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HOMOGENEITY OF THE ECA
TEMPERATURE DATA
Janet Wijngaard
Albert Klein Tank
BUDAPEST, 25-29 SEPTEMBER
HomogeneityTests
• Standard Normal Homogeneity Test (SNHT,
Alexandersson)
• Range test (Buishand)
• Von Neumann ratio
Testing method
• No reference stations used
- stations are diverse
• Annual DTR series tested
- artificial changes
opposite effect
- natural changes
same effect
CONCLUSIONS
• Test results for the examples are satisfactory
• Summarised results for SNHT, Range-test
and Von Neumann Ratio
overview of homogeneity
• Meta data should be used to take full
advantage of the ECA data set
Von Neumann Ratio
for Eelde Groningen
• N= 0.55
period: 1910-1998
• N=1.85
period: 1958-1998
SNHT
2
2
T0 = max T (a) = max { a z1  (n  a) z 2 } a  1,......n
1 a n
1 a n
a
n
z 1  1  (Yi  Y ) / s
a
where Y is the mean ands
z 2
i 1
1
na
 (Y
i  a 1
i
Y) / s
the standard deviation of the sample
Range test
k
S k* =
 (Y
i 1
i
Y)
S 0*
k  1,.....n and
R  (max S k*  min S k* ) / s
0 k  n
0 k  n
Von Neumann Ratio
n 1
n
i 1
i 1
N   (Yi  Yi 1 ) 2 /  (Yi  Y ) 2
=0
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