1. Report to WCRP Observations and Assimilation Panel David Goodrich Director, GCOS Secretariat Towards a GCOS Reference Upper Air Network

2. Rationale u Motivation Problems for climate in accuracy, long-term stability Changes in measurement systems u Objectives Provide long-term, high-quality climate records Constrain/calibrate data from more spatially- comprehensive global observing systems (including satellites) Measure large suite of co-related climate variables

3. Process to Date u Establish Climate Requirements Boulder Workshop 2005 Participants: Climate scientists, data users Requirements report prepared u Assess Instrumentation/Siting Options Seattle Workshop 2006 Participants: Instrumentation, network design specialists; Observing system managers Draft report prepared

4. Proposed Observing System Architecture Benchmark Network ~10 stations Upper Air Reference Network 30-40 stations GCOS Upper Air Network (GUAN) 161 stations Comprehensive observing network All stations, observing systems, reanalyses etc. Spatial density Climate driven

5. Climate Requirements – Example VariableTemperature Priority (1-4)1 Measurement Range100-350 K Vertical Range0 km to stratopause Vertical Resolution0.1 km (surface to ~30 km) 0.5 km (above ~30 km) Precision0.2 K Accuracy0.1 K in troposphere 0.2 K in stratosphere Long-Term Stability0.05 K 1 Comments 1 The signal over the satellite era is order 0.1- 0.2K/decade so long-term stability needs to be order of magnitude smaller to avoid ambiguity.

6. Proposed Site Instrumentation Level 1 (Highest Priority) Measurements l Standard surface variables (pressure, temperature, humidity and wind) l Redundant / simultaneous measurement of temperature and water vapor l Pressure and GPS / radar height l Ground-based GPS receivers (column water vapor) Level 2 Measurements l Surface radiation (BSRN suite) l Microwave radiometer (temperature/moisture profile) l Multi-channel infrared radiometer (such as AERI; temperature and humidity properties and cloud retrieval) l Integrated trace gas (at least ozone) measurements l Column aerosol measurements from sunphotometers

7. A Potential Model: Lindenberg, Germany

8. Temporal Sampling Issues for Sondes l At least some launches at 00 and/or 12 UTC l Other considerations: l Obtaining daytime, nighttime, dawn and dusk observations to span instrument behavior to varying radiative conditions l Adequate sampling of diurnal cycle for some places for limited times l Coincident launch with satellite overpass l Minimum requirement: l Twice daily with one at 00 or 12 UTC l Launch at alternating satellite overpass nodes; one/day cycling through three orbiter configuration every six days l Area of ongoing debate

9. Next Steps l Community Review and Discussion l Formation of AOPC Working Group l Consideration by Relevant Panels l CIMO Management Group l CBS ET – Evolution of Global Observing System l WOAP l GCOS Steering Committee l Coordination with Relevant Observing Systems l Solicitation of Contributions by Members l Phased Implementation, Building on Existing Sites