Empirical-Statistical Downscaling:
new developments
Credit: Øyvind Nordli
Making use of known information
ESD for different situations
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Whenever the large-scale ambient
environment sets the stage...
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Temperature statistics
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Precipitation statistics
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Storms?
Extremes?
Time series first?
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“Weather”: a
chronological time
series
“Climate”: a
frequency
distribution (PDF)
Traditional: time
series → PDF
Alternative: PDF →
time series
Traditional
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Distribution from
ENSEMBLE
spread
CMIP5 – test.
Right distribution type?
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CMIP5
members,
approximately
normally
distributed...
Can we predict the shape of the
PDFs instead?
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Already predict
the mean – e.g.
the monthly
mean.
What about the
standard
deviation?
N(x,σ)
Temperature statistics
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Not just monthly
mean values
3 following
summers
Range as well as
mean vary
5%-95%
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24-hr precipitation
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Different type of PDF
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Different dependencies to the large scales
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The hydrological cycle
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Energy flow: latent heat.
More complicated – two situations:
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Dry days
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Rainy days
Traditionally: monthly means...
Wet-day precipitation
All-day precipitation
Sensitivity test
Mean
Temperature
Number of
days with
data
Logit!
Wet-day mean
GDCN
Logit!
Number of wet
days
Simple wet-day PDF?
Exponential distribution:
qp = -ln(1-p) µ.
qp
-ln(1-p) µ
Wet-day
percentiles...
Observed q95
q95=f(µ,fw,z,d)
Mm/day
Validation of PCA-based formulae
Temporal variations...
10-year 24-hr precipitation
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10-year statistics
vary
External
dependencies?
5%-95%
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Trend analysis
Link to global mean temperature: µ
Wet-day frequency & global t(2m)
Wind & storms...
Seasonal
dependencies –
an opportunity for
statistical
modelling?
Mid-latitude storms from IMILAST
Storms...
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Temperature
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Mean [ok]
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Standard deviation? Other distributions?
Precipitation
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Wet-day mean µ and wet-day frequency fw.
Wind
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Storm tracks?