u.s. hcn temperature trends: a brief overview
DESCRIPTION
U.S. HCN Temperature Trends: A brief overview. Some Topics. The U.S. HCN Datasets What is climate data homogenization? Some examples Analysis of U.S. temperature trends Representativeness of temperature trends versus temperature means. U.S. HCN Version 1. Originally released in 1987 - PowerPoint PPT PresentationTRANSCRIPT
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U.S. HCN Temperature Trends:A brief overview
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Some Topics
• The U.S. HCN Datasets• What is climate data homogenization?• Some examples• Analysis of U.S. temperature trends• Representativeness of temperature trends
versus temperature means
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U.S. HCN Version 1
• Originally released in 1987• 1221 stations • Addresses
– Time of observation bias (Karl et al. 1986; Vose et al. 2003)
– Station History Changes (Karl and Williams 1987)
– MMTS instrument change (Quayle et al. 1991)– Urbanization (Karl et al. 1988)
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U.S. HCN Version 2
• 1218 stations • Addresses
– Time of observation bias (Karl et al. 1986; Vose et al. 2003)
– Station History and Undocumented Changes (Menne and Williams, Journal of Climate, in review)
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The Time of Observation Bias
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The Time of Observation Bias
1950s 1960s
1980s
2000-2006
1970s
1990s
• Since the 1950s, observation times have shifted from afternoon/ evening to morning
Hour of observation histograms at bottom of each U.S. decadal map(Figure courtesy of Xioamoa Lin, University of Nebraska)
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Impact of Time of Observation Changes
Average year by year difference over the conterminous United States between the Time of Observation Bias (TOB)-adjusted data and the unadjusted (raw) data.
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Homogenization
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σ (°C)
Simulated temperature series with random shifts caused by station moves/site changes
•Series in red treated as the target in subsequent figures
•All shifts are considered to be undocumented
•True “climate” trend in all simulated series is zero
(Annual Averages)
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Case 7 unadjustedTarget series and differences with neighbors before adjustment for undocumented shifts
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Target series and differences with neighbors following adjustment by pairwise algorithm
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σ (°C)
Simulated temperature series following adjustment by pairwise algorithm
•Original Target Series in Red
•Adjusted Target Series in Green
•Adjusted Neighbor Series in Black
(Annual Averages)
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An Example: Reno, NevadaFrom: http://wattsupwiththat.wordpress.com/2008/01/10/how-not-to-measure-temperature-part-46-renos-ushcn-station/
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Reno, Nevada
(a) Mean annual TOB and fully adjusted (TOB+Pairwise) minimum temperatures at Reno, Nevada(b) Difference between minimum temperatures at Reno and the mean from its 10 nearest neighbors.
Move toAirport
Likely urbanwarming
ASOS Equip.Moves
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U.S. HCN Version 2 Temperature Trends (1895 to 2006)
Unadjusted Adjusted
Minimum Temperature Adjusted
°C dec-1
Unadjusted
Maximum Temperature
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Impact of Documented and Undocumented Changes
Year by year differences averaged over the conterminous United States between the fully adjusted (TOB+pairwise homogenization algorithm) HCN V2 data
and the TOB-only adjusted data.
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What about siting?
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SurfaceStations.Org
Stations in red have a classification >= 3
Station in black have a classification of 1 or 2
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U.S. HCN Version 2 Temperature Trends (1895 to 2006)
All Stations Rating 3, 4 or 5
Minimum Temperature
°C dec-1
Maximum Temperature
All Stations Rating 3, 4 or 5
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U.S. HCN Version 2 Temperature Trends (1895 to 2006)
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Impact of Siting on Trends
Season Maximum Temperature Minimum Temperature
All Stations Ratings 3, 4 & 5 All Stations Ratings 3, 4 & 5
Annual 0.056 0.048 0.070 0.054
D-J-F 0.094 0.074 0.101 0.073
M-A-M 0.069 0.061 0.059 0.040
J-J-A 0.036 0.033 0.064 0.060
S-O-N 0.014 0.012 0.046 0.037
U.S. annual and seasonal temperature trends (°C dec-1) 1895 to 2006
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Trends Versus Means
Here is a not-so-well maintained or well sited USHCN station at Marysville
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Can station measurements be unrepresentative, and the (adjusted) trend be representative?
°C
Difference between Annual Minimum Temperature at Marysville, CA and Surrounding Stations
Documented and undocumented shifts identified by pairwise algorithm (using monthly values) indicated by vertical bars
Raw data in red
Adjusted data in green
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Adjusted Minimum Temperature Series at Marysville, CA