draft science questions for integrated precipitation and cloud processes mission as discussed at...

DRAFT Science Questions for Integrated Precipitation and Cloud Processes Mission as discussed at July 9-11, 2013 meeting 11

Draft Science Question Slides

As reported during the Integrated Precipitation and Cloud Processes Working Group Meeting

An Integrated Precipitation and Cloud Processes Working Group science meeting was held July 9-11, 2013 at NASA Goddard 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.

These slides report the science questions identified during the meeting as well as an initial list of measurement needs and identified trade studies. A separate document

provides meeting minutes.


Science Question Slides

Table of Contents

• Slide 3: Overarching Mission Question• Slide 4: Impact Statement• Slide 5: Overarching Unknowns• Slides 6-7: Key Problems and Questions for Convective Systems• Slides 8-9: Key Problems and Questions for Frontal Systems• Slides 10-11: Key Problems and Questions for Shallow Systems• Slides 12-13: Key Problems and Questions for Orographic Systems• Slide 14: Other Questions asked by participants• Slides 15-16: Measurement Recommendations • Slide 17: Identified trade studies• Slide 18: Next Steps


Overarching Question• How can we better understand and predict

precipitation variability, changes, and the role of cloud processes?– Advances in understanding the role of cloud processes

are critical to reducing the uncertainty in precipitation and water cycle prediction -- a key component of the global climate system.

– We seek to understand and map the continuum of climatically important cloud regimes, globally, from heavy rain to light drizzle and snowfall. This includes deep convection, shallow cloud systems, frontal regimes, and orographic enhancement, recognizing the extreme importance of the ice phase.


Impact Statement• To achieve advances in cloud and precipitation

science it is essential to globally map 3D precipitation and describe the microphysical composition of clouds and associated dynamics, specifically vertical motion. This is essential for evaluating latent heating and improving the representation of precipitation in climate and numerical weather prediction (NWP) models.


Overarching Unknowns1. What is the 4-dimensional, global, size- and shape-resolved

distribution of cloud and hydrometeor, liquid and ice particles at process-relevant spatial scales?

2. How are the mean patterns and the intensity distributions of precipitation changing? How are associated cloud properties and processes changing?

3. What is the fraction of condensate within a cloud that falls to the ground as precipitation versus that which is detrained back into the atmosphere? What factors control this ratio?

4. How does the environment in various regimes impact the processes that convert clouds to precipitation and how do these controls impact the water and energy balance in future environments?


Key Problems in Deep Convection (1a/4)

• Convective/stratiform separation• Controls on convective updraft strength• Detrainment and evolution of stratiform

clouds, which has important radiative and water budget implications


Key Questions in Deep Convection (1b/4)• Climate Extremes: Under what conditions is heavy precipitation dependent on water vapor availability (versus being limited by dynamics),

where are these conditions currently met and how might that change in the future? This is a potential societal benefit, to assess where flooding risks might change. •How has the fine-scale climatology of precipitation rates (PDF) changed over the satellite precipitation radar era?•What impacts do changes in ice and/or drop size distributions have on radiative forcing and latent heating? • Future climate simulations exhibit large sensitivity to the sedimentation rate of ice. This affects the ice clouds lifetime, their radiative impact

and the evolution deep convective systems. The Integrated Precipitation & Clouds mission should aim to provide accurate, global estimate of ice particle sedimentation rates.•How does the environment impact the processes that convert clouds to precipitation and how does this impact the water and energy balance

in future environments? • Precipitation efficiency: What is the fraction of condensate within a cloud that falls to the ground as precipitation versus that which is

detrained back into the atmosphere? What factors control this ratio? This is important for energy budgets and part of the cloud-radiative feedback puzzle.•How much ice & water is produced by precipitating systems and what is its effect on Earth's water and energy cycles? •What is the distribution and spatial variability of precipitation? •How do shifts in ice and/or drop size distributions impact surface precipitation rates and totals?•How does Doppler velocity, both mean and spread, footprint-by-footprint and as range-resolved spatial patterns illuminate convective-

stratiform separation and provide calibration for traditional measures of conv.-strat. separation?•What roles do DSD and ice density play in determining the rainfall efficiency and organization of convective systems? and is this captured in

our microphysical models used for climate simulations?•How does cloud fraction vary with rain rate as a function of regime and spatial scales; What does this imply about cloud feedbacks in a

changing climate? •What impact do environmental conditions (RH, shear, CAPE, static stability etc) have on ice and drop size distributions? •What are the feedbacks between ice and/or drop size distributions and updraft/downdraft dynamics (need to consider both the impacts of

dynamics on DSDs and DSDs on dynamics)? •What impact do environmental factors exert on the amounts of small ice, snow crystals, aggregates, grapple and hail? •How is the mean pattern of rainfall and the intensity distribution of precipitation changing over the long term (30-50yrs)?• Current CRMs have a known bias: Deep convection is too strong. What is the fundamental reason for this bias and what is needed to correct

it? Evaluation Tool: Global measurement of PDF of convective vertical velocity in the upper troposphere and of overshooting tops penetrating the tropopause. Relatively easy to measure, because only small ice particles exist close to cloud top. Compare model vs. observed PDF of W regionally and seasonally, correct model.


Key Problems in Frontal Systems (3a/4)

• Dominance of cold cloud processes (ice and mixed phase) in the development of precipitation

• Mesoscale organization and vertical motion, and feedbacks to precipitation processes- Slantwise convection- Multi-layer clouds


Key Questions in Frontal Systems (3b/4)•Future climate simulations exhibit large sensitivity to the sedimentation rate of ice. This affects the ice clouds lifetime, their radiative impact and the evolution deep convective systems. The Integrated Prec & Clouds mission should aim to provide accurate, global estimate of ice particle sedimentation rates.•How does the environment impact the processes that convert clouds to precipitation and how does this impact the water and energy balance in future environments? •What is the fraction of condensate within a cloud that falls to the ground as precipitation versus that which is detrained back into the atmosphere? What factors control this ratio?•How do shifts in ice and/or drop size distributions impact surface precipitation rates and totals? •What impact does riming and/or droplet breakup have on surface precipitation rates? •How does Doppler velocity, both mean and spread, footprint-by-footprint and as range-resolved spatial patterns illuminate convective-stratiform separation and provide calibration for more traditional measures of convective-stratiform separation?•Which processes (e.g. autoconversion/accretion) dominate the conversion of cloud water to rain water in various cloud regimes? •What impact do environmental conditions (RH, shear, CAPE, static stability, etc.) have on ice and drop size distributions? •What impact do environmental factors exert on the relative amounts of small ice, snow crystals, aggregates, grapple and hail? •How are the mean patterns of rainfall and the intensity distribution of precipitation changing over the long term (30-50yrs)?


Key Problems in Shallow Precipitation (2a/4)

• cloud particle/precipitation content separation – autoconversion and accretion processes–Precipitation susceptibility

• Ice particle nucleation and phase partitioning• Characterizing cloud-scale vertical motion• Sensitivity to environmental conditions


•Future climate simulations exhibit large sensitivity to the sedimentation rate of ice. This affects the ice clouds lifetime, their radiative impact and the evolution deep convective systems. The Integrated Prec & Clouds mission should aim to provide accurate, global estimate of ice particle sedimentation rates.• Is climate changing? First indicator is Arctic precipitation since it is a very efficient process - where there might not be any clouds or clouds are thin - and therefore reacts efficiently to temperature and aerosol changes. This can be covered by process/precipitation efficiency studies. •Precipitation efficiency: What is the fraction of condensate within a cloud that falls to the ground as precipitation versus that which is detrained back into the atmosphere? What factors control this ratio?•What is the efficiency of cold season cloud and precipitation formation in high and Arctic latitudes and in complex terrain?•What is the distribution and spatial variability of precipitation? •How can we improve our measurements of Polar precipitation systems? (For example, Polar Lows, Lake/open ocean snowfall, etc. particularly with respect to climate change and decreasing sea ice).•What is the contribution of snowfall to the global water and energy cycle?•What is the vertical distribution of precipitation across the globe? (curently, ropics with TRMM only >0.7mm/h, up to 65 N/S with GPM only >0.2 mm/h).•What is the 4-dimensional, global, size- and shape-resolved distribution of ice and liquid particles (cloud and hydrometeor) at process-relevant spatial scales? •What is the relationship between crystal shape and surface precipitation rate? •What impact do environmental factors exert on the relative amounts of small ice, snow crystals, aggregates, grappel and hail? •What are the cloud/microphysical properties needed for process study? [answer: DSDs at various layers (gamma or exponential distributions for cloud water, rain, cloud ice, snow, and graupel), 3D liquid and ice water contents and median diameters, mixed phase information, particle number concentrations for cloud ice, snow, graupel and hail, aerial ratios (ice habits), particle density, fall speed, and the liquid water fraction of melting snow, graupel and hail, over the life cycle of clouds and cloud systems as a function of cloud type, cloud dynamics and environmental characteristics. The amount of super saturation wrt ice.]

Key Questions in Shallow Precipitation (2b/4)


Key Problems in Orographic Systems (4a/4)

• Gravity waves / mountain waves• Seeder/feeder • Very low-altitude precipitation enhancement

Key Question: How does orography impact clouds and precipitation?Rationale: precipitation falling in complex terrain is difficult to measure, both from conventional observations and using current satellite sensors. It is necessary to provide observations at resolutions commensurate with scales associated with topographic features in order to observe and understand the orographic influence upon clouds and precipitation.

Desired sensor requirements: fine spatial (1 km) and vertical (100 m) resolutions, Doppler capability also useful in determining orographic uplift.


Key Questions in Orographic Systems (4b/4)

•How does terrain affect the distribution and characteristics of precipitation? •How does the environment impact the processes that convert clouds to precipitation and how does this impact the water and energy balance in future environments? •What is the distribution and spatial variability of precipitation? •How do shifts in ice and/or drop size distributions impact surface precipitation rates and totals? •What is the 4-dimensional, global, size- and shape-resolved distribution of ice and liquid particles (cloud and hydrometeor) at process-relevant spatial scales? •What impact do environmental factors exert on the relative amounts of small ice, snow crystals, aggregates, grappel and hail? •Precipitation efficiency: What is the fraction of condensate within a cloud that falls to the ground as precipitation versus that which is detrained back into the atmosphere? What factors control this ratio?•What is the efficiency of cold season cloud and precipitation formation in high and Arctic latitudes and in complex terrain?•What impact does riming and/or droplet breakup have on surface precipitation rates? •What is the relationship between snow in the air and snow/water reaching the ground?


Other Questions Asked by Participants•How does cloud fraction vary with rain rate as a function of regime and spatial scales; What does this imply about cloud feedbacks in a changing climate? •What is the evolution/lifecycle of precipitating systems? How do we best measure evolution: Geostationary? Multiple satellites in close formation? Global Hawk focused studies?•How can the an orbiting system of discrete measurements be assembled and jointly analyzed to account for the dynamical nature of the cloud/precip processes? What are the time scales of the measurements that we need to make, and where and how should they be made? •How is cloud cover and vertical structure responding to anthropogenic emissions of greenhouse gases and aerosols?•What are the key microphysical processes needed for validation and or for improvements? [Answer: Riming; Breakup (precipitating particles - ice/liquid); Melting; Evaporation; Sedimentation]•What are the aerosol information needed for aerosol/cloud/precipitation interaction? [Answer: Need CCN, IN and GCCN for Activation (pre, during and after convection); Need 3D distribution]•What is the relationship between snow in the air and snow/water on the ground?


Measurement RecommendationsThis mission should build upon enhanced radar capabilities (to gain better physical insights) together with complementary passive instrumentation (for spatial coverage). The detailed specifications of all instruments will be evaluated through cost-benefit science trade-off studies. • A baseline radar system would comprise a triple-frequency system centered

upon scanning Ku, Ka and W-band (13, 35 and 94 GHz) radars, with Doppler capability at all frequencies. To retrieve light, shallow precipitation the radar system would need a high-sensitivity, fine range resolution capability (see figure on slide 15 for radar specs discussed at the meeting)

• For extended spatial coverage, a multi-channel, wide-swath, multi-frequency range microwave radiometer will provides crucial information profiling from surface characteristics to thin cirrus clouds. Frequencies of interest include: 10-89, 50-60, 118, 183-640 GHz, with V and H polarizations as appropriate. These channels also provide solid integral constraints for profile retrievals to help resolve vertical processes as measured over narrow radar swaths.

• A multi-channel visible/infrared radiometer is essential to provide additional complementary information on atmospheric and cloud-top properties.


Radar measurement recommendations as discussed at meeting

Image provided by Simone Tanelli


Trade Studies/Not complete• Coverage and process: Global precipitation maps require space/time coverage with wide swath and a transfer

standard to other satellites while process studies need narrow swath, higher sensitivity, enhanced capabilities-Doppler, etc. Can we construct an instrument payload to accommodate both?

• Non-Sun-synchronous orbit (to provide a common reference for inter-satellite calibration and to collect diurnal cycle information over a wide range of latitudes) versus Sun-synchronous orbit (with better sampling in high latitudes and polar regions). And related: Sampling through the diurnal cycle (e.g. inclined orbit) versus of polar precipitation processes (polar orbit).

• Roles of passive observations beyond ‘mapping’ (e.g. what quantifiable benefits are to be gained with mm and sub-mm both for mapping precipitation and inferring process). What space/time sampling characteristics can we really expect from passive? Exactly which radiometer channels are required for mission objectives?

• Cost-benefit studies for all instrument recommendations• Lidar is highly desired, Issue is emission to space at tops of high clouds. Need study.• Science Q: What is the difference between radar vertical resolution of 100 versus 300m for the surface clutter?

How much dBZ sensitivity is needed at lowest range gate?• Should we scan with matched beams? VIS/IR Should have same swath as MW. Which radar beams should be

matched?• How wide a radar swath is needed, process is not necessarily a curtain radar, and how sensitivity trades off with

coverage?• 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?• How do we use EV/field experiments to learn about process evolution, from a program management point of

view?


Next Steps• Schedule– End of July: drafts of meeting minutes and science

questions 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

• Need to get to a strawman of a mission/draft white paper

• What is a larger community? (discuss at Oct telecon)