Federal Department of Home Affairs FDHAFederal Office of Meteorology and Climatology MeteoSwiss

Weather types and gridding of daily precipitation in the Alpine region –

early finger exercises

Reinhard Schiemann and Christoph Frei

COST733 WG4 meeting, Brussels

March 6/7, 2008

2 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/7 2008Reinhard Schiemann and Christoph Frei

COST733 @ MeteoSwiss

1. Weather types and Alpine precipitation• Description of the statistical relationship for the

COST733 classifications• Selection and more detailed investigation for a

"particularly suitable" weather type classification

2. Gridding• Construction of daily precipitation grids based on

rain gauge data and other meteorological information

1. Weather types and Alpine precipitation• Description of the statistical relationship for the

COST733 classifications• Selection and more detailed investigation for a

"particularly suitable" weather type classification

2. GriddingGridding• Construction of daily precipitation grids based on Construction of daily precipitation grids based on

rain gauge data and other meteorological rain gauge data and other meteorological informationinformation

3 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/7 2008Reinhard Schiemann and Christoph Frei

Finger exercise I: Precipitation composites

Example: Hess-Brezowsky Grosswetterlagen (29 types)

Westlage anticyclonic Westlage cyclonic

(COST733)

4 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/7 2008Reinhard Schiemann and Christoph Frei

Finger exercise I: Precipitation composites

Example: Hess-Brezowsky Grosswetterlagen (29 types)

Westlage anticyclonic Westlage cyclonic

ME

AN

90%

-qua

ntile

mm/d

mm/d mm/d

mm/d

5 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/7 2008Reinhard Schiemann and Christoph Frei

Finger exercise II: Locally "explained" precipitation variance

0.04 0.08 0.12 0.16 0.20 0.24

total variance = between-type variance + within-type variance

variancetotal

variancetype-betweenEV

PETISCO, D06,37 types

PETISCO, D06,37 types

SANDRA, D06, 22 types

SANDRA, D06, 22 types

PCACA, D06,5 types

PCACA, D06,5 types

SCHUEEPP, (D06),40 types

SCHUEEPP, (D06),40 types

6 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/7 2008Reinhard Schiemann and Christoph Frei

Aims

1. Weather types and Alpine PrecipitationWeather types and Alpine Precipitation• Description of the statistical relationship for the Description of the statistical relationship for the

COST733 classificationsCOST733 classifications• Selection and more detailed investigation for a Selection and more detailed investigation for a

"particularly suitable" weather type classification"particularly suitable" weather type classification

2. Gridding• Construction of daily precipitation grids based on

rain gauge data and other meteorological information

7 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/7 2008Reinhard Schiemann and Christoph Frei

Gridding: What is our problem?

data from only few stations in the days immediately succeeding an interesting precipitation event

8 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/7 2008Reinhard Schiemann and Christoph Frei

Gridding: What is our problem?

provisional analysis(2007.08.29)

final analysis(2007.08.29)

Christoph Frei, MeteoSwiss

9 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/7 2008Reinhard Schiemann and Christoph Frei

Gridding: What is our problem?

LD stations~real-time

HD stationsnot real-time

weather type SLP, Z850, Q850, ...

precipitation grids• daily• "high" spatial resolution• realistic estimation of the (spatial) error structure• available in near real time

precipitation grids• daily• "high" spatial resolution• realistic estimation of the (spatial) error structure• available in near real time

10 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/7 2008Reinhard Schiemann and Christoph Frei

Analogy: Reconstruction

time

#S

tatio

ne

n

Reconstruction

LD stations

HD gride.g., Schmidli et al., 2001:optimal interpolation

Gridding

HD stations

HD grid

e.g., Frei and Schär, 1998

"Nowstruction"

LD stations

HD grid

???

11 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/7 2008Reinhard Schiemann and Christoph Frei

But...

daily precipitation is „annoyingly“ distributed

Example: rain gauge at Interlaken, CH

Existing reconstructions handle more pleasantlydistributed data, e.g. monthly precipitation, (SS)Ts.

Methods may not carry over in a straightforward way.

12 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/7 2008Reinhard Schiemann and Christoph Frei

Finger exercise III: Regression with univariate target variable

Y ~ XINT + XULR + XVIS + XGRHY ~ XINT + XULR + XVIS + XGRH

13 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/7 2008Reinhard Schiemann and Christoph Frei

Finger exercise III: Regression with univariate target variable

distribution of errors (QQ-plot):st

and

. re

sid

uals

theor. quantileserroneous confidence intervals for model parametersand forecasting intervals

14 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/7 2008Reinhard Schiemann and Christoph Frei

Reconstruction method: Optimal interpolation

time

#S

tatio

ne

n

Step 1: PCA during calibration period

Step 2: Least squares estimation of PC coefficients during reconstruction period

Kaplan et al., 1997; Schmidli et al., 2001

15 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/7 2008Reinhard Schiemann and Christoph Frei

PCA of daily precipitation

MEAN (mm/d) PC1 (32%)

PC2 (15%) PC3 (12%)

16 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/7 2008Reinhard Schiemann and Christoph Frei

PCA of daily precipitationScatterplots of PC-scoresColours: Weather types according to PCACA, D06 (5 types)

17 Weather types and daily Alpine precipitation | COST733 WG4 meeting, Brussels, March 6/7 2008Reinhard Schiemann and Christoph Frei

Summary and preliminary conclusions

• Daily precipitation composites with respect to different weather types clearly differ from one another. This holds true not only for the mean but also for quantiles of the precipitation distribution.

• In the Alpine region, the locally explained variance is in the order of 10-20%. WTCs differ considerably in subregions of low/high EV (e.g., north vs. south,west vs. east of the Alpine ridge).

• Days corresponding to different weather types occupy different but overlapping regions in principal-component space.

• The added value of WTCs for precipitation gridding remains to be quantified.