Transcript Status of GCOS Upper-Air Reference Network Planning

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
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
2
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
3
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:
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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
1958-2004
1979-2004
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)
8
50-year Temperature Trend Error Rate (%)
Effect of Unadjusted "Interventions" on
Temperature Trend Estimates
40
30
20
10
0
0.0
0.5
1.0
1.5
2.0
2.5
Maximum Intervention (deg K)
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.
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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
Spatial
density
Benchmark Network
~10 stations
Climate
driven
Upper Air Reference Network
30-40 stations
GCOS Upper Air Network
(GUAN)
161 stations
Comprehensive observing network
All stations, observing systems,
satellites, reanalyses etc.
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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 spatiallycomprehensive 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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Temperature
Water Vapor
Pressure
Variable
Priority (1-4)
1
1
1
Measurement
Range
100-350 K
0.1 ppm to 55 g/kg
1 to 1100 hPa
Vertical
Range
0 km to stratopause
0 to ~30 km
0 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
Precision
0.2 K
0.1 g/kg in lower
troposphere
0.001 g/kg in upper
troposphere
0.1 ppm stratosphere
0.1 hPa
Accuracy
0.1 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 K1
11%
0.1 hPa
Comments
1The
1Stability
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.
is given in
percent, but note that
accuracy
and
precision vary by
orders of magnitude
with height.
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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/Implementation_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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Temperature
Water Vapor
Pressure
Variable
Priority (1-4)
1
1
1
Measurement
Range
100-350 K
0.1 ppm to 55 g/kg
1 to 1100 hPa
Vertical
Range
0 km to stratopause
0 to ~30 km
0 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
Precision
0.2 K
0.1 g/kg in lower
troposphere
0.001 g/kg in upper
troposphere
0.1 ppm stratosphere
0.1 hPa
Accuracy
0.1 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 K1
11%
0.1 hPa
Comments
1The
1Stability
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.
is given in
percent, but note that
accuracy
and
precision vary by
orders of magnitude
with height.
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Vector Wind
Variable
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
Precision
0.5 m/s in
troposphere
1.0 m/s in
stratosphere
Accuracy
1.0 m/s1
Long-Term
Stability
0.5 m/s in
troposphere
1.0 m/s in
stratosphere
Comments
1to
delineate calm
conditions from light
winds. Direction may
be problematic under
these circumstances.
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Ozone
Carbon Dioxide
Methane
Variable
Priority (1-4)
2
Measurement
Range
0.005-20 ppmV
Vertical
Range
Surface to 100 km
Vertical
Resolution
0.5 km in stratosphere
1 km in troposphere
3
2
Precision
Accuracy
3% total column
5% stratosphere
5% troposphere
Long-Term
Stability
0.2% total column
0.6% stratosphere
1% troposphere
Comments
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Net Radiation
Incoming Shortwave
Radiation
Variable
Priority (1-4)
1
Outgoing
Shortwave
Radiation
2
2
Measurement
Range
0-1500 W/m2
0-2000 W/m21
0-1365 W/m2
Vertical
Range
Surface
Surface
Surface
Precision
5 W/m21
3 W/m22
2 W/m21
Accuracy
5 W/m21
5 W/m22
3%1
Long-Term
Stability
0.1 W/m2
0.1 W/m2
0.1 W/m2
Comments
1Accuracy
1Incorporates
1Accuracy
and
precision units from
BSRN.
cloud
reflection effects.
2Accuracy
and
precision units from
BSRN.
and
precision units from
BSRN.
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Incoming Longwave
Radiation
Outgoing Longwave
Radiation
2
2
Radiances
Variable
Priority (1-4)
1
Measurement
Range
0-900 W/m2
0-900 W/m2
Full spectral range
300-1700 cm-1
190 K<Tb<330 K
Vertical
Range
Surface
Surface
Surface to top of
atmosphere.
Need
TOA
upwelling
and
surface
downwelling
but
not
levels
in
between.
Vertical
Resolution
N/A
N/A
N/A
Precision
1 W/m21
1 W/m21
0.01%
Accuracy
3 W/m21
3 W/m21
0.15%
Long-Term
Stability
0.1 W/m2
0.1 W/m2
0.03% per decade
Comments
1Accuracy
1Accuracy
Stability
requirement
achievable through
SI
traceability;
precision/accuracy
requirement
for
mean
seasonal
radiances at ~1000
km spatial scale.
and
precision units from
BSRN.
and
precision units from
BSRN.
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Aerosol Optical
Depth
Total Mass Conc.
Chemical Mass
Conc.
Variable
Priority (1-4)
2
2
2
Measurement
Range
0.005 - 5
0.1-100 mg m-3
0.1-30 mg m-3
Vertical
Range
Total column
0-6 km
0-6 km
Vertical
Resolution
N/A
500 m
500 m
Precision
0.005
10%
10%
Accuracy
0.005
10%
10%
Long-Term
Stability
0.005
10%
10%
Comments
Spectral
measurements
Size-fractionated
Size-fractionated
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Light Scattering
Light Absorption
Variable
Priority (1-4)
2
2
Measurement
Range
0.1-1000 Mm-1
0.1-1000 Mm-1
Vertical
Range
0-6 km
0-6 km
Vertical
Resolution
500 m
500 m
Precision
10%
10%
Accuracy
10%
10%
Long-Term
Stability
10%
10%
Comments
Size-fractionated,
spectral
Size-fractionated,
spectral
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Cloud
Amount/Frequency
Cloud Base Height
Variable
Priority (1-4)
2
Cloud Layer
Heights and
Thicknesses
2
2
Measurement
Range
0-100%
0-20 km1 (1000-50
mb)
0-20 km
Vertical
Range
0 to 20Km
surface to 50 mb
Surface to 50mb
Vertical
Resolution
50 m
5 mb
50 m1
Precision
0.1-0.3%1
100 m (10-40 mb2)
50 m2
Accuracy
0.1-0.3%1
100 m (10-40 mb2)
50 m2
Long-Term
Stability
0.1-0.2%2
20 m/decade3
50 m/decade
Comments
11-3%
1 1000-50mb
1the
variations
ISCCP
21-2%/decade
(Norris 2005)
from
trend
(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)
minimum layer
thickness of ~30 m
(cirrus) (Del Genio et
al. 2002; Winker and
Vaughan 1994)
2the standard deviation
of >= 100 m (Wang et
al. 2000)
30
Cloud Top Height
Cloud Top Pressure
Cloud Top
Temperature
Variable
Priority (1-4)
3
3
3
Measurement
Range
0-20 km
1013-15 hPa
190-310 K
Vertical
Range
0-20 km
0-20 km
0-20 km
Vertical
Resolution
150 m
150m
1 km
Precision
50m
1 hPa
Accuracy
150 m
15 hPa
1
K/(cloud
emissivity)
Long-Term
Stability
30 m
3 hPa
0.2
K/(cloud
emissivity)
Comments
31
Cloud Particle Size
Cloud Optical Depth
Cloud Liquid
Water/Ice
Variable
Priority (1-4)
4
4
4
Measurement
Range
Vertical
Range
0-20 km
0-20 km
0-20 km
Vertical
Resolution
1 km
1 km
1 km
Accuracy
10% water
20% ice
10%
25% water
0.025 mm ice
Long-Term
Stability
2% water
4% ice
2%
5% water
0.005 mm ice
Precision
Comments
32
1958-2004
1979-2004
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)
33
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.
34