Status of GCOS UpperAir Reference Network Planning

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Status of GCOS Upper-Air Reference Network
Planning
Dian Seidel NOAA Air Resources Laboratory Silver
Spring, Maryland

• Achieving Satellite Instrument Calibration for
  Climate Change Workshop
• 16-18 May 2006, Landsdowne, VA

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Radiosondes

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

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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

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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.

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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

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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

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Temperature Trends from Different Observing
Systems and Datasets
1979-2004
1958-2004
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)
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Source Seidel, D.J., and M. Free, Measurement
requirements for climate monitoring of upper-air
temperature derived from reanalysis data, J.
Climate, 19, 854871.
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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.
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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.

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Cascade of Upper-Air Observations
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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.

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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.

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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.

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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)

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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.

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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.

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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/Im
  plementation_Plan_(GCOS).pdf

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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.

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Requirements Tables
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1979-2004
1958-2004
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)
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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.