Correction of daily values Correction of daily values for for inhomogeneities inhomogeneities P. Štěpánek Czech Hydrometeorological Institute, Regional Office Brno, Czech Republic E-mail: [email protected]COST-ESO601 meeting, Tarragona, 9-11 March 2009
Correction of daily values for inhomogeneities. P. Štěpánek. Czech Hydrometeorological Institute, Regional Office Brno, Czech Republic. E-mail: [email protected]. COST-ESO601 meeting, Tarragona, 9-11 March 2009. Using daily data for inhomogeniety detection , is it meaningful ?. - PowerPoint PPT Presentation
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Correction of daily valuesCorrection of daily values for for inhomogeneitiesinhomogeneities
P. Štěpánek
Czech Hydrometeorological Institute, Regional Office Brno, Czech Republic
Very few approaches actually calculate special corrections for daily data.
Most approaches either
– Do nothing (discard data)
– Apply monthly factors
– Interpolate monthly factors
The survey points out several other alternatives that WG5 needs to investigate
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Trust metadata only
Use a technique to detect breaks
Detect on lower resolution
Daily data correction mDaily data correction methodsethods
„Delta“ methods Variable correction methods – one element Variable correction methods – several
elements
Daily data correction mDaily data correction methodsethods
Interpolation of monthly factors– MASH– Vincent et al (2002) - cublic spline interpolation
Nearest neighbour resampling models, by Brandsma and Können (2006)
Higher Order Moments (HOM), by Della Marta and Wanner (2006) Two phase non-linear regression (O. Mestre) Modified percentiles approach, by Stepanek Using weather types classifications (HOWCLASS), by I. Garcia-
Borés, E. Aguilar, ...
AdjustAdjustinging daily values daily values for inhomogeneitiesfor inhomogeneities, , from from monthlymonthly versus versus dailydaily adjustmentsadjustments(„delta“ method)(„delta“ method)
AdjustingAdjusting from from monthlymonthly data data
monthly adjustments smoothed with Gaussian low pass filter (weights approximately 1:2:1)
smoothed monthly adjustments are then evenly distributed among individual days
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AdjustingAdjusting straight from straight from dailydaily data data
Adjustment estimated for each individual day (series of 1st Jan, 2nd Jan etc.)
Daily adjustments smoothed with Gaussian low pass filter for 90 days (annual cycle 3 times to solve margin values)
The same final adjustments may be obtained from either monthly averages or through direct use of daily data
(for the daily-values-based approach, it seems reasonable to smooth with a low-pass filter for 60 days. The same results may be derived using a low-pass filter for two months (weights approximately 1:2:1) and
subsequently distributing the smoothed monthly adjustments into daily values)
(1 – raw adjustments, 2 – smoothed adjustments, 3 – smoothed adjustments distributed into individual days), b) daily-based approach (4 – individual calendar day adjustments, 5 – daily adjustments smoothed by low-pass filter for 30 days, 6 – for 60 days, 7 – for 90 days)
Spline through monthly temperature Spline through monthly temperature adjustmentsadjustments („delta“ method)(„delta“ method)
Easy to implement No assumptions about changes in variance Integrated daily adjustments = monthly adjustments But, is it natural?
Variable correction Variable correction
f(C(d)|R), function build with the reference dataset R, d – daily data
cdf, and thus the pdf of the adjusted candidate series C*(d) is exactly the same as the cdf or pdf of the original candidate series C(d)
Trewin & Trevitt (1996) method: Use simultaneous observations of old and new conditions
Variable correctionVariable correction
Variable correctionVariable correction
1996
The HOM method concept: Fitting a modelThe HOM method concept: Fitting a model Locally weighted regression (LOESS)
(Cleveland & Devlin,1998)
HSP2 HSP1
The HOM method concept: Calculating the The HOM method concept: Calculating the binned difference seriesbinned difference series
Decile 1, k=1
Decile 10, k=10
The HOM method concept: The The HOM method concept: The binned differencesbinned differences