1. Second International Workshop on Space-based Snowfall Measurement 31 March - 4 April 2008 Steamboat Ski Village, Colorado Organizing Committee Ralf Bennartz (University of Wisconsin), Ralph Ferraro (NOAA/NESDIS), Gail Skofronick Jackson (Goddard Space Flight Center), Paul Joe (Meteorological Service of Canada), Chris Kummerow (Colorado State University), Ian McCubbin (Storm Peak Laboratory, DRI), Gregory Tripoli (University of Wisconsin), Deborah Vane (Jet Propulsion Laboratory)

2. Workshop Objective Assess the state of the science and measurement technology and to recommend future directions in research and technology development.

4. Five Working groups Applications (Chair D. Lettenmeier) Detection & Estimation (Chair C. Kummerow) Modeling (Chairs G. Petty, W-K Tao) New Technology (Chairs S. Tanelli, T. Iguchi) Validation (Chairs, D. Hudak, J. Koistinen)

5. Workshop Recommendation 1 Use “modeling chains” as a basic research tool to develop an understanding of the relationship between snowfall and radiative transfer Basic research of complex problem needed Simplification for operational retrieval or assimilation schemes Snowfall rate estimation must be solved through multivariate techniques Snow estimation will ultimately most certainly involve models

6. Modeling Chain A priori statistics (assumed!) Conventional Observations Satellite Observations Radar Observations Global Data Assimilation Analysis Non-Conventional Observations (aircraft, etc) Global Prediction Model (GFS/ECMWF) Limited Area Cloud Resolving Model (WRF, MM5, NMS, GCE, RAMS) Explicit Spectral Microphysics Spectral Microphysics Assume shape/habit, density Microwave Single Scatter and extinction Properties Modeled Sensor radiances and/or reflectivities Microwave Properties of the Lower Boundary Modeled Surface Precipitation/Snow Rates Surface Precipitation Observations Bulk Microphysics Analysis Global Prediction Nested CRM Radiative Transfer Retrieved Surface Precipitation Rates Precipitation Retrieval Scheme Verification Statistical relationships Verification with Microwave Observations Assume size

7. Workshop Recommendation 2 Encourage the generation of community CRM/NWP model profile databases that represent natural variability. Capture the variability between different types of snow-producing weather A parallel effort for databases from observations or combined model simulations and observations is also encouraged.

8. CRM/NWP Profile Database Modeled Surface Precipitation/Snow Rates Global Data Assimilation Analysis Global Prediction Model (GFS/ECMWF) Limited Area Cloud Resolving Model (WRF, MM5, NMS, GCE, RAMS) Explicit Spectral Microphysics Spectral Microphysics Assume shape/habit, density Bulk Microphysics Analysis Global Prediction Nested CRM Radiative Transfer Assume size Conventional Observations Satellite Observations Radar Observations Non-Conventional Observations (aircraft, etc) Surface Precipitation Observations Observations Microwave Single Scatter and extinction Properties Modeled Sensor radiances and/or reflectivities Microwave Properties of the Lower Boundary Data Base Profiles containing: Atmospheric State Microphysics Radiances Reflectivity Synoptic Tags Site Characteristics Samplings of all types of snow producing weather

9. Workshop Recommendation 3 Recognize “Data Assimilation” as a necessary component of snow analysis from space-based measurements. Recognize “Data Assimilation” as a necessary component of snow analysis from space-based measurements. It was recognized by virtually all of the working groups that a full direct measurement of snowfall by any single space- borne measurement alone is most likely an unattainable goal. It was recognized by virtually all of the working groups that a full direct measurement of snowfall by any single space- borne measurement alone is most likely an unattainable goal. Models will be necessary to: Models will be necessary to: Interpret the physics behind radiance patterns Interpret the physics behind radiance patterns Help distinguish surface radiance from air borne hydrometeors Help distinguish surface radiance from air borne hydrometeors Localize patterns of precipitation where satellites cannot resolve variability Localize patterns of precipitation where satellites cannot resolve variability Bring together multiple instruments taking observations a multiple times Bring together multiple instruments taking observations a multiple times Determine PDF of analysis, ie ensemble analysis techniques Determine PDF of analysis, ie ensemble analysis techniques Recognize “Data Assimilation” as a necessary component of snow analysis from space-based measurements. Recognize “Data Assimilation” as a necessary component of snow analysis from space-based measurements. It was recognized by virtually all of the working groups that a full direct measurement of snowfall by any single space- borne measurement alone is most likely an unattainable goal. It was recognized by virtually all of the working groups that a full direct measurement of snowfall by any single space- borne measurement alone is most likely an unattainable goal. Models will be necessary to: Models will be necessary to: Interpret the physics behind radiance patterns Interpret the physics behind radiance patterns Help distinguish surface radiance from air borne hydrometeors Help distinguish surface radiance from air borne hydrometeors Localize patterns of precipitation where satellites cannot resolve variability Localize patterns of precipitation where satellites cannot resolve variability Bring together multiple instruments taking observations a multiple times Bring together multiple instruments taking observations a multiple times Determine PDF of analysis, ie ensemble analysis techniques Determine PDF of analysis, ie ensemble analysis techniques

10. Data Assimilation Based Snow Analysis Modeled Surface Precipitation/Snow Rates Cloud Resolving Assimilation System 4DDA EnKf Global Data Assimilation Analysis Global Prediction Model (GFS/ECMWF) Limited Area Cloud Resolving Model (WRF, MM5, NMS, GCE, RAMS) Explicit Spectral Microphysics Spectral Microphysics Assume shape/habit, density Bulk Microphysics Analysis Global Prediction Nested CRM Forward Model Assume size Conventional Observations Satellite Observations Radar Observations Non-Conventional Observations (aircraft, etc) Surface Precipitation Observations Observations Microwave Single Scatter and extinction Properties Modeled Sensor radiances and/or reflectivities Microwave Properties of the Lower Boundary Assimilated Surface Precipitation/Snow Analysis Assimilation Loop Verification

11. Satellite-Based Cloud-Resolving Probabilistic Analysis System

12. Workshop Recommendation 4 Continuing community efforts to study and development of high-latitude surface emissivity products (10-200 GHz) including error estimates are strongly recommended. Continuing community efforts to study and development of high-latitude surface emissivity products (10-200 GHz) including error estimates are strongly recommended. Community efforts led by the International TOVS Working Group (ITWG) have successfully led to the emissivity databases and inventories. Community efforts led by the International TOVS Working Group (ITWG) have successfully led to the emissivity databases and inventories. Continuing community efforts to study and development of high-latitude surface emissivity products (10-200 GHz) including error estimates are strongly recommended. Continuing community efforts to study and development of high-latitude surface emissivity products (10-200 GHz) including error estimates are strongly recommended. Community efforts led by the International TOVS Working Group (ITWG) have successfully led to the emissivity databases and inventories. Community efforts led by the International TOVS Working Group (ITWG) have successfully led to the emissivity databases and inventories.

14. Workshop Recommendation 5 The use of combined active and passive satellite data for snowfall detection/retrieval should be further encouraged. The use of combined active and passive satellite data for snowfall detection/retrieval should be further encouraged. Snow difficult, perhaps impossible to detect against surface background of blowing snow and ice/snow cover from passive radiometers Snow difficult, perhaps impossible to detect against surface background of blowing snow and ice/snow cover from passive radiometers Active space-borne instruments need to have a low detectability threshold (smaller than roughly 5 dBZ) to detect light rainfall and snowfall. Active space-borne instruments need to have a low detectability threshold (smaller than roughly 5 dBZ) to detect light rainfall and snowfall. CloudSat as well as the planned missions ACE and EarthCare will provide space-borne cloud radars. CloudSat as well as the planned missions ACE and EarthCare will provide space-borne cloud radars. The use of combined active and passive satellite data for snowfall detection/retrieval should be further encouraged. The use of combined active and passive satellite data for snowfall detection/retrieval should be further encouraged. Snow difficult, perhaps impossible to detect against surface background of blowing snow and ice/snow cover from passive radiometers Snow difficult, perhaps impossible to detect against surface background of blowing snow and ice/snow cover from passive radiometers Active space-borne instruments need to have a low detectability threshold (smaller than roughly 5 dBZ) to detect light rainfall and snowfall. Active space-borne instruments need to have a low detectability threshold (smaller than roughly 5 dBZ) to detect light rainfall and snowfall. CloudSat as well as the planned missions ACE and EarthCare will provide space-borne cloud radars. CloudSat as well as the planned missions ACE and EarthCare will provide space-borne cloud radars.

15. Workshop Recommendation 6 The use of combined active and passive satellite data for snowfall detection/retrieval should be further encouraged. The use of combined active and passive satellite data for snowfall detection/retrieval should be further encouraged. Snow difficult, perhaps impossible to detect against surface background of blowing snow and ice/snow cover from passive radiometers Snow difficult, perhaps impossible to detect against surface background of blowing snow and ice/snow cover from passive radiometers Active space-borne instruments need to have a low detectability threshold (smaller than roughly 5 dBZ) to detect light rainfall and snowfall. Active space-borne instruments need to have a low detectability threshold (smaller than roughly 5 dBZ) to detect light rainfall and snowfall. CloudSat as well as the planned missions ACE and EarthCare will provide space-borne cloud radars. CloudSat as well as the planned missions ACE and EarthCare will provide space-borne cloud radars. The use of combined active and passive satellite data for snowfall detection/retrieval should be further encouraged. The use of combined active and passive satellite data for snowfall detection/retrieval should be further encouraged. Snow difficult, perhaps impossible to detect against surface background of blowing snow and ice/snow cover from passive radiometers Snow difficult, perhaps impossible to detect against surface background of blowing snow and ice/snow cover from passive radiometers Active space-borne instruments need to have a low detectability threshold (smaller than roughly 5 dBZ) to detect light rainfall and snowfall. Active space-borne instruments need to have a low detectability threshold (smaller than roughly 5 dBZ) to detect light rainfall and snowfall. CloudSat as well as the planned missions ACE and EarthCare will provide space-borne cloud radars. CloudSat as well as the planned missions ACE and EarthCare will provide space-borne cloud radars.

16. Workshop Recommendation 7 New passive microwave instruments and new channel combinations need to be studied. New passive microwave instruments and new channel combinations need to be studied. Initial results using the 118 GHz oxygen absorption band and also extended use of the window frequencies are promising Initial results using the 118 GHz oxygen absorption band and also extended use of the window frequencies are promising New passive microwave instruments and new channel combinations need to be studied. New passive microwave instruments and new channel combinations need to be studied. Initial results using the 118 GHz oxygen absorption band and also extended use of the window frequencies are promising Initial results using the 118 GHz oxygen absorption band and also extended use of the window frequencies are promising

17. Workshop Recommendation 8 High level coordination of international GV programs for snowfall (e.g., through GPM, GEWEX, IPWG) should move forward on 3 fronts High level coordination of international GV programs for snowfall (e.g., through GPM, GEWEX, IPWG) should move forward on 3 fronts Network Validation. Satellite validation against traditional observations. Leverage off operational systems. Network Validation. Satellite validation against traditional observations. Leverage off operational systems. Radar Radar Voluntary observing networks Voluntary observing networks Governmental observing systems Governmental observing systems Physical Validation. Here we observe in situ cloud properties. Geared toward testing and refinement of satellite simulators and retrieval algorithms Physical Validation. Here we observe in situ cloud properties. Geared toward testing and refinement of satellite simulators and retrieval algorithms Integrated Validation. Integrate satellite products into weather, land surface and hydrological predicion models. Evaluate strengths and weaknesses of satellite products in this context Integrated Validation. Integrate satellite products into weather, land surface and hydrological predicion models. Evaluate strengths and weaknesses of satellite products in this context High level coordination of international GV programs for snowfall (e.g., through GPM, GEWEX, IPWG) should move forward on 3 fronts High level coordination of international GV programs for snowfall (e.g., through GPM, GEWEX, IPWG) should move forward on 3 fronts Network Validation. Satellite validation against traditional observations. Leverage off operational systems. Network Validation. Satellite validation against traditional observations. Leverage off operational systems. Radar Radar Voluntary observing networks Voluntary observing networks Governmental observing systems Governmental observing systems Physical Validation. Here we observe in situ cloud properties. Geared toward testing and refinement of satellite simulators and retrieval algorithms Physical Validation. Here we observe in situ cloud properties. Geared toward testing and refinement of satellite simulators and retrieval algorithms Integrated Validation. Integrate satellite products into weather, land surface and hydrological predicion models. Evaluate strengths and weaknesses of satellite products in this context Integrated Validation. Integrate satellite products into weather, land surface and hydrological predicion models. Evaluate strengths and weaknesses of satellite products in this context

18. Workshop Recommendation 9 Important new Validation Technologies Needed: Important new Validation Technologies Needed: MW transmission links with parallel particle probing MW transmission links with parallel particle probing Snow measurement technologies in hard to get to places such as Antarctica Snow measurement technologies in hard to get to places such as Antarctica Important new Validation Technologies Needed: Important new Validation Technologies Needed: MW transmission links with parallel particle probing MW transmission links with parallel particle probing Snow measurement technologies in hard to get to places such as Antarctica Snow measurement technologies in hard to get to places such as Antarctica

19. Click to edit Master title style Click to edit Master text styles Second level Third level Fourth level Fifth level 19 The first global snowfall maps from CloudSat - Liu, 2008

20. Conclusions  There are challenges to snowfall measurement that will requires the use of multiple types of observing combined with models to yield a competent snow fall measurement  Probabilistic data assimilation for snow analysis will be necessary to bring all instruments and theory together  Forward Models relating precipitation physics to radiance are critical for both retrieval and data assimilation  There is a critical need to better understand the physics of snow formation and the radiative transfer in ice hydrometeors at a complex level before we move toward the simplification necessary for measurement  All indications are that there are actually a limited set of key variants  To understand this we must understand the complex problem

21. Conclusions (cont.)  There is some important low-hanging fruit in the area of validation, namely the massive voluntary observing systems present over North America and world wide. But supported coordination may be helpful  More attention must be given to validation and measurement technology over the remote areas of the Antarctica continent.