1. Status of GCOS Upper-Air Reference Network Planning Achieving Satellite Instrument Calibration for Climate Change Workshop 16-18 May 2006, Landsdowne, VA Dian Seidel NOAA Air Resources Laboratory Silver Spring, Maryland

2. 2 Radiosondes Workhorse of the global observing system since 1950’s “Gold standard” for validation of GPS data (as quoted in Science, April 2006) A blessing and a curse for climate studies

3. 3 Value of In Situ Sounding Data High vertical resolution Possibility of co-located measurements of a suite of variables Continuity with historical radiosonde archive Independent alternative to remotely sensed observations Potential for calibration of satellite observations

4. 4 Inadequacy of Exisiting Radiosonde Network for Climate Monitoring Observations from many networks - by many types of instruments - are not referenced to standards, or to each other. Instrument and observing method changes are not well documented, and there is no overlap to guide data adjustments. Humidity observations are not accurate enough, particularly in cold, dry regions.

5. 5

6. 6 Need for a Reference Upper-Air Network To ensure that climate monitoring findings, climate projections and predictions, and climate policy decisions are based on reliable observations Reliability requires: –Redundant measurements and analyses –Small uncertainty in observations –Long-term continuity of observing system –Stability of observations and their accuracy –Complete metadata –Ongoing data quality control and analysis –Dedicated data center

7. 7 Key Climate Science Drivers for a Reference Upper-Air Network Monitoring and detecting climate variability and change Understanding the vertical profile of temperature trends Understanding the climatology and variability of water vapor, particularly in the upper-troposphere and lower stratosphere Understanding and monitoring tropopause characteristics Understanding and monitoring the vertical profile of ozone, aerosols and other constituents Reliable reanalyses of climate change Prediction of climate variations Understanding climate mechanisms and improving climate models

8. 8 Temperature Trends from Different Observing Systems and Datasets Source: Temperature Trends in the Lower Atmosphere: Steps for Understanding and Reconciling Differences. Thomas R. Karl, Susan J. Hassol, Christopher D. Miller, and William L. Murray, editors, 2006. A Report by the Climate Change Science Program and the Subcommittee on Global Change Research,ashington, DC. (Figure from Executive Summary, page 9) 1979-20041958-2004

9. 9 Source: Seidel, D.J., and M. Free, Measurement requirements for climate monitoring of upper-air temperature derived from reanalysis data, J. Climate, 19, 854–871.

10. 10 Importance of Upper-Tropospheric Water Vapor Observations Source: Soden, B.J, and I.M. Held: An assessment of climate feedbacks in coupled ocean-atmosphere models, J. Climate, submitted.

11. 11 Defining Observational Requirements “NOAA/GCOS Workshop to Define Climate Requirements for Upper-Air Observations” - Boulder, CO, February 2005. ~ 70 scientists and data users from a wide cross-section of the climate community. Workshop report reviewed by a larger group.

12. 12 Cascade of Upper-Air Observations 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, satellites, reanalyses etc. Spatial density Climate driven

13. 13 Benchmark Network Problem: Current observations have both known and unknown biases that are very difficult to correct. Solution: Continuous, stable observations whose accuracy is traceable to international standards. How to get there: A research question.

14. 14 Comprehensive Network Provides the detailed spatial resolution necessary to relate climate change and variability to human activities and the environment. Includes multiple data types, including satellite data. Relies not only on network measurements but also on assimilation and analysis of the observations. Meets other (non-climate) requirements.

15. 15 Reference Network Establishing a reference upper-air network is articulated in the GCOS Implementation Plan (2004). Goals: –Provide long-term, high-quality climate records –Serve to constrain and calibrate data from more spatially- comprehensive global observing systems (inc. satellites) –Measure a larger suite of co-related climate variables than can be provided at benchmark observations Boulder workshop (Feb 2005) focused on requirements for the reference network. Seattle workshop (May 2006) will focus on instrumentation and deployments for the reference network.

16. 16 Terms Used in Requirements Tables Priority - Ranking from 1 to 4, with 1 as highest priority for GCOS. Based on GCOS “Essential Climate Variables” concept. Precision – repeatability; standard deviation of random errors Accuracy – systematic error; measured minus actual value Long-Term Stability – Maximum tolerable change in systematic error over time (multiple decades)

17. 17 Related Issues Measurement frequency is not specified, but for radiosonde-type measurements, a program of two observations per day, every 2 or 3 days would provide a reasonable climate record. Sonde launch schedule would likely combine fixed synoptic times and times of satellite overpass Spatial location of network stations is TBD. Candidates include existing upper-air stations and stations already operating as part of other climate observing networks.

18. 18 Variable TemperatureWater VaporPressure Priority (1-4)111 Measurement Range 100-350 K0.1 ppm to 55 g/kg1 to 1100 hPa Vertical Range 0 km to stratopause0 to ~30 km0 km to stratopause Vertical Resolution 0.1 km (surface to ~30 km) 0.5 km (above ~30 km) 0.05 km (surface to 5 km) 0.1 km (5 to ~30 km) 0.1 hPa Precision0.2 K0.1 g/kg in lower troposphere 0.001 g/kg in upper troposphere 0.1 ppm stratosphere 0.1 hPa Accuracy0.1 K in troposphere 0.2 K in stratosphere 0.5 g/kg in lower troposphere 0.005 g/kg in upper troposphere 0.1 ppm stratosphere 0.1 hPa Long-Term Stability 0.05 K 11 1%0.1 hPa Comments 1 The signal over the satellite era is order 0.1-0.2K/decade (Section 2.1.1) so long-term stability needs to be order of magnitude smaller to avoid ambiguity. 1 Stability is given in percent, but note that accuracy and precision vary by orders of magnitude with height.

19. 19 Satellite Calibration/Validation Proposals have been made to launch soundings coincident with satellite overpasses. Reference network concept presupposes a comprehensive network, anchored by reference and benchmark. Reference observations can provide transfer functions from one satellite to the next Coordination between satellite community and reference network should be established before implementation.

20. 20 Websites for More Information On requirements (Boulder workshop, Feb. 2005) www.oco.noaa.gov/docs/ua_workshopreport_v7.pdf On Seattle workshop www.oco.noaa.gov/workshop2 On GCOS Implementation Plan www.wmo.ch/web/gcos/Implementation_Plan_(GCOS).pdf

21. 21 Summary Reference upper-air network for climate research and monitoring would complement satellite observations. In situ observations could be optimized for satellite calibration. Requirements have been developed for several “essential climate variables”. Technologies and deployments to meet the requirements are TBD. Workshop 24-26 May 2006 will address this. Implementation will require long term US and international support, under GCOS auspices.

22. 22 Requirements Tables

23. 23 Variable TemperatureWater VaporPressure Priority (1-4)111 Measurement Range 100-350 K0.1 ppm to 55 g/kg1 to 1100 hPa Vertical Range 0 km to stratopause0 to ~30 km0 km to stratopause Vertical Resolution 0.1 km (surface to ~30 km) 0.5 km (above ~30 km) 0.05 km (surface to 5 km) 0.1 km (5 to ~30 km) 0.1 hPa Precision0.2 K0.1 g/kg in lower troposphere 0.001 g/kg in upper troposphere 0.1 ppm stratosphere 0.1 hPa Accuracy0.1 K in troposphere 0.2 K in stratosphere 0.5 g/kg in lower troposphere 0.005 g/kg in upper troposphere 0.1 ppm stratosphere 0.1 hPa Long-Term Stability 0.05 K 11 1%0.1 hPa Comments 1 The signal over the satellite era is order 0.1-0.2K/decade (Section 2.1.1) so long-term stability needs to be order of magnitude smaller to avoid ambiguity. 1 Stability is given in percent, but note that accuracy and precision vary by orders of magnitude with height.

24. 24 Variable Vector Wind Priority (1-4)2 Measurement Range 0 – 300 m/s Vertical Range 0 km to stratopause Vertical Resolution 0.05 km in troposphere 0.25 km in stratosphere Precision0.5 m/s in troposphere 1.0 m/s in stratosphere Accuracy1.0 m/s 1 Long-Term Stability 0.5 m/s in troposphere 1.0 m/s in stratosphere Comments 1 to delineate calm conditions from light winds. Direction may be problematic under these circumstances.

25. 25 Variable OzoneCarbon DioxideMethane Priority (1-4)232 Measurement Range 0.005-20 ppmV Vertical Range Surface to 100 km Vertical Resolution 0.5 km in stratosphere 1 km in troposphere Precision Accuracy3% total column 5% stratosphere 5% troposphere Long-Term Stability 0.2% total column 0.6% stratosphere 1% troposphere Comments

26. 26 Variable Net RadiationIncoming Shortwave Radiation Outgoing Shortwave Radiation Priority (1-4)122 Measurement Range 0-1500 W/m20-2000 W/m2 1 0-1365 W/m2 Vertical Range Surface Precision5 W/m2 1 3 W/m2 2 2 W/m2 1 Accuracy5 W/m2 1 5 W/m2 2 3% 1 Long-Term Stability 0.1 W/m2 Comments 1 Accuracy and precision units from BSRN. 1 Incorporates cloud reflection effects. 2 Accuracy and precision units from BSRN. 1 Accuracy and precision units from BSRN.

27. 27 Variable Incoming Longwave Radiation Outgoing Longwave Radiation Radiances Priority (1-4)221 Measurement Range 0-900 W/m2 Full spectral range 300-1700 cm -1 190 K<T b <330 K Vertical Range Surface Surface to top of atmosphere. Need TOA upwelling and surface downwelling but not levels in between. Vertical Resolution N/A Precision1 W/m2 1 0.01% Accuracy3 W/m2 1 0.15% Long-Term Stability 0.1 W/m2 0.03% per decade Comments 1 Accuracy and precision units from BSRN. Stability requirement achievable through SI traceability; precision/accuracy requirement for mean seasonal radiances at ~1000 km spatial scale.

28. 28 Variable Aerosol Optical Depth Total Mass Conc.Chemical Mass Conc. Priority (1-4)222 Measurement Range 0.005 - 5 0.1-100  g m ‑ 3 0.1-30  g m ‑ 3 Vertical Range Total column0-6 km Vertical Resolution N/A500 m Precision0.00510% Accuracy0.00510% Long-Term Stability 0.00510% CommentsSpectral measurements Size-fractionated

29. 29 Variable Light ScatteringLight Absorption Priority (1-4)22 Measurement Range 0.1-1000 Mm ‑ 1 Vertical Range 0-6 km Vertical Resolution 500 m Precision10% Accuracy10% Long-Term Stability 10% CommentsSize-fractionated, spectral

30. 30 Variable Cloud Amount/Frequency Cloud Base HeightCloud Layer Heights and Thicknesses Priority (1-4)222 Measurement Range 0-100%0-20 km 1 (1000-50 mb) 0-20 km Vertical Range 0 to 20Kmsurface to 50 mbSurface to 50mb Vertical Resolution 50 m5 mb50 m 1 Precision0.1-0.3% 1 100 m (10-40 mb 2 )50 m 2 Accuracy0.1-0.3% 1 100 m (10-40 mb 2 )50 m 2 Long-Term Stability 0.1-0.2% 2 20 m/decade 3 50 m/decade Comments 1 1-3% variations from ISCCP 2 1-2%/decade trend (Norris 2005) 1 1000-50mb (Rossow and Schiffer 1999) 2 10-40 mb variations from ISCCP 3 44/154 m/decade for base/top from Chernykh et al. (2001), which was questioned by Seidel and Durre (2002) 1 the minimum layer thickness of ~30 m (cirrus) (Del Genio et al. 2002; Winker and Vaughan 1994) 2 the standard deviation of >= 100 m (Wang et al. 2000)

31. 31 Variable Cloud Top HeightCloud Top PressureCloud Top Temperature Priority (1-4)333 Measurement Range 0-20 km1013-15 hPa190-310 K Vertical Range 0-20 km Vertical Resolution 150 m 1 km Precision50m1 hPa Accuracy150 m15 hPa1 K/(cloud emissivity) Long-Term Stability 30 m3 hPa0.2 K/(cloud emissivity) Comments

32. 32 Variable Cloud Particle SizeCloud Optical DepthCloud Liquid Water/Ice Priority (1-4)444 Measurement Range Vertical Range 0-20 km Vertical Resolution 1 km Precision Accuracy10% water 20% ice 10%25% water 0.025 mm ice Long-Term Stability 2% water 4% ice 2%5% water 0.005 mm ice Comments

33. 33 Source: Temperature Trends in the Lower Atmosphere: Steps for Understanding and Reconciling Differences. Thomas R. Karl, Susan J. Hassol, Christopher D. Miller, and William L. Murray, editors, 2006. A Report by the Climate Change Science Program and the Subcommittee on Global Change Research,ashington, DC. (Figure from Executive Summary, page 9) 1979-20041958-2004

34. 34 Notes on Water Vapor Feedback Figure from Soden and Held The magnitude water vapor feedback as a function of height and latitude under the assumption of a uniform warming and constant relative humidity moistening in units of W/m2/K/100 mb. Results shown are zonal and annual means. The main contribution to the positive feedback is the increase in water vapor content with increased temperature, leading to increased greenhouse effect and thus further temperature increases. Note that the maximum feedback occurs in the tropical upper troposphere.