1. Water Cycle Breakout Session Attendees: June Wang, Julie Haggerty, Tammy Weckwerth, Steve Nesbitt, Carlos Welsh, Vivek, Kathy Sharpe, Brad Small Two objectives: 1.Identify Scientific Initiatives and Research Topics to advance Water Cycle research; 2.Assess the ability of NSF facilities to support these activities: retaining, new acquisition, and new development.

2. 1.Colorado Headwaters project: Focus on critical questions concerning the effect of climate change on snow processes in the western cordillera of North America. Measurement of snow depth is very important for the project. Currently don’t have good observations of snow pack. Radar not useful in mountains. Snotel network provides data to USGS(?). Need in situ snowpack measurements, including snow water equivalent. Collaborations with RAL is important. 2. Global Precipitation Measurement (GPM): GPM will provide global precipitation map, eventually available every 3 hours over +/- 70 degrees latitude. Snow detection is a challenge for remote sensing techniques. NSF/NCAR should be involved in ground validation of GPM as in LBA, etc. G-V cloud radar could observe areas that are inaccessible to ground-based radar. CSU also active in this area; investigating detection of mixed phase conditions.

3. 3. Spatial variability of precipitation: Need to understand scaling differences between satellite footprint and other measurements. Polarimetric radar bridges the spatial gap between satellite and ground- based measurements. Need more disdrometers, research and mobile, spaced at ~100 m. 4. Water vapor in lower troposphere: Need 3-dimensional moisture fields at 500 m (or less) horizontal resolution for mesoscale research. Acquisition of existing instruments and development of new instruments and algorithms. Synthesize existing data sets into a 3-d analysis (aircraft, lidar, GPS, microwave radiometer, radar retrievals).

4. 5. Water vapor in UT/LS region: Characterizing UT/LS water vapor is very important (radiative, chemical and microphysical roles) No capability at NCAR other than G-V TDL sensors. Satellite observations need more validation in this region. Development of balloon-borne reference hygrometers in UT/LS is essential. Ground-based remote sensing techniques (lidar) would supplement the radiosonde observations. 6. Satellite validation: NCAR has done precip validation (TRMM), but not water vapor. This could be a niche for NCAR with targeted field programs assuming we could access better water vapor instruments.

5. 7. Process studies: Provide a better understanding of water cycle dynamics, improve measurements of surface atmosphere fluxes, improve model parameterizations, relate to cloud physics and radiation. Special field projects are designed to utilize integration of different instruments and careful experimental and network designs. 8. Climate policy: Disagreements between measurements and modeling hamper the policy making. Water cycle is a key issue for adaptation to climate change. Water vapor isotope measurement is important for discerning historical water levels; need better methods for measurement of water vapor isotopes.

6. 9. Hydrology: Need soil moisture, stream flow, ground water measurements. Such instruments are difficult to maintain in the field. 10. Cloud ice: It is challenging because we have fewer winter measurements. Less validation of radar algorithms. Aircraft validation is limited by flight safety concerns.

7. Recommendations on Facility Needs FacilitiesNeedsSciences 35 GHz, Ka, S, X band radarsRetainingGPM High-quality disdrometers & networkAcquisition and development Mapping precipitation MWR, GPS for continuous WV profiles AcquisitionMesoscale & others Scanning WV DIALDevelopmentMesoscale & others Balloon-borne reference hygrometers for UT/LS DevelopmentClimate, UT/LS UT/LS airborne microwave radiometers DevelopmentUT/LS Algorithm development (VAP & integration) DevelopmentAll areas Airborne cloud radar/lidar (HSRL & HCR) Retaining (under development) Cloud ice