionscanbemitigatedbothbythescaleofthefacility(i.e.,keepingtheareaofinteresta sufficient distance from thewalls) and by applying flow‐control technologies if needed.Strictcontrolofheattransferforestablishingandmaintainingthermalboundaryconditionsmightbeaccomplishedviatheuseofhighlyinsulatedwalls,activetemperatureregulation,oracombinationofthetwo.If very large scales and extremely efficient insulation are required for such a facility, aprecedent exists in the petroleum industry, which has been constructing ever‐largercryogenicstoragefacilitiesforliquefiednaturalgas(LNG)sincethe1960s.Currentstate‐of‐the‐art storage facilities have volume capacities in the 2x105 m3 range and can storeliquefiedmethaneat‐160oCatatmosphericpressurewithaminimumof"boiloff"duetosuperbinsulationcharacteristics. Typicalconstructionconsistsofapre‐stressedconcreteouter shell, a high‐performance insulation blanket, and an inner nickel alloy shell. AnexampleofaoneofthelargestfacilitiesinexistenceisElPasoCorp.'sElbaIsland,Georgiafacilitywithadiameterof88m(similar to theLNG tank shown inFigure7). Even largerfacilitiesarebeingproposed,suchasaJapanesedesignfora95m‐diametertankshell.ItisdifficulttodeterminehowmuchofthecostofsuchanLNGstoragefacilityisgermanetoapotentiallargecloudchambersinceitisunknownhowmuchofthecostofthesefacilitiesisrelatedtospecifictechnicalorregulatoryrequirements,industry‐specificequipment,etc.Additionally, unit cost estimates for existing and proposed facilities available in the openliteraturearescarce.A2006publication(Ref.48)statesthatunitvolumecostsforanLNGstorage facility is in the $400/m3 range. The 88m‐diameter Elba Island tank has anapproximate gross volume of 2.3x105 m3, resulting in an estimated (tank only) cost of$92x106. Conversely, a smaller facility (the 62m diameter LNG tank at Mt. Hayes, B.C.,Canada,Ref.49)wascompletedinthelate2000sandhasacost2007estimate(couchedasa90% confidence estimate since the facilitywasnot completely finished at the timeof thewritingofthereport)givenas$186x106.Giventhespreadofthesetwofigures,itisclearthat significantly more research will be required to formulate a more precise estimate.

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Clearly, if a smaller scale facility with less extreme insulation characteristics is deemedadequate,thenitfollowsthatthecostofthebasicstructurecouldbelowerthanthatfortheLNGstoragetankanalogyusedhere.

Beyondasuitablecontainmentstructure,equipmentforproducingthedesiredfluidstatesandconditionsforparticularexperiments,andinstrumentationarethemostcriticalaspectsofthefacility.Whiletherewillbenoattempttoproduceanexhaustivelist,itisclearthatalargesuiteofsophisticatedequipmentand instrumentswouldbe“core” topracticallyanyexperimentthatcouldbeenvisioned.Asastartingpoint,thedescriptionsoftheEuropeanfacilities noted above (particularly Refs. 38 and 39) provide insight for the beginnings ofsuchalist:

Temperaturecontrol Humiditycontrol Flowconditioning(settingdesiredflowstate,controlofwalleffects,generationand

controlofturbulencescaleandintensity,etc.) Aerosolgeneration Waterdroplet/icecrystalinjectors/otherparticleinjectors Spectrometers(infrared,particle,mass,etc.)

Figure 7. Example of Large Cryogenic Storage Tank for Liquified Natural Gas (public domain image courtesy of ferc.gov)

24

Particle counters and sizers (condensation particle counters, cloud condensationnucleuscounters,etc.)

Particleimagersandtrackers Differentialmobilityanalyzers Gaschromatagraphs Hygrometers Tracegasanalyzers/monitors

Ultimately,theusercommunitywilldrivesensorandinstrumentationrequirements,sothefacilitywillhavetobedesignedwiththeflexibilitytoadaptothermorespecializeddeviceson an as‐needed basis. For example, in such a large facility, the need to track individualtrajectorieswithinlargegroupsofinteractingparticleswillbeakeycapability. Equallyasimportant,sensorsarepoisedforarevolutioninminiturization,costreduction,capability,andspeed,makingitlikelythatbythetimealargefacilitycouldbedesignedandbuilt,muchbetter technology in this area can be leveraged to improve the scientific experiemntsconducted.Clearly,alarge,highlyinstrumentedfacilitywithmanyuniquecapabilitieswouldhavemanyuses other thandirect cloud‐aerosol interactiondiscovery andmodeling. Other potentialusesinterrestrialclimatescienceinclude,butarenotlimitedto,instrumentationandsensordevelopmentforfieldmeasurementcampaigns,directvalidationandcalibrationnumericalsimulations,studiesofthe impactsofaircraftoperationsuponclimate,“pollution”studies,andideationofapproachestomitigateclimatechangeincludingemissionsdesignedtoalterhygroscopicity to enhance aerosol negative feedback (as one example). Additionally,atmospheric studies of planets and moons, free space optical communication throughclouds,andmanyotherimportantandusefultechnologiescouldbeenabledinafacilityofthistypeiftherightdiscipleneconstituencies are engaged. NextSteps

This reportarticulates theneedandhigh‐level requirements fora largeground facility tocomplimentandaugmentcurrentand futureatmospheric‐science fieldmeasurmentswiththe goal of strengthening the understanding of clouds and cloud‐aerosol interactions andtheir impact on prediction of climate change. There is ample evidence in the recenttechnical literaturethat therearemanymajorgaps instate‐of‐the‐artmodelingofclimatedynamicsonregionalandglobalscales,andthatthesegapsare(andwillcontinue)hobblingour ability to predict future climate states with the accuracy and precision needed fordecisionmakerstooptimallydeployresources.

25

Aconcensusamongtheclimatescienceexpertsneedstobereachedbeforefurtherprogresscan bemade. Aworkshop, along the lines of the 1985 gathering noted in Reference 30,couldbeconvenedtoupdateandrefineboththeneedandmoredetailedrequirementsforalarge ground facility. It is suggested that a "virtualworkshop", similar to that used for arecentmodelingandsimulationstate‐of‐the‐artassessment(Ref.50)isanefficientwaytogather inputs from a large, geographically dispersed group of participants. However, atraditional"facetoface"workshopcanalsobeaccomplishedifthatapproachisfoundtobepreferable. If thescientificcommunityendorsesa largescalechamber,nextstepsarethespecification of the capabilities and parameter ranges to be "designed in", evaluation ofcandidateengineeringapproaches,androughorderofmagnitude(ROM)costestimates.

Conclusions

Basedonareviewoftheliterature,itappearsthatmanyresearchersintheclimatesciencefieldareinagreementthathighly‐fidelityclimatechangeprojectionsarehighlydependantupon cloud‐aerosol interactions and thatmodeling, and indeed even understanding, suchinteractionsareatthepresenttimeinagrosslyunsatisfactorystate.Therearemyraid2,3,and4‐phasephenomena that are dependent upondetails of specific chemistry, radiation,and numerous other parameters including turbulence that require detailed study andunderstanding. Such detailed scientific work is extremely difficult to conduct with dataextractedfromfieldcampaignsalone.Thereisanimmenseamountoflaboratoryresearchrequiredtoapproachtheaccuracyandprecisionneededforbelieveableclimateprojectionsgoingforward. It isof interestthatalarge‐scale chamber, necessary to begin to sort out the cloud level changes in aerosolimpacts, physics, and behaviors, would probably take the better part of a decade toauthorizeandconstruct. Inthatsametimeframethecomputingmachineswilladvancetotheexaflopstage,whichisstillfarlesscapabilitythanneededtoab‐initiosimulateallofthemultitudinous cloud and aerosol issues. Thus, modeling will be required for decades tocome, making climate change prediction an "experimental science". A key part of thatexperimental effort needs to be a resurgence of serious, detailed, and creative laboratorystudies.Itisupontheneedfordiscoveryandmodelingofthesecloud‐levelinteractionsthatthe justification fora100mclasscloudchamberrests. Theoverall justification forcloud‐aerosol interaction research, for both discovery and modeling, could not be stronger asexemplified by this quote from Reference 51: “(The study's author) has shown that inmodelrunsusinganAGCM,thewarmingeffectofdoublingCO2concentrationmaybeoffsetbyreducinganassumed(cloud)dropleteffectiveradiusof10micronstoavaluebetween7.9 and 8.6 microns”. In other words, a change in the assumed magnitude of an cloudparameterinaclimatemodelofonly15%to20%hasthepotentialtomasktheprojectedimpactof large changes ingreenhousegas concentration. It is clear thatwesimplymust

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Part1:SystemDescriptionandGrowthofIcebyVaporDeposition.JournaloftheAtmosphericSciences,Vol.51,No.1,Jan.1994,pp.91‐103.

42. Pruppacher,H.R.,andKlett,J.D.:MicrophysicsofCloudsandPrecipitation,Kluwer

AcademicPublishers,1997.43. Riemer,N.,andWexler,A.:"GrowingCloudDropletsinModerateTurbulence",BAMS

Vol.86,No.5,May2005,pp.632‐633.44. Pinsky,M.B.,Khain,A.P.:"TurbulenceEffectsonDropletGrowthandSize

DistributioninClouds‐AReview",J.AerosolScience,Vol.28,No.7,Oct.1997,pp.1177‐1214.

45. Gu,Yu,andLiou,K.N.:"InteractionsofRadiation,Microphysics,andTurbulencein

theEvolutionofCirrusClouds",J.Atmos.Science,Vol.57,August2000,pp.2463‐2479.

46. Duru,P.,Koch,D.L.,andCohen,C.:"ExperimentalStudyofTurbulence‐Induced

CoalescenceinAerosols",InternationalJournalofMultiphaseFlows,Vol.33,2007,pp.987‐1005.

47. Vohl,O.,etal.:AWindTunnelStudyoftheEffectsofTurbulenceontheGrowthof

CloudDropsbyCollisionandCoalescence",JournalofAtmosphericScience,Vol.56,1999,pp.4088‐4099.

30

48. Powell,J.:LiquefiedNaturalGas–MarketChallengesandOpportunitiesfor

Innovation.HydrocarbonWorld,Dec.2006.49. Anon.:"Mt.HayesLNGStorageFacility‐SubmittedtoBritishColumbiaUtilities

CommissionbyTerasenGas,Inc.",June2007.50. Malik,M.R.,andBushnell,D.M.(eds.):RoleofComputationalFluidDynamicsand

WindTunnelsinAeronauticsR&D,NASATechnicalPublication(publicationpending).

51. Bower,K.N.,andChoularton,T.W.:AParameterizationoftheEffectiveRadiusofIceFreeCloudsForUseinGlobalClimateModels,AtmosphericResearch,Vol.27,1992,pp.305‐339.

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ChamberResearchFacilities,NASALangleyinternalwhitepaper,July2010.

31

Appendix

Partial List of Existing Ground-Based Aerosol and Cloud Chamber Research Facilities and Summary of Capabilities (from Ref. 52)

1. DOEFacilitiesatPacificNorthwestNationalLab(PNNL)

AtmosphericResearchChamber● Aerosolformationandtransformation● Roleofaerosolsascondensationnuclei● Aerosolprocessesassociatedwithanthropogenic,biogenic,andbiomass

burningcompounds

IceNucleationChamber● Artificialcloudsunderpreciselycontrolledtemperatureandsupersaturation

conditions● Isolationofparticlesfromaerosoltostudyicenucleation● Portabletostudyambientaerosols

2. UCRiversideAtmosphericProcessLab● Aerosolformationandevolutioninthetroposphere● Consistsoftwo90m3reactors● Nocloudprocessabilities SupportedbyEPA

3. DRIIcePhysicsLab● Staticdiffusionchamber● Icenucleationandelectrificationstudies● Producesstudyonicehabitsonglassfiber Nothighlysubscribed

4. DRIStormPeakLab

STORMVEx● Location:3220mhighmountaininColorado● Equipmentforairbornecloudresearch● Willstudysitucloudandprecipitationpropertymeasurements

32

ISPA● Studieseffectsofpollutionaerosolsonsnowgrowthbyrimingandsnowfall

amountsontheground● Resultshaveimplicationsforwaterresourcesintheinnermountainwest SupportedbyNevada,NSF,DOE

5. NASAGRCParticulateAerosolLab(SE‐11)● ProvidedaerosolandiceparticlemeasurementsduringrecentACCRItests● Flowthroughchamber(N2)● Pressure:Sealevelto50,000ft● Temp:Ambientto‐70C● Humidity:0‐100%(RHi)● ChamberVelocity:0.5to3m/s● 3Windowsandpanelforprobeinsertion● Capabilityforexhaustintroduction● Studiedeffectofsootandsulfuricacidoniceformation

6. LeipzigAerosolCloudInteractionChamber● Investigatesphysicalandchemicalprocessesinthepollutedtroposphere● Flowthroughchamber● Flowtube1‐10minlength● Temp:‐40Cmin● UsedforCCNstudies

7. AIDA● Location:Germany,KarlsruheInstituteofTechnology● Size:4mdiameter,7mhigh,84.5m3● Pressure:0.01to1013hPa● Temp:183Kto323K● Usesairasworkingfluid● Icesaturationsachievedbyexpansion● Walltemperatureactivelycontrolled● UsedforbothINandCCNstudies● Manytechniquesforgeneratingtestaerosols● Capabilityforadditionofinstruments

8. NationalInstituteofRadiologicalSciences● Location:Japan● Volume:25m3

33

● Radon‐aerosolchamber● Temp:278‐303K● Humidity:30‐90%● Pressurebetweeninsideandoutsideofchambercanbenegative● ParticleConcentration:108‐1010m‐3

9. InstituteofChemistryandDynamicsoftheGeosphere(ICG)● Volume:260m3● Studiesreactionsofthesurfaceofaerosols● UseshighresolutionFTIRspectroscopytotrackgasconcentrations● Equippedwithascanningelectrostaticclassifier

10.ARMMobileFacility(AMF)

● Tracksinteractionbetweencloudsandaerosolparticles● Measuresoptical,chemical,physical,andcloudactivationproperties● Equippedwithmanyadditionalinletstoenableadditionalequipmenttobe

added● CondensationNucleiCounter● Multiple‐SupersaturationCloudNucleiandCondensationNucleiCounter● Particle/SootAbsorptionPhotometer

11.MeteorologicalResearchInstituteCloudSimulationChamber

● Location:Tsukuba,Japan● 1pressurevesselandonetemperaturevessel● Volume:1.4m3● Pressure:1000tobelow30hPa● Temp:30to‐100C● ChamberVelocity:0to30m/s● Studiescloudformationandiceproperties

12.ColoradoStateUniversity● ContinuousFlowDiffusionChamber● Studiesiceformationonaerosolparticles● SomefundingfromNASA

13.EnergyResearchCenteroftheNetherlands● Location:Netherlands● Usedtostudythecloudactivationofambientaerosol● Veryhighflowrate(30m3/min)

34

● Usesforwardscatteringspectrometerprobeformeasuringclouddropletnumberconcentration

● Useshigh‐flowcascadeimpactorsforchemicalcharacterizationofaerosol● Comparedthenumberofclouddropletscreatedincleanmarineairvs.

pollutedmarineair14.VectorGmbHBremenAerosolChamber

● Location:Germany● Volume:9m3● Usedtostudyα‐Pineneozonolysisinthepresenceofammoniumsulfateor

sulfuricacidseedparticles

15. OakRidgeNationalLabEnvironmentalSciencesDivision

● Mission:“(1)investigationofparticlebehaviorintheatmosphereandindustrialworkplaces,(2)interactionsofengineeredandanthropogenicpollutionparticleswithbiologicalsystems,and(3)developmentofadvancedinstrumentationandmeasurementmethodology”

● RelationtoJaguar(largestexistingsupercomputer)(seebelow)● FundingsourcesincludeDOEandDOD

16.EuropeanSupersitesforAtmosphericAerosolResearch(EUSAAR)

Aspvreten Research Station (ASP): Location:About80kmsouthofStockholmattheBalticcoast Determinesthephysicalandchemicalpropertiesoftheaerosolandcontains

additionalmeteorologicalinstrumentsaswellasbasicinstrumentationforgaseouscompounds

Measuresparticlesizedistributionfrom10to500nm Particlemassintwofractions,PM10andPM2.5 Particlemass,carbonaceousmaterial(OrganicCarbon,ElementalCarbon) BlackCarbon,soot Meteorologicalconditions Tracksairpollutionlevelsovertime

Zeppelin Research Station (ZEP): Location:Svalbard´swestcoast,474mabovesealevelinanundisturbed

Arcticenvironment OwnedbytheNorwegianPolarResearchInstituteandisusedmostlybythe

NorwegianInstituteforAtmosphericResearch

35

Performsstudiesontheatmosphere,snowandiceproperties,andEarth’senergybalance

BEO Moussala Research Station (BEO):

Location:HighmountaininBulgariaawayfrompollution Equippedwithmeteorologicalinstrumentation,O3andNOxconcentration

equipment,devicesforradioaerosolresearch,X‐rayflorescenceanalysis,neutronandgammameasurements

RunbytheBulgarianAcademyofScience

Cabauw Experimental Site for Atmospheric Research (CBW): Location:AnagriculturalareainthewesternpartofTheNetherlands Hasavarietyofairmassesaroundfromcleanmaritimetocontinental

polluted Measureslandatmosphereinteractionandcloud,aerosolandradiation

interaction Alsomeasuresaerosolproperties,aerosolopticaldepthusingaCIMELsun

photometer,andaerosolextinctionandbackscatterprofilesusingabackscatterlidar

RunbyKIMI

Finokalia Research Station (FKL): Location:SEMediterraneanawayfromlocalsourcesofpollution Airisrepresentativeofsynopticscaleatmosphericcomposition Equippedwithin‐situmeteorologicalinstrumentationaswellascontinuous

measurementsofgaseous(O3,CO,NOx,andNOy),particulate(opticalproperties,chemicalcomposition,mass,andmasssizedistribution)andwetdeposition

Locationhasfrequentdusteventswhichisidealforstudyingtheinteractionofgaseouscompoundswithheterogeneoussurfaces(likedustandsea‐salt)

RunbytheEnvironmentalChemicalProcessesLaboratory

Harwell Research Station (HWL): Location:Harwell,UnitedKingdom Usedasaruralstationrepresentativeoflargescaleairmassesaffecting

SouthernEngland Equippedwithin‐situmeteorologicalinstrumentationaswellascontinuous

measurementsofgasphase(O3,NOx,SO2)andparticulate(massconcentration,sizedistribution,chemicalcomposition)pollutants

RunbyUniversityofBirmingham

36

High Altitude Research Station Jungfraujoch (JFJ):

Location:Jungfraujoch,Switzerland Locatedfarfromlocalpollutionsources;wellsuitedtodeterminethe

backgroundaboveacontinentalarea Equippedwithafullsuiteofgasphasecomponents(measuresbothsituand

columnproperties),andaerosolmeasurementsareperformedbyPSI Thestationiswithinclouds40%ofthetime,makingitwellsuitedforcloud‐

aerosolinteractionstudy RunbytheInternationalFoundationHighAltitudeResearchStations

JungfraujochandGornergra

JRC-Ispra Atmospheric Research Station (JRC): Location:JRC‐Ispra,Italy Locatedtensofkilometersfromlocalsourcesofpollutionandis

representativeoftheregionalpollutedbackground Equippedwithin‐situmeteorologicalinstrumentationalongwithcontinuous

measurementsofgaseous,particulate(opticalproperties,sizedistribution,chemicalcomposition)species

WilluseLIDARinfuture RunbytheInstituteforEnvironmentandSustainabilityoftheEC‐DGJoint

ResearchCentre

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OMB No. 0704-0188

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Technical Memorandum 4. TITLE AND SUBTITLE

A State-of-the-Art Experimental Laboratory for Cloud and Cloud-Aerosol Interaction Research

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Fremaux, Charles M.; Bushnell, Dennis M.

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NASA Langley Research CenterHampton, VA 23681-2199

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National Aeronautics and Space AdministrationWashington, DC 20546-0001

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NASA

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14. ABSTRACT

The state of the art for predicting climate changes due to increasing greenhouse gasses in the atmosphere with high accuracy is problematic. Confidence intervals on current long-term predictions (on the order of 100 years) are so large that the ability to make informed decisions with regard to optimum strategies for mitigating both the causes of climate change and its effects is in doubt. There is ample evidence in the literature that large sources of uncertainty in current climate models are various aerosol effects. One approach to furthering discovery as well as modeling, and verification and validation (V&V) for cloud-aerosol interactions is use of a large "cloud chamber" in a complimentary role to in-situ and remote sensing measurement approaches. Reproducing all of the complex interactions is not feasible, but it is suggested that the physics of certain key processes can be established in a laboratory setting so that relevant fluid-dynamic and cloud-aerosol phenomena can be experimentally simulated and studied in a controlled environment. This report presents a high-level argument for significantly improved laboratory capability, and is meant to serve as a starting point for stimulating discussion within the climate science and other interested communities.

15. SUBJECT TERMS

Climate; Clouds; Aerosols; Greenhouse effect; Global warming; Facilities

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