Integrated Precipitation and Cloud Processes Working Group Meeting

Integrated Precipitation and Cloud Processes Working Group Meeting Meeting: July 9-11, 2013, NASA Goddard Minutes Draft: August 1, 2013

An Integrated Precipitation and Cloud Processes Working Group science meeting was held to identify common objectives in cloud and precipitation measurements and joint mission needs. An inherent synergy and common interest exists that links precipitation to clouds and this meeting brought together a subset of these communities (e.g., TRMM, ACE, GPM, CloudSat) to develop an integrated approach to precipitation and cloud measurements for joint mission goals and requirements, including the mapping of precipitation and related cloud processes across the globe.

Overall assessment of the meeting: Both the cloud and precipitation communities agreed that major science objectives would be met by combining precipitation measurements with cloud measurements, preferably on the same satellite platform. It was suggested that we encourage the aerosol community to plan for and submit a separate proposal to the decadal survey for a related aerosol mission. At the meeting appropriate science questions for a precipitation+cloud mission were brainstormed, as well as requested instrument measurements. A summary on the presentations and discussions follow below. A separate meeting summary document details science questions and measurement requests.

Attending: Gail Skofronick-Jackson, Dave Starr, Ralf Bennartz, Chandra, Ziad Haddad, Gerry Heymsfield, George Huffman, Eastwood Im, Paul Joe, Chris Kidd, Pavlos Kollias, Chris Kummerow, Matt Lebsock, Jay Mace, Hal Maring, Bob Meneghini, Joe Munchak, Paul Racette, Wei-Kuo Tao, Simone Tanelli, Joe Turk, Sue van den Heever, Eric Wilcox, Ed Zipser, Jeff Reid, Deb Vane and Piers Sellers, Lisa Callahan, Art Azarbarzin

Contacts: Gail Skofronick-Jackson ([email protected]); Arthur Hou ([email protected]) Graeme Stephens ([email protected]), David Starr ([email protected])

9:30-9:45 HQ Perspective on the upcoming Earth Science Decadal Survey (H. Maring)  Current Decadal Survey: multiple EVs still undefined, ISS platform available  ESA planning “convoys”, like A-train, but no definite missions selected yet  Next Decadal Survey (DS): will come out in 2017. May not be as specific regarding mission concepts as the 1st decadal survey (i.e., may be more focus on science questions). Unfulfilled objectives from 1st decadal survey may be required to be resubmitted for new DS. CLARREO probably will be high on the list (but smaller/cheaper). ACE elements probably will need to be resubmitted too. Smaller, cheaper satellites/constellations (i.e. Earth Venture) not considered in last DS, but becoming popular. But don’t put too much money into EV because it does take from other missions.

9:45-10:45 Background Presentations GEWEX Grand science questions (C. Kummerow with inputs from G. Stephens)  What are the problems going to be in 15 years?  Changes in water availability, aerosol/precip, and climate extremes GEWEX focus areas are relevant to us. For climate extremes, data resolution and statistics are difficulties.  What phenomena and physical processes lead to extreme events?  Water availability is broken into cloud physics and circulation – what are influences of energy budget and cloud physics?

1  Trenberth energy flow diagram – recent changes to radiation estimates (allegedly) imply we need another 20Watts from precipitation; that should be solved in GPM/Clarreo with 2-3W uncertainties. On the other hand, CMIP5 regional biases are large and need to be solved by understanding processes (not just mapping).  Going forward – more about process, not mapping, model improvement is important – joint clouds, aerosols, precip – prediction on decadal time scale – precip and clouds a key driver in climate sensitivity – frequency & duration, intensity, organization, phase, and vertical motion matter – models generate too much precip too early in warm rain – cloud/precip transition couples the water and energy cycles  The mapping function continues to be a requirement to serve applications

Global Cloud challenges of the coming decade(s) (Sue van den Heever with W-K. Tao)  Multi-scale, global CRM or embedded CRM models maturing as tools to understanding climate. Synoptic-scale dynamics well-understood, cloud-scale and microphysics still need work. Latent heating products still depend more on CRM than direct measurements.  Basic processes move water through climate system via formation and evolution of particles from aerosol to cloud to precip in turbulent vertical motions  Global models moving to cloud resolving, microphysics the weak link  Need measurements that constrain all the profiles at the same time, plus vertical motion  Ice processes are poorly understood, many pathways to same result, difficult to observe remotely, but large impacts on dynamics (e.g., hail vs. graupel fraction). Climate models and CRM tend to use different ice schemes.  Microphysics central to the other physical processes - latent heating helps drive dynamics - need updrafts and downdrafts ~0.5 m/s, 1km and turbulence  Microphysics key to ice processes, which feedback to dynamics - droplet breakup and riming are two big issues - treatment in bins is better than bulk but expensive  Aerosol indirect effects - an issue in mixed-phase - need aerosol profiles, not just optical depth, co-located with environmental profiles  Ultimate goal – collocated 1. Vertical velocity, 2. Ice and liquid microphysical process, 3. Environmental profiles, 4. Aerosol concentrations on reasonable resolutions  Discussion: - Is swath necessary? - Don’t want to give up on a system simply because it’s not highly accurate – might still be useful - Snapshots are hard to translate into processes – took a few years of accumulation to figure out what “extreme” was, so plan should be for years of observations; and field campaigns helped identify what processes were implied by observations OR design satellite systems that observe at short/continuous time scales OR incorporate field campaigns that use Global Hawks with long measurement times - How do we deal with DSDs that change over the lifetime of a precip event? Global Precipitation challenges of the coming decade(s) (C. Kidd with inputs from A. Hou) Gains by GPM need to be exploited in future missions  Are we retrieving light (sub 1 mm/hr) rainfall well enough? In-situ and radar obs suggest high occurrence and contribution to total rainfall in some regions  High resolution (1km) observations needed to properly resolve heaviest rain, while hydrological model require similar resolutions over small drainage basins  Models have problems with diurnal cycle – non-sun-synchronous orbits useful (but better co- ordination between LEO systems might do a similar job).  Better vertical resolution (by radar) would permit better resolution of shallow and multi-layer precipitation systems  Precipitation measurements: Need good resolution AND coverage, polar sampling AND diurnal sampling/intersection of polar orbiters, backward compatibility, Doppler capabilities  European Polar System (EPS) – Second generation (SG) (planned for 2020 onwards) – conically scanning Microwave imager (MWI) 18.7-183 GHz and ice cloud imager (ICI) 183-664 GHz alongside ‘traditional’ microwave sounder (2 satellite tandem polar orbiters)  Need to think about how much overlap is possible between hydrological needs and atmosphere/clouds/precip process needs

1:45 Group Discussion of challenges in relationship to clouds and precipitation (discussion guides: D. Starr and G. Skofronick-Jackson)  Precipitation is needed at better than GPM scale (i.e., 1 km, < hourly, < 1 mm/hr)  Precip has societal aspects that can’t be avoided  Can high-frequency MW sufficiently constrain assimilation? Not yet proved, maybe process studies are needed  Climate continuity mission for TRMM/GPM? How important to keep flying radar (vs radiometer only), especially for extremes?  What’s currently missing – arctic clouds, shallow precip, understanding of ice processes in deep convection  Starr – wide swath of all sensors imperative to understand processes on global scale in a reasonable amount of time. Much more useable for a wider community  We need to make better use of geostationary data to track system evolution in process studies  Is it worth having a separate aerosol/pollution mission (supported by the aerosol community) and detach that part from the cloud/precip mission, and rely on synergy between the two? Aerosol community has large support from health, climate, transport.  For aerosol – are both polarimeter and HSRL lidar needed? Tradeoff studies needed by a separate aerosol group  Can any instruments be relegated to aircraft and occasional underflights?  Is Vis/IR needed for clouds+precip mission? Yes if you really want to learn about clouds – science tradeoff study needed.  Want the profiles of all hydrometeors (like ACE)  Kummerow: Process mission – get the sampling piece however also want mapping: SmallSats, assimilation, …  Starr: Process info composited for 5 years to characterize different regimes in different regions. What do systems look like stratified by phenomenology, season, etc.?  Paul – need to do it all; cloud, precip, aerosols; presumably parameterizations different in different places - who will use it? Hydrology, snow people

3 3-5pm Focused Discussion (discussion guides: C. Kummerow and P. Joe) o Identify key science questions for the clouds and precipitation mission concept o Identification of needed science tradeoff studies (See separate slides for organized science questions instead of the stream of discussion listed below) . Climate models differ by factor of 5 in ice concentration – but climate temperatures are not sensitive to this. But is precipitation sensitive? . Precipitation efficiency (dR/dQ) as function of temperature, humidity, cloud regimes . Precipitation susceptibility (dlogRain/dlogNc) . Can we relate (understand and integrate): o DSD o Vertical velocity o Ice particle species/density o Environment (regime) o Lifecycle/diurnal cycle o Sedimentation  If we knew ice PSD perfectly, how much would that help CRM dynamics (cold pool, precip distribution)? How many knobs can we eliminate from CRMs?  How do clouds microphysically develop, and how does that affect generation of precipitation and the TOA radiatively impacting ice clouds?  How will clouds and precip change in a changing environment?  What conditions predict ice type/DSD?  What is the evolution of shallow cumulus, what % precipitates?High-latitude mixed phase clouds – what determines liquid/frozen fraction?  What controls the cloud fraction in marine boundary layers? Shallow clouds need high vertical resolution measurements that aren’t affected by ground  What is the cloud base in precipitation?  We need to measure light precipitation in high latitudes – can we “calibrate” other sensors that observe these areas frequently, or are they not sensitive enough to be useful? Can we develop snow climatology? What processes control high-latitude precipitation (ice nuclei, source regions)?  Processes are key  Climate models issues - deep convection - ice phase treatment seems unimportant for energy cycle - thin clouds - life cycle and diurnal cycle - assume embedded CRM or CRM physics - precip efficiency/susceptibility by cloud type and role of environment (regimes)  If we can measure the PDFs can we therefore constrain the models “enough”?  “How do clouds microphysically develop and how does that affect the precipitation efficiency, and the generation of upper tropospheric ice cloud radiative properties?” Knowing the complete picture of the dynamics and microphysics within cloud systems will impact many science areas.  How do the precip-cloud-ice properties change by regime?  What factors control which hydrometeor types (convective, stratiform, shallow)?  What factors control the partitioning of cloud phase (and maintenance of mixed)?  What controls cloud fraction?  What controls the fraction of strato-cu?  What is the snow climatology? – measurement of snowfall rate  What processes control high-lat. precip (mixed phase, aerosol recycling, liquid water)?

July 10, 2013 Day Two: Technological and Next Step presentations 9:00-9:30am Review and discussion of Monday key science questions (G. Skofronick-Jackson)  Overarching theme: “How does cloud transition to precipitation, what governs this process, and do we know enough about it to model it in a changing climate to predict how it may change?”  Being able to monitor evolution of these processes is key. Potential for EV/Global Hawk missions in area of interest? Adaptable sampling to repeat coverage over a given storm for 3-5 minutes? What is the relevant timescale for the processes we are interested in, and is this achievable from a single platform? Multiple platforms? Single platform + geostationary?  Need to assess what parts GPM is answering, what needs new or more work  New: need to [provide data to] evaluate assumptions that are made today in today’s studies, algorithms, and parameterizations  Focus on how to measure clouds, precipitation, vertical motion

9:30-10:15am Current & planned mission/instrument capabilities (TRMM, CloudSat, etc) No summary of discussion needed

11:25-12:00noon Global precipitation and cloud mission instrument characteristics discussion o Active Radar Instruments (discussion guides: P. Racette and S. Tanelli))  Prioritization necessary to get an affordable instrument  Trade space is freq., sensitivity, swath, Doppler resolution, polarization, min. height, adaptive operation; airborne vs. satellite  Diagram of radar measurement recommendations is on next page, details will be provided later in a separate document generated by the radar members in the meeting

o Passive Radiometer Instruments (discussion guides: R. Bennartz and J. Turk) . Radiometers: frequencies, resolution, swath, polarization requirements  Provide spatial coverage, transfer to other instruments, integral constraints  Freq.: SSMI set (V,H) + 50-60, 118, + mm + sub-mm (183-640 [V,H] GHz). Beyond mapping, these channels help with vertically resolving process over narrow swath by providing solid integral constraints for profile retrievals from radar  Res.: @ radar res. for HF; although that depends on orbit altitude  Decadal Survey might advocate a convoy concept for international participation: e.g., build support for a 460km constellation (1 ESA, 1 JAXA, 1 NASA)  Radiometer members of the meeting will provide details later in a separate document

o Other Instruments if mission science requires them (discussion guides: J. Mace and Z. Haddad)  Something to get environment, but will reanalysis be good enough?  IR/VIS imager (what will be available from geostationary/other polar orbiters?)  VIS/IR ranked as rather important by meeting attendees  Vis channels (0.4,0.8,1.6,2.1,3.7, 100m res)

5 -10/ -20/ -40 dBZ MINIMUM Cloud: #1 5 # (±45˚) with LDR +5/ -10/ -35 dBZ FORE-AFT DETECTABLE Precip: #3 VIEWS SIGNAL MATCHED BEAMS 100/ 100/ 100 km CROSS-TRACK 2/ 1/ 1 km SCANNING 50/ 50/ 50 km HORIZONTAL Cloud: #3 4/ 2/ 1 km Precip: #1 RESOLUTION Cloud: #3 Precip: #3

1/ 0.2/ 0.2 m/ s 1/ 0.5/ 0.2 m/ s DOPPLER POLARIMETRIC Cloud: #1 ACCURACY -25/ --/ -20 dB Precip: #5 -25/ --/ -- dB 250/ 125/ 125 m 300/ 150/ 150 m VERTICAL Cloud: #2 SURFACE Cloud: #2 RESOLUTION Precip: #2 CLUTTER EXTENT Precip: #2 AIRBORNE COMPONENT ADAPTIVE SCANNING

250/ 125/ 125 m Desire at Ku/Ka/W band Antagonism -25/ --/ -- dB Possibly acceptable at Ku/Ka/W band Synergy Cloud: #2 Subjec ve priority of achieving the desire Precip: #2

 IR channels (11,8,6.7,three CO2 between 12.5-14, 1km res)  Very valuable as an integral constraint on shallow clouds  Far IR (25, 50 micron)? For thin cirrus clouds  Swath matches conically scanning radiometer  Ground validation – something like ARM sites would be desirable  Lidar – CALIPSO class, or HSRL. W-band radar is not going to see tops of tropical anvils and thin cirrus. We need to wait and learn what ACE or other aerosol missions teach us, and perhaps rely on them or assimilation products.

2:50-3:00 Discussion: Global precipitation and cloud mission concept characteristics discussion (discussion guides: Eastwood Im, Deb Vane) o Strawman payload (instrument types and characteristics) 1. 3-freq. radar [first descope is in reqmt specs, not dropping a frequency] 2. multi-channel MW radiometer [first descope to number of channels] 3. vis/ir radiometer [first descope to TRMM VIRS]

o Orbit configurations, sampling discussions (e.g., diurnal cycle and inclined orbit discussion), constellation/cross-calibration architecture 1. Low altitude (460 km)? Best for radar 2. Polar orbit that we allow to drift? 3. 82 degree orbit not much worse than GPM in terms of diurnal sampling. But precession period is 180 days, so need to be careful about launch windows. Spacecraft design is sensitive to orbit 4. Is formation flying sets of missions to lower costs and increase science, preferable? At lower orbit and non-sun-synchronous orbits? Formation flying with operational missions may not be advantageous for rapid advance of science. o Scanning/beam alignment strategies 1. Radar beams should be matched at some level – high sensitivity/low sensitivity modes may be needed. But which ones should be matched? 2. Continuity (no gaps between scans) more important than swath width o Identify needed mission tradeoff studies for above discussions 1. What are the impacts of various precession times? We want good diurnal sampling, sampling at the poles, but not to have seasonal cycles aliased onto diurnal cycles. Orbital precession vs. regimes, considering aliasing of annual cycle; also impact on match-ups with sun-synchronous satellites; altitude selection to leverage with other satellites [i.e., opportunity for formation flying?] and to get best swath coverage [460 km; Starr]; consider drag also 2. What channels are necessary/important for radiometer? e.g., sounding channels at 50-60 GHz, 118 GHz, 183 GHZ – do these add any information to radar? How can these channels help with vertically resolved process over narrow swath by providing solid integral constraints for profile retrievals from radar? What is the impact of gap between scans at HF channels? 3. Should we scan with matched beams? VIS/IR Should have same swath as MW. Which radar beams should be matched? 4. Evaluate Radar design requirements as listed in the strawman requirements exercise 5. How wide a radar swath is needed, process is not necessarily a curtain radar, and how sensitivity trades off with coverage? 6. Should the radiometers and radars be on separate platforms to reduce RF interference and give the possibility of slant-path radiometer coincident with vertical radar? 7. How do we use EV/field experiments to learn about process evolution, from a program management point of view?

Next Steps/Next Meetings: • Schedule – End of July: drafts to participants – End of Aug: comments back from team, telecon just before? – Sept: tradeoff studies start – Oct: telecon – Dec: in-person meeting, Sunday prior to AGU – Early 2014: Draft a mission/white paper for the decadal survey – Spring 2014: Hold another in-person meeting with a larger community • Near-term Actions – Edit draft meeting documents – Begin tradeoff studies – Determine invitees for the larger community meeting in spring 2014

Potential Names for the mission (not explicitly discussed during the meeting) GPCM = Global Precipitation and Clouds Measurement (Mission) CPCE = Cloud and Precipitation for a Changing Environment GPCPM = Global Precipitation and Cloud Processes Measurement (Mission) CaP = Cloud and Precipitation mission CaPM = Cloud and Precipitation Mission CaPPM = Cloud and Precipitation Processes Mission MAPCaP=Mapping (Measurements?) of Atmospheric Precipitation, Clouds and their Processes CaPMaP=Cloud and Precipitation Mapping and Processes GMAPCaP, GCapMap with “Global” in front